100 files changed, 20793 insertions, 0 deletions

diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..6833f05
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,3 @@
+* text=auto
+*.txt text
+*.md text
diff --git a/38148-8.txt b/38148-8.txt
new file mode 100644
index 0000000..f5c0ad0
--- /dev/null
+++ b/38148-8.txt
@@ -0,0 +1,6348 @@
+The Project Gutenberg EBook of The Geography of the Region about Devils
+Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Geography of the Region about Devils Lake and the Dalles of the Wisconsin
+
+Author: Rollin D. Salisbury
+        Wallace W. Atwood
+
+Release Date: November 27, 2011 [EBook #38148]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+
+
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+
+
+
+
+       Wisconsin Geological and Natural History Survey.
+
+E. A. BIRGE, Director.             C. R. VAN HISE, Consulting Geologist.
+BULLETIN NO. V.                                EDUCATIONAL SERIES NO. 1.
+
+
+
+
+                       THE GEOGRAPHY
+                          OF THE
+                  REGION ABOUT DEVIL'S LAKE
+                          AND THE
+                   DALLES OF THE WISCONSIN,
+            With Some Notes on Its Surface Geology.
+
+
+
+
+                            BY
+
+                 ROLLIN D. SALISBURY, A. M.,
+   _Professor of Geographic Geology, University of Chicago,_
+
+                           AND
+
+                 WALLACE W. ATWOOD, B. S.,
+       _Assistant in Geology, University of Chicago._
+
+
+                      MADISON, WIS.
+                 Published by the State.
+                          1900.
+
+
+       Wisconsin Geological and Natural History Survey.
+
+
+  -------------------------------------------------------------------
+
+
+                  BOARD OF COMMISSIONERS.
+
+
+  EDWARD SCOFIELD,
+     Governor of the State.
+
+  L. D. HARVEY,
+     State Superintendent of Public Instruction.
+
+  CHARLES K. ADAMS, President,
+     President of the University of Wisconsin.
+
+  EDWIN E. BRYANT, Vice-President,
+     President of the Commissioners of Fisheries.
+
+  CHARLES S. SLICHTER, Secretary,
+     President of the Wisconsin Academy of Sciences, Arts, and
+     Letters.
+
+  --------------------------------------------------------------
+
+  E. A. BIRGE, Director of the Survey.
+
+  C. R. VAN HISE, Consulting Geologist.
+
+  E. R. BUCKLEY, Assistant Geologist.
+     In charge of Economic Geology.
+
+  S. WEIDMAN, Assistant Geologist.
+     In charge of Geology of Wausau District.
+
+  L. S. SMITH, in charge of Hydrography.
+
+  S. V. PEPPEL, Chemist.
+
+  F. R. DENNISTON, Artist.
+
+
+[Illustration: THE DALLES OF THE WISCONSIN.]
+
+
+
+
+                             CONTENTS.
+
+      ---------------------------------------------------------
+
+
+     PART I. THE TOPOGRAPHY WITH SOME NOTES ON THE SURFACE GEOLOGY.
+
+
+                             CHAPTER I.
+
+                      GENERAL GEOGRAPHIC FEATURES
+
+
+     I. The Plain Surrounding the Quartzite Ridges.
+
+           Topography
+
+           Structure
+
+           Origin of the Sandstone and Limestone
+
+           Origin of the Topography
+
+
+    II. The Quartzite Ridges
+
+           Topography
+
+           The Structure and Constitution of the Ridges
+
+
+   III. Relations of the Sandstone of the
+          Plain to the Quartzite of the Ridges
+
+
+
+
+                   PART II. HISTORY OF THE TOPOGRAPHY.
+
+
+                             CHAPTER II.
+
+
+              OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS
+                  WHICH SHOW THEMSELVES AT THE SURFACE.
+
+
+    I. The Pre-Cambrian History of the Quartzite
+
+         From loose Sand to Quartzite
+
+         Uplift and Deformation. Dynamic Metamorphism
+
+         Erosion of the Quartzite
+
+         Thickness of the Quartzite
+
+
+  II. The History of the Paleozoic Strata
+
+         The Subsidence
+
+         The Potsdam Sandstone (and Conglomerate)
+
+         The Lower Magnesian Limestone
+
+         The St. Peters Sandstone
+
+         Younger Beds
+
+         Climatic Conditions
+
+         Time involved
+
+         The Uplift
+
+
+                             CHAPTER III.
+
+
+               GENERAL OUTLINE OF RAIN AND RIVER EROSION
+
+
+         Elements of Erosion
+
+         Weathering
+
+         Corrasion
+
+         Erosion without Valleys
+
+         The Beginning of a Valley
+
+         The Course of a Valley
+
+         Tributary Valleys
+
+         How a Valley gets a Stream
+
+         Limits of a Valley
+
+         A Cycle of Erosion
+
+         Effects of unequal Hardness
+
+         Falls and Rapids
+
+         Narrows
+
+         Erosion of folded Strata
+
+         Base-level Plains and Peneplains
+
+         Transportation and Deposition
+
+         Topographic Forms resulting from Stream Deposition
+
+         Rejuvenation of Streams
+
+         Underground Water
+
+
+                               CHAPTER IV.
+
+
+             EROSION AND THE DEVELOPMENT OF STRIKING SCENIC FEATURES
+
+
+         Establishment of Drainage
+
+         Striking scenic Features
+
+         The Baraboo Bluffs
+
+         The Narrows in the Quartzite
+
+         Glens
+
+         Natural Bridge
+
+         The Dalles of the Wisconsin
+
+         The Mounds and Castle Rocks
+
+
+                            CHAPTER V.
+
+
+                        THE GLACIAL PERIOD.
+
+
+         The Drift
+
+         Snow Fields and ice Sheets
+
+         The North American ice Sheets
+
+         The Work of glacier Ice
+
+         Erosive Work of Ice. Effect on Topography
+
+         Deposition by the Ice. Effect on Topography
+
+         Direction of ice Movement
+
+         Effect of Topography on Movement
+
+         Glacial Deposits
+
+         The ground Moraine
+
+         Constitution
+
+         Topography
+
+         Terminal Moraines
+
+         Topography of terminal Moraines
+
+         The terminal Moraine about Devil's Lake
+
+         The Moraine on the main Quartzite Range
+
+         Constitution of the marginal Ridge
+
+         The Slope of the upper Surface of the Ice at the Margin
+
+         Stratified Drift
+
+         Its Origin
+
+         Glacial Drainage
+
+         Stages in the History of an Ice Sheet
+
+    Deposits made by extraglacial Waters during the maximum Extension
+      of the Ice
+
+         At the Edge of the Ice, on Land
+
+         Beyond the Edge of the Ice, on Land
+
+         Deposits at and beyond the Edge of the Ice in standing Water
+
+   Deposits made by extraglacial Waters during the Retreat of the Ice
+
+   Deposits made by extraglacial Waters during the Advance of the Ice
+
+   Deposits made by subglacial Streams
+
+   Relations of stratified to unstratified Drift
+
+         Complexity of Relations
+
+   Classification of stratified Drift on the Basis of Position
+
+         Extraglacial Deposits
+
+         Supermorainic deposits
+
+         The submorainic (basal) Deposits
+
+         Intermorainic stratified Drift
+
+         Changes in Drainage effected by the Ice
+
+         While the Ice was on
+
+         Wisconsin Lake
+
+         Baraboo Lake
+
+         Devil's Lake in glacial Times
+
+         After the Ice had disappeared
+
+         Lakes
+
+         Existing Lakes
+
+         Changes in Streams
+
+         Skillett Creek
+
+         The Wisconsin
+
+         The Driftless Area
+
+         Contrast between glaciated and unglaciated Areas
+
+               Topography
+
+               Drainage
+
+               Mantle Rock
+
+
+
+
+                      LIST OF ILLUSTRATIONS.
+
+
+    ------------------------------------------------------------
+
+
+                              PLATES.
+
+
+        Plate
+
+Frontispiece.  The Dalles of the Wisconsin
+
+           I. General map of the Devil's Lake region
+
+          II. Local map of the Devil's Lake region
+
+         III. Fig. 1--Ripple marks on a slab of sandstone
+              Fig. 2--Piece of Potsdam conglomerate
+
+          IV. Lower Narrows of the Baraboo
+
+           V. Devil's Lake notch
+
+          VI. East bluff of Devil's Lake
+
+         VII. East bluff at the Upper Narrows of the Baraboo near Ableman's
+
+        VIII. Vertical shear zone face of east bluff at Devil's Lake
+
+          IX. Massive quartzite in situ in road through Upper Narrows near
+                Ableman's
+
+           X. Brecciated quartzite
+
+          XI. Northwest wall of the Upper Narrows
+
+         XII. Steamboat Rock
+
+        XIII. Fig. 1--A very young valley
+              Fig. 2--A valley at later stage of development
+              Fig. 3--Young valleys
+
+         XIV. Fig. 1--Same valleys as shown in Pl. XIII, Fig. 3,
+                        but at a later stage of development
+              Fig. 2--Same valleys as shown in Fig. 1 in later stage of
+                        development
+
+          XV. Diagram illustrating how a hard inclined layer of rock
+                becomes a ridge in the process of degradation
+
+         XVI. Skillett Falls
+
+        XVII. A group of mounds on the plain northwest from Camp Douglas
+
+       XVIII. Castle Rock near Camp Douglas
+
+         XIX. Fig. 1--Sketch of a young valley
+              Fig. 2--Same valleys as shown in Fig. 1 in later stage of
+                        development
+
+          XX. Fig. 1--Sketch of a part of a valley at a stage of
+                        development corresponding to the cross section
+                        shown in Figure 21
+              Fig. 2--Sketch of a section of the Baraboo valley
+
+         XXI. Cleopatra's Needle
+
+        XXII. Turk's Head
+
+       XXIII. Devil's Doorway
+
+        XXIV. Talus slope on east bluff of Devil's Lake
+
+         XXV. Dorward's Glen
+
+        XXVI. Natural Bridge near Denzer
+
+       XXVII. The Navy Yard
+
+      XXVIII. Chimney Rock
+
+        XXIX. An island in the Lower Dalles
+
+         XXX. View in Lower Dalles
+
+        XXXI. Stand Rock
+
+       XXXII. Petenwell Peak
+
+      XXXIII. North American ice sheet
+
+       XXXIV. Owl's Head
+
+        XXXV. Cut in glacial drift
+
+       XXXVI. Glaciated stones
+
+      XXXVII. Topographic map of a small area about Devil's Lake
+
+     XXXVIII. Distorted laminæ of silt and clay
+
+
+
+
+                          FIGURES IN TEXT.
+
+
+  Figure
+
+   1. Profile across the Baraboo quartzite ranges through Baraboo
+
+   2. Profile across the Baraboo ranges through Merrimac
+
+   Transcriber's note: There is no figure 3.
+
+   4. Diagram showing the structure of the quartzite
+
+   5. Diagram showing the relation of the Potsdam sandstone to the Baraboo
+      quartzite
+
+   6. Diagram illustrating effect of faulting on outcrop
+
+   7. Diagram showing the disposition of sediments about an island
+
+   8. The same as 7 after subsidence
+
+   9. Diagram showing relation of Potsdam conglomerate to quartzite at
+      Devil's Lake
+
+  10. Cross section of a delta
+
+  11. The geological formations of southern Wisconsin
+
+  12. A typical river system
+
+  13. Diagram illustrating the relations of ground water to streams
+
+  14. Diagram illustrating the shifting of divides
+
+  15. Diagram showing topography at the various stages of an erosion cycle
+
+  16. Diagram illustrating the development of rapids and falls
+
+  17. Sketch looking northwest from Camp Douglas
+
+  18. Diagrammatic cross section of a young valley
+
+  19. Diagrammatic profile of a young valley
+
+  20. Diagrammatic cross section of a valley in a later stage of
+      development
+
+  21. The same at a still later stage
+
+  22. Diagram illustrating the topographic effect or rejuvenation of a
+      stream by uplift
+
+  23. Normal profile of a valley bottom
+
+  24. Profile of a stream rejuvenated by uplift
+
+  25. Diagram illustrating monoclinal shifting
+
+  26. Diagram showing the relation of the Potsdam sandstone to the
+      quartzite at the Upper Narrows
+
+  27. Diagrammatic cross section of a field of ice and snow
+
+  28. Shape of an erosion hill before glaciation
+
+  29. The same after glaciation
+
+  30. Diagram showing the effect of a valley on the movement of ice
+
+  31. The same under different conditions
+
+  32. Diagram showing the relation of drift to the underlying rock where
+      the drift is thick
+
+  33. The same where the drift is relatively thin
+
+  34. Diagrammatic representation of the effect of a hill on the edge of
+      the ice
+
+  35. The same at a later stage of the ice advance
+
+  36. Map showing the relation of the ice lobes during the Wisconsin epoch
+      of the glacial period
+
+  37. Sketch of the terminal moraine topography east of Devil's Lake
+
+  38. Cut through the terminal moraine east of Kirkland
+
+  39. Cross section of the marginal ridge of the moraine on the south
+      slope of the Devil's nose
+
+  40. Cross section of the marginal ridge of the moraine on the crest of
+      the quartzite range
+
+  41. Morainic outwash plain
+
+  42. The same in other relations
+
+  43. Skillett Creek and its peculiarities
+
+  44. The Wisconsin valley near Kilbourn city
+
+  45. Drainage in the driftless area
+
+  46. Drainage in the glaciated area
+
+  47. Section in the driftless region showing relation of the soil to the
+      solid rock beneath
+
+
+
+
+                             PART I.
+
+    ------------------------------------------------------------
+
+                         THE TOPOGRAPHY.
+
+               WITH SOME NOTES ON THE SURFACE GEOLOGY.
+
+
+
+
+       GEOGRAPHY AND SURFACE GEOLOGY OF THE DEVIL'S LAKE REGION.
+
+
+
+                           CHAPTER I.
+
+
+                  GENERAL GEOGRAPHIC FEATURES.
+
+
+This report has to do with the physical geography of the area in south
+central Wisconsin, shown on the accompanying sketch map, Plate I. The
+region is of especial interest, both because of its striking scenery,
+and because it illustrates clearly many of the principles involved in
+the evolution of the geography of land surfaces.
+
+Generally speaking, the region is an undulating plain, above which rise
+a few notable elevations, chief among which are the Baraboo quartzite
+ranges, marked by diagonal lines on Plates I and II. These elevations
+have often been described as two ranges. The South or main range lies
+three miles south of Baraboo, while the North or lesser range, which is
+far from continuous, lies just north of the city.
+
+The main range has a general east-west trend, and rises with bold and
+sometimes precipitous slopes 500 to 800 feet above its surroundings. A
+deep gap three or four miles south of Baraboo (Plates II, V, and
+XXXVII) divides the main range into an eastern and a western
+portion, known respectively as the _East and West bluffs_ or _ranges_.
+In the bottom of the gap lies Devil's lake (i, Plate II and Plate
+XXXVII), perhaps the most striking body of water of its size in the
+state, if not in the whole northern interior. A general notion of the
+topography of a small area in the immediate vicinity of the lake may be
+obtained from Plate XXXVII.
+
+The highest point in the range is about four miles east of the lake, and
+has an elevation of more than 1,600 feet above sea level, more than
+1,000 feet above Lake Michigan, and about 800 feet above the Baraboo
+valley at its northern base. The eastward extension of the west range
+(Plate XXXVII) lying south of the lake, and popularly known as the
+_Devil's nose_, reaches an elevation of a little more than 1,500 feet.
+
+The lesser or North quartzite range (Plate II) rises 300 feet to 500
+feet above its surroundings. It assumes considerable prominence at the
+Upper and Lower narrows of the Baraboo (b and c, Plate II, c, Plate
+XXXVII and Plate IV). The North range is not only lower than the
+South range, but its slopes are generally less steep, and, as Plate II
+shows, it is also less continuous. The lesser elevation and the gentler
+slopes make it far less conspicuous. About three miles southwest of
+Portage (Plate II) the North and South ranges join, and the elevation at
+the point of union is about 450 feet above the Wisconsin river a few
+miles to the east.
+
+The lower country above which these conspicuous ridges rise, has an
+average elevation of about 1,000 feet above the sea, and extends far
+beyond the borders of the area with which this report is concerned. The
+rock underlying it in the vicinity of Baraboo is chiefly sandstone, but
+there is much limestone farther east and south, in the area with which
+the Baraboo region is topographically continuous. Both the sandstone and
+limestone are much less resistant than the quartzite, and this
+difference has had much to do with the topography of the region.
+
+The distinctness of the quartzite ridges as topographic features is
+indicated in Plate XXXVII by the closeness of the contour lines on their
+slopes. The same features are shown in Figs. 1 and 2, which represent
+profiles along two north-south lines passing through Baraboo and
+Merrimac respectively.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. I.
+
+General map showing the location of the chief points mentioned in this
+report. The location of the area shown in Plate XXXVII, centering about
+Baraboo, is indicated.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. II.
+
+Map of Area considered in this Report.]
+
+[Illustration: Fig. 1.--Profile along a line extending due north and
+south from Baraboo across the north and south ranges. The dotted
+continuation northward, represents the extension of the profile beyond
+the topographic map, Plate XXXVII.]
+
+[Illustration: Fig. 2.--Profile north from Merrimac across the quartzite
+ranges. The dotted continuation northward represents the extension of
+the profile beyond the topographic map, Plate XXXVII.]
+
+
+         I. THE PLAIN SURROUNDING THE QUARTZITE RIDGES.
+
+_Topography._--As seen from the top of the quartzite ridges, the
+surrounding country appears to be an extensive plain, but at closer
+range it is seen to have considerable relief although there are
+extensive areas where the surface is nearly flat.
+
+The relief of the surface is of two somewhat different types. In some
+parts of the area, especially in the western part of the tract shown on
+Plate II, the surface is made up of a succession of ridges and valleys.
+The ridges may be broken by depressions at frequent intervals, but the
+valleys are nowhere similarly interrupted. It would rarely be possible
+to walk along a ridge or "divide" for many miles without descending into
+valleys; but once in a valley in any part of the area, it may be
+descended without interruption, until the Baraboo, the Wisconsin, the
+Mississippi, and finally the gulf is reached. In other words, the
+depressions are continuous, but the elevations are not. This is the
+first type of topography.
+
+Where this type of topography prevails its relation to drainage is
+evident at a glance. All the larger depressions are occupied by streams
+continuously, while the smaller ones contain running water during some
+part of the year. The relations of streams to the depressions, and the
+wear which the streams effect, whether they be permanent or temporary,
+suggest that running water is at least one of the agencies concerned in
+the making of valleys.
+
+An idea of the general arrangement of the valleys, as well as many
+suggestions concerning the evolution of the topography of the broken
+plain in which they lie might be gained by entering a valley at its
+head, and following it wherever it leads. At its head, the valley is
+relatively narrow, and its slopes descend promptly from either side in
+such a manner that a cross-section of the valley is V-shaped. In places,
+as west of Camp Douglas, the deep, steep-sided valleys are found to lead
+down and out from a tract of land so slightly rolling as to be well
+adapted to cultivation. Following down the valley, its progressive
+increase in width and depth is at once evident, and at the same time
+small tributary valleys come in from right and left. At no great
+distance from the heads of the valleys, streams are found in their
+bottoms.
+
+As the valleys increase in width and depth, and as the tributaries
+become more numerous and wider, the topography of which the valleys are
+a feature, becomes more and more broken. At first the tracts between the
+streams are in the form of ridges, wide if parallel valleys are distant
+from one another, and narrow if they are near. The ridges wind with the
+valleys which separate them. Whatever the width of the inter-stream
+ridges, it is clear that they must become narrower as the valleys
+between them become wider, and in following down a valley a point is
+reached, sooner or later, where the valleys, main and tributary, are of
+such size and so numerous that their slopes constitute a large part of
+the surface. Where this is true, and where the valleys are deep, the
+land is of little industrial value except for timber and grazing. When,
+in descending a valley system, this sort of topography is reached, the
+roads often follow either the valleys or the ridges, however indirect
+and crooked they may be. Where the ridges separating the valleys in such
+a region have considerable length, they are sometimes spoken of as "hog
+backs." Still farther down the valley system, tributary valleys of the
+second and lower orders cross the "hog backs," cutting them into hills.
+
+By the time this sort of topography is reached, a series of flats is
+found bordering the streams. These flats may occur on both sides of the
+stream, or on but one. The topography and the soil of these flats are
+such as to encourage agriculture, and the river flats or alluvial plains
+are among the choicest farming lands.
+
+With increasing distance from the heads of the valleys, these river
+plains are expanded, and may be widened so as to occupy the greater part
+of the surface. The intervening elevations are there relatively few and
+small. Their crests, however, often rise to the same level as that of
+the broader inter-stream areas farther up the valleys. The relations of
+the valleys and the high lands separating them, is such as to suggest
+that there are, generally speaking, two sets of flat surfaces, the
+higher one representing the upland in which the valleys lie, the lower
+one representing the alluvial plains of the streams. The two sets of
+flats are at once separated and connected by slopes. At the head of a
+drainage system, the upland flats predominate; in the lower courses, the
+river plains; in an intermediate stage, the slopes are more conspicuous
+than either upper or lower flat.
+
+Southwest from Devil's lake and northwest from Sauk City, in the valley
+of Honey creek, and again in the region southwest from Camp Douglas, the
+topography just described is well illustrated. In both these localities,
+as in all others where this type of topography prevails, the intimate
+relations of topography and drainage cannot fail to suggest that the
+streams which are today widening and deepening the valleys through which
+they flow, had much to do with their origin and development. This
+hypothesis, as applied to the region under consideration, may be tested
+by the study of the structure of the plain.
+
+The second type of topography affecting the plain about the quartzite
+ranges is found east of a line running from Kilbourn City to a point
+just north of Prairie du Sac. Though in its larger features the area
+east of this line resembles that to the west, its minor features are
+essentially different. Here there are many depressions which have no
+outlets, and marshes, ponds, and small lakes abound. Not only this, but
+many of the lesser elevations stand in no definite relation to valleys.
+The two types of topography make it clear that they were developed in
+different ways.
+
+_Structure._--Examination of the country surrounding the Baraboo ridges
+shows that its surface is underlaid at no great depth by horizontal or
+nearly horizontal beds of sandstone and limestone (see Plates XVI,
+XXVIII, and Frontispiece). These beds are frequently exposed on opposite
+sides of a valley, and in such positions the beds of one side are found
+to match those on the other. This is well shown along the narrow valley
+of Skillett creek just above the "Pewit's nest." Here the swift stream
+is rapidly deepening its channel, and it is clear that a few years
+hence, layers of sandstone which are now continuous beneath the bed of
+the creek will have been cut through, and their edges will appear on
+opposite sides of the valley just as higher layers do now. Here the most
+skeptical might be convinced that the layers of rock on either side of
+the narrow gorge were once continuous across it, and may see, at the
+same time, the means by which the separation was effected. Between the
+slight separation, here, where the valley is narrow, and the great
+separation where the valleys are wide, there are all gradations. The
+study of progressively wider valleys, commencing with such a gorge as
+that referred to, leaves no room for doubt that even the wide valleys,
+as well as the narrow ones, were cut out of the sandstone by running
+water.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. III.
+
+Illustration: FIG. 1.
+
+Ripple marks on a slab of Potsdam sandstone.
+
+Illustration: FIG. 2.
+
+Piece of Potsdam conglomerate. The larger pebbles are about three inches
+in diameter.]
+
+The same conclusion as to the origin of the valleys may be reached in
+another way. Either the beds of rock were formed with their present
+topography, or the valleys have been excavated in them since they were
+formed. Their mode of origin will therefore help to decide between these
+alternatives.
+
+_Origin of the sandstone and limestone._--The sandstone of the region,
+known as the Potsdam sandstone, consists of medium sized grains of
+sand, cemented together by siliceous, ferruginous, or calcareous cement.
+If the cement were removed, the sandstone would be reduced to sand, in
+all respect similar to that accumulating along the shores of seas and
+lakes today.
+
+The surfaces of the separate layers of sandstone are often distinctly
+ripple-marked (Fig. 1, Pl. III), and the character of the markings is
+identical in all essential respects with the ripples which affect the
+surface of the sand along the shores of Devil's lake, or sandy beaches
+elsewhere, at the present time. These ripple marks on the surfaces of
+the sandstone layers must have originated while the sand was movable,
+and therefore before it was cemented into sandstone.
+
+In the beds of sandstone, fossils of marine animals are found. Shells,
+or casts of shells of various sorts are common, as are also the tracks
+and burrowings of animals which had no shells. Among these latter signs
+of life may be mentioned the borings of worms. These borings are not now
+always hollow, but their fillings are often so unlike the surrounding
+rock, that they are still clearly marked. These worm borings, like the
+ripple marks, show that the sand was once loose.
+
+The basal beds of the sandstone are often conglomeratic. The
+conglomeratic layers are made up of water-worn pieces of quartzite,
+Plate III, Fig. 2, ranging in size from small pebbles to large bowlders.
+The interstices of the coarse material are filled by sand, and the whole
+cemented into solid rock. The conglomeratic phase of the sandstone may
+be seen to advantage at Parfrey's glen (a, Plate XXXVII) and Dorward's
+glen, (b, same plate) on the East bluff of Devil's lake above the Cliff
+House, and at the Upper narrows of the Baraboo, near Ablemans. It is
+also visible at numerous other less accessible and less easily
+designated places.
+
+From these several facts, viz.: the horizontal strata, the ripple-marks
+on the surfaces of the layers, the fossils, the character of the sand,
+and the water-worn pebbles and bowlders of the basal conglomerate,
+positive conclusions concerning the origin of the formation may be
+drawn.
+
+The arrangement in definite layers proves that the formation is
+sedimentary; that is, that its materials were accumulated in water
+whither they had been washed from the land which then existed. The
+ripple-marks show that the water in which the beds of sand were
+deposited was shallow, for in such water only are ripple-marks made.[1]
+Once developed on the surface of the sand they may be preserved by
+burial under new deposits, just as ripple-marks on sandy shores are now
+being buried and preserved.
+
+    [1] Ripple marks are often seen on the surface of wind-blown
+    sand, but the other features of this sandstone show that this
+    was not its mode of accumulation.
+
+The conglomerate beds of the formation corroborate the conclusions to
+which the composition and structure of the sandstone point. The
+water-worn shapes of the pebbles and stones show that they were
+accumulated in water, while their size shows that the water must have
+been shallow, for stones of such sizes are handled only by water of such
+slight depth that waves or strong currents are effective at the bottom.
+Furthermore, the large bowlders show that the source of supply
+(quartzite) must have been close at hand, and that therefore land
+composed of this rock must have existed not far from the places where
+the conglomerate is found.
+
+The fossils likewise are the fossils of aquatic life. Not only this, but
+they are the fossils of animals which lived in salt water. The presence
+of salt water, that is, the sea, in this region when the sand of the
+sandstone was accumulating, makes the wide extent of the formation
+rational.
+
+From the constitution and structure of the sandstone, it is therefore
+inferred that it accumulated in shallow sea water, and that, in the
+vicinity of Devil's lake, there were land masses (islands) of quartzite
+which furnished the pebbles and bowlders found in the conglomerate beds
+at the base of the formation.
+
+This being the origin of the sandstone, it is clear that the layers
+which now appear on opposite sides of valleys must once have been
+continuous across the depressions; for the sand accumulated in shallow
+water is never deposited so as to leave valleys between ridges. It is
+deposited in beds which are continuous over considerable areas.
+
+Within the area under consideration, limestone is much less widely
+distributed than sandstone. Thin beds of it alternate with layers of
+sandstone in the upper portion of the Potsdam formation, and more
+massive beds lie above the sandstone on some of the higher elevations of
+the plain about the quartzite ridge. This is especially true in the
+southern and southwestern parts of the region shown on Plate II. The
+limestone immediately overlying the sandstone is the _Lower Magnesian_
+limestone.
+
+The beds of limestone, like those of the sandstone beneath, are
+horizontal or nearly so, and the upper formation lies conformably on the
+lower. The limestone does not contain water-worn pebbles, and the
+surfaces of its layers are rarely if ever ripple-marked; yet the
+arrangement of the rock in distinct layers which carry fossils of marine
+animals shows that the limestone, like the sandstone beneath, was laid
+down in the sea. The bearing of this origin of the limestone on the
+development of the present valleys is the same as that of the sandstone.
+
+_Origin of the topography._--The topography of the plain surrounding the
+quartzite ridges, especially that part lying west of Devil's lake, is
+then an erosion topography, developed by running water. Its chief
+characteristic is that every depression leads to a lower one, and that
+the form of the elevations, hills or ridges, is determined by the
+valleys. The valleys were made; the hills and ridges left. If the
+material carried away by the streams could be returned, the valleys
+would be filled to the level of the ridges which bound them. Were this
+done, the restored surface would be essentially flat. It is the
+sculpturing of such a plain, chiefly by running water, which has given
+rise to the present topography.
+
+In the development of this topography the more resistant limestone has
+served as a capping, tending to preserve the hills and ridges. Thus many
+of the hills, especially in the southwest portion of the area shown in
+Plate II, are found to have caps of the Lower Magnesian formation. Such
+hills usually have flat tops and steep or even precipitous slopes down
+to the base of the capping limestone, while the sandstone below,
+weathering more readily, gives the lower portions of the hills a gentler
+slope.
+
+The elevations of the hills and ridges above the axes of the valleys or,
+in other words, the relief of the plain is, on the average, about 300
+feet, only a few of the more prominent hills exceeding that figure.
+
+The topography east of the line between Kilbourn City and Prairie du Sac
+is not of the unmodified erosion type, as is made evident by marshes,
+ponds and lakes. The departure from the erosion type is due to a mantle
+of glacial drift which masks the topography of the bedded rock beneath.
+Its nature, and the topographic modifications which it has produced, will
+be more fully considered in a later part of this report.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IV.
+
+The Lower Narrows of the Baraboo from a point on the South range.]
+
+
+                 II. THE QUARTZITE RIDGES.
+
+_Topography._--The South or main quartzite range, about 23 miles in
+length and one to four miles in width, rises 500 feet to 800 feet above
+the surrounding sandstone plain. Its slopes are generally too steep for
+cultivation, and are clothed for the most part with a heavy growth of
+timber, the banks of forest being broken here and there by cultivated
+fields, or by the purple grey of the rock escarpments too steep for
+trees to gain a foothold. With the possible exception of the Blue mounds
+southwest of Madison, this quartzite range is the most obtrusive
+topographic feature of southern Wisconsin.
+
+As approached from the south, one of the striking features of the range
+is its nearly even crest. Extending for miles in an east-west direction,
+its summit gives a sky-line of long and gentle curves, in which the
+highest points are but little above the lowest. Viewed from the north,
+the evenness of the crest is not less distinct, but from this side it is
+seen to be interrupted by a notable break or notch at Devil's lake
+(Plates V and XXXVII). The pass across the range makes a right-angled
+turn in crossing the range, and for this reason is not seen from the
+south.
+
+The North or lesser quartzite range lying north of Baraboo is both
+narrower and lower than the south range, and its crest is frequently
+interrupted by notches or passes, some of which are wide. Near its
+eastern end occurs the striking gap known as the _Lower narrows_ (Plate
+IV) through which the Baraboo river escapes to the northward, flowing
+thence to the Wisconsin. At this narrows the quartzite bluffs rise
+abruptly 500 feet above the river. At a and b, Plate II, there are
+similar though smaller breaks in the range, also occupied by streams.
+The connection between the passes and streams is therefore close.
+
+There are many small valleys in the sides of the quartzite ranges
+(especially the South range) which do not extend back to their crests,
+and therefore do not occasion passes across them. The narrow valleys at
+a and b in Plate XXXVII, known as Parfrey's and Dorward's glens,
+respectively, are singularly beautiful gorges, and merit mention as well
+from the scenic as from the geologic point of view. Wider valleys, the
+heads of which do not reach the crest, occur on the flanks of the main
+range (as at d and e, Plate II) at many points. One such valley
+occurs east of the north end of the lake (x, Plate XXXVII), another
+west of the south end (y, Plate XXXVII), another on the north face of
+the west bluff west of the north end of the lake and between the East
+and West Sauk roads, and still others at greater distances from the lake
+in both directions. It is manifest that if the valleys were extended
+headward in the direction of their axes, they would interrupt the even
+crest. Many of these valleys, unlike the glens mentioned above, are very
+wide in proportion to their length. In some of these capacious valleys
+there are beds of Potsdam sandstone, showing that the valleys existed
+before the sand of the sandstone was deposited.
+
+_The structure and constitution of the ridges._--The quartzite of the
+ridges is nothing more nor less than altered sandstone. Its origin dates
+from that part of geological time known to geologists as the Upper
+Huronian period. The popular local belief that the quartzite
+is of igneous origin is without the slightest warrant. It appears to
+have had its basis in the notion that Devil's lake occupies an extinct
+volcanic crater. Were this the fact, igneous rock should be found about
+it.
+
+Quartzite is sandstone in which the intergranular spaces have been
+filled with silica (quartz) brought in and deposited by percolating
+water subsequent to the accumulation of the sand. The conversion of
+sandstone into quartzite is but a continuation of the process which
+converts sand into sandstone. The Potsdam or any other sandstone
+formation might be converted into quartzite by the same process, and it
+would then be a _metamorphic_ rock.
+
+Like the sandstone, the quartzite is in layers. This is perhaps nowhere
+so distinctly shown on a large scale as in the bluffs at Devil's lake,
+and at the east end of the Devil's nose. On the East bluff of the lake,
+the stratification is most distinctly seen from the middle of the lake,
+from which point the photograph reproduced in Plate VI was taken.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. V.
+
+The Notch in the South quartzite range, at Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VI.
+
+The east bluff of Devil's lake, showing the dip of quartzite (to the
+left), and talus above and below the level where the beds are shown.]
+
+Unlike the sandstone and limestone, the beds of quartzite are not
+horizontal. The departure from horizontality, technically known as the
+_dip_, varies from point to point (Fig. 4). In the East bluff of the
+lake as shown in Plate VI, the dip is about 14° to the north. At the
+Upper and Lower narrows of the Baraboo (b and c, Plate II) the beds
+are essentially vertical, that is, they have a dip of about 90°. Between
+these extremes, many intermediate angles have been noted. Plate VII
+represents a view near Ablemans, in the Upper narrows, where the nearly
+vertical beds of quartzite are well exposed.
+
+The position of the beds in the quartzite is not always easy of
+recognition. The difficulty is occasioned by the presence of numerous
+cleavage planes developed in the rock after its conversion into
+quartzite. Some of these secondary cleavage planes are so regular and so
+nearly parallel to one another as to be easily confused with the bedding
+planes. This is especially liable to make determinations of the dip
+difficult, since the true bedding was often obscured when the cleavage
+was developed.
+
+In spite of the difficulties, the original stratification can usually be
+determined where there are good exposures of the rock. At some points
+the surfaces of the layers carry ripple marks, and where they are
+present, they serve as a ready means of identifying the bedding planes,
+even though the strata are now on edge. Layers of small pebbles are
+sometimes found. They were horizontal when the sands of the quartzite
+were accumulating, and where they are found they are sufficient to
+indicate the original position of the beds.
+
+Aside from the position of the beds, there is abundant evidence of
+dynamic action[2] in the quartzite. Along the railway at Devil's lake,
+half a mile south of the Cliff House, thin zones of schistose rock may
+be seen parallel to the bedding planes. These zones of schistose rock a
+few inches in thickness were developed from the quartzite by the
+slipping of the rock on either side. This slipping presumably occurred
+during the adjustment of the heavy beds of quartzite to their new
+positions, at the time of tilting and folding, for no thick series of
+rock can be folded without more or less slipping of the layers on one
+another. The slipping (adjustment) takes place along the weaker zones.
+Such zones of movement are sometimes known as _shear zones_, for the
+rock on the one side has been sheared (slipped) over that on the other.
+
+    [2] Irving: "The Baraboo Quartzite Ranges." Vol. II, Geology
+    of Wisconsin, pp. 504-519. Van Hise: "Some Dynamic Phenomena
+    Shown by the Baraboo Quartzite Ranges of Central Wisconsin."
+    Jour. of Geol., Vol. I, pp. 347-355.
+
+[Illustration: Fig. 4.--Diagram made by plotting the different dips now
+at hand along a section from A to B, Plate II, and connecting
+them so as to show the structure indicated by the known data. The full
+lines, oblique or vertical, represent the beds of quartzite. The
+continuous line above them represents the present surface of the
+quartzite, while the dotted lines suggest the continuation of the beds
+which completed the great folds of which the present exposures appear to
+be remnants.]
+
+[Illustration: Fig. 5.--A diagrammatic section showing the relation of
+the sandstone to the quartzite.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VII.
+
+The East Bluff at the Upper Narrows of the Baraboo near Ablemans,
+showing the vertical position of the beds of quartzite. In the lower
+right-hand corner, above the bridge, appears some breccia.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VIII.
+
+Vertical shear zone in face of east bluff at Devil's lake.]
+
+Near the shear zones parallel to the bedding planes, there is one
+distinct vertical shear zone (Plate VIII) three to four feet in width.
+It is exposed to a height of fully twenty-five feet. Along this zone the
+quartzite has been broken into angular fragments, and at places the
+crushing of the fragments has produced a "friction clay." Slipping along
+vertical zones would be no necessary part of folding, though it might
+accompany it. On the other hand, it might have preceded or followed the
+folding.
+
+Schistose structure probably does not always denote shearing, at least
+not the shearing which results from folding. Extreme pressure is likely
+to develop schistosity in rock, the cleavage planes being at right
+angles to the direction of pressure. It is not always possible to say
+how far the schistosity of rock at any given point is the result of
+shear, and how far the result of pressure without shear.
+
+Schistose structure which does not appear to have resulted from shear,
+at least not from the shear involved in folding, is well seen in the
+isolated quartzite mound about four miles southwest of Baraboo on the
+West Sauk road (f, Plate II). These quartzite schists are to be looked
+on as metamorphosed quartzite, just as quartzite is metamorphosed
+sandstone.
+
+At the Upper narrows of the Baraboo also (b, Plate II), evidence
+of dynamic action is patent. Movement along bedding planes with
+attendant development of quartz schist has occurred here as at the lake
+(Plate IX). Besides the schistose belts, a wide zone of quartzite
+exposed in the bluffs at this locality has been crushed into angular
+fragments, and afterwards re-cemented by white quartz deposited from
+solution by percolating waters (Plate X). This quartzite is said to be
+brecciated. Within this zone there are spots where the fragments of
+quartzite are so well rounded as to simulate water-worn pebbles. Their
+forms appear to be the result of the wear of the fragments on one
+another during the movements which followed the crushing. Conglomerate
+originating in this way is _friction conglomerate_ or _Reibungsbreccia_.
+
+The crushing of the rock in this zone probably took place while the beds
+were being folded; but the brecciated quartzite formed by the
+re-cementation of the fragments has itself been fractured and broken in
+such a manner as to show that the formation has suffered at least one
+dynamic movement since the development of the breccia. That these
+movements were separated by a considerable interval of time is shown by
+the fact that the re-cementation of the fragmental products of the first
+movement preceded the second.
+
+What has been said expresses the belief of geologists as to the origin
+of quartzite and quartz schists; but because of popular misconception on
+the point it may here be added that neither the changing of the
+sandstone into quartzite, nor the subsequent transformation of the
+quartzite to schist, was due primarily to heat. Heat was doubtless
+generated in the mechanical action involved in these changes, but it was
+subordinate in importance, as it was secondary in origin.
+
+Igneous rock is associated with the quartzite at a few points. At g
+and h, Plate II there are considerable masses of porphyry,
+sustaining such relations to the quartzite as to indicate that they were
+intruded into the sedimentary beds after the deposition of the latter.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IX.
+
+A mass of quartzite _in situ_, in the road through the Upper Narrows
+near Ableman's. The bedding, which is nearly vertical, is indicated by
+the shading, while the secondary cleavage approaches horizontality.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. X.
+
+Brecciated quartzite near Ablemans in the Upper Narrows. The darker
+parts are quartzite, the lighter parts the cementing quartz.]
+
+
+ III. RELATIONS OF THE SANDSTONE OF THE PLAIN TO THE QUARTZITE OF THE
+                            RIDGES.
+
+The horizontal beds of Potsdam sandstone may be traced up to the bases
+of the quartzite ranges, where they may frequently be seen to abut
+against the tilted beds of quartzite. Not only this, but isolated
+patches of sandstone lie on the truncated edges of the dipping beds of
+quartzite well up on the slopes, and even on the crest of the ridge
+itself. In the former position they may be seen on the East bluff at
+Devil's lake, where horizontal beds of conglomerate and sandstone rest
+on the layers of quartzite which dip 14° to the north.
+
+The stratigraphic relations of the two formations are shown in Fig. 5
+which represents a diagrammatic section from A to B, Plate II. Plate XI
+is reproduced from a photograph taken in the Upper narrows of the
+Baraboo near Ablemans, and shows the relations as they appear in the
+field. The quartzite layers are here on edge, and on them rest the
+horizontal beds of sandstone and conglomerate. Similar stratigraphic
+relations are shown at many other places. This is the relationship of
+_unconformity_.
+
+Such an unconformity as that between the sandstone and the quartzite of
+this region shows the following sequence of events: (1) the quartzite
+beds were folded and lifted above the sea in which the sand composing
+them was originally deposited; (2) a long period of erosion followed,
+during which the crests of the folds were worn off; (3) the land then
+sank, allowing the sea to again advance over the region; (4) while the
+sea was here, sand and gravel derived from the adjacent lands which
+remained unsubmerged, were deposited on its bottom. These sands became
+the Potsdam sandstone.
+
+This sequence of events means that between the deposition of the
+quartzite and the sandstone, the older formation was disturbed and
+eroded. Either of these events would have produced an unconformity; the
+two make it more pronounced. That the disturbance of the older formation
+took place before the later sandstone was deposited is evident from the
+fact that the latter formation was not involved in the movements which
+disturbed the former.
+
+Although the sandstone appears in patches on the quartzite ranges, it is
+primarily the formation of the surrounding plains, occupying the broad
+valley between the ranges, and the territory surrounding them. The
+quartzite, on the other hand, is the formation of the ridges, though it
+outcrops at a few points in the plain. (Compare Plates II and XXXVII.)
+The striking topographic contrasts between the plains and the ridges is
+thus seen to be closely related to the rock formations involved. It is
+the hard and resistant quartzite which forms the ridges, and the less
+resistant sandstone which forms the lowlands about them.
+
+That quartzite underlies the sandstone of the plain is indicated by the
+occasional outcrops of the former rock on the plain, and from the fact
+that borings for deep wells have sometimes reached it where it is not
+exposed.
+
+The sandstone of the plain and the quartzite of the ridges are not
+everywhere exposed. A deep but variable covering of loose material or
+_mantle rock (drift)_ is found throughout the eastern part of the area,
+but it does not extend far west of Baraboo. This mantle rock is so thick
+and so irregularly disposed that it has given origin to small hills and
+ridges. These elevations are superimposed on the erosion topography of
+the underlying rock, showing that the drift came into the region after
+the sandstone, limestone, and quartzite had their present relations, and
+essentially their present topography. Further consideration will be
+given to the drift in a later part of this report.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XI.
+
+The northeast wall of the Upper Narrows, north of Ableman's, showing the
+horizontal Potsdam sandstone and conglomerate lying unconformably on the
+quartzite, the beds of which are vertical.]
+
+
+
+
+                            PART II.
+
+
+                   HISTORY OF THE TOPOGRAPHY.
+
+
+
+
+                          CHAPTER II.
+
+
+ OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS WHICH SHOW THEMSELVES AT
+                         THE SURFACE.
+
+
+          I. THE PRE-CAMBRIAN HISTORY OF THE QUARTZITE.
+
+_From loose sand to quartzite._--To understand the geography of a region
+it is necessary to understand the nature of the materials, the sculpture
+of which has made the geography.
+
+It has already been indicated that the Huronian quartzite of
+which the most prominent elevations of this region are composed, was
+once loose sand. Even at the risk of repetition, the steps in its
+history are here recounted. The source of the sand was probably the
+still older rocks of the land in the northern part of Wisconsin. Brought
+down to the sea by rivers, or washed from the shores of the land by
+waves, the sand was deposited in horizontal or nearly horizontal beds at
+the bottom of the shallow water which then covered central and southern
+Wisconsin. Later, perhaps while it was still beneath the sea, the sand
+was converted into sandstone, the change being effected partly by
+compression which made the mass of sand more compact, but chiefly by the
+cementation of its constituent grains into a coherent mass. The water
+contained in the sand while consolidation was in progress, held in
+solution some slight amount of silica, the same material of which the
+grains of sand themselves are composed. Little by little this silica in
+solution was deposited on the surfaces of the sand grains, enlarging
+them, and at the same time binding them together. Thus the sand became
+sandstone. Continued deposition of silica between and around the grains
+finally filled the interstitial spaces, and when this process was
+completed, the sandstone had been converted into quartzite. While
+quartzite is a metamorphic sandstone, it is not to be understood that
+sandstone cannot be metamorphosed in other ways.
+
+_Uplift and deformation. Dynamic metamorphism._--After the deposition of
+the sands which later became the quartzite, the beds were uplifted and
+deformed, as their present positions and relations show. It is
+not possible to say how far the process of transformation of sand into
+quartzite was carried while the formation was still beneath the shallow
+sea in which it was deposited. The sand may have been changed to
+sandstone, and the sandstone to quartzite, before the sea bottom was
+converted into land, while on the other hand, the formation may have
+been in any stage of change from sand to quartzite, when that event
+occurred. If the process of change was then incomplete, it may have been
+continued after the sea retired, by the percolating waters derived from
+the rainfall of the region.
+
+Either when first converted into land, or at some later time, the beds
+of rock were folded, and suffered such other changes as attend profound
+dynamic movements. The conversion of the sandstone into quartzite
+probably preceded the deformation, since many phenomena indicate that
+the rock was quartzite and not sandstone when the folding took place.
+For example, the crushing of the quartzite (now re-cemented into
+brecciated quartzite) at Ablemans probably dates from the orogenic
+movements which folded the quartzite, and the fractured bits of rock
+often have corners and edges so sharp as to show that the rock was
+thoroughly quartzitic when the crushing took place.
+
+The uplift and deformation of the beds was probably accomplished slowly,
+but the vertical and highly tilted strata show that the changes were
+profound (see Fig. 4).
+
+The dynamic metamorphism which accompanied this profound deformation has
+already been referred to. The folding of the beds involved the
+slipping of some on others, and this resulted in the development of
+quartz schist along the lines of severest movement. Changes effected in
+the texture and structure of the rock under such conditions constitute
+_dynamic metamorphism_. In general, the metamorphic changes effected
+by dynamic action are much more profound than those brought about in
+other ways, and most rocks which have been profoundly metamorphosed,
+were changed in this way. Dynamic action generates heat, but contrary to
+the popular notion, the heat involved in profound metamorphism is
+usually secondary, and the dynamic action fundamental.
+
+At the same time that quartz schist was locally developed from the
+quartzite, crushing probably occurred in other places. This is
+_demorphism_, rather than metamorphism.
+
+_Erosion of the quartzite._--When the Huronian beds were raised to the
+estate of land, the processes of erosion immediately began to work on
+them. The heat and the cold, the plants and the animals, the winds, and
+especially the rain and the water which came from the melting of the
+snow, produced their appropriate effects. Under the influence of these
+agencies the surface of the rock was loosened by weathering, valleys
+were cut in it by running water, and wear and degradation went on at all
+points.
+
+The antagonistic processes of uplift and degradation went on for
+unnumbered centuries, long enough for even the slow processes involved
+to effect stupendous results. Degradation was continuous after the
+region became land, though uplift may not have been. On the whole,
+elevation exceeded degradation, for some parts of the quartzite finally
+came to stand high above the level of the sea,--the level to which all
+degradation tends.
+
+Fig. 4 conveys some notion of the amount of rock which was
+removed from the quartzite folds about Baraboo during this long period
+of erosion. The south range would seem to represent the stub of one side
+of a great anticlinal fold, a large part of which (represented by the
+dotted lines) was carried away, while the north range may be the core of
+another fold, now exposed by erosion.
+
+Some idea of the geography of the quartzite at the close of this period
+of erosion may be gained by imagining the work of later times undone.
+The younger beds covering the quartzite of the plains have a thickness
+varying from zero to several hundred feet, and effectually mask the
+irregularities of the surface of the subjacent quartzite. Could they be
+removed, the topography of the quartzite would be disclosed, and found
+to have much greater relief than the present surface; that is, the
+vertical distance between the crest of the quartzite ridge, and the
+surface of the quartzite under the surrounding lowlands, would be
+greater than that between the same crest and the surface of the
+sandstone. But even this does not give the full measure of the relief of
+the quartzite at the close of the long period of erosion which followed
+its uplift, for allowance must be made for the amount of erosion which
+the crests of the quartzite ranges have suffered since that time. The
+present surface therefore does not give an adequate conception of the
+irregularity of the surface at the close of the period of erosion which
+followed the uplift and deformation of the quartzite. So high were the
+crests of the quartzite ranges above their surroundings at that time,
+that they may well be thought of as mountainous. From this point of
+view, the quartzite ranges of today are the partially buried mountains
+of the pre-Potsdam land of south central Wisconsin.
+
+When the extreme hardness of the quartzite is remembered and also the
+extent of the erosion which affected it (Fig. 4) before the next
+succeeding formation was deposited, it is safe to conclude that the
+period of erosion was very long.
+
+_Thickness of the quartzite._--The thickness of the quartzite is not
+known, even approximately. The great thickness in the south range
+suggested by the diagram (Fig. 4) may perhaps be an exaggeration.
+Faulting which has not been discovered may have occurred, causing
+repetition of beds at the surface (Fig. 6), and so an exaggerated
+appearance of thickness. After all allowances have been made, it is
+still evident that the thickness of the quartzite is very great.
+
+
+             II. THE HISTORY OF THE PALEOZOIC STRATA.
+
+_The subsidence._--Following the long period of erosion, the irregular
+and almost mountainous area of central Wisconsin was depressed
+sufficiently to submerge large areas which had been land. The subsidence
+was probably slow, and as the sea advanced from the south, it covered
+first the valleys and lowlands, and later the lower hills and ridges,
+while the higher hills and ridges of the quartzite stood as islands in
+the rising sea. Still later, the highest ridges of the region were
+themselves probably submerged.
+
+[Illustration: Fig. 6.--A diagrammatic cross-section, showing how, by
+faulting, the apparent thickness of the quartzite would be increased.]
+
+_The Potsdam sandstone (and conglomerate)._--So soon as the sea began to
+overspread the region, its bottom became the site of deposition, and the
+deposition continued as long as the submergence lasted. It is to the
+sediments deposited during the earlier part of this submergence that the
+name _Potsdam_ is given.
+
+The sources of the sediments are not far to seek. As the former land was
+depressed beneath the sea, its surface was doubtless covered with the
+products of rock decay, consisting of earths, sands, small bits and
+larger masses of quartzite. These materials, or at least the finer
+parts, were handled by the waves of the shallow waters, for they were at
+first shallow, and assorted and re-distributed. Thus the residuary
+products on the submerged surface, were one source of sediments.
+
+From the shores also, so long as land areas remained, the waves derived
+sediments. These were composed in part of the weathered products of the
+rock, and in part of the undecomposed rock against which the waves
+beat, after the loose materials had been worn away. These sediments
+derived from the shore were shifted, and finally mingled with those
+derived from the submerged surface.
+
+So long as any part of the older land remained above the water, its
+streams brought sediments to the sea. These also were shifted by the
+waves and shore currents, and finally deposited with the others on the
+eroded surface of the quartzite. Thus sediments derived in various ways,
+but inherently essentially similar, entered into the new formation.
+
+[Illustration: Fig. 7.--Diagram to illustrate the theoretical
+disposition of sediments about an island.]
+
+[Illustration: Fig. 8.--Same as Fig. 7, except that the land has been
+depressed.]
+
+The first material to be deposited on the surface of the quartzite as it
+was submerged, was the coarsest part of the sediment. Of the sediment
+derived by the waves from the coasts, and brought down to the sea by
+rivers, the coarsest would at each stage be left nearest the shore,
+while the finer was carried progressively farther and farther from it.
+Thus at each stage the sand was deposited farther from the shore than
+the gravel, and the mud farther than the sand, where the water was so
+deep that the bottom was subject to little agitation by waves. The
+theoretical distribution of sediments about an island as it was
+depressed, is illustrated by the following diagrams, Figs. 7 and 8. It
+will be seen that the surface of the quartzite is immediately overlain
+by conglomerate, but that the conglomerate near its top is younger than
+that near its base.
+
+In conformity with this natural distribution of sediments, the basal
+beds of the Potsdam formation are often conglomeratic (Fig. 9, Plate
+III, Fig. 2, and Plate XXV). This may oftenest be seen near
+the quartzite ridges, for here only is the base of the formation
+commonly exposed. The pebbles and larger masses of the conglomerate are
+quartzite, like that of the subjacent beds, and demonstrate the source
+of at least some of the material of the younger formation. That the
+pebbles and bowlders are of quartzite is significant, for it shows that
+the older formation had been changed from sandstone to quartzite, before
+the deposition of the Potsdam sediments. The sand associated with the
+pebbles may well have come from the breaking up of the quartzite, though
+some of it may have been washed in from other sources by the waters in
+which the deposition took place.
+
+[Illustration: Fig. 9.--Sketch showing relation of basal Potsdam
+conglomerate and sandstone to the quartzite, on the East bluff at
+Devil's lake, behind the Cliff house.]
+
+The basal conglomerate may be seen at many places, but nowhere about
+Devil's lake is it so well exposed as at Parfrey's glen (a, Plate
+XXXVII), where the rounded stones of which it is composed vary
+from pebbles, the size of a pea, to bowlders more than three feet in
+diameter. Other localities where the conglomerates may be seen to
+advantage are Dorward's glen (b, Plate XXXVII), the East bluff at
+Devil's lake just above the Cliff house, and at the Upper narrows of the
+Baraboo, above Ablemans.
+
+While the base of the Potsdam is conglomeratic in many places, the main
+body of it is so generally sandstone that the formation as a whole is
+commonly known as the Potsdam sandstone.
+
+The first effect of the sedimentation which followed submergence was to
+even up the irregular surface of the quartzite, for the depressions in
+the surface were the first to be submerged, and the first to be filled.
+As the body of sediment thickened, it buried the lower hills and the
+lower parts of the higher ones. The extent to which the Potsdam
+formation buried the main ridge may never be known. It may have buried
+it completely, for as already stated patches of sandstone are
+found upon the main range. These patches make it clear that some
+formation younger than the quartzite once covered essentially all of the
+higher ridge. Other evidence to be adduced later, confirms this
+conclusion. It has, however, not been demonstrated that the high-level
+patches of sandstone are Potsdam.
+
+There is abundant evidence that the subsidence which let the Potsdam
+seas in over the eroded surface of the Huronian quartzite was gradual.
+One line of evidence is found in the cross-bedding of the sandstone
+(Plate XII) especially well exhibited in the Dalles of the Wisconsin.
+The beds of sandstone are essentially horizontal, but within the
+horizontal beds there are often secondary layers which depart many
+degrees from horizontality, the maximum being about 24°. Plates XXVII
+and XII give a better idea of the structure here referred to than
+verbal description can.
+
+The explanation of cross-bedding is to be found in the varying
+conditions under which sand was deposited. Cross-bedding denotes shallow
+water, where waves and shore currents were effective at the bottom where
+deposition is in progress. For a time, beds were deposited off shore at
+a certain angle, much as in the building of a delta (Fig. 10). Then by
+subsidence of the bottom, other layers with like structure were
+deposited over the first. By this sequence of events, the dip of the
+secondary layers should be toward the open water, and in this region
+their dip is generally to the south. At any stage of deposition the waves
+engendered by storms were liable to erode the surface of the deposits
+already made, and new layers, discordant with those below, were likely
+to be laid down upon them. The subordinate layers of each deposit might
+dip in any direction. If this process were repeated many times during
+the submergence, the existing complexity would be explained.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XII.
+
+Steamboat rock,--an island in the Dalles of the Wisconsin.]
+
+[Illustration: Fig. 10.--A diagrammatic cross-section of a delta.]
+
+The maximum known thickness of the Potsdam sandstone in Wisconsin is
+about 1,000 feet, but its thickness in this region is much less. Where
+not capped by some younger formation, its upper surface has suffered
+extensive erosion, and the present thickness therefore falls short of
+the original. The figures given above may not be too great for the
+latter.
+
+_The Lower Magnesian limestone._--The conditions of sedimentation
+finally changed in the area under consideration. When the sand of the
+sandstone was being deposited, adjacent lands were the source whence the
+sediments were chiefly derived. The evidence that the region was sinking
+while the sand was being deposited shows that the land masses which were
+supplying the sand, were becoming progressively smaller. Ultimately the
+sand ceased to be washed out to the region here described, either
+because the water became too deep[3] or because the source of supply
+was too distant. When these relations were brought about, the conditions
+were favorable for the deposition of sediments which were to become
+limestone. These sediments consisted chiefly of the shells of marine
+life, together with an unknown amount of lime carbonate precipitated
+from the waters of the sea. The limestone contains no coarse, and but
+little fine material derived from the land, and the surfaces of its
+layers are rarely if ever ripple-marked. The materials of which it is
+made must therefore have been laid down in quiet waters which were
+essentially free from land-derived sediments. The depth of the water in
+which it was deposited was not, however, great, for the fossils are not
+the remains of animals which lived in abysmal depths.
+
+    [3] A few hundred feet would suffice.
+
+The deposition of limestone sediments following the deposition of the
+Potsdam sands, does not necessarily mean that there was more or
+different marine life while the younger formation was making, but only
+that the shells, etc., which before had been mingled with the sand,
+making fossiliferous sandstone, were now accumulated essentially free
+from land-derived sediment, and therefore made limestone.
+
+Like the sandstone beneath, the limestone formation has a wide
+distribution outside the area here under discussion, showing that
+conditions similar to those of central Wisconsin were widely distributed
+at this time.
+
+The beds of limestone are conformable on those of the sandstone, and the
+conformable relations of the two formations indicate that the deposition
+of the upper followed that of the lower, without interruption.
+
+The thickness of the Lower Magnesian limestone varies from less than 100
+to more than 200 feet, but in this region its thickness is nearer the
+lesser figure than the larger. The limestone is now present only in the
+eastern and southern parts of the area, though it originally covered the
+whole area.
+
+_The St. Peters sandstone._--Overlying the Lower Magnesian limestone at
+a few points, are seen remnants of St. Peters sandstone. The
+constitution of this formation shows that conditions of sedimentation
+had again changed, so that sand was again deposited where the conditions
+had been favorable to the deposition of limestone but a short time
+before. This formation has been recognized at but two places (d and
+e) within the area shown on Plate XXXVII, but the relations at these
+two points are such as to lead to the conclusion that the formation may
+once have covered the entire region. This sandstone formation is very
+like the sandstone below. Its materials doubtless came from the lands
+which then existed. The formation is relatively thin, ranging from
+somewhat below to somewhat above 100 feet.
+
+The change from the deposition of limestone sediments to sand may well
+have resulted from the shoaling of the waters, which allowed the sand to
+be carried farther from shore. Rise of the land may have accompanied the
+shoaling of the waters, and the higher lands would have furnished more
+and coarser sediments to the sea.
+
+_Younger beds._--That formations younger than the St. Peters sandstone
+once overlaid this part of Wisconsin is almost certain, though no
+remnants of them now exist. Evidence which cannot be here detailed[4]
+indicates that sedimentation about the quartzite ridges went on not only
+until the irregularities of surface were evened up, but until even the
+highest peaks of the quartzite were buried, and that formations as high
+in the series as the Niagara limestone once overlay their crests. Before
+this condition was reached, the quartzite ridges had of course ceased to
+be islands, and at the same time had ceased to be a source of supply of
+sediments. The aggregate thickness of the Paleozoic beds in the region,
+as first deposited, was probably not less than 1,500 feet, and it may
+have been much more. This thickness would have buried the crests of the
+quartzite ridges under several hundred feet of sediment (see Fig. 11).
+
+    [4] Jour. of Geol., Vol. III (pp. 655-67).
+
+[Illustration: Fig. 11.--The geological formations of southern Wisconsin
+in the order of their occurrence. Not all of these are found about
+Devil's lake.]
+
+It is by no means certain that south central Wisconsin was continuously
+submerged while this thick series of beds was being deposited. Indeed,
+there is good reason to believe that there was at least one period of
+emergence, followed, after a considerable lapse of time, by
+re-submergence and renewed deposition, before the Paleozoic series of
+the region was complete. These movements, however, had little effect on
+the geography of the region.
+
+Finally the long period of submergence, during which several changes in
+sedimentation had taken place, came to an end, and the area under
+discussion was again converted into land.
+
+_Time involved._--Though it cannot be reduced to numerical terms, the
+time involved in the deposition of these several formations of the
+Paleozoic must have been very long. It is probably to be reckoned in
+millions of years, rather than in denominations of a lower order.
+
+_Climatic conditions._--Little is known concerning the climate of this
+long period of sedimentation. Theoretical considerations have usually
+been thought to lead to the conclusion that the climate during this part
+of the earth's history was uniform, moist, and warm; but the conclusion
+seems not to be so well founded as to command great confidence.
+
+_The uplift._--After sedimentation had proceeded to some such extent as
+indicated, the sea again retired from central Wisconsin. This may have
+been because the sea bottom of this region rose, or because the sea
+bottom in other places was depressed, thus drawing off the water. The
+topography of this new land, like the topography of those portions of
+the sea bottom which are similarly situated, must have been for the most
+part level. Low swells and broad undulations may have existed, but no
+considerable prominences, and no sudden change of slope. The surface was
+probably so flat that it would have been regarded as a level surface had
+it been seen.
+
+The height to which the uplift carried the new land surface at the
+outset must ever remain a matter of conjecture. Some estimate may be
+made of the amount of uplift which the region has suffered since the
+beginning of this uplift, but it is unknown how much took place at this
+time, and how much in later periods of geological history.
+
+The new land surface at once became the site of new activities. All
+processes of land erosion at once attacked the new surface, in the
+effort to carry its materials back to the sea. The sculpturing of this
+plain, which, with some interruption, has continued to the present day,
+has given the region the chief elements of its present topography. But
+before considering the special history of erosion in this region, it may
+be well to consider briefly the general principles and processes of land
+degradation.
+
+
+                          CHAPTER III.
+
+
+           GENERAL OUTLINE OF RAIN AND RIVER EROSION.
+
+
+_Elements of erosion._--The general process of subaerial erosion is
+divisible into the several sub-processes of weathering, transportation,
+and corrasion.[5]
+
+    [5] There is an admirable exposition of this subject in
+    Gilbert's "Henry Mountains."
+
+_Weathering_ is the term applied to all those processes which
+disintegrate and disrupt exposed surfaces of rock. It is accomplished
+chiefly by solution, changes in temperature, the wedge-work of ice and
+roots, the borings of animals, and such chemical changes as surface
+water and air effect. The products of weathering are transported by the
+direct action of gravity, by glaciers, by winds, and by running water.
+Of these the last is the most important.
+
+_Corrasion_ is accomplished chiefly by the mechanical wear of streams,
+aided by the hard fragments such as sand, gravel and bowlders, which
+they carry. The solution effected by the waters of a stream may also be
+regarded as a part of corrasion. Under ordinary circumstances solution
+by streams is relatively unimportant, but where the rock is relatively
+soluble, and where conditions are not favorable for abrasion, solution
+may be more important than mechanical wear.
+
+So soon as sea bottom is raised to the estate of land, it is attacked by
+the several processes of degradation. The processes of weathering at
+once begin to loosen the material of the surface if it be solid; winds
+shift the finer particles about, and with the first shower
+transportation by running water begins. Weathering prepares the material
+for transportation and transportation leads to corrasion. Since the goal
+of all material transported by running water is the sea, subaerial
+erosion means degradation of the surface.
+
+_Erosion without valleys._--In the work of degradation the valley
+becomes the site of greatest activity, and in the following pages
+especial attention is given to the development of valleys and to the
+phases of topography to which their development leads.
+
+If a new land surface were to come into existence, composed of materials
+which were perfectly homogeneous, with slopes of absolute uniformity in
+all directions, and if the rain, the winds and all other surface
+agencies acted uniformly over the entire area, valleys would not be
+developed. That portion of the rainfall which was not evaporated and did
+not sink beneath the surface, would flow off the land in a sheet. The
+wear which it would effect would be equal in all directions from the
+center. If the angle of the slope were constant from center to shore, or
+if it increased shoreward, the wear effected by this sheet of water
+would be greatest at the shore, because here the sheet of flowing water
+would be deepest and swiftest, and therefore most effective in
+corrasion.
+
+_The beginning of a valley._--But land masses as we know them do not
+have equal and uniform slopes to the sea in all directions, nor is the
+material over any considerable area perfectly homogeneous. Departure
+from these conditions, even in the smallest degree, would lead to very
+different results.
+
+That the surface of newly emerged land masses would, as a rule, not be
+rough, is evident from the fact that the bottom of the sea is usually
+rather smooth. Much of it indeed is so nearly plane that if the water
+were withdrawn, the eye would scarcely detect any departure from
+planeness. The topography of a land mass newly exposed either by its own
+elevation or by the withdrawal of the sea, would ordinarily be similar
+to that which would exist in the vicinity of Necedah and east of Camp
+Douglas, if the few lone hills were removed, and the very shallow
+valleys filled. Though such a surface would seem to be moderately
+uniform as to its slopes, and homogeneous as to its material, neither
+the uniformity nor the homogeneity are perfect, and the rain water would
+not run off in sheets, and the wear would not be equal at all points.
+
+Let it be supposed that an area of shallow sea bottom is raised above
+the sea, and that the elevation proceeds until the land has an altitude
+of several hundred feet. So soon as it appears above the sea, the rain
+falling upon it begins to modify its surface. Some of the water
+evaporates at once, and has little effect on the surface; some of it
+sinks beneath the surface and finds its way underground to the sea; and
+some of it runs off over the surface and performs the work
+characteristic of streams. So far as concerns modifications of the
+surface, the run-off is the most important part.
+
+The run-off of the surface would tend to gather in the depressions of
+the surface, however slight they may be. This tendency is shown on
+almost every hillside during and after a considerable shower. The water
+concentrated in the depressions is in excess of that flowing over other
+parts of the surface, and therefore flows faster. Flowing faster, it
+erodes the surface over which it flows more rapidly, and as a result the
+initial depressions are deepened, and _washes_ or _gullies_ are started.
+
+Should the run-off not find irregularities of slope, it would, at the
+outset, fail of concentration; but should it find the material more
+easily eroded along certain lines than along others, the lines of easier
+wear would become the sites of greater erosion. This would lead to the
+development of gullies, that is, to irregularities of slope. Either
+inequality of slope or material may therefore determine the location of
+a gully, and one of these conditions is indispensable.
+
+Once started, each wash or gully becomes the cause of its own growth,
+for the gully developed by the water of one shower, determines greater
+concentration of water during the next. Greater concentration means
+faster flow, faster flow means more rapid wear, and this means
+corresponding enlargement of the depression through which the flow takes
+place. The enlargement effected by successive showers affects a gully in
+all dimensions. The water coming in at its head carries the head back
+into the land (head erosion), thus lengthening the gully; the water
+coming in at its sides wears back the lateral slopes, thus widening it;
+and the water flowing along its bottom deepens it. Thus gullies grow to
+be ravines, and farther enlargement by the same processes converts
+ravines into valleys. A river valley therefore is often but a gully
+grown big.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIII.
+
+FIG. 1.
+
+A very young valley.
+
+Illustration: FIG. 2.
+
+A valley in a later stage of development.
+
+Illustration: FIG. 3.
+
+Young valleys.]
+
+_The course of a valley._--In the lengthening of a gully or valley
+headward, the growth will be in the direction of greatest wear. Thus in
+Plate XIII, Fig. 1, if the water coming in at the head of the gully
+effects most wear in the direction a, the head of the gully will
+advance in that direction; if there be most wear in the direction b or
+c, the head will advance toward one of these points. The direction of
+greatest wear will be determined either by the slope of the surface, or
+by the nature of the surface material. The slope may lead to the
+concentration of the entering waters along one line, and the surface
+material may be less resistant in one direction than in another. If
+these factors favor the same direction of head-growth, the lengthening
+will be more rapid than if but one is favorable. If there be more rapid
+growth along two lines, as b and c, Plate XIII, Fig. 1, than between
+them, two gullies may develop (Plate XIII, Fig. 2). The frequent and
+tortuous windings common to ravines and valleys are therefore to be
+explained by the inequalities of slope or material which affected the
+surface while the valley was developing.
+
+_Tributary valleys._--Following out this simple conception of valley
+growth, we have to inquire how a valley system (a main valley and its
+tributaries) is developed. The conditions which determine the location
+and development of gullies in a new land surface, determine the location
+and development of tributary gullies. In flowing over the lateral slopes
+of a gully or ravine, the water finds either slope or surface material
+failing of uniformity. Both conditions lead to the concentration of the
+water along certain lines, and concentration of flow on the slope of an
+erosion depression, be it valley or gully, leads to the development of
+a tributary depression. In its growth, the tributary repeats, in all
+essential respects, the history of its main. It is lengthened headward
+by water coming in at its upper end, is widened by side wash, and
+deepened by the downward cutting of the water which flows along its
+axis. The factors controlling its development are the same as those
+which controlled the valley to which it is tributary.
+
+There is one peculiarity of the courses of tributaries which deserves
+mention. Tributaries, as a rule, join their mains with an acute angle up
+stream. In general, new land surfaces, such as are now under
+consideration, slope toward the sea. If a tributary gully were to start
+back from its main at right angles, more water would come in on the side
+away from the shore, on account of the seaward slope of the land. This
+would be true of the head of the gully as well as of other portions, and
+the effect would be to turn the head more and more toward parallelism
+with the main valley. Local irregularities of surface may, and
+frequently do, interfere with these normal relations, so that the
+general course of a tributary is occasionally at right angles to its
+main. Still more rarely does the general course of a tributary make an
+acute angle with its main on the down stream side. Local irregularities
+of surface determine the windings of a tributary, so that their courses
+for longer or shorter distances may be in violation of the general rule
+(c, Fig. 43); but on the whole, the valleys of a system whose
+history has not been interrupted in a region where the surface material
+is not notably heterogeneous, follow the course indicated above. This is
+shown by nearly every drainage system on the Atlantic Coastal plain
+which represents more nearly than any other portion of our continent,
+the conditions here under consideration. Fig. 12 represents the drainage
+system of the Mullica river in southern New Jersey and is a type of the
+Coastal plain river system.
+
+_How a valley gets a stream._--Valleys may become somewhat deep and long
+and wide without possessing permanent streams, though from their
+inception they have _temporary_ streams, the water for which is
+furnished by showers or melting snow. Yet sooner or later, valleys come
+to have permanent streams. How are they acquired? Does the valley find
+the stream or the stream the valley? For the answer to these questions,
+a brief digression will be helpful.
+
+[Illustration: Fig. 12.--A typical river system of the Coastal plain
+type.]
+
+In cultivated regions, wells are of frequent occurrence. In a flat
+region of uniform structure, the depth at which well water may be
+obtained is essentially constant at all points. If holes (wells 1 and 2,
+Fig. 13) be excavated below this level, water seeps into them, and in a
+series of wells the water stands at a nearly common level. This means
+that the sub-structure is full of water up to that level. These
+relations are illustrated by Fig. 13. The diagram represents a vertical
+section through a flat region from the surface (s s) down below the
+bottom of wells. The water stands at the same level in the two cells (1
+and 2), and the plane through them, at the surface of the water, is the
+_ground water level_. If in such a surface a valley were to be cut until
+its bottom was below the ground water level, the water would seep into
+it, as it does into the wells; and if the amount were sufficient, a
+permanent stream would be established. This is illustrated in Fig. 13.
+The line A A represents the ground water level, and the level at which
+the water stands in the wells, under ordinary circumstances. The bottom
+of the valley is below the level of the ground water, and the water
+seeps into it from either side. Its tendency is to fill the valley to
+the level A A. But instead of accumulating in the open valley as it does
+in the enclosed wells, it flows away, and the ground water level on
+either hand is drawn down.
+
+[Illustration: Fig. 13.--Diagram illustrating the relations of ground
+water to streams.]
+
+The level of the ground water fluctuates. It is depressed when the
+season is dry (A' A'), and raised when precipitation is abundant (A''
+A''). When it is raised, the water in the wells rises, and the stream in
+the valley is swollen. When it falls, the ground water surface is
+depressed, and the water in the wells becomes lower. If the water
+surface sinks below the bottom of the wells, the wells "go dry;" if
+below the bottom of the valley, the valley becomes for the time being, a
+"dry run." When a well is below the lowest ground-water level its supply
+of water never fails, and when the valley is sufficiently below the same
+level, its stream does not cease to flow, even in periods of drought. On
+account of the free evaporation in the open valley, the valley
+depression must be somewhat below the level necessary for a well, in
+order that the flow may be constant.
+
+It will be seen that _intermittent_ streams, that is, streams which flow
+in wet seasons and fail in dry, are intermediate between streams which
+flow after showers only, and those which flow without interruption. In
+the figure the stream would become dry if the ground water level sank to
+A' A'.
+
+It is to be noted that a permanent stream does not normally precede its
+valley, but that the valley, developed through gully-hood and
+ravine-hood to valley-hood by means of the temporary streams supplied by
+the run-off of occasional showers, _finds a stream_, just as diggers of
+wells find water. The case is not altered if the stream be fed by
+springs, for the valley finds the spring, as truly as the well-digger
+finds a "vein" of water.
+
+_Limits of a valley._--So soon as a valley acquires a permanent stream,
+its development goes on without the interruption to which it was subject
+while the stream was intermittent. The permanent stream, like the
+temporary one which preceded it, tends to deepen and widen its valley,
+and, under certain conditions, to lengthen it as well. The means by
+which these enlargements are affected are the same as before. There are
+limits, however, in length, depth, and width, beyond which a valley may
+not go. No stream can cut below the level of the water into which it
+flows, and it can cut to that level only at its outlet. Up stream from
+that point, a gentle gradient will be established over which the water
+will flow without cutting. In this condition the stream is _at grade_.
+Its channel has reached _baselevel_, that is, the level to which the
+stream can wear its bed. This grade is, however, not necessarily
+permanent, for what was baselevel for a small stream in an early stage
+of its development, is not necessarily baselevel for the larger stream
+which succeeds it at a later time.
+
+Weathering, wash, and lateral corrasion of the stream continue to widen
+the valley after it has reached baselevel. The bluffs of valleys are
+thus forced to recede, and the valley is widened at the expense of the
+upland. Two valleys widening on opposite sides of a divide, narrow the
+divide between them, and may ultimately wear it out. When this is
+accomplished, the two valleys become one. The limit to which a valley
+may widen on either side is therefore its neighboring valley, and since,
+after two valleys have become one by the elimination of the ridge
+between them, there are still valleys on either hand, the final result
+of the widening of all valleys must be to reduce all the area which
+they drain to baselevel. As this process goes forward, the upper flat
+into which the valleys were cut is being restricted in area, while the
+lower flats developed by the streams in the valley bottoms are being
+enlarged. Thus the lower flats grow at the expense of the higher.
+
+There are also limits in length which a valley may not exceed. The head
+of any valley may recede until some other valley is reached. The
+recession may not stop even there, for if, on opposite sides of a
+divide, erosion is unequal, as between 1A and 1B, Fig. 14, the divide
+will be moved toward the side of less rapid erosion, and it will cease
+to recede only when erosion on the two sides becomes equal (4A and
+4B). In homogeneous material this will be when the slopes on the two
+sides are equal.
+
+[Illustration: Fig. 14.--Diagram showing the shifting of a divide. The
+slopes 1A and 1B are unequal. The steeper slope is worn more rapidly and
+the divide is shifted from 1 to 4, where the two slopes become equal and
+the migration of the divide ceases.]
+
+It should be noted that the lengthening of a valley headward is not
+normally the work of the permanent stream, for the permanent stream
+begins some distance below the head of the valley. At the head,
+therefore, erosion goes on as at the beginning, even after a permanent
+stream is acquired.
+
+Under certain circumstances, the valley may be lengthened at its
+debouchure. If the detritus carried by it is deposited at its mouth, or
+if the sea bottom beyond that point rise, the land may be extended
+seaward, and over this extension the stream will find its way. Thus at
+their lower, as well as at their upper ends, both the stream and its
+valley may be lengthened.
+
+_A cycle of erosion._--If, along the borders of a new-born land mass, a
+series of valleys were developed, essentially parallel to one another,
+they would constitute depressions separated by elevations, representing
+the original surface not yet notably affected by erosion (see Plate XIV,
+Fig. 1). These inter-valley areas might at first be wide or narrow, but
+in process of time they would necessarily become narrow, for, once, a
+valley is started, all the water which enters it from either side helps
+to wear back its slopes, and the wearing back of the slopes means the
+widening of the valleys on the one hand and the narrowing of the
+inter-valley ridges on the other. Not only would the water running over
+the slopes of a valley wear back its walls, but many other processes
+conspire to the same end. The wetting and drying, the freezing and the
+thawing, the roots of plants and the borings of animals, all tend to
+loosen the material on the slopes or walls of the valleys, and gravity
+helps the loosened material to descend. Once in the valley bottom, the
+running water is likely to carry it off, landing it finally in the sea.
+Thus the growth of the valley is not the result of running water alone,
+though this is the most important single factor in the process.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIV.
+
+FIG. 1.
+
+The same valleys as shown in Plate XIII, Fig. 3, in a later stage of
+development.
+
+Illustration: FIG. 2.
+
+Same valleys as shown in Fig. 1, in a still later stage of
+development.]
+
+Even if valleys developed no tributaries, they would, in the course of
+time, widen to such an extent as to nearly obliterate the intervening
+ridges. The surface, however, would not easily be reduced to perfect
+flatness. For a long time at least there would remain something of slope
+from the central axis of the former inter-stream ridge, toward the
+streams on either hand; but if the process of erosion went on for a
+sufficiently long period of time, the inter-stream ridge would be
+brought very low, and the result would be an essentially flat surface
+between the streams, much below the level of the old one.
+
+The first valleys which started on the land surface (see Plate XIII,
+Fig. 3) would be almost sure to develop numerous tributaries. Into
+tributary valleys water would flow from their sides and from their
+heads, and as a result they would widen and deepen and lengthen just as
+their mains had done before them. By lengthening headward they would
+work back from their mains some part, or even all of the way across the
+divides separating the main valleys. By this process, the tributaries
+cut the divides between the main streams into shorter cross-ridges. With
+the development of tributary valleys there would be many lines of
+drainage instead of two, working at the area between two main streams.
+The result would be that the surface would be brought low much more
+rapidly, for it is clear that many valleys within the area between the
+main streams, widening at the same time, would diminish the aggregate
+area of the upland much more rapidly than two alone could do.
+
+The same thing is made clear in another way. It will be seen (Plate XIV,
+Figs. 1 and 2) that the tributaries would presently dissect an area of
+uniform surface, tending to cut it into a series of short ridges or
+hills. In this way the amount of sloping surface is greatly increased,
+and as a result, every shower would have much more effect in washing
+loose materials down to lower levels, whence the streams could carry
+them to the sea.
+
+[Illustration: Fig. 15.--Cross-sections showing various stages of
+erosion in one cycle.]
+
+The successive stages in the process of lowering a surface are suggested
+by Fig. 15, which represents a series of cross-sections of a land mass
+in process of degradation. The uppermost section represents a level
+surface crossed by young valleys. The next lower represents the same
+surface at a later stage, when the valleys have grown larger, while the
+third and succeeding sections represent still later stages in the
+process of degradation. Plate XIII, Fig. 3, and Plate XIV, Figs. 1 and
+2, represent in another way the successive stages of stream work in the
+general process of degradation.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XV.
+
+Diagram illustrating how a hard inclined layer of rock becomes a ridge
+in the process of degradation.]
+
+In this manner a series of rivers, operating for a sufficiently long
+period of time, might reduce even a high land mass to a low level,
+scarcely above the sea. The new level would be developed soonest near
+the sea, and the areas farthest from it would be the last--other things
+being equal--to be brought low. The time necessary for the development
+of such a surface is known as a _cycle of erosion_, and the resulting
+surface is a _base-level plain_, that is, a plain as near sea level as
+river erosion can bring it. At a stage shortly preceding the base-level
+stage the surface would be a _peneplain_. A peneplain, therefore, is a
+surface which has been brought toward, but not to base-level. Land
+surfaces are often spoken of as young or old in their erosion history
+according to the stage of advancement which has been made toward
+base-leveling. Thus the Colorado canyon, deep and impressive as it is,
+is, in terms of erosion, a young valley, for the river has done but a
+small part of the work which must be done in order to bring its basin to
+baselevel.
+
+_Effects of unequal hardness._--The process of erosion thus sketched
+would ultimately bring the surface of the land down to base-level, and
+in case the material of the land were homogeneous, the last points to be
+reduced would be those most remote from the axes of the streams doing
+the work of leveling. But if the material of the land were of unequal
+hardness, those parts which were hardest would resist the action of
+erosion most effectively. The areas of softer rock would be brought low,
+and the outcrops of hard rock (Plate XV) would constitute ridges during
+the later stages of an erosion cycle. If there were bodies of hard rock,
+such as the Baraboo quartzite, surrounded by sandstone, such as the
+Potsdam, the sandstone on either hand would be worn down much more
+readily than the quartzite, and in the course of degradation the latter
+would come to stand out prominently. The region in the vicinity of Devil's
+lake is in that stage of erosion in which the quartzite ridges are
+conspicuous (Plate XXXVII). The less resistant sandstone has been
+removed from about them, and erosion has not advanced so far since the
+isolation of the quartzite ridges as to greatly lower their crests. The
+harder strata are at a level where surface water can still work
+effectively, even though slowly, upon them, and in spite of their great
+resistance they will ultimately be brought down to the common level. It
+will be seen that, from the point of view of subaerial erosion, a
+base-level plain is the only land surface which is in a condition of
+approximate stability.
+
+_Falls and rapids._--If in lowering its channel a stream crosses one
+layer of rock much harder than the next underlying, the deepening will
+go on more rapidly on the less resistant bed. Where the stream crosses
+from the harder to the less hard, the gradient is likely to become
+steep, and a rapids is formed. These conditions are suggested in Fig. 16
+which represents the successive profiles (a b, a c, d e, f e, g e,
+and h e) of a stream crossing from a harder to a softer formation. Below
+the point a the stream is flowing over rock which is easily eroded, while
+above that point its course is over a harder formation. Just below a
+(profile a b) the gradient has become so steep that there are rapids.
+Under these conditions, erosion is rapid just beyond the crossing of the
+hard layer, and the gradient becomes higher and higher. When the steep
+slope of the rapids approaches verticality, the rapids become a _fall_
+(profile a c).
+
+[Illustration: Fig. 16.--Diagram to illustrate the development of a
+rapid and fall. The upper layer is harder than the strata below. The
+successive profiles of the stream below the hard layer are represented
+by the lines a b, a c, d e, f e, g e, and h e.]
+
+As the water falls over the precipitous face and strikes upon the softer
+rock below, part of it rebounds against the base of the vertical face
+(Fig. 16). The result of wear at this point is the undermining of the
+hard layer above, and sooner or later, portions of it will fall. This
+will occasion the recession of the fall (profile d e and f e). As the
+fall recedes, it grows less and less high. When the recession has
+reached the point i, or, in other words, when the gradient of the stream
+below the fall crosses the junction of the beds of unequal hardness, as
+it ultimately must, effective undermining ceases, and the end of the
+fall is at hand.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVI.
+
+Skillett Falls, in the Potsdam formation, three miles southwest of
+Baraboo. The several small falls are occasioned by slight inequalities
+in the hardness of the layers.]
+
+When the effective undercutting ceases because the softer bed is no
+longer accessible, the point of maximum wear is transferred to the top
+of the hard bed just where the water begins to fall (g, Fig. 16). The
+wear here is no greater than before, though it is greater relatively.
+The relatively greater wear at this point destroys the verticality of
+the face, converting it into a steep slope. When this happens, the fall
+is a thing of the past, and rapids succeed. With continued flow the bed
+of the rapids becomes less and less steep, until it is finally reduced
+to the normal gradient of the stream (h e), when the rapids disappear.
+
+When thin layers of rock in a stream's course vary in hardness, softer
+beds alternating with harder ones, a series of falls such as shown in
+Plate XVI, may result. As they work up stream, these falls will be
+obliterated one by one. Thus it is seen that falls and rapids are not
+permanent features of the landscape. They belong to the younger period
+of a valley's history, rather than to the older. They are marks of
+topographic youth.
+
+_Narrows._--Where a stream crosses a hard layer or ridge of rock lying
+between softer ones, the valley will not widen so rapidly in the hard
+rock as above and below. If the hard beds be vertical, so that their
+outcrop is not shifted as the degradation of the surface proceeds, a
+notable constriction of the valley results. Such a constriction is a
+_narrows_. The Upper and Lower narrows of the Baraboo (Plate IV)
+are good examples of the effect of hard rock on the widening of a
+valley.
+
+_Erosion of folded strata._--The processes of river erosion would not be
+essentially different in case the land mass upon which erosion operated
+were made of tilted and folded strata. The folds would, at the outset,
+determine the position of the drainage lines, for the main streams would
+flow in the troughs (synclines) between the folds (anticlines). Once
+developed, the streams would lower their beds, widen their valleys, and
+lengthen their courses, and in the long process of time they would bring
+the area drained nearly to sea-level, just as in the preceding case. It
+was under such conditions that the general processes of subaerial
+erosion operated in south central Wisconsin, after the uplift of the
+quartzite and before the deposition of the Potsdam sandstone. It was
+then that the principal features of the topography of the quartzite were
+developed.
+
+In regions of folded strata, certain beds are likely to be more
+resistant than others. Where harder beds alternate with softer, the
+former finally come to stand out as ridges, while the outcrops of the
+latter mark the sites of the valleys. Such alternations of beds of
+unequal resistance give rise to various peculiarities of drainage,
+particularly in the courses of tributaries. These peculiarities find no
+illustration in this region and are not here discussed.
+
+_Base-level plains and peneplains._--It is important to notice that a
+plane surface (base-level) developed by streams could only be developed
+at elevations but slightly above the sea, that is, at levels at which
+running water ceases to be an effective agent of erosion; for so long as
+a stream is actively deepening its valley, its tendency is to roughen
+the area which it drains, not to make it smooth. The Colorado river,
+flowing through high land, makes a deep gorge. All the streams of the
+western plateaus have deep valleys, and the manifest result of their
+action is to roughen the surface; but given time enough, and the streams
+will have cut their beds to low gradients. Then, though deepening of the
+valleys will cease, widening will not, and inch by inch and shower by
+shower the elevated lands between the valleys will be reduced in area,
+and ultimately the whole will be brought down nearly to the level of the
+stream beds. This is illustrated by Fig. 15.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVII.
+
+A group of mounds on the plain southwest from Camp Douglas. The
+base-level surface is well shown, and above it rise the remnants of the
+higher plain from which the lower was reduced.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVIII.
+
+Castle Rock near Camp Douglas. In this view the relation of the erosion
+remnant to the extensive base-leveled surface is well shown.]
+
+It is important to notice further that if the original surface on which
+erosion began is level, there is no stage intermediate between the
+beginning and the end of an erosion cycle, when the surface is again
+level, or nearly so, though in the stage of a cycle next preceding the
+last--the peneplain stage (fourth profile, Fig. 15)--the surface
+approaches flatness. It is also important to notice that when streams
+have cut a land surface down to the level at which they cease to erode,
+that surface will still possess some slight slope, and that to seaward.
+
+No definite degree of slope can be fixed upon as marking a base-level.
+The angle of slope which would practically stop erosion in a region of
+slight rainfall would be great enough to allow of erosion if the
+precipitation were greater. All that can be said, therefore, is that the
+angle of slope must be low. The Mississippi has a fall of less than a
+foot per mile for some hundreds of miles above the gulf. A small stream
+in a similar situation would have ceased to lower its channel before so
+low a gradient was reached.
+
+The nearest approach to a base-leveled region within the area here under
+consideration is in the vicinity of Camp Douglas and Necedah (see Plate
+I). This is indeed one of the best examples of a base-leveled plain
+known. Here the broad plain, extending in some directions as far as the
+eye can reach, is as low as it could be reduced by the streams which
+developed it. The erosion cycle which produced the plain was, however,
+not completed, for above the plain rise a few conspicuous hills (Plates
+XVII and XVIII, and Fig. 17), and to the west of it lie the highlands
+marking the level from which the low plain was reduced.
+
+Where a region has been clearly base-leveled, isolated masses or ridges
+of resistant rock may still stand out conspicuously above it. The
+quartzite hill at Necedah is an example. Such hills are known as
+_monadnocks_. This name was taken from Mount Monadnock which owes its
+origin to the removal of the surrounding less resistant beds. The name
+has now become generic. Many of the isolated hills on the peneplain east
+of Camp Douglas are perhaps due to superior resistance, though the rock
+of which they are composed belongs to the same formation as that which
+has been removed.
+
+[Illustration: Fig. 17.--Sketch, looking northwest from Camp Douglas.]
+
+
+    CHARACTERISTICS OF VALLEYS AT VARIOUS STAGES OF DEVELOPMENT.
+
+In the early stages of its development a depression made by erosion has
+steep lateral slopes, the exact character of which is determined by many
+considerations. Its normal cross-section is usually described as
+V-shaped (Fig. 18). In the early stages of its development, especially
+if in unconsolidated material, the slopes are normally convex inward. If
+cut in solid rock, the cross section may be the same, though many
+variations are likely to appear, due especially to the structure of the
+rock and to inequalities of hardness. If a stream be swift enough to
+carry off not only all the detritus descending from its slopes, but to
+abrade its bed effectively besides, a steep-sided gorge develops. If it
+becomes deep, it is a canyon. For the development of a canyon, the
+material of the walls must be such as is capable of standing at a high
+angle. A canyon always indicates that the down-cutting of a stream keeps
+well ahead of the widening.
+
+[Illustration: Fig. 18.--Diagrammatic cross-section of a young valley.]
+
+Of young valleys in loose material (drift) there are many examples in
+the eastern portion of the area here described. Shallow canyons or
+gorges in rock are also found. The gorge of Skillett creek at and above
+the Pewit's nest about three miles southwest from Baraboo, the gorge of
+Dell creek two miles south of Kilbourn City, and the Dalles of the
+Wisconsin at Kilbourn City may serve as illustrations of this type of
+valley.
+
+[Illustration: Fig. 19.--Diagrammatic profile of a young valley.]
+
+The profile of a valley at the stage of its development corresponding to
+the above section is represented diagrammatically by the curve A B in
+Fig. 19. The sketch (Pl. XIX, Fig. 1) represents a bird's-eye view of a
+valley in the same stage of development.
+
+[Illustration: Fig. 20.--Diagrammatic cross-section of a valley at a
+stage corresponding with that shown in Plate XIX, Fig. 2.]
+
+At a stage of development later than that represented by the V-shaped
+cross-section, the corresponding section is U-shaped, as shown in Fig.
+20. The same form is sketched in Plate XIX, Fig. 2. This represents a
+stage of development where detritus descending the slopes is not all
+carried away by the stream, and where the valley is being widened faster
+than it is deepened. Its slopes are therefore becoming gentler. The
+profile of the valley at this stage would be much the same as that in
+the preceding, except that the gradient in the lower portion would be
+lower.
+
+Still later the cross section of the valley assumes the shape shown in
+Fig. 21, and in perspective the form sketched in Plate XX, Fig. 1. This
+transformation is effected partly by erosion, and partly by deposition
+in the valley. When a stream has cut its valley as low as conditions
+allow, it becomes sluggish. A sluggish stream is easily turned from side
+to side, and, directed against its banks, it may undercut them, causing
+them to recede at the point of undercutting. In its meanderings, it
+undercuts at various points at various times, and the aggregate result
+is the widening of the valley. By this process alone the stream would
+develop a flat grade. At the same time all the drainage which comes in
+at the sides tends to carry the walls of the valley farther from its
+axis.
+
+[Illustration: Fig. 21.--Diagrammatic cross-section of a valley at a
+stage later than that shown in Fig. 20.]
+
+A sluggish stream is also generally a depositing stream. Its deposits
+tend to aggrade (build up) the flat which its meanderings develop. When
+a valley bottom is built up, it becomes wider at the same time, for the
+valley is, as a rule, wider at any given level than at any lower one.
+Thus the U-shaped valley is finally converted into a valley with a flat
+bottom, the flat being due in large part to erosion, and in smaller part
+to deposition. Under exceptional circumstances the relative importance
+of these two factors may be reversed.
+
+It will be seen that the cross-section of a valley affords a clue to its
+age. A valley without a flat is young, and increasing age is indicated
+by increasing width. Valleys illustrating all stages of development are
+to be found in the Devil's lake region. The valley of Honey creek
+southwest of Devil's lake may be taken as an illustration of a valley at
+an intermediate stage of development, while examples of old valleys are
+found in the flat country about Camp Douglas and Necedah.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIX.
+
+FIG. 1.
+
+Sketch of a valley at the stage of development corresponding to the
+cross section shown in Fig. 18.
+
+Illustration: FIG. 2.
+
+Sketch of a valley at the stage of development corresponding to the
+cross section shown in Fig. 20.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XX.
+
+FIG. 1.
+
+Sketch of a part of a valley at the stage of development corresponding
+to the cross section shown in Fig 21.
+
+Illustration: FIG. 2.
+
+Sketch of a section of the Baraboo valley.]
+
+
+               _Transportation and Deposition._
+
+Sediment is carried by streams in two ways: (1) by being rolled along
+the bottom, and (2) by being held in suspension. Dissolved mineral
+matter (which is not sediment) is also carried in the water. By means of
+that rolled along the bottom and carried in suspension, especially the
+former, the stream as already stated abrades its bed.
+
+The transporting power of a stream of given size varies with its
+velocity. Increase in the declivity or the volume of a stream increases
+its velocity and therefore its transportive power. The transportation
+effected by a stream is influenced (1) by its transporting power, and (2)
+by the size and amount of material available for carriage. Fine material
+is carried with a less expenditure of energy than an equal amount of
+coarse. With the same expenditure of energy therefore a stream can carry
+a greater amount of the former than of the latter.
+
+Since the transportation effected by a stream is dependent on its
+gradient, its size, and the size and amount of material available, it
+follows that when these conditions change so as to decrease the carrying
+power of the river, deposition will follow, if the stream was previously
+fully loaded. In other words, a stream will deposit when it becomes
+overloaded.
+
+Overloading may come about in the following ways: (1) By decrease in
+gradient, checking velocity and therefore carrying power; (2) by
+decrease in amount of water, which may result from evaporation,
+absorption, etc.; (3) by change in the shape of the channel, so that the
+friction of flow is increased, and therefore the force available for
+transportation lessened; (4) by lateral drainage bringing in more
+sediment than the main stream can carry; (5) by change in the character
+of the material to which the stream has access; for if it becomes finer,
+the coarse material previously carried will be dropped, and the fine
+taken; and (6) by the checking of velocity when a stream flows into a
+body of standing water.
+
+_Topographic forms resulting from stream deposition._--The topographic
+forms resulting from stream deposition are various. At the bottoms of
+steep slopes, temporary streams build _alluvial cones_ or _fans_. Along
+its flood-plain portion, a stream deposits more or less sediment on its
+flats. The part played by deposition in building a river flat has
+already been alluded to. A depositing stream often wanders about in an
+apparently aimless way across its flood plain. At the bends in its
+course, cutting is often taking place on the outside of a curve while
+deposition is going on in the inside. The valley of the Baraboo
+illustrates this process of cutting and building. Fig. 2, Plate XX, is
+based upon the features of the valley within the city of Baraboo.
+
+Besides depositing on its flood-plain, a stream often deposits in its
+channel. Any obstruction of a channel which checks the current of a
+loaded stream occasions deposition. In this way "bars" are formed. Once
+started, the bar increases in size, for it becomes an obstacle to flow,
+and so the cause of its own growth. It may be built up nearly to the
+surface of the stream, and in low water, it may become an island by the
+depression of the surface water. In some parts of its course, as about
+Merrimac, the Wisconsin river is marked by such islands at low water,
+and by a much larger number of bars.
+
+At their debouchures, streams give up their loads of sediment. Under
+favorable conditions deltas are built, but delta-building has not
+entered into the physical history of this region to any notable extent.
+
+
+                     _Rejuvenation of Streams._
+
+After the development of a base-level plain, its surface would suffer
+little change (except that effected by underground water) so long as it
+maintained its position. But if, after its development, a base-level
+plain were elevated, the old surface in a new position would be subject
+to a new series of changes identical in kind with those which had gone
+before. The elevation would give the established streams greater fall,
+and they would reassume the characteristics of youth. The greater fall
+would accelerate their velocities; the increased velocities would entail
+increased erosion; increased erosion would result in the deepening of
+the valleys, and the deepening of the valleys would lead to the
+roughening of the surface. But in the course of time, the _rejuvenated_
+streams would have cut their valleys as low as the new altitude of the
+land permitted, that is, to a new base-level. The process of deepening
+would then stop, and the limit of vertical relief which the streams were
+capable of developing, would be attained. But the valleys would not stop
+widening when they stopped deepening, and as they widened, the
+intervening divides would become narrower, and ultimately lower. In the
+course of time they would be destroyed, giving rise to a new level
+surface much below the old one, but developed in the same position which
+the old one occupied when it originated; that is, a position but little
+above sea level.
+
+If at some intermediate stage in the development of a second base-level
+plain, say at a time when the streams, rejuvenated by uplift, had
+brought half the elevated surface down to a new base-level, another
+uplift were to occur, the half completed cycle would be brought to an
+end, and a new one begun. The streams would again be quickened, and as a
+result they would promptly cut new and deeper channels in the bottoms of
+the great valleys which had already been developed. The topography which
+would result is suggested by the following diagram (Fig. 22) which
+illustrates the cross-section which would be found after the following
+sequence of events: (1) The development of a base-level, A A; (2)
+uplift, rejuvenation of the streams, and a new cycle of erosion half
+completed, the new base-level being at B B; (3) a second uplift,
+bringing the second (incomplete) cycle of erosion to a close, and by
+rejuvenating the streams, inaugurating the third cycle. As represented
+in the diagram, the third cycle has not progressed far, being
+represented only by the narrow valley C. The base-level is now 2-2, and
+the valley represented in the diagram has not yet reached it.
+
+[Illustration: Fig. 22.--Diagram (cross-section), illustrating the
+topographic effect of rejuvenation by uplift.]
+
+[Illustration: Fig. 23.--Normal profile of a valley bottom in a
+non-mountainous region.]
+
+The rejuvenation of a stream shows itself in another way. The normal
+profile of a valley bottom in a non-mountainous region is a gentle
+curve, concave upward with gradient increasing from debouchure to
+source. Such a profile is shown in Fig. 23. Fig. 24, on the other hand,
+is the profile of a rejuvenated stream. The valley once had a profile
+similar to that shown in Fig. 23. Below B its former continuation is
+marked by the dotted line B C. Since rejuvenation the stream has
+deepened the lower part of its valley, and established there a profile
+in harmony with the new conditions. The upper end of the new curve has
+not yet reached beyond B.
+
+[Illustration: Fig. 24.--Profile of a stream rejuvenated by uplift.]
+
+
+                       _Underground Water._
+
+In what has preceded, reference has been made only to the results
+accomplished by the water which runs off over the surface. The water
+which sinks beneath it is, however, of no small importance in reducing a
+land surface. The enormous amount of mineral matter in solution in
+spring water bears witness to the efficiency of the ground water in
+dissolving rock, for since the water did not contain the mineral matter
+when it entered the soil, it must have acquired it below the surface. By
+this means alone, areas of more soluble rock are lowered below those of
+less solubility. Furthermore, the water is still active as a solvent
+agent after a surface has been reduced to so low a gradient that the
+run-off ceases to erode mechanically.
+
+
+
+
+                            CHAPTER IV.
+
+
+        EROSION AND THE DEVELOPMENT OF STRIKING SCENIC FEATURES.
+
+
+The uplift following the period of Paleozoic deposition in south central
+Wisconsin, inaugurated a period of erosion which, with some
+interruptions, has continued to the present day. The processes of
+weathering began as soon as the surface was exposed to the weather, and
+corrasion by running water began with the first shower which fell upon
+it. The sediment worn from the land was carried back to the sea, there
+to be used in the building of still younger formations.
+
+The rate of erosion of a land surface depends in large measure upon its
+height. As a rule, it is eroded rapidly if high, and but slowly if low.
+
+It is not known whether the lands of central Wisconsin rose to slight or
+to great heights at the close of the period of Paleozoic sedimentation.
+It is therefore not known whether the erosion was at the outset rapid or
+slow. If the land of southern Wisconsin remained low for a time after
+the uplift which brought the Paleozoic sedimentation to a close,
+weathering would have exceeded transportation and corrasion. A large
+proportion of the rainfall would have sunk beneath the surface, and
+found its way to the sea by subterranean routes. Loosening of material
+by alternate wetting and drying, expansion and contraction, freezing and
+thawing, and by solution, might have gone on steadily, but so long as
+the land was low, there would have been little run-off, and that little
+would have flowed over a surface of gentle slopes, and transportation
+would have been at a minimum. On the whole, the degradation of the land
+under these conditions could not have advanced rapidly.
+
+If, on the other hand, the land was raised promptly to a considerable
+height, erosion would have been vigorous at the outset. The surface
+waters would soon have developed valleys which the streams would have
+widened, deepened and lengthened. Both transportation and corrasion
+would have been active, and whatever material was prepared for
+transportation by weathering, and brought into the valleys by side-wash,
+would have been hurried on its way to the sea, and degradation would
+have proceeded rapidly.
+
+_Establishment of drainage._--Valleys were developed in this new land
+surface according to the principles already set forth. Between the
+valleys there were divides, which became higher as the valleys became
+deeper, and narrower as the valleys widened. Ultimately the ridges were
+lowered, and many of them finally eliminated in the manner already
+outlined. The distance below the original surface and that at which the
+first series of new flats were developed is conjectural, but it would
+have depended on the height of the land. So far as can now be inferred,
+the new base-plain toward which the streams cut may have been 400 or 500
+feet below the crests of the quartzite ridges. It was at this level that
+the oldest base-plain of which this immediate region shows evidence, was
+developed.
+
+Had the quartzite ranges not been completely buried by the Paleozoic
+sediments, they would have appeared as ridges on the new land surface,
+and would have had a marked influence on the development of the drainage
+of the newly emerged surface. But as the ranges were probably completely
+buried, the drainage lines were established regardless of the position
+of the hard, but buried ridges. When in the process of degradation the
+quartzite surfaces were reached, the streams encountered a formation far
+more resistant than the surrounding sandstone and limestone. As the less
+resistant strata were worn away, the old quartzite ridges, long buried,
+again became prominent topographic features. In this condition they were
+"resurrected mountains."
+
+If, when erosion on the uplifted surface of Paleozoic rocks began, a
+valley had been located directly over the buried quartzite ridge, and
+along its course, it would have been deepened normally until its bottom
+reached the crest of the hard formation. Then, instead of sinking its
+valley vertically downward into the quartzite, the stream would have
+shifted its channel down the slope of the range along the junction of
+the softer and harder rock (Fig. 25). Such changes occasioned by the
+nature and position of the rock concerned, are known as _adjustments_.
+
+[Illustration: Fig. 25.--Diagram illustrating the hypothetical case of a
+stream working down the slope of the quartzite range. The successive
+sections of the valley are suggested by the lines ae, be, ce and de.]
+
+Streams which crossed the quartzite ridges on the overlying strata might
+have held their courses even after their valleys were lowered to the
+level of the quartzite. Such streams would have developed narrows at the
+crossing of the quartzite. In so far as there were passes in the
+quartzite range before the deposition of the Paleozoic beds, they were
+filled during the long period of sedimentation, to be again cleared out
+during the subsequent period of erosion. The gap in the South range now
+occupied by the lake was a narrows in a valley which existed, though
+perhaps not to its present depth, before the Potsdam sandstone was
+deposited. It was filled when the sediments of that formation were laid
+down, to be again opened, and perhaps deepened, in the period of erosion
+which followed the deposition of the Paleozoic series.
+
+During the earliest period of erosion of which there is positive
+evidence, after the uplift of the Paleozoic beds, the softer formations
+about the quartzite were worn down to a level 400 or 500 feet below the
+crests of the South quartzite range. At this lower level, an approximate
+plain, a peneplain, was developed, the level of which is shown by
+numerous hills, the summits of which now reach an elevation of from
+1,000 to 1,100 feet above the sea. At the time of its development, this
+peneplain was but little above sea level, for this is the only elevation
+at which running water can develop such a plain. Above the general level
+of this plain rose the quartzite ranges as elongate monadnocks, the
+highest parts of which were fully 500 feet above the plain. A few other
+points in the vicinity failed to be reduced to the level of the
+peneplain. The 1,320 foot hill (d, Plate XXXVII), one and one-half miles
+southeast of the Lower narrows, and Gibraltar Rock (e, same Plate), two
+miles southeast of Merrimac, rose as prominences above it. It is
+possible that these crests are remnants of a base-level plain older than
+that referred to above. If while the quartzite remained much as now, the
+valleys in the sandstone below 1,000 or 1,100 feet were filled, the
+result would correspond in a general way to the surface which existed in
+this region when the first distinctly recognizable cycle of erosion was
+brought to a close. Above the undulating plain developed in the
+sandstone and limestone, the main quartzite ridge would have risen as a
+conspicuous ridge 400 to 500 feet.
+
+This cycle had not been completed, that is, the work of base-leveling
+had not been altogether accomplished, when the peneplain was elevated,
+and the cycle, though still incomplete, brought to a close. By the
+uplift, the streams were rejuvenated, and sunk their valleys into the
+elevated peneplain. Thus a new cycle of erosion was begun, and the
+uplifted peneplain was dissected by the quickened streams which sank
+their valleys promptly into the slightly resistant sandstone. At their
+new base-level, they ultimately developed new flats. This cycle of
+erosion appears to have advanced no farther than to the development of
+wide flats along the principal streams, such as the Wisconsin and the
+Baraboo, and narrow ones along the subordinate water courses, when it
+was interrupted. Along the main streams the new flats were at a level
+which is now from 800 to 900 feet above the sea, and 700 to 800 feet
+below the South quartzite range. It was at this time that the plains
+about Camp Douglas and Necedah, already referred to, were developed.
+During this second incomplete cycle, the quartzite ranges, resisting
+erosion, came to stand up still more prominently than during the first.
+
+The interruption of this cycle was caused by the advent of the glacial
+period which disturbed the normal course of erosion. This period was
+accompanied and followed by slight changes of level which also had their
+influence on the streams. The consideration of the effects of glaciation
+and of subsequent river erosion are postponed, but it may be stated that
+within the area which was glaciated the post-glacial streams have been
+largely occupied in removing the drift deposited by the ice from the
+preglacial valleys, or in cutting new valleys in the drift. The streams
+outside the area of glaciation were less seriously disturbed.
+
+At levels other than those indicated, partial base-levels are suggested,
+and although less well marked in this region, they might, in the study
+of a broader area, bring out a much more complicated erosion history. As
+already suggested, one cycle may have preceded that the remnants of
+which now stand 1,000-1,100 feet above sea level, and another may have
+intervened between this and that marked by the 800 to 900 foot level.
+
+From the foregoing it is clear that the topography of the region is, on
+the whole, an erosion topography, save for certain details in its
+eastern portion. The valleys differ in form and in size, with their age,
+and with the nature of the material in which they are cut; while the
+hills and ridges differ with varying relations to the streams, and with
+the nature of the material of which they are composed.
+
+
+                   _Striking Scenic Features._
+
+In a region so devoid of striking scenery as the central portion of the
+Mississippi basin, topographic features which would be passed without
+special notice in regions of greater relief, become the objects of
+interest. But in south central Wisconsin there are various features
+which would attract attention in any region where the scenery is not
+mountainous.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXI.
+
+Cleopatra's Needle. West Bluff of Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXII.
+
+Turk's Head. West Bluff of Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIII.
+
+Devil's Doorway. East of Devil's Lake.]
+
+On the bluffs at Devil's lake there are many minor features which are
+sure to attract the attention of visitors. Such are "Cleopatra's Needle"
+(Plate XXI), "Turk's Head" (Plate XXII), and the "Devil's Doorway"
+(Plate XXIII).
+
+These particular forms have resulted from the peculiar weathering of the
+quartzite. The rock is affected by several systems of vertical or nearly
+vertical joint planes (cracks), which divide the whole formation into a
+series of vertical columns. There are also horizontal and oblique planes
+of cleavage dividing the columns, so that the great quartzite pile may
+be said to be made up of a series of blocks, which are generally in
+contact with one another. The isolated pillars and columns which have
+received special names have been left as they now stand by the falling
+away of the blocks which once surrounded them. They themselves must soon
+follow. The great talus slopes at the base of the bluffs, such as those
+on the west side of the lake and on the East bluff near its southeast
+corner, Plate XXIV, are silent witnesses of the extent to which this
+process has already gone. The blocks of rock of which they are composed
+have been loosened by freezing water, by the roots of trees, and by
+expansion and contraction due to changing temperature, and have fallen
+from their former positions to those they now occupy. Their descent,
+effected by gravity directly, is, it will be noted, the first step in
+their journey to the sea, the final resting place of all products of
+land degradation.
+
+_The Baraboo bluffs._--Nowhere in southern Wisconsin, or indeed in a
+large area adjacent to it, are there elevations which so nearly approach
+mountains as the ranges of quartzite in the vicinity of Baraboo and
+Devil's lake. So much has already been said of their history that there
+is need for little further description. Plate IV gives some idea of the
+appearance of the ranges. The history of the ranges, already outlined,
+involves the following stages: (1) The deposition of the sands in
+Huronian time; (2) the change of the sand to sandstone and the sandstone
+to quartzite; (3) the uplift and deformation of the beds; (4) igneous
+intrusions, faulting, crushing, and shoaring, with the development of
+schists accompanying the deformation; (5) a prolonged period of erosion
+during which the folds of quartzite were largely worn away, though
+considerable ridges, the Huronian mountains of early Cambrian times,
+still remained high above their surroundings; (6) the submergence of the
+region, finally involving even the crests of the ridges of quartzite;
+(7) a protracted period of deposition during which the Potsdam sandstone
+and several later Paleozoic formations were laid down about, and finally
+over, the quartzite, burying the mountainous ridges; (8) the elevation
+of the Paleozoic sea-bottom, converting it into land; (9) a long period
+of erosion, during which the upper Paleozoic beds were removed, and the
+quartzite re-discovered. Being much harder than the Paleozoic rocks, the
+quartzite ridges again came to stand out as prominent ridges, as the
+surrounding beds of relatively slight resistance were worn away. They
+are "resurrected" mountains, though not with the full height which they
+had in pre-Cambrian time, for they are still partially buried by younger
+beds.
+
+_The narrows in the quartzite._--There are four narrows or passes in the
+quartzite ridges, all of which are rather striking features. One of them
+is in the South range, one in the North range near its eastern end,
+while the others are in an isolated area of quartzite at Ablemans which
+is really a continuation of the North range. Two of these narrows are
+occupied by the Baraboo river, one by Narrows creek, and the fourth by
+Devil's lake.
+
+From Ablemans to a point several miles east of Baraboo, the Baraboo
+river flows through a capacious valley. Where it crosses the North
+range, six miles or more north of east of Baraboo, the broad valley is
+abruptly constricted to a narrow pass with precipitous sides, about 500
+feet high (c, Plate XXXVII). This constriction is the Lower narrows,
+conspicuous from many points on the South range, and from the plains to
+the north. Beyond the quartzite, the valley again opens out into a broad
+flat.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIV.
+
+Talus slope on the east bluff of Devil's lake.]
+
+Seen from a distance, the narrows has the appearance of an abrupt notch
+in the high ridge (Plate IV). Seen at closer range, the gap is
+still more impressive. It is in striking contrast with the other narrows
+in that there are no talus accumulations at the bases of the steep
+slopes, and in that the slopes are relatively smooth and altogether free
+from the curious details of sculpture seen in the other gaps where the
+slopes are equally steep.
+
+The Upper narrows of the Baraboo at Ablemans (b, Plate II) is in some
+ways similar to the Lower, though less conspicuous because less deep.
+Its slopes are more rugged, and piles of talus lie at their bases as at
+Devil's lake. This narrows also differs from the Lower in that the
+quartzite on one side is covered with Potsdam conglomerate, which
+overlies the truncated edges of the vertical layers of quartzite with
+unconformable contact. So clear an example of unconformity is not often
+seen. Potsdam sandstone is also seen to rest against the quartzite on
+either side of the narrows (Fig. 26), thus emphasizing the unconformity.
+The beauty and interest of this narrows is enhanced by the quartzite
+breccia ( which appears on its walls.
+
+[Illustration: Fig. 26.--A generalized diagrammatic cross-section at the
+Upper narrows, to show the relation of the sandstone to the quartzite.]
+
+One and one-half miles west of Ablemans (a, Plate II) is the third
+pass in the north quartzite ridge. This pass is narrower than the
+others, and is occupied by Narrows creek. Its walls are nearly vertical
+and possess the same rugged beauty as those at Ablemans. As at the Upper
+narrows, the beds of quartzite here are essentially vertical. They are
+indeed the continuation of the beds exposed at that place.
+
+The fourth narrows is across the South range (i, Plate II). It is not
+now occupied by a stream, though like the others it was cut by a stream,
+which was afterwards shut out from it. Because of its depth, 600 feet,
+and the ruggedness of its slopes, and because of its occupancy by the
+lake, this pass is the center of interest for the whole region. So much
+has already been said concerning it in other portions of this report
+that further description is here omitted. The manner in which the pass
+was robbed of its stream will be discussed later.
+
+The history of these several narrows, up to the time of the glacial
+period may now be summarized. Since remnants of Potsdam sandstone are
+found in some of them, it is clear that they existed in pre-Cambrian
+time,[6] and there is no reason to doubt that they are the work of the
+streams of those ancient days, working as streams now work. Following
+the pre-Cambrian period of erosion during which the notches were cut,
+came the submergence of the region, and the gaps were filled with sand
+and gravel, and finally the ridges themselves were buried. Uplift and a
+second period of erosion followed, during which the quartzite ranges
+were again exposed by the removal of the beds which overlay them, and
+the narrows cleaned out and deepened, and again occupied by streams.
+This condition of things lasted up to the time when the ice invaded the
+region.
+
+    [6] It is not here asserted that these notches were as deep
+    as now, in pre-Cambrian time. It is, however, certain that
+    the quartzite was deeply eroded, previous to the deposition
+    of the Potsdam sandstone.
+
+_Glens._--No enumeration of the special scenic features of this region
+would be complete without mention of Parfrey's and Dorward's glens (a
+and b, Plate XXXVII, and Plate XXV). Attention has already been
+directed to them as illustrations of young valleys, and as places where
+the Potsdam conglomerate is well shown, but they are attractive from the
+scenic point of view. Their frequent mention in earlier parts of this
+report makes further reference to them at this point unnecessary.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXV.
+
+In Dorward's Glen. The basal conglomerate of the Potsdam formation is
+shown at the lower right-hand corner, and is overlain by sandstone.
+(Photograph furnished by Mr. Wilfred Dorward).]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVI.
+
+Natural bridge near Denzer.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVII.
+
+Navy Yard. Dalles of the Wisconsin.]
+
+Pine Hollow (k, Plate II) is another attractive gorge on the south flank
+of the greater quartzite range. The rock at this point is especially
+well exposed. This gorge is beyond the drift-covered portion of the
+range, and therefore dates from the pre-glacial time.
+
+The Pewit's nest, about three miles southwest of Baraboo (m, Plate II),
+is another point of interest. Above the "nest," Skillett creek flows
+through a narrow and picturesque gorge in the Potsdam sandstone. The
+origin of this gorge is explained elsewhere.
+
+_Natural Bridge._--About two miles north and a little west of the
+village of Denzer (Sec. 17, T. 10 N., R. 5 E.), is a small natural
+bridge, which has resulted from the unequal weathering of the sandstone
+(see Plate XXVI). The "bridge" is curious, rather than beautiful or
+impressive.
+
+_The Dalles of the Wisconsin._--The _dalles_ is the term applied to a
+narrow canyon-like stretch of the Wisconsin valley seven miles in
+length, near Kilbourn City (see frontispiece). The depth of the gorge is
+from 50 to 100 feet. The part above the bridge at Kilbourn City is the
+"Upper dalles;" that below, the "Lower dalles." Within this stretch of
+the valley are perhaps the most picturesque features of the region.
+
+The sides of the gorge are nearly vertical much of the way, and at many
+points are so steep on both sides that landing would be impossible.
+Between these sandstone walls flows the deep and swift Wisconsin river.
+
+Such a rock gorge is in itself a thing of beauty, but in the dalles
+there are many minor features which enhance the charm of the whole.
+
+One of the features which deserves especial mention is the peculiar
+crenate form of the walls at the banks of the river. This is perhaps
+best seen in that part of the dalles known as the "Navy Yard." Plate
+XXVII. The sandstone is affected by a series of vertical cracks or
+joints. From weathering, the rock along these joints becomes softened,
+and the running water wears the softened rock at the joint planes more
+readily than other parts of its bank, and so develops a reëntrant at
+these points. Rain water descending to the river finds and follows the
+joint planes, and thus widens the cracks. As a result of stream and rain
+and weathering, deep reëntrant angles are produced. The projections
+between are rounded off so that the banks of the stream have assumed the
+crenate form shown in Plate XXVIII, and Frontispiece.
+
+When this process of weathering at the joints is carried sufficiently
+far, columns of rock become isolated, and stand out on the river bluffs
+as "chimneys" (Plate XXVIII). At a still later stage of development,
+decay of the rock along the joint planes may leave a large mass of rock
+completely isolated. "Steamboat rock" (Plate XII) and "Sugar
+bowl" (Plate XXIX) are examples of islands thus formed.
+
+The walls of sandstone weather in a peculiar manner at some points in
+the Lower dalles, as shown on Plate XXX. The little ridges stand out
+because they are harder and resist weathering better than the other
+parts. This is due in part at least to the presence of iron in the more
+resistant portions, cementing them more firmly. In the process of
+segregation, cementing materials are often distributed unequally.
+
+The effect of differences in hardness on erosion is also shown on a
+larger scale and in other ways. Perhaps the most striking illustration
+is _Stand rock_ (Plate XXXI), but most of the innumerable and
+picturesque irregularities on the rock walls are to be accounted for by
+such differences.
+
+Minor valleys tributary to the Wisconsin, such as _Witch's gulch_ and
+_Cold Water canyon_ deserve mention, both because of their beauty, and
+because they illustrate a type of erosion at an early stage of valley
+development. In character they are comparable to the larger gorge to
+which they are tributary. In the downward cutting, which far exceeds the
+side wear in these tributary canyons, the water has excavated large bowl
+or jug-like forms. In Witch's gulch such forms are now being excavated.
+They are developed just below falls, where the water carrying debris,
+eddies, and the jugs or pot-holes are the result of the wear effected by
+the eddies. The "Devil's jug" and many similar hollows are thus
+explained.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVIII.
+
+Chimney Rock. Dalles of the Wisconsin. Cross-bedding well shown in
+foreground near bottom.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIX.
+
+An Island in the Lower Dalles.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXX.
+
+View in lower Dalles showing peculiar honeycomb weathering.]
+
+_The mounds and castle rocks._--In the vicinity of Camp Douglas and over
+a large area to the east, are still other striking topographic forms,
+which owe their origin to different conditions, though they were
+fashioned by the same forces. Here there are many "tower" or "castle"
+rocks, which rise to heights varying from 75 to 190 feet above the
+surrounding plain. They are remnants of beds which were once continuous
+over the low lands above which the hills now rise. In Plates XVII and
+XVIII the general character of these hills is shown. The rock of
+which they are composed is Potsdam sandstone, the same formation which
+underlies most of the area about Baraboo. The effect of the vertical
+joints and of horizontal layers of unequal hardness is well shown.
+Rains, winds, frosts, and roots are still working to compass the
+destruction of these picturesque hills, and the talus of sand bordering
+the "castle" is a reminder of the fate which awaits them. These hills
+are the more conspicuous and the more instructive since the plain out of
+which they rise is so flat. It is indeed one of the best examples of a
+base-level plain to be found on the continent.
+
+The crests of these hills reach an elevation of between 1,000 and 1,100
+feet. They appear to correspond with the level of the first peneplain
+recognized in the Devil's lake region. It was in the second cycle of
+erosion, when their surroundings were brought down to the new
+base-level, that these hills were left. West of Camp Douglas, there are
+still higher elevations, which seem to match Gibraltar rock.
+
+The Friendship "mounds" north of Kilbourn City, the castellated hills a
+few miles northwest of the same place, and Petenwell peak on the banks
+of the Wisconsin (Plate XXXII), are further examples of the same class
+of hills. All are of Potsdam sandstone.
+
+In addition to the "castle" rocks and base-level plain about Camp
+Douglas, other features should be mentioned. No other portion of the
+area touched upon in this report affords such fine examples of the
+different types of erosion topography. In the base-level plain are found
+"old-age" valleys, broad and shallow, with the stream meandering in a
+wide flood-plain. Traveling up such a valley, the topography becomes
+younger and younger, and the various stages mentioned earlier in the
+text, and suggested in Plate XIX, Figs. 1 and 2, and Plate XX, Fig. 1,
+are here illustrated.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXI.
+
+Stand Rock. Upper end of the Upper Dalles.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXII.
+
+Petenwell Peak.]
+
+
+                             CHAPTER V.
+
+
+                         THE GLACIAL PERIOD.
+
+
+The eastern part of the area with which this report deals, is covered
+with a mantle of drift which, as already pointed out, has greatly
+modified the details of its topography. To the consideration of the
+drift and its history attention is now turned.
+
+_The drift._--The drift consists of a body of clay, sand, gravel and
+bowlders, spread out as a cover of unequal thickness over the rock
+formations beneath. These various classes of material may be confusedly
+commingled, or they may be more or less distinctly separated from one
+another. When commingled, all may be in approximately equal proportions,
+or any one may predominate over any or all the others to any extent.
+
+It was long since recognized that the materials of the drift did not
+originate where they now lie, and that, in consequence, they sustain no
+genetic relationship to the strata on which they rest. Long before the
+drift received any special attention from geologists, it was well known
+that it had been transported from some other locality to that where it
+now occurs. The early conception was that it had been drifted into its
+present position from some outside source by water. It was this
+conception of its origin which gave it the name of _drift_. It is now
+known that the drift was deposited by glacier ice and the waters which
+arose from its melting, but the old name is still retained.
+
+Clearly to understand the origin of the drift, and the method by which
+it attained its present distribution, it may be well to consider some
+elementary facts and principles concerning climate and its effects, even
+at the risk of repeating what is already familiar.
+
+_Snow fields and ice sheets._--The temperature and the snowfall of a
+region may stand in such a relation to each other that the summer's heat
+may barely suffice to melt the winter's snow. If under these
+circumstances the annual temperature were to be reduced, or the fall of
+snow increased, the summer's heat would fail to melt all the winter's
+snow, and some portion of it would endure through the summer, and
+through successive summers, constituting a perennial snow-field. Were
+this process once inaugurated, the depth of the snow would increase from
+year to year. The area of the snow-field would be extended at the same
+time, since the snow-field would so far reduce the surrounding
+temperature as to increase the proportion of the annual precipitation
+which fell as snow. In the course of time, and under favorable
+conditions, the area of the snow-field would attain great dimensions,
+and the depth of the snow would become very great.
+
+As in the case of existing snow fields the lower part of the snow mass
+would eventually be converted into ice. Several factors would conspire
+to this end. 1. The pressure of the overlying snow would tend to
+compress the lower portion, and snow rendered sufficiently compact by
+compression would be regarded as ice. 2. Water arising from the melting
+of the surface snow by the sun's heat, would percolate through the
+superficial layers of snow, and, freezing below, take the form of ice.
+3. On standing, even without pressure or partial melting, snow appears
+to undergo changes of crystallization which render it more compact. In
+these and perhaps other ways, a snow-field becomes an ice-field, the
+snow being restricted to its surface.
+
+Eventually the increase in the depth of the snow and ice in a snow-field
+will give rise to new phenomena. Let a snow and ice field be assumed in
+which the depth of snow and ice is greatest at the center, with
+diminution toward its edges. The field of snow, if resting on a level
+base, would have some such cross-section as that represented in the
+diagram, Fig. 27.
+
+When the thickness of the ice has become considerable, it is evident
+that the pressure upon its lower and marginal parts will be great. We
+are wont to think of ice as a brittle solid. If in its place there were
+some plastic substance which would yield to pressure, the weight of the
+ice would cause the marginal parts to extend themselves in all
+directions by a sort of flowing motion.
+
+[Illustration: Fig. 27.--Diagrammatic cross-section of a field of ice
+and snow (c) resting on a level base A-B.]
+
+Under great pressure, many substances which otherwise appear to be
+solid, exhibit the characteristics of plastic bodies. Among the
+substances exhibiting this property, ice is perhaps best known. Brittle
+and resistant as it seems, it may yet be molded into almost any
+desirable form if subjected to sufficient pressure, steadily applied
+through long intervals of time. The changes of form thus produced in ice
+are brought about without visible fracture. Concerning the exact nature
+of the movement, physicists are not agreed; but the result appears to be
+essentially such as would be brought about if the ice were capable of
+flowing, with extreme slowness, under great pressure continuously
+applied.
+
+In the assumed ice-field, there are the conditions for great pressure
+and for its continuous application. If the ice be capable of moving as a
+plastic body, the weight of the ice would induce gradual movement
+outward from the center of the field, so that the area surrounding the
+region where the snow accumulated would gradually be encroached upon by
+the spreading of the ice. Observation shows that this is what takes
+place in every snow-field of sufficient depth. Motion thus brought about
+is glacier motion, and ice thus moving is glacier ice.
+
+Once in motion, two factors would determine the limit to which the ice
+would extend itself: (1) the rate at which it advances; and (2) the rate
+at which the advancing edge is wasted. The rate of advance would depend
+upon several conditions, one of which, in all cases, would be the
+pressure of the ice which started and which perpetuates the motion. If
+the pressure be increased the ice will advance more rapidly, and if it
+advance more rapidly, it will advance farther before it is melted. Other
+things remaining constant, therefore, increase of pressure will cause
+the ice-sheet to extend itself farther from the center of motion.
+Increase of snowfall will increase the pressure of the snow and ice
+field by increasing its mass. If, therefore, the precipitation over a
+given snow-field be increased for a period of years, the ice-sheet's
+marginal motion will be accelerated, and its area enlarged. A decrease
+of precipitation, taken in connection with unchanged wastage would
+decrease the pressure of the ice and retard its movement. If, while the
+rate of advance diminished, the rate of wastage remained constant, the
+edge of the ice would recede, and the snow and ice field be contracted.
+
+The rate at which the edge of the advancing ice is wasted depends
+largely on the climate. If, while the rate of advance remains constant,
+the climate becomes warmer, melting will be more rapid, and the ratio
+between melting and advance will be increased. The edge of the ice will
+therefore recede. The same result will follow, if, while temperature
+remains constant, the atmosphere becomes drier, since this will increase
+wastage by evaporation. Were the climate to become warmer and drier at
+the same time, the rate of recession of the ice would be greater than if
+but one of these changes occurred.
+
+If, on the other hand, the temperature over and about the ice field be
+lowered, melting will be diminished, and if the rate of movement be
+constant, the edge of the ice will advance farther than under the
+earlier conditions of temperature, since it has more time to advance
+before it is melted. An increase in the humidity of the atmosphere,
+while the temperature remains constant, will produce the same result,
+since increased humidity of the atmosphere diminishes evaporation. A
+decrease of temperature, decreasing the melting, and an increase of
+humidity, decreasing the evaporation, would cause the ice to advance
+farther than either change alone, since both changes decrease the
+wastage. If, at the same time that conditions so change as to increase
+the rate of movement of the ice, climatic conditions so change as to
+reduce the rate of waste, the advance of the ice before it is melted
+will be greater than where only one set of conditions is altered. If,
+instead of favoring advance, the two series of conditions conspire to
+cause the ice to recede, the recession will likewise be greater than
+when but one set of conditions is favorable thereto.
+
+Greenland affords an example of the conditions here described. A large
+part of the half million or more square miles which this body of land is
+estimated to contain, is covered by a vast sheet of snow and ice,
+thousands of feet in thickness. In this field of snow and ice, there is
+continuous though slow movement. The ice creeps slowly toward the
+borders of the island, advancing until it reaches a position where the
+climate is such as to waste (melt and evaporate) it as rapidly as it
+advances.
+
+The edge of the ice does not remain fixed in position. There is reason
+to believe that it alternately advances and retreats as the ratio
+between movement and waste increases or decreases. These oscillations in
+position are doubtless connected with climatic changes. When the ice
+edge retreats, it may be because the waste is increased, or because the
+snowfall is decreased, or both. In any case, when the ice edge recedes
+from the coast, it tends to recede until its edge reaches a position
+where the melting is less rapid than in its former position, and where
+the advance is counterbalanced by the waste. This represents a condition
+of equilibrium so far as the edge of the ice is concerned, and here the
+edge of the ice would remain so long as the conditions were unchanged.
+
+When for a period of years the rate of melting of the ice is diminished,
+or the snowfall increased, or both, the ice edge advances to a new line
+where melting is more rapid than at its former edge. The edge of the ice
+would tend to reach a position where waste and advance balance. Here its
+advance would cease, and here its edge would remain so long as climatic
+conditions were unchanged.
+
+If the conditions determining melting and flowage be continually
+changing, the ice edge will not find a position of equilibrium, but will
+advance when the conditions are favorable for advance, and retreat when
+the conditions are reversed.
+
+Not only the edge of the ice in Greenland, but the ends of existing
+mountain glaciers as well, are subject to fluctuation, and are delicate
+indices of variations in the climate of the regions where they occur.
+
+_The North American ice sheet._--In an area north of the eastern part of
+the United States and in another west of Hudson Bay it is believed that
+ice sheets similar to that which now covers Greenland began to
+accumulate at the beginning of the glacial period. From these areas as
+centers, the ice spread in all directions, partly as the result of
+accumulation, and partly as the result of movement induced by the weight
+of the ice itself.
+
+The ice sheets spreading from these centers came together south of
+Hudson's bay, and invaded the territory of the United States as a single
+sheet, which, at the time of its greatest development, covered a large
+part of our country (Plate XXXIII), its area being known by the extent
+of the drift which it left behind when it was melted. In the east, it
+buried the whole of New England, most of New York, and the northern
+parts of New Jersey and Pennsylvania. Farther west, the southern margin
+of the ice crossed the Ohio river in the vicinity of Cincinnati, and
+pushed out over the uplands a few miles south of the river. In Indiana,
+except at the extreme east, its margin fell considerably short of the
+Ohio; in Illinois it reached well toward that river, attaining here its
+most southerly latitude. West of the Mississippi, the line which marks
+the limit of its advance curves to the northward, and follows, in a
+general way, the course of the Missouri river. The total area of the
+North American ice sheet, at the time of its maximum development, has
+been estimated to have been about 4,000,000 square miles, or about ten
+times the estimated area of the present ice-field of Greenland.
+
+Within the general area covered by the ice, there is an area of several
+thousand square miles, mainly in southwestern Wisconsin, where there is
+no drift. The ice, for some reason, failed to cover this _driftless
+area_ though it overwhelmed the territory on all sides.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIII.
+
+The North American Ice Sheet, at the time of maximum development.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIV.
+
+View from the north of the Owl's Head, a hill two miles north of east of
+Merrimac, which has been shaped by the ice. The side to the left is the
+stone side.]
+
+Plate II shows the limit of ice advance in the area here described. The
+region may have been affected by the ice of more than one glacial epoch,
+but the chief results now observable were effected during the last, and
+the others need not be considered.
+
+
+                    _The Work of Glacier Ice._
+
+As the edge of an ice sheet, or as the end of a glacier, retreats, the
+land which it has previously covered is laid bare, and the effects which
+the passage of the ice produced may be seen. In some cases one may
+actually go back a short distance beneath the ice now in motion, and see
+its mode of work and the results it is effecting. The beds of living
+glaciers, and the beds which glaciers have recently abandoned, are found
+to present identical features. Because of their greater accessibility,
+the latter offer the better facilities for determining the effects of
+glaciation.
+
+The conspicuous phenomena of abandoned glacier beds fall into two
+classes, (1) those which pertain to the bed rock over which the ice
+moved, and (2) those which pertain to the drift left by the ice.
+
+_Erosive work of the ice._--_Effect on topography._--The leading
+features of the rock bed over which glacier ice has moved, are easily
+recognized. Its surface is generally smoothed and polished, and
+frequently marked by lines (striæ) or grooves, parallel to one another.
+An examination of the bottom of an active glacier discloses the method
+by which the polishing and scoring are accomplished.
+
+The lower surface of the ice is thickly set with a quantity of clay,
+sand, and stony material of various grades of coarseness. These earthy
+and stony materials in the base of the ice are the tools with which it
+works. Thus armed, the glacier ice moves slowly forward, resting down
+upon the surfaces over which it passes with the whole weight of its
+mass, and the grinding action between the stony layer at the base of the
+ice and the rock bed over which it moves, is effective. If the material
+in the bottom of the ice be fine, like clay, the rock bed is polished.
+If coarser materials, harder than the bed-rock, be mingled with the
+fine, the rock bed of the glacier will be scratched as well as polished.
+If there are bowlders in the bottom of the ice they may cut grooves or
+gorges in the underlying rock. The grooves may subsequently be polished
+by the passage over and through them of ice carrying clay or other fine,
+earthy matter.
+
+All these phases of rock wear may be seen about the termini of receding
+glaciers, on territory which they have but recently abandoned. There can
+thus be no possible doubt as to the origin of the polishing, planing and
+scoring.
+
+There are other peculiarities, less easily defined, which characterize
+the surface of glacier beds. The wear effected is not confined to the
+mere marking of the surface over which it passes. If prominences of rock
+exist in its path, as is often the case, they oppose the movement of the
+ice, and receive a corresponding measure of abrasion from it. If they be
+sufficiently resistant they may force the ice to yield by passing over
+or around them; but if they be weak, they are likely to be destroyed.
+
+As the ice of the North American ice sheet advanced, seemingly more
+rigid when it encountered yielding bodies, and more yielding when it
+encountered resistant ones, it denuded the surface of its loose and
+movable materials, and carried them forward. This accumulation of earthy
+and stony debris in the bottom of the ice, gave it a rough and grinding
+lower surface, which enabled it to abrade the land over which it passed
+much more effectively than ice alone could have done. Every hill and
+every mound which the ice encountered contested its advance. Every
+sufficiently resistant elevation compelled the ice to pass around or
+over it; but even in these cases the ice left its marks upon the surface
+to which it yielded. The powerful pressure of pure ice, which is
+relatively soft, upon firm hills of rock, which are relatively hard,
+would effect little. The hills would wear the ice, but the effect of the
+ice on the hills would be slight. But where the ice is supplied with
+earthy and stony material derived from the rock itself, the case is
+different. Under these conditions, the ice, yielding only under great
+pressure and as little as may be, rubs its rock-shod base over every
+opposing surface, and with greatest severity where it meets with
+greatest resistance. Its action may be compared to that of a huge
+"flexible-rasp" fitting down snugly over hills and valleys alike, and
+working under enormous pressure.
+
+The abrasion effected by a moving body of ice under such conditions
+would be great. Every inch of ice advance would be likely to be attended
+by loss to the surface of any obstacle over or around which it is
+compelled to move. The sharp summits of the hills, and all the angular
+rugosities of their surfaces would be filed off, and the hills smoothed
+down to such forms as will offer progressively less and less resistance.
+If the process of abrasion be continued long enough, the forms, even of
+the large hills, may be greatly altered, and their dimensions greatly
+reduced. Among the results of ice wear, therefore, will be a lowering of
+the hills, and a smoothing and softening of their contours, while their
+surfaces will bear the marks of the tools which fashioned them, and will
+be polished, striated or grooved, according to the nature of the
+material which the ice pressed down upon them during its passage. Figs.
+28 and 29 show the topographic effects which ice is likely to produce by
+erosion. Plate XXXIV is a hill two miles northeast of Merrimac, which
+shows how perfectly the wear actually performed corresponds to that
+which might be inferred.
+
+[Illustration: Fig. 28.--A hill before the ice passes over it.]
+
+A rock hill was sometimes left without covering of drift after having
+been severely worn by the ice. Such a hill is known as a _roche
+moutonnée_. An example of this type of hill occurs three miles north of
+east of Baraboo at the point marked z on Plate XXXVII. This hill,
+composed of quartzite, is less symmetrical than those shown in Figs. 28
+and 29. Its whole surface, not its stoss side only, has been smoothed
+and polished by the ice. This hill is the most accessible, the most
+easily designated, and, on the whole, the best example of a _roche
+moutonnée_ in the region, though many other hills show something of the
+same form.
+
+[Illustration: Fig. 29.--The same hill after it has been eroded by the
+ice. A the stoss side. B the lee side.]
+
+It was not the hills alone which the moving ice affected. Where it
+encountered valleys in its course they likewise suffered modification.
+Where the course of a valley was parallel to the direction of the ice
+movement, the ice moved through it. The depth of moving ice is one of
+the determinants of its velocity, and because of the greater depth of
+ice in valleys, its motion here was more rapid than on the uplands
+above, and its abrading action more powerful. Under these conditions the
+valleys were deepened and widened.
+
+Where the courses of the valleys were transverse to the direction of ice
+movement, the case was different. The ice was too viscous to span the
+valleys, and therefore filled them. In this case it is evident that the
+greater depth of the ice in the valley will not accelerate its motion,
+since the ice in the valley-trough and that above it are in a measure
+opposed. If left to itself, the ice in the valley would tend to flow in
+the direction of the axis of the valley. But in the case under
+consideration, the ice which lies above the valley depression is in
+motion at right angles to the axis of the valley. Under these
+circumstances three cases might arise:
+
+(1) If the movement of the ice sheet over the valley were able to push
+the valley ice up the farther slope, and out on the opposite highland,
+this work would retard the movement of the upper ice, since the
+resistance to movement would be great. In this case, the thickness of
+the ice is not directly and simply a determinant of its velocity. Under
+these conditions the bottom of the valley would not suffer great
+erosion, since ice did not move along it; but that slope of the valley
+against which the ice movement was projected would suffer great wear
+(Fig. 30). The valley would therefore be widened, and the slope
+suffering greatest wear would be reduced to a lower angle. Shallow
+valleys, and those possessing gentle slopes, favor this phase of ice
+movement and valley wear.
+
+[Illustration: Fig. 30.--Diagram showing effect on valley of ice moving
+transversely across it.]
+
+(2) The ice in the valley might become stationary, in which case it
+might serve as a bridge for the upper ice to cross on (Fig. 31). In this
+case also the total thickness of ice will not be a determinant of its
+velocity, for it is the thickness of the moving ice only, which
+influences the velocity. In this case the valley would not suffer much
+wear, so long as this condition of things continued. Valleys which have
+great depth relative to the thickness of the ice, and valleys whose
+slopes are steep, favor this phase of movement.
+
+(3) In valleys whose courses are transverse to the direction of ice
+movement, transverse currents of ice may exist, following the direction
+of the valleys. If the thickness of the ice be much greater than the
+depth of the valley, if the valley be capacious, and if one end of it be
+open and much lower than the other, the ice filling it may move along
+its axis, while the upper ice continues in its original course at right
+angles to the valley. In this case the valley would be deepened and
+widened, but this effect would be due to the movement along its course,
+rather than to that transverse to it.
+
+[Illustration: Fig. 31--Diagram to illustrate case where ice fills a
+valley (C) and the upper ice then moves on over the filling.]
+
+If the course of a valley were oblique to the direction of ice movement,
+its effect on the movement of ice would be intermediate between that of
+valleys parallel to the direction of movement, and those at right angles
+to it.
+
+It follows from the foregoing that the corrasive effects of ice upon the
+surface over which it passed, were locally dependent on pre-existent
+topography, and its relation to the direction of ice movement. In
+general, the effort was to cut down prominences, thus tending to level
+the surface. But when it encountered valleys parallel to its movement
+they were deepened, thus locally increasing relief. Whether the
+reduction of the hills exceeded the deepening of the valleys, or whether
+the reverse was true, so far as corrasion alone is concerned, is
+uncertain. But whatever the effect of the erosive effect of ice action
+upon the total amount of relief, the effect upon the contours was to
+make them more gentle. Not only were the sharp hills rounded off, but
+even the valleys which were deepened were widened as well, and in the
+process their slopes became more gentle. A river-erosion topography,
+modified by the wearing (not the depositing) action of the ice, would be
+notably different from the original, by reason of its gentler slopes and
+softer contours (Figs. 28 and 29).
+
+_Deposition by the ice. Effect on topography._--On melting, glacier ice
+leaves its bed covered with the debris which it gathered during its
+movement. Had this debris been equally distributed on and in and beneath
+the ice during its movement, and had the conditions of deposition been
+everywhere the same, the drift would constitute a mantle of uniform
+thickness over the underlying rock. Such a mantle of drift would not
+greatly alter the topography; it would simply raise the surface by an
+amount equal to the thickness of the drift, leaving elevations and
+depressions of the same magnitude as before, and sustaining the same
+relations to one another. But the drift carried by the ice, in whatever
+position, was not equally distributed during transportation, and the
+conditions under which it was deposited were not uniform, so that it
+produced more or less notable changes in the topography of the surface
+on which it was deposited.
+
+The unequal distribution of the drift is readily understood. The larger
+part of the drift transported by the ice was carried in its basal
+portion; but since the surface over which the ice passed was variable,
+it yielded a variable amount of debris to the ice. Where it was hilly,
+the friction between it and the ice was greater than where it was plain,
+and the ice carried away more load. From areas where the surface was
+overspread by a great depth of loose material favorably disposed for
+removal, more debris was taken than from areas where material in a
+condition to be readily transported was meager. Because of the
+topographic diversity and lithological heterogeneity of the surface of
+the country over which it passed, some portions of the ice carried much
+more drift than others, and when the ice finally melted, greater depths
+of drift were left in some places than in others. Not all of the
+material transported by the ice was carried forward until the ice
+melted. Some of it was probably carried but a short distance from its
+original position before it lodged. Drift was thus accumulating at some
+points beneath the ice during its onward motion. At such points the
+surface was being built up; at other points, abrasion was taking place,
+and the surface was being cut down. The drift mantle of any region does
+not, therefore, represent simply the material which was on and in and
+beneath the ice of that place at the time of its melting, but it
+represents, in addition, all that lodged beneath the ice during its
+movement.
+
+The constant tendency was for the ice to carry a considerable part of
+its load forward toward its thinned edge, and there to leave it. It
+follows that if the edge of the ice remained constant in position for
+any considerable period of time, large quantities of drift would have
+accumulated under its marginal portion, giving rise to a belt of
+relatively thick drift. Other things being equal, the longer the time
+during which the position of the edge was stationary, the greater the
+accumulation of drift. Certain ridge-like belts where the drift is
+thicker than on either hand, are confidently believed to mark the
+position where the edge of the ice-sheet stood for considerable periods
+of time.
+
+Because of the unequal amounts of material carried by different parts of
+the ice, and because of the unequal and inconstant conditions of
+deposition under the body of the ice and its edge, the mantle of drift
+has a very variable thickness; and a mantle of drift of variable
+thickness cannot fail to modify the topography of the region it covers.
+The extent of the modification will depend on the extent of the
+variation. This amounts in the aggregate, to hundreds of feet. The
+continental ice sheet, therefore, modified the topography of the region
+it covered, not only by the wear it effected, but also by the deposits
+it made.
+
+In some places it chanced that the greater thicknesses of drift were
+left in the positions formerly marked by valleys. Locally the body of
+drift was so great that valleys were completely filled, and therefore
+completely obliterated as surface features. Less frequently, drift not
+only filled the valleys but rose even higher over their former positions
+than on either side. In other places the greater depths of drift,
+instead of being deposited in the valleys, were left on pre-glacial
+elevations, building them up to still greater heights. In short, the
+mantle of drift of unequal thickness was laid down upon the rock
+surface in such a manner that the thicker parts sometimes rest on hills
+and ridges, sometimes on slopes, sometimes on plains, and sometimes in
+valleys.
+
+[Illustration: Fig. 32.--Diagrammatic section showing relation of drift
+to underlying rock, where the drift is thick relative to the relief of
+the rock. a and b represent the location of post-glacial valleys.]
+
+These relations are suggested by Figs. 32 and 33. From them it will be
+seen that in regions where the thickness of the drift is great, relative
+to the relief of the underlying rock, the topography may be completely
+changed. Not only may some of the valleys be obliterated by being
+filled, but some of the hills may be obliterated by having the lower
+land between them built up to their level. In regions where the
+thickness of the drift is slight, relative to the relief of the rock
+beneath, the hills cannot be buried, and the valleys cannot be
+completely filled, so that the relative positions of the principal
+topographic features will remain much the same after the deposition of
+the drift, as before (Fig. 33).
+
+[Illustration: Fig. 33.--Diagrammatic section showing relation of drift
+to underlying rock where the drift is thin relative to the relief of the
+underlying rock.]
+
+In case the pre-glacial valleys were filled and the hills buried, the
+new valleys which the surface waters will in time cut in the drift
+surface will have but little correspondence in position with those
+which existed before the ice incursion. A new system of valleys, and
+therefore a new system of ridges and hills, will be developed, in some
+measure independent of the old. These relations are illustrated by Fig.
+32.
+
+Inequalities in the thickness of drift lead to a still further
+modification of the surface. It frequently happened that in a plane or
+nearly plane region a slight thickness of drift was deposited at one
+point, while all about it much greater thicknesses were left. The area
+of thin drift would then constitute a depression, surrounded by a higher
+surface built up by the thicker deposits. Such depressions would at
+first have no outlets, and are therefore unlike the depressions shaped
+by rain and river erosion. The presence of depressions without outlets
+is one of the marks of a drift-covered (glaciated) country. In these
+depressions water may collect, forming lakes or ponds, or in some cases
+only marshes and bogs.
+
+
+                   DIRECTION OF ICE MOVEMENT.
+
+The direction in which glacier ice moved may be determined in various
+ways, even after the ice has disappeared. The shapes of the rock hills
+over which the ice passed, the direction from which the materials of the
+drift came, and the course of the margin of the drift, all show that the
+ice of south central Wisconsin was moving in a general southwest
+direction. In the rock hills, this is shown by the greater wear of their
+northeast ("stoss") sides (Plate XXXIV). From the course of the drift
+margin, the general direction of movement may be inferred when it is
+remembered that the tendency of glacier ice on a plane surface is to
+move at right angles to its margin.
+
+For the exact determination of the direction of ice movement, recourse
+must be had to the striæ on the bed-rock. Were the striated rock surface
+perfectly plane, and were the striæ even lines, they would only tell
+that the ice was moving in one of two directions. But the rock surface
+is not usually perfectly plane, nor the striæ even lines, and between
+the two directions which lines alone might suggest, it is usually
+possible to decide. The minor prominences and depressions in the rock
+surface were shaped according to the same principles that govern the
+shaping of hills (Fig. 29) and valleys (Fig. 30); that is, the stoss
+sides of the minor prominences, and the distal sides of small
+depressions suffered the more wear. With a good compass, the direction
+of the striæ may be measured to within a fraction of a degree, and thus
+the direction of ice movement in a particular place be definitely
+determined. The striæ which have been determined about Baraboo are shown
+on Plate II.
+
+_Effect of topography on movement._--The effect of glaciation on
+topography has been sketched, but the topography in turn exerted an
+important influence on the direction of ice movement. The extreme degree
+of topographic influence is seen in mountain regions like the Alps,
+where most of the glaciers are confined strictly to the valleys.
+
+As an ice sheet invades a region, it advances first and farthest along
+the lines of least resistance. In a rough country with great relief,
+tongues or lobes of ice would push forward in the valleys, while the
+hills or other prominences would tend to hold back or divide the onward
+moving mass. The edge of an ice sheet in such a region would be
+irregular. The marginal lobes of ice occupying the valleys would be
+separated by re-entrant angles marking the sites of hills and ridges.
+
+If the ice crossed a plane surface above which rose a notable ridge or
+hill, the first effect of the hill would be to indent the ice. The ice
+would move forward on either side, and if its thickness became
+sufficiently great, the parts moving forward on either side would again
+unite beyond it. A hill thus surrounded by ice is a nunatak. Later, as
+the advancing mass of ice became thicker, it might completely cover the
+hill; but the thickness of ice passing over the hill would be less than
+that passing on either side by an amount equal to the height of the
+hill. It follows that as ice encounters an isolated elevation, three
+stages in its contest with the obstruction may be recognized: (1) the
+stage when the ridge or hill acts as a wedge, dividing the moving ice
+into lobes, Fig. 34; (2) the nunatak stage, when the ice has pushed
+forward and reunited beyond the hill, Fig. 35; (3) the stage when the ice
+has become sufficiently deep to cover the hill.
+
+[Illustration: Fig. 34.--Diagrammatic representation of the effect of a
+hill on the edge of the ice.]
+
+After the ice has disappeared, the influence of the obstruction might be
+found in the disposition of the drift. If recession began during the
+first stage, that is, when the ice edge was separated into lobes, the
+margin of the drift should be lobate, and would loop back around the
+ridge from its advanced position on either side. If recession began
+during the second stage, that is, when the lobes had become confluent
+and completely surrounded the hill, a _driftless area_ would appear in
+the midst of drift. If recession began during the third stage, that is,
+after the ice had moved on over the obstruction, the evidence of the
+sequence might be obliterated; but if the ice moved but a short distance
+beyond the hill, the thinner ice over the hill would have advanced less
+far than the thicker ice on either side (Fig. 35), and the margin of
+the drift would show a re-entrant pointing back toward the hill, though
+not reaching it. All these conditions are illustrated in the Devil's
+lake region.
+
+[Illustration: Fig. 35.--Same as Fig. 34, when the ice has advanced
+farther.]
+
+
+                      _Limit of the Ice._
+
+The region under description is partly covered with drift, and partly
+free from it. The limit of the ice, at the time of its maximum expansion
+is well defined at many points, and the nature and position of the drift
+limit are so unique as to merit attention (see Plates II and XXXVII).
+They illustrate many of the principles already discussed.
+
+The ice which covered the region was the western margin of the Green Bay
+lobe (Fig. 36) of the last continental ice sheet. Its limit in this
+region is marked by a ridge-like accumulation of drift, the _terminal
+moraine_, which here has a general north-south direction. The region
+may have been affected by the ice of more than one epoch, but since the
+ice of the last epoch advanced as far to the west in this region as that
+of any earlier epoch, the moraine is on the border between the glaciated
+country to the east, and the driftless area to the west (Plates I and
+II). That part of the moraine which lies west of the Wisconsin river
+follows a somewhat sinuous course from Kilbourn City to a point a short
+distance north of Prairie du Sac. The departures from this general
+course are especially significant of the behavior of glacier ice.
+
+[Illustration: Fig. 36.--Map showing relations of lobes of ice during
+the Wisconsin ice epoch, to the driftless area.]
+
+In the great depression between the quartzite ranges, the moraine bends
+westward, showing that the ice advanced farther on the lowlands than on
+the ridges. As the moraine of this low area approaches the south range,
+it curves to the east. At the point southwest of Baraboo where the
+easterly curve begins to show itself, the moraine lies at the north base
+of the quartzite range; but as it is traced eastward, it is found to lie
+higher and higher on the slope of the range, until it reaches the crest
+nearly seven miles from the point where the eastward course was assumed.
+At this point it crosses the range, and, once across the crest, it turns
+promptly to the westward on the lower land to the south. Here the ice
+advanced up the valley between the East bluff (east of the lake) and the
+Devil's nose (Plate XXXVII), again illustrating the fact that lowlands
+favor ice advance. The valley between the Devil's nose and the East
+bluff is a narrow one, and the ice advanced through it nearly to the
+present site of the lake. Meanwhile the restraining influence of the
+"nose" was making itself felt, and the margin of the ice curved back
+from the bottom of the bluff near Kirkland, to the top of the bluff at
+the end of the nose. Here the edge of the ice crossed the point of the
+nose, and after rounding it, turned abruptly to the west. Thence its
+edge lay along the south slope of the ridge, descending from the crest
+of the ridge at the nose, to the base of the ridge two miles farther
+west. Here the ice reached its limit on the lowland, and its edge, as
+marked by the moraine, turned southward, reaching the Wisconsin river
+about a mile and a half above Prairie du Sac.
+
+The course of the terminal moraine across the ridges is such as the
+margin of the ice would normally have when it advanced into a region of
+great relief. The great loop in the moraine with its eastern extremity
+at k, Plate XXXVII, is explained by the presence of the quartzite
+ridge which retarded the advancing ice while it moved forward on either
+side. The minor loop around the Devil's nose is explained in the same
+way. Both the main loop, and the smaller one on the nose, illustrate
+the point made earlier in the text.
+
+The narrow and curious loop at m, is of a slightly different origin,
+though in principle the same. It is in the lee of a high point in the
+quartzite ridge. The ice surmounted this point, and descended its
+western slope; but the thickness of the ice passing over the summit was
+so slight that it advanced but a short distance down the slope before
+its force was exhausted, while the thicker ice on either side advanced
+farther before it was melted.
+
+
+                     _Glacial Deposits._
+
+Before especial reference is made to the drift of this particular
+region, it will be well to consider the character of drift deposits in
+general. When the ice of the continental glacier began its motion, it
+carried none of the stony and earthy debris which constitute the drift.
+These materials were derived from the surface over which the ice moved.
+
+From the method by which it was gathered, it is evident that the drift
+of any locality may contain fragments of rock of every variety which
+occurs along the route followed by the ice which reached that locality.
+Where the ice had moved far, and where there were frequent changes in
+the character of the rock constituting its bed, the variety of materials
+in the drift is great. The heterogeneity of the drift arising from the
+diverse nature of the rocks which contributed to it is _lithological
+heterogeneity_--a term which implies the commingling of materials
+derived from different rock formations. Thus it is common to find pieces
+of sandstone, limestone, quartzite, granite, gneiss, schist, etc.,
+intimately commingled in the drift, wherever the ice which produced it
+passed over formations of these several sorts of rock. Lithological
+heterogeneity is one of the notable characteristics of glacial
+formations.
+
+Another characteristic of the drift is its _physical heterogeneity_. As
+first gathered from the bed of moving ice, some of the materials of the
+drift were fine and some coarse. The tendency of the ice in all cases
+was to reduce its load to a still finer condition. Some of the softer
+materials, such as soft shale, were crushed or ground to powder, forming
+what is known in common parlance as clay. Clayey (fine) material is
+likewise produced by the grinding action of ice-carried bowlders upon
+the rock-bed, and upon one another. Other sorts of rock, such as soft
+sandstone, were reduced to the physical condition of sand, instead of
+clay, and from sand to bowlders all grades of coarseness and fineness
+are represented in the glacial drift.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXV.
+
+Cut in drift, showing its physical heterogeneity.]
+
+Since the ice does not assort the material which it carries, as water
+does, the clay, sand, gravel and bowlders will not, by the action of the
+ice, be separated from one another. They are therefore not stratified.
+As left by the ice, these physically heterogeneous materials are
+confusedly commingled. The finer parts constitute a matrix in which the
+coarser are embedded.
+
+Physical heterogeneity (Plate XXXV), therefore, is another
+characteristic of glacial drift. It is not to be understood that the
+proportions of these various physical elements, clay, sand, gravel, and
+bowlders, are constant. Locally any one of them may predominate over any
+or all the others to any extent.
+
+Since lithological and physical heterogeneity are characteristics of
+glacial drift, they together afford a criterion which is often of
+service in distinguishing glacial drift from other surface formations.
+It follows that this double heterogeneity constitutes a feature which
+can be utilized in determining the former extension of existing
+glaciers, as well as the former existence of glaciers where glaciers do
+not now exist.
+
+Another characteristic of glacial drift, and one which clearly
+distinguishes it from all other formations with which it might be
+confounded, is easily understood from its method of formation. If the
+ice in its motion holds down rock debris upon the rock surface over
+which it passes with such pressure as to polish and striate the
+bed-rock, the material carried will itself suffer wear comparable to
+that which it inflicts. Thus the stones, large and small, of glacial
+drift, will be smoothed and striated. This sort of wear on the
+transported blocks of rock, is effected both by the bed-rock reacting on
+the bowlders transported over it, and by bowlders acting on one another
+in and under the ice. The wear of bowlders by bowlders is effected
+wherever adjacent ones are carried along at different rates. Since the
+rate of motion of the ice is different in different parts of the
+glacier, the mutual abrasion of transported materials is a process
+constantly in operation. A large proportion of the transported stone and
+blocks of rock may thus eventually become striated.
+
+From the nature of the wear to which the stones are subjected when
+carried in the base of the ice, it is easy to understand that their
+shapes must be different from those of water-worn materials. The latter
+are rolled over and over, and thus lose all their angles and assume a
+more or less rounded form. The former, held more or less firmly in the
+ice, and pressed against the underlying rock or rock debris as they are
+carried slowly forward, have their faces planed and striated. The
+planation and striation of a stone need not be confined to its under
+surface. On either side or above it other stones, moving at different
+rates, are made to abrade it, so that its top and sides may be planed
+and scored. If the ice-carried stones shift their positions, as they may
+under various circumstances, new faces will be worn. The new face thus
+planed off may meet those developed at an earlier time at sharp angles,
+altogether unlike anything which water-wear is capable of producing. The
+stone thus acted upon shows a surface bounded by planes and more or less
+beveled, instead of a rounded surface such as water wear produces. We
+find, then, in the shape of the bowlders and smaller stones of the
+drift, and in the markings upon their surfaces, additional criteria for
+the identification of glacier drift (Plate XXXVI).
+
+The characteristics of glacial drift, so far as concerns its
+constitution, may then be enumerated as, (1) its lithological, and (2)
+physical heterogeneity; (3) the shapes, and (4) the markings of the stones
+of the drift. In structure, the drift which is strictly glacial, is
+unstratified.
+
+In the broadest sense of the term, all deposits made by glacier ice are
+_moraines_. Those made beneath the ice and back from its edge constitute
+the _ground moraine_, and are distinguished from the considerable
+marginal accumulations which, under certain conditions, are accumulated
+at or near the margin. These marginal accumulations are _terminal
+moraines_. Associated with the moraines which are the deposits of the
+ice directly, there are considerable bodies of stratified gravel and
+sand, the structure of which shows that they were laid down by water.
+This is to be especially noted, since lack of stratification is
+popularly supposed to be the especial mark of the formations to which
+the ice gave rise.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVI.
+
+Glaciated stones, showing both form and striæ. (Matz.)]
+
+These deposits of stratified drift lie partly beyond the terminal
+moraine, and partly within it. They often sustain very complicated
+relations both to the ground and terminal moraines.
+
+The drift as a whole is therefore partly stratified and partly
+unstratified. Structurally the two types are thoroughly distinct, but
+their relations are often most complex, both horizontally and
+vertically. A fuller consideration of these relations will be found on a
+later page.
+
+
+                      _The Ground Moraine._
+
+The ground moraine constitutes the great body of the glacial drift.
+_Bowlder clay_, a term descriptive of its constitution in some places,
+and _till_, are other terms often applied to the ground moraine. The
+ground moraine consists of all the drift which lodged beneath the ice
+during its advance, all that was deposited back from its edge while its
+margin was farthest south, and most of that which was deposited while
+the ice was retreating. From this mode of origin it is readily seen that
+the ground moraine should be essentially as widespread as the ice
+itself. Locally, however, it failed of deposition. Since it constitutes
+the larger part of the drift, the characteristics already enumerated
+as belonging to drift in general are the characteristics of the
+till. Wherever obstacles to the progress of the ice lay in its path,
+there was a chance that these obstacles, rising somewhat into the
+lower part of the ice, would constitute barriers against which debris in
+the lower part of the ice would lodge. It might happen also that the
+ice, under a given set of conditions favoring erosion, would gather a
+greater load of rock-debris than could be transported under the changed
+conditions into which its advance brought it. In this case, some part of
+the load would be dropped and over-ridden. Especially near the margin of
+the ice where its thickness was slight and diminishing, the ice must
+have found itself unable to carry forward the loads of debris which it
+had gathered farther back where its action was more vigorous. It will be
+readily seen that if not earlier deposited, all material gathered by the
+under surface of the ice would ultimately find itself at the edge of the
+glacier, for given time enough, ablation will waste all that part of the
+ice occupying the space between the original position of the debris, and
+the margin of the ice. Under the thinned margin of the ice, therefore,
+considerable accumulations of drift must have been taking place while
+the ice was advancing. While the edge of the ice sheet was advancing
+into territory before uninvaded, the material accumulated beneath its
+edge at one time, found itself much farther from the margin at another
+and later time. Under the more forcible ice action back from the margin,
+the earlier accumulations, made under the thin edge, were partially or
+wholly removed by the thicker ice of a later time, and carried down to
+or toward the new and more advanced margin. Here they were deposited, to
+be in turn disturbed and transported still farther by the farther
+advance of the ice.
+
+Since in its final retreat the margin of the ice must have stood at all
+points once covered by it, these submarginal accumulations of drift must
+have been made over the whole country once covered by the ice. The
+deposits of drift made beneath the marginal part of the ice during its
+retreat, would either cover the deposits made under the body of the ice
+at an earlier time, or be left alongside them. The constitution of the
+two phases of till, that deposited during the advance of the ice, and
+that deposited during its retreat, is essentially the same, and there
+is nothing in their relative positions to sharply differentiate them.
+They are classed together as _subglacial till_.
+
+Subglacial till was under the pressure of the overlying ice. In keeping
+with these conditions of accumulation, the till often possesses a
+firmness suggestive of great compression. Where its constitution is
+clayey it is often remarkably tough. Where this is the case, the quality
+here referred to has given rise to the suggestive name "hard pan." Where
+the constitution of the till is sandy, rather than clayey, this firmness
+and toughness are less developed, or may be altogether wanting, since
+sand cannot be compressed into coherent masses like clay.
+
+_Constitution._--The till is composed of the more or less comminuted
+materials derived from the land across which the ice passed. The soil
+and all the loose materials which covered the rock entered into its
+composition. Where the ice was thick and its action vigorous, it not
+only carried away the loose material which it found in its path, but,
+armed with this material, it abraded the underlying rock, wearing down
+its surface and detaching large and small blocks of rock from it. It
+follows that the constitution of the till at any point is dependent upon
+the nature of the soil and rock from which it was derived.
+
+If sandstone be the formation which has contributed most largely to the
+till, the matrix of the till will be sandy. Where limestone instead of
+sandstone made the leading contribution to it, the till has a more
+earthy or clayey matrix. Any sort of rock which may be very generally
+reduced to a fine state of division under the mechanical action of the
+ice, will give rise to clayey till.
+
+The nature and the number of the bowlders in the till, no less than the
+finer parts, depend on the character of the rock overridden. A hard and
+resistant rock, such as quartzite, will give rise to more bowlders in
+proportion to the total amount of material furnished to the ice, than
+will softer rock. Shale or soft sandstone, possessing relatively slight
+resistance, will be much more completely crushed. They will, therefore,
+yield proportionately fewer bowlders than harder formations, and more
+of the finer constituents of till.
+
+The bowlders taken up by the ice as it advanced over one sort of rock
+and another, possessed different degrees of resistance. The softer ones
+were worn to smaller dimensions or crushed with relative ease and speed.
+Bowlders of soft rock are, therefore, not commonly found in any
+abundance at great distances from their sources. The harder ones yielded
+less readily to abrasion, and were carried much farther before being
+destroyed, though even such must have suffered constant reduction in
+size during their subglacial journey. In general it is true that
+bowlders in the till, near their parent formations, are larger and less
+worn than those which have been transported great distances.
+
+The ice which covered this region had come a great distance and had
+passed over rock formations of many kinds. The till therefore contains
+elements derived from various formations; that is, it is lithologically
+heterogeneous. This heterogeneity cannot fail to attract the attention
+of one examining any of the many exposures of drift about Baraboo at
+road gradings, or in the cuts along the railway. Among the stones in the
+drift at these exposures are limestone, sandstone, quartzite, diabase,
+gabbro, gneiss, granite, schist, and porphyry, together with pieces of
+flint and chert.
+
+Such an array may be found at any of the exposures within the immediate
+vicinity of Devil's lake. To the north, and a few miles to the south of
+the Baraboo ranges, the quartzite from these bluffs, and the porphyry
+from the point marked h in Plate II, are wanting, though other
+varieties of porphyry are present. The ice moved in a general
+west-southwest direction in this region, and the quartzite in the drift,
+so far as derived from the local formation, is therefore restricted to a
+narrow belt.
+
+The physical heterogeneity may be seen at all exposures, and is
+illustrated in Plate XXXV. The larger stones of the drift are
+usually of some hard variety of rock. Near the Baraboo ranges, the local
+quartzite often predominates among the bowlders, and since such
+bowlders have not been carried far, they are often little worn. Away
+from the ranges, the bowlders are generally of some crystalline rock,
+such as granite and diabase. Bowlders of these sorts of rock are from a
+much more distant source, and are usually well worn.
+
+In general the till of any locality is made up largely of material
+derived from the formations close at hand. This fact seems to afford
+sufficient warrant for the conclusion that a considerable amount of
+deposition must have gone on beneath the ice during its movement, even
+back from its margin. To take a concrete illustration, it would seem
+that the drift of southeastern Wisconsin should have had a larger
+contribution than it has of material derived from Canadian territory, if
+material once taken up by the ice was all or chiefly carried down to its
+thinned edge before deposition. The fact that so little of the drift
+came from these distant sources would seem to prove that a large part of
+the material moved by the ice, is moved a relatively short distance
+only. The ice must be conceived of as continually depositing parts of
+its load, and parts which it has carried but a short distance, as it
+takes up new material from the territory newly invaded.
+
+In keeping with the character of till in general, that about Devil's
+lake was derived largely from the sandstone, limestone and quartzite of
+the immediate vicinity, while a much smaller part of it came from more
+distant sources. This is especially noticeable in the fine material,
+which is made up mostly of the comminuted products of the local rock.
+
+_Topography._--The topography of the ground moraine is in general the
+topography already described in considering the modification of
+preglacial topography effected by ice deposition. As left by the ice,
+its surface was undulating. The undulations did not take the form of
+hills and ridges with intervening valleys, but of swells and depressions
+standing in no orderly relationship to one another. Undrained
+depressions are found in the ground moraine, but they are, as a rule,
+broader and shallower than the "kettles" common to terminal moraines.
+
+It is in the broad, shallow depressions of the ground moraine that many
+of the lakes and more of the marshes of southeastern Wisconsin are
+located.
+
+The rolling, undulating topography characteristic of ground moraines is
+well shown about the City of Baraboo and between that point and the
+lake, and at many less easily designated points about Merrimac.
+
+In thickness the ground moraine reaches at least 160 feet, though its
+average is much less--too little to obliterate the greater topographic
+features of the rock beneath. It is, however, responsible for many of
+the details of the surface.
+
+
+                    _Terminal Moraines._
+
+The marginal portion of the ice sheet was more heavily loaded--certainly
+more heavily loaded relative to its thickness--than any other. Toward
+its margin the thinned ice was constantly losing its transportive power,
+and at its edge this power was altogether gone. Since the ice was
+continually bringing drift down to this position and leaving it there,
+the rate of drift accumulation must have been greater, on the average,
+beneath the edge of the ice than elsewhere.
+
+Whenever, at any stage in its history, the edge of the ice remained
+essentially constant in position for a long period of time, the
+corresponding submarginal accumulation of drift was great, and when the
+ice melted, the former site of the stationary edge would be marked by a
+broad ridge or belt of drift, thicker than that on either side. Such
+thickened belts of drift are _terminal moraines_. It will be seen that a
+terminal moraine does not necessarily mark the terminus of the ice at
+the time of its greatest advance, but rather its terminus at any time
+when its edge was stationary or nearly so.
+
+From the conditions of their development it will be seen that these
+submarginal moraines may be made up of materials identical with those
+which constitute the ground moraine, and such is often the case. But
+water arising from the melting of the ice, played a much more
+important role at its margin than farther back beneath it. One result of
+its greater activity may be seen in the greater coarseness which
+generally characterizes the material of the terminal moraine as compared
+with that of the adjacent ground moraine. This is partly because the
+water carried away such of the finer constituents as it was able to
+transport, leaving the coarser behind. Further evidence of the great
+activity of water near the margin of the ice is to be seen in the
+relatively large amount of assorted and stratified sand and gravel
+associated with the terminal moraine.
+
+Such materials as were carried on the ice were dropped at its edge when
+the ice which bore them melted from beneath. If the surface of the ice
+carried many bowlders, many would be dropped along the line of its edge
+wherever it remained stationary for any considerable period of time. A
+terminal moraine therefore embraces (1) the thick belt of drift
+accumulated beneath the edge of the ice while it was stationary, or
+nearly so; and (2) such debris as was carried on the surface of the ice
+and dumped at its margin. In general the latter is relatively
+unimportant.
+
+At various stages in its final retreat, the ice made more or less
+protracted halts. These halting places are marked by marginal moraines
+of greater or less size, depending on the duration of the stop, and the
+amount of load carried.
+
+A terminal moraine is not the sharp and continuous ridge we are wont to
+think it. It is a belt of thick drift, rather than a ridge, though it is
+often somewhat ridge-like. In width, it varies from a fraction of a mile
+to several miles. In the region under consideration it is rarely more
+than fifty feet high, and rarely less than a half mile wide, and a ridge
+of this height and width is not a conspicuous topographic feature in a
+region where the relief is so great as that of the Devil's lake region.
+
+_Topography of terminal moraines._--The most distinctive feature of a
+terminal moraine is not its ridge-like character, but its peculiar
+topography. In general, it is marked by depressions without outlets,
+associated with hillocks and short ridges comparable in dimensions to
+the depressions. Both elevations and depressions are, as a rule, more
+abrupt than in the ground moraine. In the depressions there are many
+marshes, bogs, ponds and small lakes. The shapes and the abundance of
+round and roundish hills have locally given rise to such names as "The
+Knobs," "Short Hills," etc. Elsewhere the moraine has been named the
+"Kettle Range" from the number of kettle-like depressions in its
+surface. It is to be kept in mind that it is the association of the
+"knobs" and "kettles," rather than either feature alone, which is the
+distinctive mark of terminal moraine topography.
+
+[Illustration: Fig. 37.--Sketch of terminal moraine topography, on the
+quartzite ridge east of Devil's lake. (Matz.)]
+
+The manner in which the topography of terminal moraines was developed is
+worthy of note. In the first place, the various parts of the ice margin
+carried unequal amounts of debris. This alone would have caused the
+moraine of any region to have been of unequal height and width at
+different points. In the second place, the margin of the ice, while
+maintaining the same _general_ position during the making of a moraine,
+was yet subject to many minor oscillations. It doubtless receded to some
+slight extent because of increased melting during the summer, to advance
+again during the winter. In its recession, the ice margin probably did
+not remain exactly parallel to its former position. If some parts
+receded more than others, the details of the line of its margin may have
+been much changed during a temporary retreat. When the ice again
+advanced, its margin may have again changed its form in some slight
+measure, so as to be parallel neither with its former advanced position,
+nor with its position after its temporary retreat. With each successive
+oscillation of the edge, the details of the margin may have altered, and
+at each stage the marginal deposits corresponded with the edge. There
+might even be considerable changes in the edge of the ice without any
+general recession or advance, as existing glaciers show.
+
+It was probably true of the margin of the American ice sheet, as of
+existing glaciers, that there were periods of years when the edge of the
+ice receded, followed by like periods when it remained stationary or
+nearly so, and these in turn followed by periods of advance. During any
+advance, the deposits made during the period of recession would be
+overridden and disturbed or destroyed.
+
+If the ice were to retreat and advance repeatedly during a considerable
+period of time, always within narrow limits, and if during this
+oscillation the details of its margin were frequently changing, the
+result would be a complex or "tangle" of minor morainic ridges of
+variable heights and widths. Between and among the minor ridges there
+would be depressions of various sizes and shapes. Thus, it is conceived,
+many of the peculiar hillocks and hollows which characterize terminal
+moraines may have arisen.
+
+Some of the depressions probably arose in another way. When the edge of
+the ice retreated, considerable detached masses of ice might be left
+beyond the main body. This might be buried by gravel and sand washed out
+from the moraine. On melting, the former sites of such blocks of ice
+would be marked by "kettles." In the marginal accumulations of drift as
+first deposited, considerable quantities of ice were doubtless left.
+When this melted, the drift settled and the unequal settling may have
+given rise to some of the topographic irregularities of the drift.
+
+_The terminal moraine about Devil's lake._--On the lower lands, the
+terminal moraine of the Devil's lake region has the features
+characteristic of terminal moraines in general. It is a belt of thick
+drift varying in width from half a mile or less to three-quarters of a
+mile or more. Its surface is marked by numerous hills and short ridges,
+with intervening depressions or "kettles." Some of the depressions among
+the hills contain water, making ponds or marshes, though the rather
+loose texture of the drift of this region is not favorable to the
+retention of water. The moraine belt, as a whole, is higher than the
+land on either side. It is therefore somewhat ridge-like, and the small,
+short hills and ridges which mark its surface, are but constituent parts
+of the larger, broader ridge.
+
+Approached from the west, that is from the driftless side, the moraine
+on the lower lands is a somewhat prominent topographic feature, often
+appearing as a ridge thirty, forty or even fifty feet in height.
+Approached from the opposite direction, that is, from the ground
+moraine, it is notably less prominent, and its inner limit wherever
+located, is more or less arbitrary.
+
+[Illustration: Fig. 38.--Cut through the terminal moraine just east of
+Kirkland, partially diagrammatic.]
+
+A deep, fresh railway cut in the moraine southeast of Devil's lake
+illustrates its complexity of structure, a complexity which is probably
+no greater than that at many other points where exposures are not seen.
+The section is represented in Fig. 38. The stratified sand to the right
+retains even the ripple-marks which were developed when it was
+deposited. To the left, at the same level, there is a body of _till_
+(unstratified drift), over which is a bed of stoneless and apparently
+structureless clay. In a depression just above the clay with till both
+to the right and left, is a body of loam which possesses the
+characteristics of normal loess. It also contains calcareous
+concretions, though no shells have been found. This occurrence of loess
+is the more noteworthy, since loess is rarely found in association with
+drift of the last glacial epoch.[7]
+
+    [7] An account of loess in connection with the drift of the
+    last glacial epoch is given in the _Journal of Geology_, Vol.
+    IV, pp. 929-987. For a general account of loess, see Sixth
+    Annual Report of U.S. Geological Survey.
+
+_The moraine on the main quartzite range._--In tracing the moraine over
+the greater quartzite range, it is found to possess a unique feature in
+the form of a narrow but sharply defined ridge of drift, formed at the
+extreme margin of the ice at the time of its maximum advance. For fully
+eleven miles, with but one decided break, and two short stretches where
+its development is not strong, this unique marginal ridge separates the
+drift-covered country on the one hand, from the driftless area on the
+other. In its course the ridge lies now on slopes, and now on summits,
+but in both situations preserves its identity. Where it rests on a
+plain, or nearly plain surface, its width at base varies from six to
+fifteen rods, and its average height is from twenty to thirty feet. Its
+crest is narrow, often no more than a single rod. Where it lies on a
+slope, it is asymmetrical in cross section (see Fig. 39), the shorter
+slope having a vertical range of ten to thirty-five feet, and its longer
+a range of forty to one hundred feet. This asymmetrical form persists
+throughout all that portion of the ridge which lies on an inclined
+surface, the slope of which does not correspond with the direction of
+the moraine. Where it lies on a flat surface, or an inclined surface
+the slope of which corresponds in direction with the course of the ridge
+itself, its cross section is more nearly symmetrical (see Fig. 40). In
+all essential characteristics this marginal ridge corresponds with the
+_End-Moräne_ of the Germans.
+
+[Illustration: Fig. 39.--Diagrammatic cross-section of the marginal
+ridge as it occurs on the south slope of the Devil's Nose. The slope
+below, though glaciated, is nearly free from drift.]
+
+[Illustration: Fig. 40.--Diagrammatic cross-section of the marginal
+ridge as it appears when its base is not a sloping surface.]
+
+For the sake of bringing out some of its especially significant
+features, the ridge may be traced in detail, commencing on the south
+side of the west range. Where the moraine leaves the lowlands south of
+the Devil's nose, and begins the ascent of the prominence, the marginal
+ridge first appears at about the 940-foot contour (f, Plate XXXVII).
+Though at first its development is not strong, few rods have been passed
+before its crest is fifteen to twenty feet above the driftless area
+immediately to the north (see Fig. 39) and from forty to one hundred
+feet above its base to the south, down the slope. In general the ridge
+becomes more distinct with increasing elevation, and except for two or
+three narrow post-glacial erosion breaks, is continuous to the very
+summit at the end of the nose (g). The ridge in fact constitutes the
+uppermost forty or forty-five feet of the crest of the nose, which is
+the highest point of the west range within the area shown on the map.
+Throughout the whole of this course the marginal ridge lies on the south
+slope of the nose, and has the asymmetrical cross section shown in Fig.
+39. Above (north of) the ridge at most points not a bowlder of drift
+occurs. So sharply is its outer (north) margin defined, that at many
+points it is possible to locate it within the space of less than a yard.
+
+At the crest of the nose (g) the marginal ridge, without a break,
+swings northward, and in less than a quarter of a mile turns again to
+the west. Bearing to the north it presently reaches (at h) the edge of
+the precipitous bluff, bordering the great valley at the south end of
+the lake. Between the two arms of the loop thus formed, the surface of
+the nose is so nearly level that it could have offered no notable
+opposition to the progress of the ice, and yet it failed to be covered
+by it.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVII.
+
+Topographic map (contour interval 100 feet) of a small area about
+Devil's lake, taken from the Baraboo sheet of the United States
+Geological Survey. Each contour line connects points of the same
+elevation, and the figures upon them give the heights above sea level.
+Where contour lines lie close together, they indicate steep slopes.]
+
+In the great valley between the nose and the east bluff, the marginal
+ridge does not appear. In the bottom of the valley the moraine takes on
+its normal form, and the slopes of the quartzite ridges on either hand
+are much too steep to allow any body of drift, or loose material of any
+sort, to lodge on them.
+
+Ascending the east bluff a little east of the point where the drift
+ridge drops off the west bluff, the ridge is again found (at i) in
+characteristic development. For some distance it is located at the edge
+of the precipitous south face of the bluff. Farther on it bears to the
+north, and soon crosses a col (j) in the ridge, building it up many
+feet above the level of the bed-rock. From this point eastward for about
+three miles the marginal ridge is clearly defined, the slopes about
+equal on either side, and the crest as nearly even as the topography of
+the underlying surface permits. The topographic relations in this part
+of the course are shown in Fig. 40.
+
+At k, this marginal ridge attains its maximum elevation, 1,620 feet.
+At this great elevation, the ridge turns sharply to the northwest at an
+angle of more than 90°. Following this direction for little more than
+half a mile, it turns to the west. At some points in this vicinity the
+ridge assumes the normal morainic habit, but this is true for short
+distances only. Farther west, at l, it turns abruptly to the northeast
+and is sharply defined. It here loops about a narrow area less than
+sixty rods wide, and over half a mile in length, the sharpest loop in
+its whole course. The driftless tract enclosed by the arms of this loop
+is lower than the drift ridge on either hand. The ice on either side
+would need to have advanced no more than thirty rods to have covered the
+whole of it.
+
+From the minor loop just mentioned, the marginal ridge is continued
+westward, being well developed for about a mile and a half. At this
+point the moraine swings south to the north end of Devil's lake, loses
+the unique marginal ridge which has characterized its outer edge
+across the quartzite range for so many miles, and assumes the topography
+normal to terminal moraines. At no other point in the United States, so
+far as known to the writers, is there so sharply marked a marginal ridge
+associated with the terminal moraine, for so long a distance.
+
+From Plate II it will be seen that the moraine as a whole makes a
+great loop to the eastward in crossing the quartzite range. From the
+detailed description just given of the course of the marginal ridge, it
+will be seen that it has three distinct loops; one on the Devil's nose
+(west of g, Plate XXXVII); one on the main ridge (west of k)
+and a minor one on the north side of the last (southwest of m). The
+first and third are but minor irregularities on the sides of the great
+loop, the head of which is at k.
+
+The significant fact in connection with these irregularities in the
+margin of the moraine is that each loop stands in a definite relation to
+a prominence. The meaning of this relation is at once patent. The great
+quartzite range was a barrier to the advance of the ice. Acting as a
+wedge, it caused a re-entrant in the advancing margin of the glacier.
+The extent and position of the re-entrant is shown by the course of the
+moraine in Plate II. Thus the great loop in the moraine, the head of
+which is at k, Plate XXXVII, was caused by the quartzite range itself.
+
+The minor loops on the sides of the major are to be explained on the
+same principle. Northeast of the minor loop on the north side of the
+larger one (m) there are two considerable hills, reaching an elevation
+of nearly 1,500 feet. Though the ice advancing from the east-northeast
+overrode them, they must have acted like a wedge, to divide it into
+lobes. The ice which reached their summits had spent its energy in so
+doing, and was unable to move forward down the slope ahead, and the
+thicker bodies of ice which passed on either side of them, failed to
+unite in their lee (compare Figs. 34 and 35). The application of the
+same principle to the loop on the Devil's nose is evident.
+
+_Constitution of the marginal ridge._--The material in the marginal
+ridge, as seen where erosion has exposed it, is till, abnormal, if at
+all, only in the large percentage of widely transported bowlders which
+it contains. This is especially true of the surface, where in some
+places 90 per cent. of the large bowlders are of very distant origin,
+and that in spite of the fact that the ice which deposited them had just
+risen up over a steep slope of quartzite, which could easily have
+yielded abundant bowlders. In other places the proportion of foreign
+bowlders is small, no more than one in ten. In general, however,
+bowlders of distant origin predominate over those derived close at hand.
+
+_The slope of the upper surface of the ice at the margin._--The marginal
+ridge on the south slope of Devil's nose leads to an inference of
+especial interest. Its course lies along the south slope of the nose,
+from its summit on the east to its base on the west. Throughout this
+course the ridge marks with exactness the position of the edge of the
+ice at the time of its maximum advance, and its crest must therefore
+represent the slope of the upper surface of the ice at its margin.
+
+The western end of the ridge (f, Plate XXXVII) has an altitude of 940
+feet, and its eastern end (g) is just above the 1,500-foot contour.
+The distance from the one point to the other is one and three-fourths
+miles, and the difference in elevation, 560 feet. These figures show
+that the slope of the ice along the south face of this bluff was about
+320 feet per mile. This, so far as known, is the first determination of
+the slope of the edge of the continental ice sheet _at its extreme
+margin_. It is to be especially noted that these figures are for the
+extreme edge of the ice only. The angle of slope back from the edge was
+doubtless much less.
+
+
+                      _Stratified Drift._
+
+While it is true that glacier ice does not distinctly stratify the
+deposits which it makes, it is still true that a very large part of the
+drift for which the ice of the glacial period was directly or indirectly
+responsible is stratified. That this should be so is not strange when it
+is remembered that most of the ice was ultimately converted into running
+water, just as the glaciers of today are. The relatively small portion
+which disappeared by evaporation was probably more than counterbalanced,
+at least near the margin of the ice, by the rain which fell upon it.
+
+It cannot be considered an exaggeration, therefore, to say that the
+total amount of water which operated on the drift, first and last, was
+hardly less than the total amount of the ice itself. The drift deposited
+by the marginal part of the ice was affected during its deposition, not
+only by the water which arose from the melting of the ice which did the
+depositing, but by much water which arose from the melting of the ice
+far back from the margin. The general mobility of the water, as
+contrasted with ice, allowed it to concentrate its activities along
+those lines which favored its motion, so that different portions of the
+drift were not affected equally by the water of the melting ice.
+
+All in all it will be seen that the water must have been a very
+important factor in the deposition of the drift, especially near the
+margin of the ice. But the ice sheet had a marginal belt throughout its
+whole history, and water must have been active and effective along this
+belt, not only during the decadence of the ice sheet, but during its
+growth as well. It is further to be noted that any region of drift stood
+good chance of being operated upon by the water after the ice had
+departed from it, so that in regions over which topography directed
+drainage after the withdrawal of the ice, the water had the last chance
+at the drift, and modified it in such a way and to such an extent as
+circumstances permitted.
+
+_Its origin._--There are various ways in which stratified drift may
+arise in connection with glacier deposits. It may come into existence by
+the operation of water alone; or by the co-operation of ice and water.
+Where water alone was immediately responsible for the deposition of
+stratified drift, the water concerned may have owed its origin to the
+melting ice, or it may have existed independently of the ice in the form
+of lakes. When the source of the water was the melting ice, the water
+may have been running, when it was actively concerned in the deposition
+of stratified drift; or it may have been standing (glacial lakes and
+ponds), when it was passively concerned. When ice co-operated with water
+in the development of stratified drift the ice was generally a passive
+partner.
+
+_Glacial drainage._--The body of an ice sheet during any glacial period
+is probably melting more or less at some horizons all the time, and at
+all horizons some of the time. Most of the water which is produced at
+the surface during the summer sinks beneath it. Some of it may congeal
+before it sinks far, but much of it reaches the bottom of the ice
+without refreezing. It is probable that melting is much more nearly
+continuous in the body of a moving ice sheet than at its surface, and
+that some of the water thus produced sinks to the bottom of the ice
+without refreezing. At the base of the ice, so long as it is in
+movement, there is doubtless more or less melting, due both to friction
+and to the heat received by conduction from the earth below. Thus in the
+ice and under the ice there must have been more or less water in motion
+throughout essentially all the history of an ice sheet.
+
+If it be safe to base conclusions on the phenomena of existing glaciers,
+it may be assumed that the waters beneath the ice, and to a less extent
+the waters in the ice, organized themselves to a greater or less degree
+into streams. For longer or shorter distances these streams flowed in
+the ice or beneath it. Ultimately they escaped from its edge. The
+subglacial streams doubtless flowed, in part, in the valleys which
+affected the land surface beneath the ice, but they were probably not
+all in such positions.
+
+The courses of well-defined subglacial streams were tunnels. The bases
+of the tunnels were of rock or drift, while the sides and tops were of
+ice. It will be seen, therefore, that their courses need not have
+corresponded with the courses of the valleys beneath the ice. They may
+sometimes have followed lines more or less independent of topography,
+much as water may be forced over elevations in closed tubes. It is not
+to be inferred, however, that the subglacial streams were altogether
+independent of the sub-ice topography. The tunnels in which the water
+ran probably had too many leaks to allow the water to be forced up over
+great elevations. This, at least, must have been the case where the ice
+was thin or affected by crevasses. Under such circumstances the
+topography of the land surface must have been the controlling element
+in determining the course of the subglacial drainage.
+
+When the streams issued from beneath the ice the conditions of flow were
+more or less radically changed, and from their point of issue they
+followed the usual laws governing river flow. If the streams entered
+static water as they issued from the ice, and this was true where the
+ice edge reached the sea or a lake, the static water modified the
+results which the flowing waters would otherwise have produced.
+
+_Stages in the history of an ice sheet._--The history of an ice sheet
+which no longer exists involves at least two distinct stages. These are
+(1) the period of growth, and (2) the period of decadence. If the latter
+does not begin as soon as the former is complete, an intervening stage,
+representing the period of maximum ice extension, must be recognized. In
+the case of the ice sheets of the glacial period, each of these stages
+was probably more or less complex. The general period of growth of each
+ice sheet is believed to have been marked by temporary, but by more or
+less extensive intervals of decadence, while during the general period
+of decadence, it is probable that the ice was subject to temporary, but
+to more or less extensive intervals of recrudescence. For the sake of
+simplicity, the effects of these oscillations of the edge of the ice
+will be neglected at the outset, and the work of the water accompanying
+the two or three principal stages of an ice sheet's history will be
+outlined as if interruptions in the advance and in the retreat,
+respectively, had not occurred.
+
+As they now exist, the deposits of stratified drift made at the edge of
+the ice or beyond it during the period of its maximum extension present
+the simplest, and at the same time most sharply defined phenomena, and
+are therefore considered first.
+
+
+ _Deposits Made by Extraglacial Waters During the Maximum Extension of
+                           the Ice._
+
+The deposits made by the water at the time of the maximum extension of
+the ice and during its final retreat, were never disturbed by subsequent
+glacier action. So far as not destroyed by subsequent erosion, they
+still retain the form and structure which they had at the outset. Such
+drift deposits, because they lie at the surface, and because they are
+more or less distinct topographically as well as structurally, are
+better known than the stratified drift of other stages of an ice sheet's
+history. Of stratified drift made during the maximum extension of the
+ice, and during its final retreat, there are several types.
+
+_A. At the edge of ice, on land._--If the subglacial streams flowed
+under "head," the pressure was relieved when they escaped from the ice.
+With this relief, there was diminution of velocity. With the diminution
+of velocity, deposition of load would be likely to take place. Since
+these changes would be likely to occur at the immediate edge of the ice,
+one class of stratified drift deposits would be made in this position,
+in immediate contact with the edge of the ice, and their form would be
+influenced by it. At the stationary margin of an ice sheet, therefore,
+at the time of its maximum advance, ice and water must have co-operated
+to bring into existence considerable quantities of stratified drift.
+
+The edge of the ice was probably ragged, as the ends of glaciers are
+today, and as the waters issued from beneath it, they must frequently
+have left considerable quantities of such debris as they were carrying,
+against its irregular margin, and in its re-entrant angles and marginal
+crevasses. When the ice against which this debris was first lodged
+melted, the marginal accumulations of gravel and sand often assumed the
+form of kames. A typical kame is a hill, hillock, or less commonly a
+short ridge of stratified drift; but several or many are often
+associated, giving rise to groups and areas of _kames_. Kames are often
+associated with terminal moraines, a relation which emphasizes the fact
+of their marginal origin.
+
+So far as the superficial streams which flowed to the edge of the ice
+carried debris, this was subject to deposition as the streams descended
+from the ice. Such drift would tend to increase the body of marginal
+stratified drift from subglacial sources.
+
+Marginal accumulations of stratified drift, made by the co-operation of
+running water and ice, must have had their most extensive development,
+other things being equal, where the margin of the ice was longest in one
+position, and where the streams were heavily loaded. The deposits made
+by water at the edge of the ice differ from those of the next
+class--made beyond the edge of the ice--in that they were influenced in
+their disposition and present topography, by the presence of ice.
+
+In the Devil's lake region isolated and well-defined kames are not of
+common occurrence. There are, however, at many points hills which have
+something of a kame-like character. There is such a hill a mile
+southeast of the Court house at Baraboo, at the point marked p, Plate
+XXXVII. In this hill there are good exposures which show its structure.
+There are many hillocks of a general kame-like habit associated with the
+terminal moraine south of the main quartzite range, and north of the
+Wisconsin river. Many of them occur somewhat within the terminal moraine
+a few miles northwest of Merrimac.
+
+_B. Beyond the edge of the ice, on land._--As the waters escaping from
+the ice flowed farther, deposits of stratified drift were made quite
+beyond the edge of the ice. The forms assumed by such deposits are
+various, and depended on various conditions. Where the waters issuing
+from the edge of the ice found themselves concentrated in valleys, and
+where they possessed sufficient load, and not too great velocity, they
+aggraded the valleys through which they flowed, developing fluvial
+plains of gravel and sand, which often extended far beyond the ice. Such
+fluvial plains of gravel and sand constitute the _valley trains_ which
+extend beyond the unstratified glacial drift in many of the valleys of
+the United States. They are found especially in the valleys leading out
+from the stouter terminal moraines of late glacial age. From these
+moraines, the more extensive valley trains take their origin, thus
+emphasizing the fact that they are deposits made by water beyond a
+stationary ice margin. Valley trains have all the characteristics of
+alluvial plains built by rapid waters carrying heavy loads of detritus.
+Now and then their surfaces present slight variations from planeness,
+but they are minor. Like all plains of similar origin they decline
+gradually, and with diminishing gradient, down stream. They are of
+coarser material near their sources, and of finer material farther away.
+Valley trains constitute a distinct topographic as well as genetic type.
+
+A perfect example of a valley train does not occur within the region
+here discussed. There is such a train starting at the moraine where it
+crosses the Wisconsin river above Prairie du Sac, and extending down
+that valley to the Mississippi, but at its head this valley train is
+wide and has the appearance of an overwash plain, rather than a valley
+train. Farther from the moraine, however, it narrows, and assumes the
+normal characteristics of a valley train. It is the gravel and sand of
+this formation which underlies Sauk Prairie, and its topographic
+continuation to the westward.
+
+Where the subglacial streams did not follow subglacial valleys, they did
+not always find valleys when they issued from the ice. Under such
+circumstances, each heavily loaded stream coming out from beneath the
+ice must have tended to develop a plain of stratified material near its
+point of issue--a sort of alluvial fan. Where several such streams came
+out from beneath the ice near one another, their several plains, or
+fans, were likely to become continuous by lateral growth. Such border
+plains of stratified drift differ from valley trains particularly (1) in
+being much less elongate in the direction of drainage; (2) in being much
+more extended parallel to the margin of the ice; and (3) in not being
+confined to valleys. Such plains stood an especially good chance of
+development where the edge of the ice remained constant for a
+considerable period of time, for it was under such conditions that the
+issuing waters had opportunity to do much work. Thus arose the type of
+stratified drift variously known as _overwash plains_, _outwash plains_,
+_morainic plains_, and _morainic aprons_. These plains sometimes skirt
+the moraine for many miles at a stretch.
+
+Overwash plains may sometimes depart from planeness by taking on some
+measure of undulation, of the sag and swell (kame) type, especially near
+their moraine edges. The same is often true of the heads of valley
+trains. The heads of valley trains and the inner edges of overwash
+plains, it is to be noted, occupy the general position in which kames
+are likely to be formed, and the undulations which often affect these
+parts of the trains and plains, respectively, are probably to be
+attributed to the influence of the ice itself. Valley trains and
+overwash plains, therefore, at their upper ends and edges respectively,
+may take on some of the features of kames. Indeed, either may head in a
+kame area.
+
+Good examples of overwash or outwash plains may be seen at various
+points in the vicinity of Baraboo. The plain west of the moraine just
+south of the main quartzite ridge has been referred to under valley
+trains. In Sauk Prairie, however, its characteristics are those of an
+outwash plain, rather than those of a valley train.
+
+[Illustration: Fig. 41.--The morainic or outwash plain bordering the
+terminal moraine. The figure is diagrammatic, but represents, in cross
+section, the normal relation as seen south of the quartzite range at the
+east edge of Sauk Prairie, north of the Baraboo river and at some points
+between the South range and the Baraboo.]
+
+A good example of an outwash plain occurs southwest of Baraboo, flanking
+the moraine on the west (Fig. 41). Seen from the west, the moraine just
+north of the south quartzite range stands up as a conspicuous ridge
+twenty to forty feet above the morainic plain which abuts against it.
+Traced northward, the edge of the outwash plain, as it abuts against
+the moraine, becomes higher, and in Section 4, Township 11 N., Range 6
+E., the moraine edge of the plain reaches the crest of the moraine (Fig.
+42). From this point north to the Baraboo river the moraine scarcely
+rises above the edge of the outwash beyond.
+
+[Illustration: Fig. 42.--The outwash plain is built up to the crest of
+the moraine. The figure is diagrammatic, but this relation is seen at
+the point marked W, Plate II.]
+
+North of the Baraboo river the moraine is again distinct and the
+overwash plain to the west well developed much of the way from the
+Baraboo to Kilbourn City. A portion of it is known as Webster's Prairie.
+
+Locally, the outwash plains of this region have been much dissected by
+erosion since their deposition, and are now affected by many small
+valleys. In composition these plains are nearly everywhere gravel and
+sand, the coarser material being nearer the moraine. The loose material
+is in places covered by a layer of loam several feet deep, which greatly
+improves the character of the soil. This is especially true of Sauk
+Prairie, one of the richest agricultural tracts in the state.
+
+When the waters issuing from the edge of the ice were sluggish, whether
+they were in valleys or not, the materials which they carried and
+deposited were fine instead of coarse, giving rise to deposits of silt,
+or clay, instead of sand or gravel.
+
+At many points near the edge of the ice during its maximum stage of
+advance, there probably issued small quantities of water not in the form
+of well-defined streams, bearing small quantities of detritus. These
+small quantities of water, with their correspondingly small loads, were
+unable to develop considerable plains of stratified drift, but produced
+small patches instead. Such patches have received no special
+designation.
+
+In the deposition of stratified drift beyond the edge of the ice, the
+latter was concerned only in so far as its activity helped to supply the
+water with the necessary materials.
+
+_C. Deposits at and beyond the edge of the ice in standing water._--The
+waters which issued from the edge of the ice sometimes met a different
+fate. The ice in its advance often moved up river valleys. When at the
+time of its maximum extension, it filled the lower part of a valley,
+leaving the upper part free, drainage through the valley stood good
+chance of being blocked. Where this happened a marginal valley lake was
+formed. Such a lake was formed in the valley of the Baraboo when the
+edge of the ice lay where the moraine now is (Plate II). The waters
+which were held back by the ice dam, reinforced by the drainage from the
+ice itself, soon developed a lake above the point of obstruction. This
+extinct lake may be named Baraboo lake. In this lake deposits of
+laminated clay were made. They are now exposed in the brick yards west
+of Baraboo, and in occasional gullies and road cuts in the flat
+bordering the river.
+
+At the point marked s (Plate XXXVII) there was, in glacial
+times, a small lake having an origin somewhat different from that of
+Baraboo lake. The former site of the lake is now marked by
+a notable flat. Excavations in the flat show that it is made up of
+stratified clay, silt, sand and gravel, to the depth of many
+feet,--locally more than sixty. These lacustrine deposits are well
+exposed in the road cuts near the northwest corner of the flat, and in
+washes at some other points. Plate XXXVIII shows some of the silt and
+clay, the laminæ of which are much distorted.
+
+_Deltas_ must have been formed where well-defined streams entered the
+lakes, and _subaqueous overwash plains_ where deltas became continuous
+by lateral growth. The accumulation of stratified drift along the
+ice-ward shores of such lakes must have been rapid, because of the
+abundant supply of detritus. These materials were probably shifted about
+more or less by waves and shore currents, and some of them may have been
+widely distributed. Out from the borders of such lakes, fine silts and
+clays must have been in process of deposition, at the same time that the
+coarse materials were being laid down nearer shore.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVIII.
+
+Distorted laminae of silt and clay.]
+
+Good examples of deltas and subaqueous overwash plains do not appear to
+exist in the region, although conditions for their development seem to
+have been present. Thus in the lake which occupied the valley of the
+Baraboo, conditions would seem to have been ideal for the development of
+such features; that is, the overwash plains previously described should,
+theoretically, have been subaqueous overwash plains; but if this be
+their character, their distinctive marks have been destroyed by
+subsequent erosion.
+
+During the maximum extension of an ice sheet, therefore, there was
+chance for the development, at its edge or beyond it, of the following
+types of stratified drift: (1) kames and kame belts, at the edge of the
+ice; (2) fluvial plains or valley trains, in virtual contact with the
+ice at their heads; (3) border plains or overwash plains, in virtual
+contact with the ice at their upper edges; (4) ill-defined patches of
+stratified drift, coarse or fine near the ice; (5) subaqueous overwash
+plains and deltas, formed either in the sea or lakes at or near the edge
+of the ice; (6) lacustrine and marine deposits of other sorts, the
+materials for which were furnished by the waters arising from the ice.
+So far as this region is concerned, all the deposits made in standing
+water were made in lakes.
+
+_Deposits Made by Extraglacial Waters During the Retreat of the Ice._
+
+During the retreat of any ice sheet, disregarding oscillations of its
+edge, its margin withdrew step by step from the position of extreme
+advance to its center. When the process of dissolution was complete,
+each portion of the territory once covered by the ice, had at some stage
+in the dissolution, found itself in a marginal position. At all stages
+in its retreat the waters issuing from the edge of the ice were working
+in the manner already outlined in the preceding paragraphs. Two points
+of difference only need be especially noted. In the first place the
+deposits made by waters issuing from the retreating ice were laid down
+on territory which the ice had occupied, and their subjacent stratum was
+often glacial drift. So far as this was the case, the stratified drift
+was super-morainic, not extra-morainic. In the second place the edge of
+the ice in retreat did not give rise to such sharply marked formations
+as the edge of the ice which was stationary. The processes which had
+given rise to valley trains, overwash plains, kames, etc., while the ice
+edge was stationary, were still in operation, but the line or zone of
+their activity (the edge of the ice) was continually retreating, so that
+the foregoing types, more or less dependent on a stationary edge, were
+rarely well developed. As the ice withdrew, therefore, it allowed to be
+spread over the surface it had earlier occupied, many incipient valley
+trains, overwash plains, and kames, and a multitude of ill-defined
+patches of stratified drift, thick and thin, coarse and fine. Wherever
+the ice halted in its retreat, these various types stood chance of
+better development.
+
+Such deposits did not cover all the surface discovered by the ice in its
+retreat, since the issuing waters, thanks to their great mobility,
+concentrated their activities along those lines which favored their
+motion. Nevertheless the aggregate area of the deposits made by water
+outside the ice as it retreated, was great.
+
+It is to be noted that it was not streams alone which were operative as
+the ice retreated. As its edge withdrew, lakes and ponds were
+continually being drained, as their outlets, hitherto choked by the ice,
+were opened, while others were coming into existence as the depressions
+in the surface just freed from ice, filled with water. Lacustrine
+deposits at the edge of the ice during its retreat were in all essential
+respects identical with those made in similar situations during its
+maximum extension.
+
+Disregarding oscillations of the ice edge at these stages, the deposits
+made by extraglacial waters during the maximum extension of an ice
+sheet, and during its retreat, were always left at the surface, so far
+as the work of that ice sheet was concerned. The stratified drift laid
+down by extraglacial waters in these stages of the last ice sheet which
+affected any region of our continent still remain at the surface in much
+the condition in which they were deposited, except for the erosion they
+have since suffered. It is because of their position at the surface that
+the deposits referable to these stages of the last ice sheet of any
+given region have received most attention and are therefore most
+familiar.
+
+
+ _Deposits Made by Extraglacial Waters During the Advance of the Ice._
+
+During the advance of an ice sheet, if its edge forged steadily forward,
+the waters issuing from it, and flowing beyond, were effecting similar
+results. They were starting valley trains, overwash plains, kames, and
+small ill-defined patches of stratified drift which the ice did not
+allow them to complete before pushing over them, thus moving forward the
+zone of activity of extraglacial waters. Unlike the deposits made by the
+waters of the retreating ice, those made by the waters of the advancing
+stage were laid down on territory which had not been glaciated, or at
+least not by the ice sheet concerned in their deposition. If the ice
+halted in its advance, there was at such time and place opportunity for
+the better development of extraglacial stratified drift.
+
+Lakes as well as streams were concerned in the making of stratified beds
+of drift, during the advance of the ice. Marginal lakes were obliterated
+by having their basins filled with the advancing ice, which displaced
+the water. But new ones were formed, on the whole, as rapidly as their
+predecessors became extinct, so that lacustrine deposits were making at
+intervals along the margin of the advancing ice.
+
+Deposits made in advance of a growing ice sheet, by waters issuing from
+it, were subsequently overridden by the ice, to the limit of its
+advance, and in the process, suffered destruction, modification, or
+burial, in whole or in part, so that now they rarely appear at the
+surface.
+
+
+              _Deposits Made by Subglacial Streams._
+
+Before their issuance from beneath the ice, subglacial waters were not
+idle. Their activity was sometimes erosive, and at such times stratified
+deposits were not made. But where the sub-glacial streams found
+themselves overloaded, as seems frequently to have been the case, they
+made deposits along their lines of flow. Where such waters were not
+confined to definite channels, their deposits probably took on the form
+of irregular patches of silt, sand, or gravel; but where depositing
+streams were confined to definite channels, their deposits were
+correspondingly concentrated.
+
+When subglacial streams were confined to definite channels, the same may
+have been constant in position, or may have shifted more or less from
+side to side. Where the latter happened there was a tendency to the
+development of a belt or strip of stratified drift having a width equal
+to the extent of the lateral migrations of the under-ice stream. Where
+the channel of the subglacial stream remained fixed in position, the
+deposition was more concentrated, and the bed was built up. If the
+stream held its course for a long period of time, the measure of
+building may have been considerable. In so far as these channel deposits
+were made near the edge of the ice, during the time of its maximum
+extension or retreat, they were likely to remain undisturbed during its
+melting. The aggraded channels then came to stand out as ridges. These
+ridges of gravel and sand are known as osars or eskers. It is not to
+be inferred that eskers never originated in other ways, but it seems
+clear that this is one method, and probably the principal one, by which
+they came into existence. Eskers early attracted attention, partly
+because they are relatively rare, and partly because they are often
+rather striking topographic features. The essential conditions,
+therefore, for their formations, so far as they are the product of
+subglacial drainage, are (1) the confining of the subglacial streams to
+definite channels; and (2) a sufficient supply of detritus. One esker
+only has been found in the region under consideration. It is located at
+the point marked j, Plate II, seven and one-half miles northeast of
+Merrimac and one and one-half miles south of Alloa (g, Plate II). The
+esker is fully a quarter of a mile long, about thirty feet high, and
+four rods wide at its base.
+
+Subglacial deposits of stratified drift were sometimes made on
+unstratified drift (till) already deposited by the ice before the
+location of the stream, and sometimes on the rock surfaces on which no
+covering of glacier drift had been spread.
+
+It is to be kept in mind that subglacial drainage was operative during
+the advance of an ice sheet, during its maximum extension, and during
+its retreat, and that during all these stages it was effecting its
+appropriate results. It will be readily seen, however, that all deposits
+made by subglacial waters, were subject to modification or destruction
+or burial, through the agency of the ice, and that those made during the
+advance of the ice were less likely to escape than those made during its
+maximum extension or retreat.
+
+
+           RELATIONS OF STRATIFIED TO UNSTRATIFIED DRIFT.
+
+When it is remembered that extraglacial and subglacial waters were
+active at all stages of an ice sheet's history, giving rise, or tending
+to give rise to all the phases of stratified drift enumerated above;
+when it is remembered that the ice of several epochs affected much of
+the drift-covered country; and when it is remembered further that the
+edge of the ice both during advance and retreat was subject to
+oscillation, and that each advance was likely to bury the stratified
+drift last deposited, beneath unstratified, it will be seen that the
+stratified drift and the unstratified had abundant opportunity to be
+associated in all relationships and in all degrees of intimacy, and that
+the relations of the one class of drift to the other may come to be very
+complex.
+
+As a result of edge oscillation, it is evident that stratified drift may
+alternate with unstratified many times in a formation of drift
+deposited during a single ice epoch, and that two beds of till,
+separated by a bed of stratified drift, do not necessarily represent two
+distinct glacial epochs. The extent of individual beds of stratified
+drift, either beneath the till or inter-bedded with it, may not be
+great, though their aggregate area and their aggregate volume is very
+considerable. It is to be borne in mind that the ice, in many places,
+doubtless destroyed all the stratified drift deposited in advance on the
+territory which it occupied later, and that in others it may have left
+only patches of once extensive sheets. This may help to explain why it
+so frequently happens that a section of drift at one point shows many
+layers of stratified drift, while another section close by, of equal
+depth, and in similar relationships, shows no stratified material
+whatsoever.
+
+Such deposits as were made by superglacial streams during the advance of
+the ice must likewise have been delivered on the land surface, but would
+have been subsequently destroyed or buried, becoming in the latter case,
+submorainic. This would be likely to be the fate of all such
+superglacial gravels as reached the edge of the ice up to the time of
+its maximum advance.
+
+Streams descending from the surface of the ice into crevasses also must
+have carried down sand and gravel where such materials existed on the
+ice. These deposits may have been made on the rock which underlies the
+drift, or they may have been made on stratified or unstratified drift
+already deposited. In either case they were liable to be covered by
+till, thus reaching an inter-till or sub-till position.
+
+Englacial streams probably do little depositing, but it is altogether
+conceivable that they might accumulate such trivial pockets of sand and
+gravel as are found not infrequently in the midst of till. The
+inter-till position would be the result of subsequent burial after the
+stratified material reached a resting place.
+
+Complexity of relations.--From the foregoing it becomes clear that
+there are diverse ways by which stratified drift, arising in connection
+with an ice sheet, may come to be interbedded with till, when due
+recognition is made of all the halts and oscillations to which the edge
+of a continental glacier may have been subject during both its advance
+and retreat.
+
+
+     CLASSIFICATION OF STRATIFIED DRIFT ON THE BASIS OF POSITION.
+
+In general the conditions and relations which theoretically should
+prevail are those which are actually found.
+
+On the basis of position stratified drift deposits may be classified as
+follows:
+
+1. Extraglacial deposits, made by the waters of any glacial epoch if
+they flowed and deposited beyond the farthest limit of the ice.
+
+2. Supermorainic deposits, made chiefly during the final retreat of
+the ice from the locality where they occur, but sometimes by
+extraglacial streams or lakes of a much later time. Locally too,
+stratified deposits of an early stage of a glacial epoch, lying on till,
+may have failed to be buried by the subsequent passage of the ice over
+them, and so remain at the surface. In origin, supermorainic deposits
+were for the most part extraglacial (including marginal), so far as the
+ice sheet calling them into existence was concerned. Less commonly they
+were subglacial, and failed to be covered, and less commonly still
+superglacial.
+
+3. The submorainic (basal) deposits were made chiefly by extraglacial
+waters in advance of the first ice which affected the region where they
+occur. They were subsequently overridden by the ice and buried by its
+deposits. Submorainic deposits, however, may have arisen in other ways.
+Subglacial waters may have made deposits of stratified drift on surfaces
+which had been covered by ice, but not by till, and such deposits may
+have been subsequently buried. The retreat of an ice sheet may have left
+rock surfaces free from till covering, on which the marginal waters of
+the ice may have made deposits of stratified drift. These may have been
+subsequently covered by till during a re-advance of the ice in the same
+epoch or in a succeeding one. Still again, the till left by one ice
+sheet may have been exposed to erosion to such an extent as to have been
+completely worn away before the next ice advance, so that stratified
+deposits connected with a second or later advance may have been made on
+a driftless surface, and subsequently buried.
+
+4. Intermorainic stratified drift may have originated at the outset in
+all the ways in which supermorainic drift may originate. It may have
+become intermorainic by being buried in any one of the various ways in
+which the stratified drift may become submorainic.
+
+
+
+
+            CHANGES IN DRAINAGE EFFECTED BY THE ICE.
+
+
+                    _While the Ice Was on._
+
+As the continental ice sheet invaded a region, the valleys were filled
+and drainage was thereby seriously disturbed. Different streams were
+affected in different ways. Where the entire basin of a stream was
+covered by ice, the streams of that basin were, for the time being,
+obliterated. Where the valley of a stream was partially filled with ice,
+the valley depression was only partially obliterated, and the remaining
+portion became the scene of various activities. Where the ice covered
+the lower course of a stream but not the upper, the ice blocked the
+drainage, giving rise to a lake. Where the ice covered the upper course
+of a stream, but not its lower, the lower portion was flooded, and
+though the river held its position, it assumed a new phase of activity.
+Streams issuing from the ice usually carry great quantities of gravel
+and sand, and make deposits along their lower courses. Long continued
+glacial drainage usually results in a large measure of aggradation. This
+was true of the streams of the glacial period.
+
+Where a stream flowed parallel or approximately parallel to the edge of
+the advancing ice it was sometimes shifted in the direction in which the
+ice was moving, keeping parallel to the front of the ice. All of these
+classes of changes took place in this region.
+
+_Wisconsin lake._--Reference has already been made to certain lakes
+which existed in the region when the ice was there. The largest of these
+lakes was that which resulted from the blocking of the Wisconsin river.
+The ice crossed its present course at Kilbourn City, and its edge lay to
+the west of the river from that point to Prairie du Sac (see Plate I).
+The waters from the area now draining into the Wisconsin must either
+have found an avenue of escape beneath the ice, or have accumulated in a
+lake west of the edge of the ice. There is reason to believe that the
+latter was what happened, and that a great lake covered much of the low
+land west of the Wisconsin river above and below Kilbourn City. The
+extensive gravel beds on the north flank of the quartzite bluff at
+Necedah, and the water-worn pebbles of local origin on the slope of
+Petenwell peak (Plate XXXII), as well as the gravels at other points,
+are presumably the work of that lake. The waters in this lake, as in
+that in the Baraboo valley, probably rose until the lowest point in the
+rim of the basin was reached, and there they had their outlet. The
+position of this outlet has not been definitely determined, but it has
+been thought to be over the divide of the Black river.[8] It is
+possible, so far as now known, that this lake was connected with that of
+the Baraboo valley. Until topographic maps of this region are made, the
+connections will not be easily determined.
+
+    [8] Chamberlin: Geology of Wisconsin, Vol. 1.
+
+Even after the ice had retreated past the Wisconsin, opening up the
+present line of drainage, the lakes did not disappear at once, for the
+ice had left considerable deposits of drift in the Wisconsin valley.
+Thus at F, Plates II and XXXVII, and perhaps at other points, the
+Wisconsin has made cuts of considerable depth in the drift. Were these
+cuts filled, as they must have been when the ice melted, the drainage
+would be ponded, the waters standing at the level of the dam. This drift
+obstruction at F would therefore have prolonged the history of the lake
+which had come into existence when the ice blocked the drainage of the
+Wisconsin. As the drift of the valley was removed the level of the lake
+sank and finally disappeared.
+
+_Baraboo lake._--Another lake which existed in this region when the ice
+was here, occupied the valley of the Baraboo and its tributaries when
+the ice blocked the valley at Baraboo. This lake occupied not only the
+valley of the Baraboo, but extended up the lower course of every
+tributary, presumably rising until it found the lowest point in the rim
+of the drainage basin. The location of this point, and therefore the
+height of the lake when at its maximum, are not certainly known, though
+meager data on this point have been collected. At a point three miles
+southeast of Ablemans on the surface of a sandstone slope, water-worn
+gravel occurs, the pebbles of which were derived from the local rock. On
+the slope below the gravel, the surface is covered with loam which has a
+suggestion of stratification, while above it, the soil and subsoil
+appear to be the product of local rock decomposition. This water-worn
+gravel of local origin on a steep slope facing the valley, probably
+represents the work of the waves of this lake, perhaps when it stood at
+its maximum height. This gravel is about 125 feet (aneroid measurement)
+above the Baraboo river to the north.
+
+Further evidence of a shore line has been found at the point marked T,
+Plate II. At this place water-worn gravel of the local rock occurs in
+much the same relationship as that already mentioned, and at the same
+elevation above the Baraboo river. At a point two and one-half miles
+southwest of Ablemans there is local water-worn gravel, with which is
+mingled glacial material (pieces of porphyry and diabase) which could
+have reached this point only by being carried thither by floating ice
+from the glacier. The level of this mixed local and glacial material is
+(according to aneroid measurement) approximately the same as that of the
+other localities.
+
+When the ice melted, an outlet was opened _via_ the Lower narrows, and
+the water of the lake drained off to the Wisconsin by this route. Had
+the ice left no drift, the lake would have been promptly drained when
+the ice melted; but the lake did not entirely disappear immediately
+after the ice retreated, for the drift which the ice left obstructed
+drainage to the east. The moraine, however, was not so high as the
+outlet of the lake while the ice was on, so that, as the ice retreated,
+the water flowed over the moraine to the east, and drew down the level
+of the lake to the level of the lowest point in the moraine. The
+postglacial cut through the moraine is about ninety feet deep.
+
+Besides being obstructed where crossed by the terminal moraine, the
+valley of the Baraboo was clogged to a less extent by drift deposits
+between the moraine and the Lower narrows. At one or two places near the
+City of Baraboo, such obstructions, now removed, appear to have existed.
+Just above the Lower narrows (c, Plate XXXVII) there is positive
+evidence that the valley was choked with drift. Here in subsequent time,
+the river has cut through the drift-filling of the preglacial valley,
+developing a passage about twenty rods wide and thirty-five feet deep.
+If this passage were filled with drift, reproducing the surface left by
+the ice, the broad valley above it would be flooded, producing a shallow
+lake.
+
+The retreat of the ice therefore left two well defined drift dams in the
+valley, one low one just above the Lower narrows, and a higher one, the
+moraine dam, just west of Baraboo. Disregarding the influence of the
+ice, and considering the Baraboo valley only, these two dams would have
+given rise to two lakes, the upper one behind the higher dam being
+deeper and broader, and covering a much larger area; the lower one
+behind the lower dam, being both small and shallow.
+
+Up to the time that the ice retreated past the Lower narrows, the waters
+of the upper and lower lakes were united, held up to a common level by
+the ice which blocked this pass. After the ice retreated past the Lower
+narrows, the level of the Baraboo lake did not sink promptly, for not
+until the ice had retreated past the site of the Wisconsin was the
+present drainage established. Meantime the waters of the Baraboo lake
+joined those of Wisconsin lake through the Lower narrows. If
+the lakes had been before connected at some point farther west, this
+connection through the narrows would not have changed the level of
+either. If they were not before connected, and if the Wisconsin lake was
+lower than the Baraboo, this connection would have drawn down the level
+of the latter.
+
+Since the drainage from the Baraboo went to the Wisconsin, the Baraboo
+lake was not at first lowered below the level of the highest obstruction
+in the valley of the Wisconsin even after the ice had retreated beyond
+that stream. As the drift obstructions of the Wisconsin valley were
+lowered, the levels of all the lakes above were correspondingly brought
+down. When the level of the waters in these lakes was brought down to
+the level of the moraine dam above Baraboo, the one Baraboo lake of
+earlier times became two. The level of the upper of these two lakes was
+determined by the moraine above Baraboo, that of the lower by the
+highest obstruction below the moraine in either the Baraboo or Wisconsin
+valley. The drift obstructions in the Baraboo valley were probably
+removed about as fast as those in the Wisconsin, and since the
+obstructions were of drift, and the streams strong, the removal of the
+dams was probably rapid. Both the upper and lower Baraboo lakes, as well
+as the Wisconsin, had probably been reduced to small proportions, if not
+been completely drained, before the glacial period was at an end.
+
+_Devil's lake in glacial times._--While the ice edge was stationary in
+its position of maximum advance, its position on the north side of the
+main quartzite range was just north of Devil's lake (Plate XXXVII). The
+high ridge of drift a few rods north of the shore is a well defined
+moraine, and is here more clearly marked than farther east or west,
+because it stands between lower lands on either side, instead of being
+banked against the quartzite ridge. North of the lake it rises about 75
+feet above the water. When the ice edge lay in this position on the
+north side of the range, its front between the East bluff and the
+Devil's nose lay a half mile or so from the south end of the lake. In
+this position also there is a well defined moraine.
+
+While the ice was at its maximum stand, it rose above these moraine
+ridges at either end of the lake. Between the ice at these two points
+there was then a notable basin, comparable to that of the present lake
+except that the barriers to the north and southeast were higher than
+now. The melting of the ice supplied abundant water, and the lake rose
+above its present level. The height which it attained is not known, but
+it is known to have risen at least 90 feet above its present level. This
+is indicated by the presence of a few drift bowlders on the West bluff
+of the lake at this height. They represent the work of a berg or bergs
+which at some stage floated out into the lake with bowlders attached.
+Bowlders dropped by bergs might be dropped at any level lower than the
+highest stand of the lake.
+
+_Other lakes._--Another glacial lake on the East quartzite bluff has
+already been referred to. Like the Devil's lake in glacial
+time, its basin was an enclosure between the ice on the one hand, and
+the quartzite ridge on the other. The location of this lake is shown on
+Plate XXXVII (s). Here the edge of the ice, as shown by the position
+of the moraine, was affected by a re-entrant curve, the two ends of
+which rested against the quartzite ridge. Between the ice on the one
+hand and the quartzite ridge on the other, a small lake was formed. Its
+position is marked by a notable flat.
+
+With the exception of the north side, and a narrow opening at the
+northwest corner, the flat is surrounded by high lands. When the ice
+occupied the region, its edge held the position shown by the line
+marking the limit of its advance, and constituted an ice barrier to the
+north.[9] The area of the flat was, therefore, almost shut in, the only
+outlet being a narrow one at t, Plate XXXVII. If the filling of
+stratified drift which underlies the flat were removed, the bottom of
+the area would be much lower than at present, and much lower than the
+outlet at t. It is therefore evident that when the ice had taken its
+position along the north side of the flat, an enclosed basin must have
+existed, properly situated for receiving and holding water. Since this
+lake had but a short life and became extinct before the ice retreated,
+its history is here given.
+
+    [9] The moraine line on the map represents the crest of the
+    marginal ridge rather than its outer limit, which is slightly
+    nearer the lake margin. Stratified drift of the nature of
+    overwash also intervenes at points between the moraine and
+    the lake border.
+
+At first the lake had no outlet and the water rose to the level of the
+lowest point (t) in the rim of the basin, and thence overflowed to the
+west. Meanwhile the sediments borne in by the glacial drainage were
+being deposited in the lake in the form of a subaqueous overwash plain,
+the coarser parts being left near the shore, while the finer were
+carried further out. Continued drainage from the ice continued to bring
+sediment into the lake, and the subaqueous overwash plain extended its
+delta-like front farther and farther into the lake, until its basin was
+completely filled. With the filling of the basin the lake became
+extinct. The later drainage from the ice followed the line of the
+outlet, the level of which corresponds with the level of the filled lake
+basin. This little extinct lake is of interest as an example of a
+glacial lake which became extinct by having its basin filled during
+glacial times, by sediments washed out from the ice.
+
+Near the northwest corner of this flat, an exposure in the sediments of
+the old lake bed shows the curiously contorted layers of sand, silt, and
+clay represented in Plate XXXVIII. The layers shown in the
+figure are but a few feet below the level of the flat which marks the
+site of the lake. It will be seen that the contorted layers are between
+two series of horizontal ones. The material throughout the section is
+made up of fine-grained sands and clays, well assorted. That these
+particular layers should have been so much disturbed, while those below
+and above remained horizontal, is strange enough. The grounding of an
+iceberg on the surface before the overlying layers were deposited, the
+action of lake ice, or the effect of expansion and contraction due to
+freezing and thawing, may have been responsible for the singular
+phenomenon. Contorted laminæ are rather characteristic of the deposits
+of stratified drift.
+
+
+                _After the Ice Had Disappeared._
+
+As has already been indicated, the irregular deposition of
+glacial drift gave rise to many depressions without outlets in which
+surface waters collected after the ice had disappeared, forming ponds or
+lakes. So abundant are lakes and ponds and marshes in recently glaciated
+regions and so rare elsewhere, that they constitute one of the more
+easily recognized characteristics of a glaciated region.
+
+After the ice had melted, the mantle of drift which it left was
+sometimes so disposed as to completely obliterate preglacial valleys.
+More commonly it filled preglacial valleys at certain points only. In
+still other cases a valley was not filled completely at any point,
+though partially at many. In this last case, the partial fillings at
+various points constituted dams above which drainage was ponded, making
+lakes. If the dams were not high enough to throw the drainage out of the
+valley, the lakes would have their outlets over them. The drift dam
+being unconsolidated would be quickly cut down by the outflowing water,
+and the lake level lowered. When the dam was removed or cut to its base,
+the lake disappeared and drainage followed its preglacial course.
+
+In case the valley was completely filled, or completely filled at
+points, the case was very different. The drainage on the drift surface
+was established with reference to the topography which obtained when the
+ice departed, and not with reference to the preglacial valleys. Wherever
+the preglacial valleys were completely filled, the postglacial drainage
+followed lines which were altogether independent of them. When
+preglacial valleys were filled by the drift in spots only, the
+postglacial streams followed them where they were not filled, only to
+leave them where the blocking occurred. In the former case the present
+drainage is through valleys which are preglacial in some places, and
+postglacial in others.
+
+Thus the drainage changes effected by the drift after the ice was gone,
+concerned both lakes and rivers. In this region there are several
+illustrations of these changes.
+
+_Lakes._--The lake basins of drift-covered regions are of various types.
+Some of them are altogether in drift, some partly in drift and partly in
+rock, and some wholly in rock. Basins in the drift were likely to be
+developed whenever heavy deposits surrounded thin ones. They are
+especially common in the depressions of terminal moraines.
+
+Another class of lake basins occurs in valleys, the basins being partly
+rock and partly drift. If a thick deposit of drift be made at one point
+in a valley, while above there is little or none, the thick deposit will
+form a dam, above which waters may accumulate, forming a pond or lake.
+Again, a ridge of drift may be deposited in the form of a curve with its
+ends against a rock-ridge, thus giving rise to a basin.
+
+In the course of time, the lakes and ponds in the depressions made or
+occasioned by the drift will be destroyed by drainage. Remembering how
+valleys develop it is readily understood that the heads of the
+valleys will sooner or later find the lakes, and drain them if their
+bottoms be not too low.
+
+Drainage is hostile to lakes in another way. Every stream which flows
+into a lake brings in more or less sediment. In the standing water this
+sediment is deposited, thus tending to fill the lake basin. Both by
+filling their basins and by lowering their outlets, rivers tend to the
+destruction of lakes, and given time enough, they will accomplish this
+result. In view of this double hostility of streams, it is not too much
+to say that "rivers are the mortal enemies of lakes."
+
+The destruction of lakes by streams is commonly a gradual process, and
+so it comes about that the abundance and the condition of the undrained
+areas in a drift-covered region is in some sense an index of the length
+of time, reckoned in terms of erosion, which has elapsed since the drift
+was deposited.
+
+In this region there were few lakes which lasted long after the ice
+disappeared. The basins of the Baraboo and Wisconsin lakes were
+partly of ice, and so soon as the ice disappeared, the basins were so
+nearly destroyed, and the drift dams that remained so easily eroded,
+that the lakes had but a brief history,--a history that was glacial,
+rather than postglacial.
+
+The history of the little lake on the East quartzite bluff as
+already pointed out, came to an end while the ice was still present.
+
+The beds of at least two other extinct ponds or small lakes above the
+level of the Baraboo are known. These are at v and w, Plate XXXVII.
+They owed their origin to depressions in the drift, but the outflowing
+waters have lowered their outlets sufficiently to bring them to the
+condition of marshes. Both were small in area and neither was deep.
+
+_Existing lakes._--Relatively few lakes now remain in this immediate
+region, though they are common in most of the country covered by the ice
+sheet which overspread this region. Devil's lake only is well known. The
+lake which stood in this position while the ice was on, has already been
+referred to. After the ice had melted away, the drift which it
+had deposited still left an enclosure suitable for holding water. The
+history of this basin calls for special mention.
+
+At the north end of the lake, and again in the capacious valley leading
+east from its south end, there are massive terminal moraines. Followed
+southward, this valley though blocked by the moraine a half mile below
+the lake, leads off towards the Wisconsin river, and is probably the
+course of a large preglacial stream. Beyond the moraine, this valley is
+occupied by a small tributary to the Wisconsin which heads at the
+moraine. To the north of the lake, the head of a tributary of the
+Baraboo comes within eighty rods of the lake, but again the terminal
+moraine intervenes. From data derived from wells it is known that the
+drift both at the north and south ends of the lake extends many feet
+below the level of its water, and at the north end, the base of the
+drift is known to be at least fifty feet below the level of the bottom
+of the lake. The draining of Devil's lake to the Baraboo river is
+therefore prevented only by the drift dam at its northern end. It is
+nearly certain also, that, were the moraine dam at the south end of the
+lake removed, all the water would flow out to the Wisconsin, though the
+data for the demonstration of this conclusion are not to be had, as
+already stated.
+
+There can be no doubt that the gorge between the East and West bluffs
+was originally the work of a pre-Cambrian stream, though the depth of
+the pre-Cambrian valley may not have been so great as that of the
+present. Later, the valley, so far as then excavated, was filled with
+the Cambrian (Potsdam) sandstone, and re-excavated in post-Cambrian and
+preglacial time. Devil's lake then occupies an unfilled portion of an
+old river valley, isolated by great morainic dams from its surface
+continuations on either hand. Between the dams, water has accumulated
+and formed the lake.
+
+
+                     _Changes in Streams._
+
+In almost every region covered by the ice, the streams which established
+themselves after its departure follow more or less anomalous courses.
+This region is no exception. Illustrations of changes which the
+deposition of the drift effected have already been given in one
+connection or another in this report.
+
+_Skillett creek._--An illustration of the sort of change which drift
+effects is furnished by Skillett creek, a small stream tributary to the
+Baraboo, southwest of the city of that name. For some distance from its
+head (a to b, Fig. 43) its course is through a capacious preglacial
+valley. The lower part of this valley was filled with the water-laid
+drift of the overwash plain. On reaching the overwash plain the creek
+therefore shifted its course so as to follow the border of that plain,
+and along this route, irrespective of material, it has cut a new channel
+to the Baraboo. The postglacial portion of the valley (b to c) is
+everywhere narrow, and especially so where cut in sandstone.
+
+The course and relations of this stream suggest the following
+explanation: Before the ice came into the region, Skillett creek
+probably flowed in a general northeasterly direction to the Baraboo,
+through a valley comparable in size to the preglacial part of the
+present valley. As the ice advanced, the lower part of this valley was
+occupied by it, and the creek was compelled to seek a new course. The
+only course open to it was to the north, just west of the advancing ice,
+and, shifting westward as fast as the ice advanced, it abandoned
+
+altogether its former lower course. Drainage from the ice then carried
+out and deposited beyond the same, great quantities of gravel and sand,
+making the overwash plain. This forced the stream still farther west,
+until it finally reached its present position across a sandstone ridge
+or plain, much higher than its former course. Into this sandstone it has
+since cut a notable gorge, a good illustration of a postglacial valley.
+The series of changes shown by this creek is illustrative of the changes
+undergone by streams in similar situations and relations all along the
+margin of the ice.
+
+[Illustration: Fig. 43.--Skillett Creek, illustrating the points
+mentioned in the text.]
+
+The picturesque glens (Parfrey's and Dorward's) on the south face of the
+East bluff are the work of post-glacial streams. The preglacial valleys
+of this slope were obliterated by being filled during the glacial epoch.
+
+_The Wisconsin._--The preglacial course of the Wisconsin river is not
+known in detail, but it was certainly different from the course which
+the stream now follows. On Plate I the relations of the present stream
+to the moraine (and former ice-front) may be seen.[10] As the ice
+approached it from the east, the preglacial valley within the area here
+under consideration was affected first by the overwash from the moraine,
+and later by the ice itself, from the latitude of Kilbourn City to
+Prairie du Sac.
+
+    [10] The preglacial course was probably east of the present
+    in the vicinity of Kilbourn City.
+
+It has already been stated that the ice probably dammed the river, and
+that a lake was formed above Kilbourn City, reaching east to the ice and
+west over the lowland tributary to the river, the water rising till it
+found an outlet, perhaps down to the Black river valley.
+
+When the ice retreated, the old valley had been partly filled, and the
+lowest line of drainage did not everywhere correspond with it. Where the
+stream follows its old course, it flows through a wide capacious valley,
+but where it was displaced, it found a new course on the broad flat
+which bordered its preglacial course. Displacement of the stream
+occurred in the vicinity of Kilbourn City, and, forced to find a new
+line of flow west of its former course, the stream has cut a new channel
+in the sandstone. To this displacement of the river, and its subsequent
+cutting, we are indebted for the far-famed Dalles of the Wisconsin.
+But not all the present route of the river through the dalles has
+been followed throughout the entire postglacial history of the stream.
+In Fig. 44, the depression A, B, C, was formerly the course of the
+stream. The present course between D and E is therefore the youngest
+portion of the valley, and from its lesser width is known as the
+"narrows." During high water in the spring, the river still sends part
+of its waters southward by the older and longer route.
+
+The preglacial course of the Wisconsin south of the dalles has never
+been determined with certainty, but rational conjectures as to its
+position have been made.
+
+The great gap in the main quartzite range, a part of which is occupied
+by Devil's lake, was a narrows in a preglacial valley. The only streams
+in the region sufficiently large to be thought of as competent to
+produce such a gorge are the Baraboo and the Wisconsin. If the Baraboo
+was the stream which flowed through this gorge in preglacial time, the
+comparable narrows in the north quartzite range--the Lower narrows of
+the Baraboo--is to be accounted for. The stream which occupied one of
+these gorges probably occupied the other, for they are in every way
+comparable except in that one has been modified by glacial action, while
+the other has not.
+
+[Illustration: Fig. 44.--The Wisconsin valley near Kilbourn City.]
+
+The Baraboo river flows through a gorge--the Upper narrows--in the north
+quartzite range at Ablemans, nine miles west of Baraboo. This gorge is
+much narrower than either the Lower narrows or the Devil's lake gorge,
+suggesting the work of a lesser stream. It seems on the whole
+probable, as suggested by Irving,[11] that in preglacial time the
+Wisconsin river flowed south through what is now the Lower narrows of
+the Baraboo, thence through the Devil's lake gorge to its present valley
+to the south. If this be true, the Baraboo must at that time have joined
+this larger stream at some point east of the city of the same name.
+
+    [11] Irving. Geology of Wisconsin, Vol. II.
+
+
+                      _The Driftless Area._
+
+Reference has already been made to the fact that the western part of the
+area here described is driftless, and the line marking the limit of ice
+advance has been defined. Beyond this line, gravel and sand, carried
+beyond the ice by water, extends some distance to the west. But a large
+area in the southwestern part of the state is essentially free from
+drift, though it is crossed by two belts of valley drift (valley trains)
+along the Wisconsin and Mississippi rivers.
+
+The "driftless area" includes, besides the southwestern portion of
+Wisconsin, the adjoining corners of Minnesota, Iowa and Illinois. In the
+earlier epochs of the glacial period this area was completely surrounded
+by the ice, but in the last or Wisconsin epoch it was not surrounded,
+since the lobes did not come together south of it as in earlier times.
+(Compare Plate XXXIII and Fig. 36.)
+
+Various suggestions have been made in the attempt to explain the
+driftless area. The following is perhaps the most satisfactory:[12]
+
+    [12] Chamberlin and Irving. Geology of Wisconsin, Vols. I and
+    II.
+
+The adjacent highlands of the upper peninsula of Michigan, are bordered
+on the north by the capacious valley of Lake Superior leading off to the
+west, while to the east lies the valley of Lake Michigan leading to the
+south. These lake valleys were presumably not so broad and deep in
+preglacial times as now, though perhaps even then considerable valleys.
+
+When the ice sheet, moving in a general southward direction from the
+Canadian territory, reached these valleys, they led off two great
+tongues or lobes of ice, the one to the south through the Lake Michigan
+depression, the other to the south of west through the Lake Superior
+trough. (Fig. 36.) The highland between the lake valleys conspired with
+the valleys to the same end. It acted as a wedge, diverting the ice to
+either side. It offered such resistance to the ice, that the thin and
+relatively feeble sheet which succeeded in surmounting it, did not
+advance far to the south before it was exhausted. On the other hand, the
+ice following the valleys of Lakes Superior and Michigan respectively,
+failed to come together south of the highland until the latitude of
+northern Iowa and Illinois was reached. The driftless area therefore
+lies south of the highlands, beyond the limit of the ice which
+surmounted it, and between the Superior and Michigan glacial lobes above
+their point of union. The great depressions, together with the
+intervening highland, are therefore believed to be responsible for the
+absence of glaciation in the driftless area.
+
+
+        _Contrast Between Glaciated and Unglaciated Areas._
+
+The glaciated and unglaciated areas differ notably in (1) topography, (2)
+drainage, and (3) mantle rock.
+
+1. _Topography._--The driftless area has long been exposed to the
+processes of degradation. It has been cut into valleys and ridges by
+streams, and the ridges have been dissected into hills. The
+characteristic features of a topography fashioned by running water are
+such as to mark it clearly from surfaces fashioned by other agencies.
+Rivers end at the sea (or in lakes). Generally speaking, every point at
+the bottom of a river valley is higher than any other point in the
+bottom of the same valley nearer the sea, and lower than any other point
+correspondingly situated farther from the sea. This follows from the
+fact that rivers make their own valleys for the most part, and a river's
+course is necessarily downward. In a region of erosion topography
+therefore, tributary valleys lead down to their mains, secondary
+tributaries lead down to the first, and so on; or, to state the same
+thing in reverse order, in every region where the surface configuration
+has been determined by rain and river erosion, every gully and every
+ravine descends to a valley. The smaller valleys descend to larger and
+lower ones, which in turn lead to those still larger and lower. The
+lowest valley of a system ends at the sea, so that the valley which
+joins the sea is the last member of the series of erosion channels of
+which the ravines and gullies are the first. It will thus be seen that
+all depressions in the surface, worn by rivers, lead to lower ones. The
+surface of a region sculptured by rivers is therefore marked by valleys,
+with intervening ridges and hills, the slopes of which descend to them.
+All topographic features are here determined by the water courses.
+
+[Illustration: Fig. 45.--Drainage in the driftless area. The absence of
+ponds and marshes is to be noted.]
+
+The relief features of the glaciated area, on the other hand, lack the
+systematic arrangement of those of the unglaciated territory, and stream
+valleys are not the controlling elements in the topography.
+
+2. _Drainage._--The surface of the driftless area is well drained. Ponds
+and lakes are essentially absent, except where streams have been
+obstructed by human agency. The drainage of the drift-covered area, on
+the other hand, is usually imperfect. Marshes, ponds and lakes are of
+common occurrence. These types are shown by the accompanying maps, Figs.
+45 and 46, the one from the driftless area, the other from the
+drift-covered.
+
+[Illustration: Fig. 46.--Drainage in a glaciated region. Walworth and
+Waukesha counties, Wisconsin, showing abundance of marshes and lakes.]
+
+3. _Mantle rock._--The unglaciated surface is overspread to an average
+depth of several feet by a mantle of soil and earth which has resulted
+from the decomposition of the underlying rock. This earthy material
+sometimes contains fragments and even large masses of rock like that
+beneath. These fragments and masses escaped disintegration because of
+their greater resistance while the surrounding rock was destroyed. This
+mantle rock grades from fine material at the surface down through
+coarser, until the solid rock is reached, the upper surface of the rock
+being often ill-defined (Fig. 47). The thickness of the mantle is
+approximately constant in like topographic situations where the
+underlying rock is uniform.
+
+The residual soils are made up chiefly of the insoluble parts of the
+rock from which they are derived, the soluble parts having been removed
+in the process of disintegration.
+
+[Illustration: Fig. 47.--Section in a driftless area, showing relation
+of the mantle rock to the solid rock beneath.]
+
+With these residuary soils of the driftless area, the mantle rock of
+glaciated tracts is in sharp contrast. Here, as already pointed out, the
+material is diverse, having come from various formations and from widely
+separated sources. It contains the soluble as well as the insoluble
+parts of the rock from which it was derived. In it there is no
+suggestion of uniformity in thickness, no regular gradation from fine to
+coarse from the surface downward. The average thickness of the drift is
+also much greater than that of the residual earths. Further, the contact
+between the drift and the underlying rock surface is usually a definite
+surface. (Compare Figs. 32 and 47.)
+
+
+                       POSTGLACIAL CHANGES.
+
+Since the ice melted from the region, the changes in its geography have
+been slight. Small lakes and ponds have been drained, the streams whose
+valleys had been partly filled, have been re-excavating them, and
+erosion has been going on at all points in the slow way in which it
+normally proceeds. The most striking example of postglacial erosion is
+the dalles of the Wisconsin, and even this is but a small gorge for so
+large a stream. The slight amount of erosion which has been accomplished
+since the drift was deposited, indicates that the last retreat of the
+ice, measured in terms of geology and geography, was very recent. It has
+been estimated at 7,000 to 10,000 years, though too great confidence is
+not to be placed in this, or any other numerical estimate of
+post-glacial time.
+
+
+                               INDEX.
+
+           --------------------------------------------------
+                                                                PAGES
+
+
+   Ablemans                                                     66,67
+
+
+   Baraboo Lake                                                   130
+
+   Baraboo Quartzite ranges                                     2, 65
+
+      Constitution of                                              14
+
+      Dynamic action in                                    15, 17, 18
+
+      Gaps in--
+
+         Devil's Lake Gap                                       3, 13
+
+         Lower Narrows                                      5, 13, 67
+
+         Narrows Creek                                             66
+
+         Upper Narrows                              5, 10, 17, 19, 67
+
+      Igneous rock in                                              18
+
+      Structure of                                                 15
+
+      Topography of                                             5, 13
+
+   Base-level                                                      47
+
+   Base-level plains                                               50
+
+   Bowlder clay                                                    97
+
+   Breccia                                                         18
+
+
+   Castle Rock                                                     71
+
+   Cleopatra's Needle                                              65
+
+   Cold Water Canyon                                               70
+
+   Conglomerate                                                10, 28
+
+      Basal (Potsdam)                                              29
+
+   Corrasion                                                       36
+
+   Cross-bedding                                                   30
+
+   Cycle of erosion                                            44, 47
+
+
+   Dalles of the Wisconsin                                         69
+
+      Origin of                                                    53
+
+      Scenery of                                              69, 140
+
+   Dell Creek                                                      53
+
+   Deltas                                                 30, 56, 120
+
+   Deposits--
+
+      By extra-glacial waters                                 115-123
+
+      By ice                                                   85, 94
+
+      By rivers                                                55, 56
+
+      By subglacial streams                                       124
+
+      Of drift classified                                         127
+
+   Devil's Doorway                                                 65
+
+   Devil's Lake                                                   132
+
+      History of                                                  132
+
+      In glacial times                                            132
+
+      Location                                                   3, 9
+
+      Origin of                                                   132
+
+   Devil's Nose                                                5, 110
+
+   Divides, Shifting of                                            44
+
+   Dorward's Glen                                      10, 14, 29, 68
+
+   Drift                                                           73
+
+      Characteristics of                                           96
+
+      Constitution of                                              94
+
+      Deposits classified                                         127
+
+      Effect on topography                                     85, 88
+
+      Relation of stratified to unstratified                      125
+
+      Stratified                                                  111
+
+         Topography of                                       101, 103
+
+   Driftless area                                             79, 142
+
+   Drainage--
+
+      Adjustment of                                                62
+
+      Changes in, effected by the ice                        128, 142
+
+      Establishment of                                             61
+
+      Glacial                                                     113
+
+      Of drift-covered area                                       144
+
+      Of driftless area                                           144
+
+      Postglacial changes in                                      146
+
+
+   Endmoräne                                                      108
+
+   Erosion--
+
+      By rain, and rivers, general outline of                   36-58
+
+      Elements of                                                  36
+
+      Of folded strata                                             50
+
+      Of rocks of unequal hardness                                 47
+
+      Of the quartzite                                             25
+
+      Preglacial                                                   60
+
+      Topography                                                   12
+
+      Without valleys                                              37
+
+   Eskers                                                         124
+
+
+   Falls                                                           48
+
+   Fossils--
+
+      In limestone                                                 12
+
+      In sandstone                                              9, 11
+
+   Friendship mounds                                               71
+
+
+   Geographic features, general                                  3-20
+
+   Glacial drainage                                               113
+
+   Glaciated area                                         78, 91, 143
+
+   Glacier ice--
+
+      Deposition by                                                85
+
+      Direction of movement                                        88
+
+      Erosive work of                                           79-84
+
+      Formation of                                                 74
+
+      Movement of, affected by topography                          89
+
+   Glens                                                           68
+
+   Green Bay lobe                                                  91
+
+   Gibraltar rock                                                  63
+
+   Ground Moraine--
+
+      Constitution of                                              99
+
+      Location of                                                  97
+
+      Topography of                                               101
+
+   Groundwater level                                               41
+
+
+   Ice sheets--
+
+      Formation of                                                 74
+
+      History of                                                  114
+
+      Movement of                                              75, 88
+
+      North American ice sheet                                     78
+
+   Igneous rock                                                    18
+
+   Intermittent streams                                            42
+
+
+   Kames                                                          115
+
+
+   Lakes--
+
+      Wisconsin Lake                                              129
+
+      Baraboo Lake                                                130
+
+      Devil's Lake                                     3, 9, 132, 137
+
+   Limestone, see Lower Magnesian.
+
+   Lower Magnesian limestone--
+
+      Fossils of                                                   12
+
+      History of                                                31-32
+
+      Occurrence of                                                11
+
+      Origin of                                                    11
+
+      Position of                                                  12
+
+      Structure of                                                  8
+
+   Lower Narrows                                            5, 13, 67
+
+
+   Mantle rock                                                20, 144
+
+   Metamorphism                                                14, 24
+
+   Monadnocks                                                      51
+
+   Moraines (see terminal moraine and ground moraine).
+
+   Morainic aprons                                                119
+
+
+   Narrows                                                         49
+
+      In quartzite                                             66, 67
+
+   Natural bridge                                                  69
+
+   Navy Yard                                                       69
+
+   Niagara limestone                                               33
+
+   North American ice sheet                                        78
+
+   Nunatak                                                         89
+
+
+   Osars (see Eskers).
+
+   Outwash plains                                            118, 120
+
+   Overwash plains                                           118, 120
+
+
+   Parfrey's Glen                                      10, 14, 29, 68
+
+   Peneplain                                                   47, 50
+
+   Pewit's nest                                             9, 53, 69
+
+   Pine Hollow                                                     69
+
+   Postglacial changes                                            146
+
+   Potsdam sandstone--
+
+      Fossils of                                                9, 11
+
+      History of                                                27-31
+
+      Origin of                                                  9-11
+
+      Relation to quartzite                                        19
+
+      Structure of                                                  8
+
+
+   Quartzite (see also Baraboo quartzite ranges)--
+
+      Dynamic Metamorphism of                                      24
+
+      Erosion of                                                   25
+
+      Origin of                                                    23
+
+      Submergence of                                               27
+
+      Thickness of                                                 26
+
+      Uplift of                                                    24
+
+
+   Rapids                                                          48
+
+   Rejuvenation of streams                                         56
+
+   Ripple marks                                                 9, 15
+
+   Roches moutonnée                                                81
+
+
+   Sandstone (see Potsdam and St. Peters).
+
+   Sauk Prarie                                          117, 118, 119
+
+   Skillett Creek                                          8, 53, 138
+
+   Slope of upper surface of ice                                  111
+
+   Snow fields                                                     74
+
+   Soil                                                   7, 144, 146
+
+   Stand rock                                                      70
+
+   Steamboat rock                                                  70
+
+   St. Peter's sandstone                                           32
+
+   Stratified drift                                      111-112, 125
+
+   Streams, changes in                                            138
+
+   Subaqueous overwash plains                                     120
+
+   Subglacial till (ground moraines)                               99
+
+   Sugar Bowl                                                      70
+
+
+   Talus slopes                                                    65
+
+   Terminal moraines--
+
+      Across the United States                                     78
+
+      Development of                                              102
+
+      In Devil's Lake region                                      105
+
+      Boundaries of                                               106
+
+      Location of                                         92, 93, 108
+
+      On the main quartzite range                                 107
+
+      Width of                                                    106
+
+      Topography of                                               103
+
+   Till                                                            97
+
+   Topography--
+
+      Effect of, on ice movement                                   89
+
+      Erosion topography                                           12
+
+      Of drift-covered country                                 8, 143
+
+      Of driftless area                                 6, 7, 12, 143
+
+      Of plain surrounding quartzite ridge                          6
+
+      Of quartzite ridges                                           5
+
+   Transportation by streams                                       55
+
+   Tributary valleys                                               39
+
+   Turk's Head                                                     65
+
+
+   Unconformity                                                    19
+
+   Underground water                                               58
+
+   Unglaciated areas                                     79, 142, 143
+
+   Unstratified drift                                    99, 102, 125
+
+   Upper Narrows                                    5, 10, 17, 19, 67
+
+
+   Valley, the--
+
+      Beginning of                                                 37
+
+      Characteristics of, at various stages                     52-54
+
+      Course of                                                    39
+
+      How a valley gets a stream                                   40
+
+      Limits of                                                    43
+
+   Valley trains                                                  116
+
+
+   Waterfalls                                                      48
+
+   Weathering                                                      36
+
+   Webster's Prarie                                               119
+
+   Wisconsin Lake                                                 129
+
+   Wisconsin River                                                139
+
+   Witch's Gulch                                                   70
+
+
+
+
+
+End of the Project Gutenberg EBook of The Geography of the Region about
+Devils Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+*** END OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+***** This file should be named 38148-8.txt or 38148-8.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/3/8/1/4/38148/
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+Updated editions will replace the previous one--the old editions
+will be renamed.
+
+Creating the works from public domain print editions means that no
+one owns a United States copyright in these works, so the Foundation
+(and you!) can copy and distribute it in the United States without
+permission and without paying copyright royalties.  Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark.  Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission.  If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy.  You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research.  They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks.  Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License (available with this file or online at
+http://gutenberg.org/license).
+
+
+Section 1.  General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A.  By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement.  If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B.  "Project Gutenberg" is a registered trademark.  It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement.  There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement.  See
+paragraph 1.C below.  There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works.  See paragraph 1.E below.
+
+1.C.  The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works.  Nearly all the individual works in the
+collection are in the public domain in the United States.  If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed.  Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work.  You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D.  The copyright laws of the place where you are located also govern
+what you can do with this work.  Copyright laws in most countries are in
+a constant state of change.  If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work.  The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E.  Unless you have removed all references to Project Gutenberg:
+
+1.E.1.  The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+1.E.2.  If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges.  If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3.  If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder.  Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4.  Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5.  Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6.  You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form.  However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form.  Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7.  Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8.  You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+     the use of Project Gutenberg-tm works calculated using the method
+     you already use to calculate your applicable taxes.  The fee is
+     owed to the owner of the Project Gutenberg-tm trademark, but he
+     has agreed to donate royalties under this paragraph to the
+     Project Gutenberg Literary Archive Foundation.  Royalty payments
+     must be paid within 60 days following each date on which you
+     prepare (or are legally required to prepare) your periodic tax
+     returns.  Royalty payments should be clearly marked as such and
+     sent to the Project Gutenberg Literary Archive Foundation at the
+     address specified in Section 4, "Information about donations to
+     the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+     you in writing (or by e-mail) within 30 days of receipt that s/he
+     does not agree to the terms of the full Project Gutenberg-tm
+     License.  You must require such a user to return or
+     destroy all copies of the works possessed in a physical medium
+     and discontinue all use of and all access to other copies of
+     Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+     money paid for a work or a replacement copy, if a defect in the
+     electronic work is discovered and reported to you within 90 days
+     of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+     distribution of Project Gutenberg-tm works.
+
+1.E.9.  If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark.  Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1.  Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection.  Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2.  LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees.  YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3.  LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from.  If you
+received the work on a physical medium, you must return the medium with
+your written explanation.  The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund.  If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund.  If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4.  Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5.  Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law.  The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6.  INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section  2.  Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers.  It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need, are critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come.  In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation web page at http://www.pglaf.org.
+
+
+Section 3.  Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service.  The Foundation's EIN or federal tax identification
+number is 64-6221541.  Its 501(c)(3) letter is posted at
+http://pglaf.org/fundraising.  Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations.  Its business office is located at
+809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
+business@pglaf.org.  Email contact links and up to date contact
+information can be found at the Foundation's web site and official
+page at http://pglaf.org
+
+For additional contact information:
+     Dr. Gregory B. Newby
+     Chief Executive and Director
+     gbnewby@pglaf.org
+
+
+Section 4.  Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment.  Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States.  Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements.  We do not solicit donations in locations
+where we have not received written confirmation of compliance.  To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit http://pglaf.org
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States.  U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses.  Donations are accepted in a number of other
+ways including checks, online payments and credit card donations.
+To donate, please visit: http://pglaf.org/donate
+
+
+Section 5.  General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart is the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone.  For thirty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included.  Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+
+Most people start at our Web site which has the main PG search facility:
+
+     http://www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
diff --git a/38148-8.zip b/38148-8.zip
new file mode 100644
index 0000000..2136e49
--- /dev/null
+++ b/38148-8.zip
diff --git a/38148-h.zip b/38148-h.zip
new file mode 100644
index 0000000..3390bdb
--- /dev/null
+++ b/38148-h.zip
diff --git a/38148-h/38148-h.htm b/38148-h/38148-h.htm
new file mode 100644
index 0000000..21a2e99
--- /dev/null
+++ b/38148-h/38148-h.htm
@@ -0,0 +1,8081 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<!-- $Id: header.txt 236 2009-12-07 18:57:00Z vlsimpson $ -->
+
+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
+  <head>
+    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
+    <meta http-equiv="Content-Style-Type" content="text/css" />
+    <title>
+      The Project Gutenberg eBook of The Geography of the Region about Devil's Lake, by R. Salisbury
+    </title>
+    <style type="text/css">
+
+body {
+    margin-left: 10%;
+    margin-right: 10%;
+}
+
+h1,h2,h3,h4,h5,h6 {
+    text-align: center;
+    clear: both;
+}
+
+p {
+    margin-top: .75em;
+    text-align: justify;
+    margin-bottom: .75em;
+}
+
+hr {
+    width: 33%;
+    margin-top: 2em;
+    margin-bottom: 2em;
+    margin-left: auto;
+    margin-right: auto;
+    clear: both;
+}
+
+table {
+    margin-left: auto;
+    margin-right: auto;
+}
+
+tr {padding-top: .75em;}
+
+.pagenum {
+    position: absolute;
+    left: 92%;
+    font-size: smaller;
+    text-align: right;
+} /* page numbers */
+
+
+.bb         {border-bottom: solid 1px;}
+
+.smcap      {font-variant: small-caps; font-size: 110%;}
+.center     {text-align: center; clear: both;}
+.right      {text-align: right;}
+.u          {text-decoration: underline;}
+
+.caption    {font-weight: bold;}
+
+.tdl        {text-align: left; vertical-align: top; padding-top: 0.25em;}
+.tdr        {text-align: right; vertical-align: top; padding-top: 0.25em;}
+.tdrr       {text-align: right; vertical-align: bottom; padding-top: 0.25em;}
+.tdc        {text-align: center; vertical-align: top; padding-top: 0.25em;}
+
+.fmedium    {font-size: 110%;}
+.flarge     {font-size: 130%;}
+.fxlarge    {font-size: 175%;}
+
+.padleft1   {padding-left: 2em;}
+.padleft2   {padding-left: 4em;}
+.padleft3   {padding-left: 1em;}
+.padbottom1 {padding-bottom: 5em;}
+.padbottom2 {padding-bottom: 1em;}
+.padbottom3 {padding-bottom: 2.5em;}
+.padtop     {padding-top: 1em;}
+.indent     {padding-left: 17em; padding-right: 17em; font-weight:bold;}
+.nowrap     {white-space: nowrap;}
+
+.tab1       {margin-left: 5em;}
+.tab2       {margin-left: 8em;}
+
+
+/* Images */
+
+.figcenter   {
+    margin: auto;
+    text-align: center;
+}
+
+.figright {
+    float: right;
+    clear: right;
+    margin-left: 1em;
+    margin-bottom: 1em;
+    margin-top: 1em;
+    margin-right: 0em;
+    padding: 0em;
+    text-align: center;
+}
+
+.imgspc {
+    width: 500px;
+    margin: auto;
+    text-align: center;
+    padding-bottom: 19em;
+}
+
+.imgspc1 {
+    width: 500px;
+    margin: auto;
+    text-align: center;
+    padding-bottom: 26em;
+}
+
+.imgspc2 {
+    width: 500px;
+    margin: auto;
+    text-align: center;
+    padding-bottom: 0em;
+}
+
+.figmleft {
+    float: left;
+    margin-left: 1em;
+    margin-bottom: 1em;
+    margin-top: 1em;
+    margin-right: 0em;
+    text-align: center;
+}
+
+.figmright {
+    float: right;
+    margin-left: 0em;
+    margin-bottom: 1em;
+    margin-top: 1em;
+    margin-right: 1em;
+    text-align: center;
+}
+
+/* Footnotes */
+.footnotes        {border: dashed 1px;}
+
+.footnote         {margin-left: 10%; margin-right: 10%; font-size: 0.9em;}
+
+.footnote .label  {position: absolute; right: 84%; text-align: right;}
+
+.fnanchor {
+    vertical-align: super;
+    font-size: .8em;
+    text-decoration:
+    none;
+}
+    </style>
+  </head>
+<body>
+
+
+<pre>
+
+The Project Gutenberg EBook of The Geography of the Region about Devils
+Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Geography of the Region about Devils Lake and the Dalles of the Wisconsin
+
+Author: Rollin D. Salisbury
+        Wallace W. Atwood
+
+Release Date: November 27, 2011 [EBook #38148]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+
+
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+
+
+
+
+</pre>
+
+
+<table border="0" style="background-color: #ccccff" cellpadding="10" summary="transcribers_note">
+  <tr>
+    <td valign="top">
+      Transcriber's note:
+    </td>
+    <td>
+      The Dalles of the Wisconsin are known today as the Wisconsin Dells. Minor punctuation
+      errors from the original text have been corrected; any unusual capitalization from the
+      original was kept. The formatting for lists has been standardized for easier reading.
+      The footnotes have been placed at the end of the document instead of at the end of the
+      page; there are links to them at their original positions in the text. I apologize
+      for the poor quality of some of the maps; they have been made as clear as possible.
+    </td>
+  </tr>
+</table>
+
+<p> <br /> <br /> <span class="pagenum"> <a name="Page_i" id="Page_i">[Pg i]</a> </span> </p>
+
+<p class="smcap center">Wisconsin Geological and Natural History Survey.</p>
+
+<table width = "100%" summary= "top" cellspacing="0">
+   <tr>
+	<td class = "tdl bb padtop padbottom2"> <b>E. A. BIRGE, Director.</b> </td>
+	<td class = "tdr bb padtop padbottom2"> <b>C. R. VAN HISE, Consulting
+						   Geologist.</b> </td>
+   </tr>
+   <tr>
+	<td class = "tdl bb padtop padbottom2">BULLETIN NO. V.</td>
+	<td class = "tdr bb padtop padbottom2">EDUCATIONAL SERIES NO. 1.</td>
+   </tr>
+</table>
+
+
+<p class="center"> <br /> <br />
+<span class="flarge">THE GEOGRAPHY</span> <br /> <br />
+OF THE <br /> <br />
+<span class="fxlarge">REGION ABOUT DEVIL'S LAKE</span> <br /> <br />
+AND THE <br /> <br />
+<span class="flarge">DALLES OF THE WISCONSIN,</span> <br /> <br />
+<span class="fmedium">With Some Notes on Its Surface Geology.</span>
+<br /> <br /> <br /> <br /> </p>
+
+
+<p class="center">BY <br /> </p>
+
+<p class="center">ROLLIN D. SALISBURY, A. M.,<br />
+<span class="fmedium"> <i>Professor of Geographic Geology, University of Chicago,</i>
+</span> <br /> <br /> </p>
+
+<p class="center">AND</p>
+
+<p class="center">WALLACE W. ATWOOD, B. S.,<br />
+<span class="fmedium"> <i>Assistant in Geology, University of Chicago.</i> </span>
+<br /> <br /> </p>
+
+
+<p class="center padbottom1">MADISON, WIS.<br />
+<span class="smcap">Published by the State.</span> <br />
+1900. <br /> <br /> </p>
+
+
+<p> <span class="pagenum"> <a name="Page_ii" id="Page_ii">[Pg ii]</a> </span> </p>
+<p class="center fmedium">Wisconsin Geological and Natural History Survey.
+<br /> <br /> <br /> </p>
+
+<hr style="width: 45%;" />
+
+<p class="center"> <br /> <br /> BOARD OF COMMISSIONERS.</p>
+
+<p class="tab1 smcap">Edward Scofield,</p>
+<p class="tab2">Governor of the State.</p>
+
+<p class="tab1 smcap">L. D. Harvey,</p>
+<p class="tab2">State Superintendent of Public Instruction.</p>
+
+<p class="tab1"> <span class="smcap">Charles K. Adams,</span> President,</p>
+<p class="tab2">President of the University of Wisconsin.</p>
+
+<p class="tab1"> <span class="smcap">Edwin E. Bryant,</span> Vice-President,</p>
+<p class="tab2">President of the Commissioners of Fisheries.</p>
+
+<p class="tab1"> <span class="smcap">Charles S. Slichter,</span> Secretary,</p>
+<p class="tab2">President of the Wisconsin Academy of Sciences, Arts, and
+Letters.<br /> <br /> </p>
+
+<hr style="width: 45%;" />
+
+<p class="tab1"> <br /> <span class="smcap">E. A. Birge,</span> Director of the
+Survey.</p>
+
+<p class="tab1"> <span class="smcap">C. R. Van Hise,</span> Consulting Geologist.</p>
+
+<p class="tab1"> <span class="smcap">E. R. Buckley,</span> Assistant Geologist.
+<br /> </p>
+<p class="tab2">In charge of Economic Geology.</p>
+
+<p class="tab1"> <span class="smcap">S. Weidman,</span> Assistant Geologist.
+<br /> </p>
+<p class="tab2">In charge of Geology of Wausau District.</p>
+
+<p class="tab1"> <span class="smcap">L. S. Smith,</span> in charge of Hydrography.</p>
+
+<p class="tab1"> <span class="smcap">S. V. Peppel,</span> Chemist.</p>
+
+<p class="tab1"> <span class="smcap">F. R. Denniston,</span> Artist.</p>
+
+<p class="center bold"> <br /> <br /> <br /> <br /> <b>Frontispiece</b> </p>
+<div class="figcenter" style="width: 200px;">
+<img src="images/frontispiece.jpg" width="200" height="155" alt="" />
+</div>
+<p class="center"> <a href="images/frontispiece.jpg">See larger image</a>
+<br /> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_iii" id="Page_iii">[Pg iii]</a> </span> </p>
+
+<h2>CONTENTS. <br /> </h2>
+
+<hr style="width: 45%;" />
+
+<table border="0" summary="Contents" width="60%">
+<tr>
+   <td class="tdc padbottom3 flarge" colspan="2">PART I. THE TOPOGRAPHY WITH SOME
+             NOTES ON THE SURFACE GEOLOGY.</td>
+</tr>
+<tr>
+   <td class="tdc flarge" colspan="2">CHAPTER I.</td>
+</tr>
+<tr>
+   <td class="tdl padbottom2"> &nbsp; </td>
+   <td class="tdr padbottom2">PAGE</td>
+</tr>
+<tr>
+   <td class="tdc padbottom2"> &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
+                               GENERAL GEOGRAPHIC FEATURES</td>
+   <td class="tdr padbottom2"> <a href="#Page_3">3</a> </td>
+</tr>
+<tr>
+   <td class="tdl smcap">I. The Plain Surrounding the Quartzite Ridges.</td>
+   <td class="tdr"> &nbsp; </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography</td>
+   <td class="tdr"> <a href="#Page_6">6</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Structure</td>
+   <td class="tdr"> <a href="#Page_8">8</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of the Sandstone and Limestone</td>
+   <td class="tdr"> <a href="#Page_9">9</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">Origin of the Topography</td>
+   <td class="tdr padbottom2"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl smcap">II. The Quartzite Ridges</td>
+   <td class="tdr"> <a href="#Page_13">13</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography</td>
+   <td class="tdr"> <a href="#Page_13">13</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">The Structure and Constitution of the
+				       Ridges</td>
+   <td class="tdr padbottom2"> <a href="#Page_14">14</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom1 smcap">III. Relations of the Sandstone of the
+                    Plain to the Quartzite of the Ridges</td>
+   <td class="tdr padbottom1"> <a href="#Page_19">19</a> </td>
+</tr>
+<tr>
+   <td class="tdc padbottom3 flarge" colspan="2">PART II. HISTORY OF THE
+						 TOPOGRAPHY.</td>
+</tr>
+<tr>
+   <td class="tdc padbottom2 flarge" colspan="2">CHAPTER II.</td>
+</tr>
+<tr>
+   <td class="tdc padbottom2" colspan="2">OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS
+                                          WHICH SHOW THEMSELVES AT THE SURFACE.</td>
+</tr>
+<tr>
+   <td class="tdl smcap">I. The Pre-Cambrian History of the Quartzite</td>
+   <td class="tdr"> <a href="#Page_23">23</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">From loose Sand to Quartzite</td>
+   <td class="tdr"> <a href="#Page_23">23</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Uplift and Deformation. Dynamic Metamorphism</td>
+   <td class="tdr"> <a href="#Page_24">24</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosion of the Quartzite</td>
+   <td class="tdr"> <a href="#Page_25">25</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">Thickness of the Quartzite</td>
+   <td class="tdr padbottom2"> <a href="#Page_26">26</a> </td>
+</tr>
+<tr>
+   <td class="tdl smcap">II. The History of the Paleozoic Strata</td>
+   <td class="tdr"> <span class="pagenum"> <a name="Page_iv" id="Page_iv">[Pg iv]
+                    </a> </span> <a href="#Page_27">27</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Subsidence</td>
+   <td class="tdr"> <a href="#Page_27">27</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Potsdam Sandstone (and Conglomerate)</td>
+   <td class="tdr"> <a href="#Page_27">27</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Lower Magnesian Limestone</td>
+   <td class="tdr"> <a href="#Page_31">31</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The St. Peters Sandstone</td>
+   <td class="tdr"> <a href="#Page_32">32</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Younger Beds</td>
+   <td class="tdr"> <a href="#Page_33">33</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Climatic Conditions</td>
+   <td class="tdr"> <a href="#Page_34">34</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Time involved</td>
+   <td class="tdr"> <a href="#Page_34">34</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">The Uplift</td>
+   <td class="tdr padbottom3"> <a href="#Page_34">34</a> </td>
+</tr>
+<tr>
+   <td class="tdc flarge" colspan="2">CHAPTER III.</td>
+</tr>
+<tr>
+   <td class="tdc padbottom2" colspan="2">GENERAL OUTLINE OF RAIN AND RIVER
+					  EROSION</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Elements of Erosion</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Weathering</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Corrasion</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosion without Valleys</td>
+   <td class="tdr"> <a href="#Page_37">37</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Beginning of a Valley</td>
+   <td class="tdr"> <a href="#Page_37">37</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Course of a Valley</td>
+   <td class="tdr"> <a href="#Page_39">39</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Tributary Valleys</td>
+   <td class="tdr"> <a href="#Page_39">39</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">How a Valley gets a Stream</td>
+   <td class="tdr"> <a href="#Page_40">40</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Limits of a Valley</td>
+   <td class="tdr"> <a href="#Page_43">43</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">A Cycle of Erosion</td>
+   <td class="tdr"> <a href="#Page_44">44</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Effects of unequal Hardness</td>
+   <td class="tdr"> <a href="#Page_47">47</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Falls and Rapids</td>
+   <td class="tdr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Narrows</td>
+   <td class="tdr"> <a href="#Page_49">49</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosion of folded Strata</td>
+   <td class="tdr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Base-level Plains and Peneplains</td>
+   <td class="tdr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Transportation and Deposition</td>
+   <td class="tdr"> <a href="#Page_55">55</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topographic Forms resulting from Stream Deposition</td>
+   <td class="tdr"> <a href="#Page_56">56</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Rejuvenation of Streams</td>
+   <td class="tdr"> <a href="#Page_56">56</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom3">Underground Water</td>
+   <td class="tdr padbottom3"> <a href="#Page_58">58</a> </td>
+</tr>
+<tr>
+   <td class="tdc flarge padbottom2" colspan="2">CHAPTER IV.</td>
+</tr>
+<tr>
+   <td class="tdc padbottom2" colspan="2">EROSION AND THE DEVELOPMENT OF STRIKING
+					  SCENIC FEATURES</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Establishment of Drainage</td>
+   <td class="tdr"> <a href="#Page_61">61</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Striking scenic Features</td>
+   <td class="tdr"> <a href="#Page_64">64</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Baraboo Bluffs</td>
+   <td class="tdr"> <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Narrows in the Quartzite</td>
+   <td class="tdr"> <a href="#Page_66">66</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Glens</td>
+   <td class="tdr"> <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Natural Bridge</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Dalles of the Wisconsin</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom3">
+             The Mounds and Castle Rocks</td>
+   <td class="tdr padbottom3"> <a href="#Page_71">71</a> </td>
+</tr>
+<tr>
+   <td class="tdc padbottom2" colspan="2"> <span class="flarge">CHAPTER V.</span>
+             <span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></td>
+</tr>
+<tr>
+   <td class="tdc padbottom2" colspan="2">THE GLACIAL PERIOD.</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Drift</td>
+   <td class="tdr"> <a href="#Page_73">73</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Snow Fields and ice Sheets</td>
+   <td class="tdr"> <a href="#Page_74">74</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The North American ice Sheets</td>
+   <td class="tdr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Work of glacier Ice</td>
+   <td class="tdr"> <a href="#Page_79">79</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosive Work of Ice. Effect on Topography</td>
+   <td class="tdr"> <a href="#Page_79">79</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Deposition by the Ice. Effect on Topography</td>
+   <td class="tdr"> <a href="#Page_85">85</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Direction of ice Movement</td>
+   <td class="tdr"> <a href="#Page_88">88</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Effect of Topography on Movement</td>
+   <td class="tdr"> <a href="#Page_89">89</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Glacial Deposits</td>
+   <td class="tdr"> <a href="#Page_94">94</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The ground Moraine</td>
+   <td class="tdr"> <a href="#Page_97">97</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Constitution</td>
+   <td class="tdr"> <a href="#Page_99">99</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography</td>
+   <td class="tdr"> <a href="#Page_101">101</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Terminal Moraines</td>
+   <td class="tdr"> <a href="#Page_102">102</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography of terminal Moraines</td>
+   <td class="tdr"> <a href="#Page_103">103</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The terminal Moraine about Devil's Lake</td>
+   <td class="tdr"> <a href="#Page_105">105</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Moraine on the main Quartzite Range</td>
+   <td class="tdr"> <a href="#Page_107">107</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Constitution of the marginal Ridge</td>
+   <td class="tdr"> <a href="#Page_110">110</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Slope of the upper Surface of the Ice at the
+			    Margin</td>
+   <td class="tdr"> <a href="#Page_111">111</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Stratified Drift</td>
+   <td class="tdr"> <a href="#Page_111">111</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Its Origin</td>
+   <td class="tdr"> <a href="#Page_112">112</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Glacial Drainage</td>
+   <td class="tdr"> <a href="#Page_113">113</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Stages in the History of an Ice Sheet</td>
+   <td class="tdr"> <a href="#Page_114">114</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Deposits made by extraglacial Waters during the maximum Extension
+		   of the Ice</td>
+   <td class="tdr"> <a href="#Page_115">115</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">At the Edge of the Ice, on Land</td>
+   <td class="tdr"> <a href="#Page_115">115</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Beyond the Edge of the Ice, on Land</td>
+   <td class="tdr"> <a href="#Page_116">116</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Deposits at and beyond the Edge of the Ice in standing
+			    Water</td>
+   <td class="tdr"> <a href="#Page_120">120</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Deposits made by extraglacial Waters during the Retreat of the
+		   Ice</td>
+   <td class="tdr"> <a href="#Page_121">121</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Deposits made by extraglacial Waters during the Advance of the
+		   Ice</td>
+   <td class="tdr"> <a href="#Page_123">123</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Deposits made by subglacial Streams</td>
+   <td class="tdr"> <a href="#Page_124">124</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Relations of stratified to unstratified Drift</td>
+   <td class="tdr"> <a href="#Page_125">125</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Complexity of Relations</td>
+   <td class="tdr"> <a href="#Page_126">126</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Classification of stratified Drift on the Basis of Position</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Extraglacial Deposits</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Supermorainic deposits</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The submorainic (basal) Deposits</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Intermorainic stratified Drift</td>
+   <td class="tdr"> <a href="#Page_128">128</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1"> <span class="pagenum"> <a name="Page_vi" id="Page_vi">
+	     [Pg vi]</a> </span> Changes in Drainage effected by the Ice</td>
+   <td class="tdr"> <a href="#Page_128">128</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">While the Ice was on</td>
+   <td class="tdr"> <a href="#Page_128">128</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Wisconsin Lake</td>
+   <td class="tdr"> <a href="#Page_129">129</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Baraboo Lake</td>
+   <td class="tdr"> <a href="#Page_130">130</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Devil's Lake in glacial Times</td>
+   <td class="tdr"> <a href="#Page_132">132</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">After the Ice had disappeared</td>
+   <td class="tdr"> <a href="#Page_135">135</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Lakes</td>
+   <td class="tdr"> <a href="#Page_136">136</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Existing Lakes</td>
+   <td class="tdr"> <a href="#Page_137">137</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Changes in Streams</td>
+   <td class="tdr"> <a href="#Page_138">138</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Skillett Creek</td>
+   <td class="tdr"> <a href="#Page_138">138</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Wisconsin</td>
+   <td class="tdr"> <a href="#Page_139">139</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">The Driftless Area</td>
+   <td class="tdr"> <a href="#Page_142">142</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Contrast between glaciated and unglaciated Areas</td>
+   <td class="tdr"> <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Topography</td>
+   <td class="tdr"> <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Drainage</td>
+   <td class="tdr"> <a href="#Page_144">144</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2 padbottom1">Mantle Rock</td>
+   <td class="tdr padbottom1"> <a href="#Page_144">144</a> </td>
+</tr>
+</table>
+
+
+<p> <span class="pagenum"> <a name="Page_vii" id="Page_vii">[Pg vii]</a> </span> </p>
+
+<h2>LIST OF ILLUSTRATIONS.</h2>
+
+<hr style="width: 45%;" />
+
+<table border="0" summary="Plates" width="60%">
+<tr>
+   <td class="tdc" colspan="3">PLATES.</td>
+</tr>
+<tr>
+   <td class="tdr" colspan="3">PAGE</td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">The Dalles of the Wisconsin</td>
+   <td class="tdrr">Frontispiece.</td>
+</tr>
+<tr>
+   <td class="tdr nowrap">Plate I.</td>
+   <td class="tdl padleft3">General map of the Devil's Lake region</td>
+   <td class="tdrr"> <a href="#Page_4">4</a> </td>
+</tr>
+<tr>
+   <td class="tdr">II.</td>
+   <td class="tdl padleft3">Local map of the Devil's Lake region</td>
+   <td class="tdrr"> <a href="#Page_4">4</a> </td>
+</tr>
+<tr>
+   <td class="tdr">III.</td>
+   <td class="tdl padleft3">Fig. 1&mdash;Ripple marks on a slab of sandstone</td>
+   <td class="tdrr"> <a href="#Page_9">9</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 2&mdash;Piece of Potsdam conglomerate</td>
+   <td class="tdrr"> <a href="#Page_9">9</a> </td>
+</tr>
+<tr>
+   <td class="tdr">IV.</td>
+   <td class="tdl padleft3">Lower Narrows of the Baraboo</td>
+   <td class="tdrr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdr">V.</td>
+   <td class="tdl padleft3">Devil's Lake notch</td>
+   <td class="tdrr"> <a href="#Page_14">14</a> </td>
+</tr>
+<tr>
+   <td class="tdr">VI.</td>
+   <td class="tdl padleft3">East bluff of Devil's Lake</td>
+   <td class="tdrr"> <a href="#Page_14">14</a> </td>
+</tr>
+<tr>
+   <td class="tdr">VII.</td>
+   <td class="tdl padleft3">East bluff at the Upper Narrows of the Baraboo near
+			    Ableman's</td>
+   <td class="tdrr"> <a href="#Page_16">16</a> </td>
+</tr>
+<tr>
+   <td class="tdr">VIII.</td>
+   <td class="tdl padleft3">Vertical shear zone face of east bluff at Devil's
+			    Lake</td>
+   <td class="tdrr"> <a href="#Page_16">16</a> </td>
+</tr>
+<tr>
+   <td class="tdr">IX.</td>
+   <td class="tdl padleft3">Massive quartzite <i>in situ</i> in road through Upper
+			    Narrows near Ableman's</td>
+   <td class="tdrr"> <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdr">X.</td>
+   <td class="tdl padleft3">Brecciated quartzite</td>
+   <td class="tdrr"> <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XI.</td>
+   <td class="tdl padleft3">Northwest wall of the Upper Narrows</td>
+   <td class="tdrr"> <a href="#Page_20">20</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XII.</td>
+   <td class="tdl padleft3">Steamboat Rock</td>
+   <td class="tdrr"> <a href="#Page_30">30</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XIII.</td>
+   <td class="tdl padleft3">Fig. 1&mdash;A very young valley</td>
+   <td class="tdrr"> <a href="#Page_38">38</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 2&mdash;A valley at later stage of development</td>
+   <td class="tdrr"> <a href="#Page_38">38</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 3&mdash;Young valleys</td>
+   <td class="tdrr"> <a href="#Page_38">38</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XIV.</td>
+   <td class="tdl padleft3">Fig. 1&mdash;Same valleys as shown in Pl. XIII, Fig. 3,
+                            but at a later stage of development</td>
+   <td class="tdrr"> <a href="#Page_45">45</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 2&mdash;Same valleys as shown in Fig. 1 in later
+			    stage of development</td>
+   <td class="tdrr"> <a href="#Page_45">45</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XV.</td>
+   <td class="tdl padleft3">Diagram illustrating how a hard inclined layer of
+                            rock becomes a ridge in the process of degradation</td>
+   <td class="tdrr"> <a href="#Page_46">46</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XVI.</td>
+   <td class="tdl padleft3">Skillett Falls</td>
+   <td class="tdrr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XVII.</td>
+   <td class="tdl padleft3">A group of mounds on the plain northwest from Camp
+			    Douglas</td>
+   <td class="tdrr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XVIII.</td>
+   <td class="tdl padleft3">Castle Rock near Camp Douglas</td>
+   <td class="tdrr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XIX. <span class="pagenum"> <a name="Page_viii" id="Page_viii">
+       [Pg viii]</a> </span> </td>
+   <td class="tdl padleft3">Fig. 1&mdash;Sketch of a young valley</td>
+   <td class="tdrr"> <a href="#Page_54">54</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 2&mdash;Same valleys as shown in Fig. 1 in later
+			    stage of development</td>
+   <td class="tdrr"> <a href="#Page_54">54</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XX.</td>
+   <td class="tdl padleft3">Fig. 1&mdash;Sketch of a part of a valley at a stage of
+			    development corresponding to the cross section shown in
+			    Fig. 21</td>
+   <td class="tdrr"> <a href="#Page_54">54</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3">Fig. 2&mdash;Sketch of a section of the Baraboo
+			    valley</td>
+   <td class="tdrr"> <a href="#Page_54">54</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXI.</td>
+   <td class="tdl padleft3">Cleopatra's Needle</td>
+   <td class="tdrr"> <a href="#Page_64">64</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXII.</td>
+   <td class="tdl padleft3">Turk's Head</td>
+   <td class="tdrr"> <a href="#Page_64">64</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXIII.</td>
+   <td class="tdl padleft3">Devil's Doorway</td>
+   <td class="tdrr"> <a href="#Page_64">64</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXIV.</td>
+   <td class="tdl padleft3">Talus slope on east bluff of Devil's Lake</td>
+   <td class="tdrr"> <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXV.</td>
+   <td class="tdl padleft3">Dorward's Glen</td>
+   <td class="tdrr"> <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXVI.</td>
+   <td class="tdl padleft3">Natural Bridge near Denzer</td>
+   <td class="tdrr"> <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXVII.</td>
+   <td class="tdl padleft3">The Navy Yard</td>
+   <td class="tdrr"> <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXVIII.</td>
+   <td class="tdl padleft3">Chimney Rock</td>
+   <td class="tdrr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXIX.</td>
+   <td class="tdl padleft3">An island in the Lower Dalles</td>
+   <td class="tdrr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXX.</td>
+   <td class="tdl padleft3">View in Lower Dalles</td>
+   <td class="tdrr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXI.</td>
+   <td class="tdl padleft3">Stand Rock</td>
+   <td class="tdrr"> <a href="#Page_72">72</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXII.</td>
+   <td class="tdl padleft3">Petenwell Peak</td>
+   <td class="tdrr"> <a href="#Page_72">72</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXIII.</td>
+   <td class="tdl padleft3">North American ice sheet</td>
+   <td class="tdrr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXIV.</td>
+   <td class="tdl padleft3">Owl's Head</td>
+   <td class="tdrr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXV.</td>
+   <td class="tdl padleft3">Cut in glacial drift</td>
+   <td class="tdrr"> <a href="#Page_94">94</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXVI.</td>
+   <td class="tdl padleft3">Glaciated stones</td>
+   <td class="tdrr"> <a href="#Page_96">96</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXVII.</td>
+   <td class="tdl padleft3">Topographic map of a small area about Devil's Lake</td>
+   <td class="tdrr"> <a href="#Page_108">108</a> </td>
+</tr>
+<tr>
+   <td class="tdr">XXXVIII.</td>
+   <td class="tdl padleft3">Distorted laminæ of silt and clay</td>
+   <td class="tdrr"> <a href="#Page_120">120</a> </td>
+</tr>
+</table>
+
+<p> <br /> <br />
+<span class="pagenum"> <a name="Page_ix" id="Page_ix">[Pg ix]</a> </span> </p>
+
+
+<table border="0" summary="Figures" width="60%">
+<tr>
+   <td class="tdc" colspan="3">FIGURES IN TEXT.</td>
+</tr>
+<tr>
+   <td class="tdr" colspan="3">PAGE</td>
+</tr>
+<tr>
+   <td class="tdr nowrap">Figure 1.</td>
+   <td class="tdl padleft3">Profile across the Baraboo quartzite ranges through
+			    Baraboo</td>
+   <td class="tdrr"> <a href="#Page_4">4</a> </td>
+</tr>
+<tr>
+   <td class="tdr">2.</td>
+   <td class="tdl padleft3">Profile across the Baraboo ranges through Merrimac</td>
+   <td class="tdrr"> <a href="#Page_5">5</a> </td>
+</tr>
+<tr>
+   <td class="tdr">&nbsp;</td>
+   <td class="tdl padleft3 colspan=2">Transcriber's note: There is no figure 3.</td>
+</tr>
+<tr>
+   <td class="tdr">4.</td>
+   <td class="tdl padleft3">Diagram showing the structure of the quartzite</td>
+   <td class="tdrr"> <a href="#Page_15">15</a> </td>
+</tr>
+<tr>
+   <td class="tdr">5.</td>
+   <td class="tdl padleft3">Diagram showing the relation of the Potsdam sandstone to
+			    the Baraboo quartzite</td>
+   <td class="tdrr"> <a href="#Page_16">16</a> </td>
+</tr>
+<tr>
+   <td class="tdr">6.</td>
+   <td class="tdl padleft3">Diagram illustrating effect of faulting on outcrop</td>
+   <td class="tdrr"> <a href="#Page_27">27</a> </td>
+</tr>
+<tr>
+   <td class="tdr">7.</td>
+   <td class="tdl padleft3">Diagram showing the disposition of sediments about an
+			    island</td>
+   <td class="tdrr"> <a href="#Page_28">28</a> </td>
+</tr>
+<tr>
+   <td class="tdr">8.</td>
+   <td class="tdl padleft3">The same as 7 after subsidence</td>
+   <td class="tdrr"> <a href="#Page_28">28</a> </td>
+</tr>
+<tr>
+   <td class="tdr">9.</td>
+   <td class="tdl padleft3">Diagram showing relation of Potsdam conglomerate to
+			    quartzite at Devil's Lake</td>
+   <td class="tdrr"> <a href="#Page_29">29</a> </td>
+</tr>
+<tr>
+   <td class="tdr">10.</td>
+   <td class="tdl padleft3">Cross section of a delta</td>
+   <td class="tdrr"> <a href="#Page_31">31</a> </td>
+</tr>
+<tr>
+   <td class="tdr">11.</td>
+   <td class="tdl padleft3">The geological formations of southern Wisconsin</td>
+   <td class="tdrr"> <a href="#Page_33">33</a> </td>
+</tr>
+<tr>
+   <td class="tdr">12.</td>
+   <td class="tdl padleft3">A typical river system</td>
+   <td class="tdrr"> <a href="#Page_41">41</a> </td>
+</tr>
+<tr>
+   <td class="tdr">13.</td>
+   <td class="tdl padleft3">Diagram illustrating the relations of ground water to
+			    streams</td>
+   <td class="tdrr"> <a href="#Page_42">42</a> </td>
+</tr>
+<tr>
+   <td class="tdr">14.</td>
+   <td class="tdl padleft3">Diagram illustrating the shifting of divides</td>
+   <td class="tdrr"> <a href="#Page_44">44</a> </td>
+</tr>
+<tr>
+   <td class="tdr">15.</td>
+   <td class="tdl padleft3">Diagram showing topography at the various stages of an
+			    erosion cycle</td>
+   <td class="tdrr"> <a href="#Page_46">46</a> </td>
+</tr>
+<tr>
+   <td class="tdr">16.</td>
+   <td class="tdl padleft3">Diagram illustrating the development of rapids and
+			    falls</td>
+   <td class="tdrr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdr">17.</td>
+   <td class="tdl padleft3">Sketch looking northwest from Camp Douglas</td>
+   <td class="tdrr"> <a href="#Page_52">52</a> </td>
+</tr>
+<tr>
+   <td class="tdr">18.</td>
+   <td class="tdl padleft3">Diagrammatic cross section of a young valley</td>
+   <td class="tdrr"> <a href="#Page_52">52</a> </td>
+</tr>
+<tr>
+   <td class="tdr">19.</td>
+   <td class="tdl padleft3">Diagrammatic profile of a young valley</td>
+   <td class="tdrr"> <a href="#Page_53">53</a> </td>
+</tr>
+<tr>
+   <td class="tdr">20.</td>
+   <td class="tdl padleft3">Diagrammatic cross section of a valley in a later stage
+			    of development</td>
+   <td class="tdrr"> <a href="#Page_53">53</a> </td>
+</tr>
+<tr>
+   <td class="tdr">21.</td>
+   <td class="tdl padleft3">The same at a still later stage</td>
+   <td class="tdrr"> <a href="#Page_54">54</a> </td>
+</tr>
+<tr>
+   <td class="tdr">22.</td>
+   <td class="tdl padleft3">Diagram illustrating the topographic effect or
+             rejuvenation of a stream by uplift</td>
+   <td class="tdrr"> <a href="#Page_57">57</a> </td>
+</tr>
+<tr>
+   <td class="tdr">23.</td>
+   <td class="tdl padleft3">Normal profile of a valley bottom</td>
+   <td class="tdrr"> <a href="#Page_58">58</a> </td>
+</tr>
+<tr>
+   <td class="tdr">24.</td>
+   <td class="tdl padleft3">Profile of a stream rejuvenated by uplift</td>
+   <td class="tdrr"> <a href="#Page_58">58</a> </td>
+</tr>
+<tr>
+   <td class="tdr">25.</td>
+   <td class="tdl padleft3">Diagram illustrating monoclinal shifting</td>
+   <td class="tdrr"> <a href="#Page_62">62</a> </td>
+</tr>
+<tr>
+   <td class="tdr">26.</td>
+   <td class="tdl padleft3">Diagram showing the relation of the Potsdam sandstone
+			    to the quartzite at the Upper Narrows</td>
+   <td class="tdrr"> <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdr">27.</td>
+   <td class="tdl padleft3">Diagrammatic cross section of a field of ice and
+			    snow</td>
+   <td class="tdrr"> <a href="#Page_75">75</a> </td>
+</tr>
+<tr>
+   <td class="tdr">28.</td>
+   <td class="tdl padleft3">Shape of an erosion hill before glaciation</td>
+   <td class="tdrr"> <a href="#Page_81">81</a> </td>
+</tr>
+<tr>
+   <td class="tdr">29.</td>
+   <td class="tdl padleft3">The same after glaciation</td>
+   <td class="tdrr"> <a href="#Page_82">82</a> </td>
+</tr>
+<tr>
+   <td class="tdr">30.</td>
+   <td class="tdl padleft3">Diagram showing the effect of a valley on the movement of
+			    ice</td>
+   <td class="tdrr"> <a href="#Page_83">83</a> </td>
+</tr>
+<tr>
+   <td class="tdr"> <span class="pagenum"> <a name="Page_x" id="Page_x">[Pg x]</a>
+	</span> 31. </td>
+   <td class="tdl padleft3">The same under different conditions</td>
+   <td class="tdrr"> <a href="#Page_84">84</a> </td>
+</tr>
+<tr>
+   <td class="tdr">32.</td>
+   <td class="tdl padleft3">Diagram showing the relation of drift to the underlying
+             rock where the drift is thick</td>
+   <td class="tdrr"> <a href="#Page_87">87</a> </td>
+</tr>
+<tr>
+   <td class="tdr">33.</td>
+   <td class="tdl padleft3">The same where the drift is relatively thin</td>
+   <td class="tdrr"> <a href="#Page_87">87</a> </td>
+</tr>
+<tr>
+   <td class="tdr">34.</td>
+   <td class="tdl padleft3">Diagrammatic representation of the effect of a hill on
+             the edge of the ice</td>
+   <td class="tdrr"> <a href="#Page_90">90</a> </td>
+</tr>
+<tr>
+   <td class="tdr">35.</td>
+   <td class="tdl padleft3">The same at a later stage of the ice advance</td>
+   <td class="tdrr"> <a href="#Page_91">91</a> </td>
+</tr>
+<tr>
+   <td class="tdr">36.</td>
+   <td class="tdl padleft3">Map showing the relation of the ice lobes during the
+			    Wisconsin epoch of the glacial period</td>
+   <td class="tdrr"> <a href="#Page_92">92</a> </td>
+</tr>
+<tr>
+   <td class="tdr">37.</td>
+   <td class="tdl padleft3">Sketch of the terminal moraine topography east of Devil's
+			    Lake</td>
+   <td class="tdrr"> <a href="#Page_104">104</a> </td>
+</tr>
+<tr>
+   <td class="tdr">38.</td>
+   <td class="tdl padleft3">Cut through the terminal moraine east of Kirkland</td>
+   <td class="tdrr"> <a href="#Page_106">106</a> </td>
+</tr>
+<tr>
+   <td class="tdr">39.</td>
+   <td class="tdl padleft3">Cross section of the marginal ridge of the moraine on the
+             south slope of the Devil's nose</td>
+   <td class="tdrr"> <a href="#Page_107">107</a> </td>
+</tr>
+<tr>
+   <td class="tdr">40.</td>
+   <td class="tdl padleft3">Cross section of the marginal ridge of the moraine on the
+             crest of the quartzite range</td>
+   <td class="tdrr"> <a href="#Page_108">108</a> </td>
+</tr>
+<tr>
+   <td class="tdr">41.</td>
+   <td class="tdl padleft3">Morainic outwash plain</td>
+   <td class="tdrr"> <a href="#Page_118">118</a> </td>
+</tr>
+<tr>
+   <td class="tdr">42.</td>
+   <td class="tdl padleft3">The same in other relations</td>
+   <td class="tdrr"> <a href="#Page_119">119</a> </td>
+</tr>
+<tr>
+   <td class="tdr">43.</td>
+   <td class="tdl padleft3">Skillett Creek and its peculiarities</td>
+   <td class="tdrr"> <a href="#Page_139">139</a> </td>
+</tr>
+<tr>
+   <td class="tdr">44.</td>
+   <td class="tdl padleft3">The Wisconsin valley near Kilbourn city</td>
+   <td class="tdrr"> <a href="#Page_141">141</a> </td>
+</tr>
+<tr>
+   <td class="tdr">45.</td>
+   <td class="tdl padleft3">Drainage in the driftless area</td>
+   <td class="tdrr"> <a href="#Page_144">144</a> </td>
+</tr>
+<tr>
+   <td class="tdr">46.</td>
+   <td class="tdl padleft3">Drainage in the glaciated area</td>
+   <td class="tdrr"> <a href="#Page_145">145</a> </td>
+</tr>
+<tr>
+   <td class="tdr padbottom1">47.</td>
+   <td class="tdl padleft3 padbottom1">Section in the driftless region showing
+             relation of the soil to the solid rock beneath</td>
+   <td class="tdrr padbottom1"> <a href="#Page_146">146</a> </td>
+</tr>
+</table>
+
+<p> <br /> <br /> <br /> <br />
+<span class="pagenum"> <a name="Page_1" id="Page_1">[Pg 1]</a> </span> </p>
+<h2>PART I.</h2>
+
+<hr style="width: 45%;" />
+
+<h1>THE TOPOGRAPHY.</h1>
+
+<h5>WITH SOME NOTES ON THE SURFACE GEOLOGY.</h5>
+
+<p> <span class="pagenum"> <a name="Page_2" id="Page_2">[Pg 2]</a> </span>
+<br /> </p>
+
+<p class="padbottom3"> <span class="pagenum"> <a name="Page_3" id="Page_3">[Pg 3]</a>
+ </span> </p>
+
+<h2>GEOGRAPHY AND SURFACE GEOLOGY OF THE DEVIL'S LAKE REGION.</h2>
+
+<hr style="width: 45%;" />
+
+
+<h2>CHAPTER I.</h2>
+<p> <br /> </p>
+
+<h4>GENERAL GEOGRAPHIC FEATURES.</h4>
+
+
+<p>This report has to do with the physical geography of the area in south central
+Wisconsin, shown on the accompanying sketch map, Plate <a href="images/i01.jpg">I</a>.
+The region is of especial interest, both because of its striking scenery, and because
+it illustrates clearly many of the principles involved in the evolution of the
+geography of land surfaces.</p>
+
+<p>Generally speaking, the region is an undulating plain, above which rise a few
+notable elevations, chief among which are the Baraboo quartzite ranges, marked by
+diagonal lines on Plates <a href="images/i01.jpg">I</a>  and
+<a href="images/i02.jpg">II</a> . These elevations have often been described as two
+ranges. The South or main range lies three miles south of Baraboo, while the North or
+lesser range, which is far from continuous, lies just north of the city.</p>
+
+<p>The main range has a general east-west trend, and rises with bold and sometimes
+precipitous slopes 500 to 800 feet above its surroundings. A deep gap three or four
+miles south of Baraboo (Plates <a href="images/i02.jpg">II</a>,
+<a href="images/i05.jpg">V</a>, and <a href="images/i37.jpg">XXXVII</a>) divides the
+main range into an eastern and a western portion, known respectively as the <i>East
+and West bluffs</i> or <i>ranges</i>. In the bottom of the gap lies Devil's lake (i,
+Plate <a href="images/i02.jpg">II</a> and Plate <a href="images/i37.jpg">XXXVII</a>),
+perhaps the most striking body of water of its size in the state, if not in the
+whole northern interior. A general notion of the topography
+<span class="pagenum"> <a name="Page_4" id="Page_4">[Pg 4]</a> </span>
+of a small area in the immediate vicinity of the lake may be
+obtained from Plate <a href="images/i37.jpg">XXXVII</a>.</p>
+
+<p>The highest point in the range is about four miles east of the lake, and
+has an elevation of more than 1,600 feet above sea level, more than
+1,000 feet above Lake Michigan, and about 800 feet above the Baraboo
+valley at its northern base. The eastward extension of the west range
+(Plate <a href="images/i37.jpg">XXXVII</a>) lying south of the lake, and popularly known as the
+<i>Devil's nose</i>, reaches an elevation of a little more than 1,500 feet.</p>
+
+<p>The lesser or North quartzite range (Plate <a href="images/i02.jpg">II</a>) rises
+300 feet to 500 feet above its surroundings. It assumes considerable prominence at the
+Upper and Lower narrows of the Baraboo (b and c, Plate <a href="images/i02.jpg">II</a>,
+c, Plate <a href="images/i37.jpg">XXXVII</a> and Plate <a href="images/i04.jpg">IV</a>).
+ The North range is not only lower than the South range, but its slopes are generally
+less steep, and, as Plate <a href="images/i02.jpg">II</a> shows, it is also less
+continuous. The lesser elevation and the gentler slopes make it far less conspicuous.
+About three miles southwest of Portage (Plate <a href="images/i02.jpg">II</a>) the
+North and South ranges join, and the elevation at the point of union is about 450
+feet above the Wisconsin river a few miles to the east.</p>
+
+<p>The lower country above which these conspicuous ridges rise, has an
+average elevation of about 1,000 feet above the sea, and extends far
+beyond the borders of the area with which this report is concerned. The
+rock underlying it in the vicinity of Baraboo is chiefly sandstone, but
+there is much limestone farther east and south, in the area with which
+the Baraboo region is topographically continuous. Both the sandstone and
+limestone are much less resistant than the quartzite, and this
+difference has had much to do with the topography of the region.</p>
+
+<p>The distinctness of the quartzite ridges as topographic features is indicated in
+Plate <a href="images/i37.jpg">XXXVII</a> by the closeness of the contour lines on their
+slopes. The same features are shown in Figs. <a href="images/fig01.jpg">1</a> and
+<a href="images/fig02.jpg">2</a>, which represent profiles along two north-south
+lines passing through Baraboo and Merrimac respectively.<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST SURVEY. BULLETIN NO. V., PL. I.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i01.jpg" width="200" height="219" alt="" />
+</div>
+<p class="center indent">General map showing the location of the chief points mentioned in this
+report. The location of the area shown in Plate <a href="images/i37.jpg">XXXVII</a>, centering about
+ Baraboo, is indicated.<br />
+<a href="images/i01.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. II.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i02.jpg" width="200" height="183" alt="" />
+</div>
+<p class="center indent">
+Map of Area considered in this Report.<br />
+<a href="images/i02.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_5" id="Page_5">[Pg 5]</a> </span> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig01.jpg" width="400" height="89" alt="" />
+</div>
+<p class="center indent">
+Fig. 1. -- Profile along a line extending due north and
+south from Baraboo across the north and south ranges. The dotted
+ continuation northward represents the extension of the profile beyond
+the topographic map, Plate <a href="images/i37.jpg">XXXVII</a>.<br />
+<a href="images/fig01.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig02.jpg" width="400" height="89" alt="" />
+</div>
+<p class="center indent">
+Fig. 2. -- Profile north from Merrimac across the quartzite
+ranges. The dotted continuation northward represents the extension of
+ the profile beyond the topographic map, Plate <a href="images/i37.jpg">XXXVII</a>.<br />
+<a href="images/fig02.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+
+<p> <span class="pagenum"> <a name="Page_6" id="Page_6">[Pg 6]</a> </span> </p>
+
+<h4>I. THE PLAIN SURROUNDING THE QUARTZITE RIDGES.</h4>
+
+<p> <i>Topography.</i>&mdash;As seen from the top of the quartzite ridges, the
+surrounding country appears to be an extensive plain, but at closer
+range it is seen to have considerable relief although there are
+extensive areas where the surface is nearly flat.</p>
+
+<p>The relief of the surface is of two somewhat different types. In some
+parts of the area, especially in the western part of the tract shown on
+Plate <a href="images/i02.jpg">II</a>,
+the surface is made up of a succession of ridges and valleys.
+The ridges may be broken by depressions at frequent intervals, but the
+valleys are nowhere similarly interrupted. It would rarely be possible
+to walk along a ridge or "divide" for many miles without descending into
+valleys; but once in a valley in any part of the area, it may be
+descended without interruption, until the Baraboo, the Wisconsin, the
+Mississippi, and finally the gulf is reached. In other words, the
+depressions are continuous, but the elevations are not. This is the
+first type of topography.</p>
+
+<p>Where this type of topography prevails its relation to drainage is
+evident at a glance. All the larger depressions are occupied by streams
+continuously, while the smaller ones contain running water during some
+part of the year. The relations of streams to the depressions, and the
+wear which the streams effect, whether they be permanent or temporary,
+suggest that running water is at least one of the agencies concerned in
+the making of valleys.</p>
+
+<p>An idea of the general arrangement of the valleys, as well as many
+suggestions concerning the evolution of the topography of the broken
+plain in which they lie might be gained by entering a valley at its
+head, and following it wherever it leads. At its head, the valley is
+relatively narrow, and its slopes descend promptly from either side in
+such a manner that a cross-section of the valley is V-shaped. In places,
+as west of Camp Douglas, the deep, steep-sided valleys are found to lead
+down and out from a tract of land so slightly rolling as to be well
+adapted to cultivation. Following down the valley, its progressive
+<span class="pagenum"> <a name="Page_7" id="Page_7">[Pg 7]</a> </span>
+increase in width and depth is at once evident, and at the same time
+small tributary valleys come in from right and left. At no great
+distance from the heads of the valleys, streams are found in their
+bottoms.</p>
+
+<p>As the valleys increase in width and depth, and as the tributaries
+become more numerous and wider, the topography of which the valleys are
+a feature, becomes more and more broken. At first the tracts between the
+streams are in the form of ridges, wide if parallel valleys are distant
+from one another, and narrow if they are near. The ridges wind with the
+valleys which separate them. Whatever the width of the inter-stream
+ridges, it is clear that they must become narrower as the valleys
+between them become wider, and in following down a valley a point is
+reached, sooner or later, where the valleys, main and tributary, are of
+such size and so numerous that their slopes constitute a large part of
+the surface. Where this is true, and where the valleys are deep, the
+land is of little industrial value except for timber and grazing. When,
+in descending a valley system, this sort of topography is reached, the
+roads often follow either the valleys or the ridges, however indirect
+and crooked they may be. Where the ridges separating the valleys in such
+a region have considerable length, they are sometimes spoken of as "hog
+backs." Still farther down the valley system, tributary valleys of the
+second and lower orders cross the "hog backs," cutting them into hills.</p>
+
+<p>By the time this sort of topography is reached, a series of flats is
+found bordering the streams. These flats may occur on both sides of the
+stream, or on but one. The topography and the soil of these flats are
+such as to encourage agriculture, and the river flats or alluvial plains
+are among the choicest farming lands.</p>
+
+<p>With increasing distance from the heads of the valleys, these river
+plains are expanded, and may be widened so as to occupy the greater part
+of the surface. The intervening elevations are there relatively few and
+small. Their crests, however, often rise to the same level as that of
+the broader inter-stream areas
+<span class="pagenum"> <a name="Page_8" id="Page_8">[Pg 8]</a> </span>
+farther up the valleys. The relations of
+the valleys and the high lands separating them, is such as to suggest
+that there are, generally speaking, two sets of flat surfaces, the
+higher one representing the upland in which the valleys lie, the lower
+one representing the alluvial plains of the streams. The two sets of
+flats are at once separated and connected by slopes. At the head of a
+drainage system, the upland flats predominate; in the lower courses, the
+river plains; in an intermediate stage, the slopes are more conspicuous
+than either upper or lower flat.</p>
+
+<p>Southwest from Devil's lake and northwest from Sauk City, in the valley
+of Honey creek, and again in the region southwest from Camp Douglas, the
+topography just described is well illustrated. In both these localities,
+as in all others where this type of topography prevails, the intimate
+relations of topography and drainage cannot fail to suggest that the
+streams which are today widening and deepening the valleys through which
+they flow, had much to do with their origin and development. This
+hypothesis, as applied to the region under consideration, may be tested
+by the study of the structure of the plain.</p>
+
+<p>The second type of topography affecting the plain about the quartzite
+ranges is found east of a line running from Kilbourn City to a point
+just north of Prairie du Sac. Though in its larger features the area
+east of this line resembles that to the west, its minor features are
+essentially different. Here there are many depressions which have no
+outlets, and marshes, ponds, and small lakes abound. Not only this, but
+many of the lesser elevations stand in no definite relation to valleys.
+The two types of topography make it clear that they were developed in
+different ways.</p>
+
+<p> <i>Structure.</i>&mdash;Examination of the country surrounding the Baraboo ridges
+that its surface is underlaid at no great depth by horizontal or
+nearly horizontal beds of sandstone and limestone (see Plates
+<a href="images/i16.jpg">XVI</a>,
+<a href="images/i38.jpg">XXVIII</a>, and
+<a href="images/frontispiece.jpg">Frontispiece</a>). These beds are frequently exposed
+on opposite sides of a valley, and in such positions the beds of one
+side are found to match those on the other. This is well shown along the
+narrow <br /> <br /> <br /> </p>
+
+<p> <a name="i03" id="i03"> </a> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. III.</p>
+
+<div class="imgspc1">
+<div class="figmleft" style="width: 134px;">
+<img src="images/i03f1.jpg" width="134" height="275" alt="FIG. 1. Ripple marks on a slab of Potsdam sandstone." />
+<span class="caption">FIG. 1. <br />Ripple marks on a slab of Potsdam sandstone.</span>
+</div>
+
+<div class="figmright" style="width: 199px;">
+<img src="images/i03f2.jpg" width="199" height="275" alt="FIG. 2. Piece of Potsdam
+ conglomerate. The larger pebbles are about three inches in diameter." />
+<span class="caption">FIG. 2. <br />Piece of Potsdam conglomerate. The larger
+ pebbles are about three inches in diameter.</span>
+</div> </div>
+
+<p> <span class="pagenum"> <a name="Page_9" id="Page_9">[Pg 9]</a> </span>
+valley of Skillett creek just above the "Pewit's nest." Here the swift
+stream is rapidly deepening its channel, and it is clear that a few
+years hence, layers of sandstone which are now continuous beneath the
+bed of the creek will have been cut through, and their edges will appear
+on opposite sides of the valley just as higher layers do now. Here the
+most skeptical might be convinced that the layers of rock on either side
+of the narrow gorge were once continuous across it, and may see, at the
+same time, the means by which the separation was effected. Between the
+slight separation, here, where the valley is narrow, and the great
+separation where the valleys are wide, there are all gradations. The
+study of progressively wider valleys, commencing with such a gorge as
+that referred to, leaves no room for doubt that even the wide valleys,
+as well as the narrow ones, were cut out of the sandstone by running
+water.</p>
+
+<p>The same conclusion as to the origin of the valleys may be reached in
+another way. Either the beds of rock were formed with their present
+topography, or the valleys have been excavated in them since they were
+formed. Their mode of origin will therefore help to decide between these
+alternatives.</p>
+
+<p> <i>Origin of the sandstone and limestone.</i>&mdash;The sandstone of the region,
+known as the <i>Potsdam</i> sandstone, consists of medium sized grains of
+sand, cemented together by siliceous, ferruginous, or calcareous cement.
+If the cement were removed, the sandstone would be reduced to sand, in
+all respect similar to that accumulating along the shores of seas and
+lakes today.</p>
+
+<p>The surfaces of the separate layers of sandstone are often distinctly
+ripple-marked (Plate <a href="#i03">III Fig. 1</a>), and the character of the markings is
+identical in all essential respects with the ripples which affect the
+surface of the sand along the shores of Devil's lake, or sandy beaches
+elsewhere, at the present time. These ripple marks on the surfaces of
+the sandstone layers must have originated while the sand was movable,
+and therefore before it was cemented into sandstone.</p>
+
+<p>In the beds of sandstone, fossils of marine animals are found. Shells,
+or casts of shells of various sorts are common, as are also
+<span class="pagenum"> <a name="Page_10" id="Page_10">[Pg 10]</a> </span>
+the tracks and burrowings of animals which had no shells. Among these latter signs
+of life may be mentioned the borings of worms. These borings are not now
+always hollow, but their fillings are often so unlike the surrounding
+rock, that they are still clearly marked. These worm borings, like the
+ripple marks, show that the sand was once loose.</p>
+
+<p>The basal beds of the sandstone are often conglomeratic. The
+conglomeratic layers are made up of water-worn pieces of quartzite, Plate
+<a href="#i03">III Fig. 2</a>, ranging in size from small pebbles to large
+bowlders. The interstices of the coarse material are filled by sand, and
+the whole cemented into solid rock. The conglomeratic phase of the
+sandstone may be seen to advantage at Parfrey's glen (<i>a</i>, Plate
+<a href="images/i37.jpg">XXXVII</a>) and Dorward's glen, (<i>b</i>, same plate)
+on the East bluff of Devil's lake above the Cliff House, and at the Upper narrows of the
+Baraboo, near Ablemans. It is also visible at numerous other less
+accessible and less easily designated places.</p>
+
+<p>From these several facts, viz.: the horizontal strata, the ripple-marks
+on the surfaces of the layers, the fossils, the character of the sand,
+and the water-worn pebbles and bowlders of the basal conglomerate,
+positive conclusions concerning the origin of the formation may be
+drawn.</p>
+
+<p>The arrangement in definite layers proves that the formation is
+sedimentary; that is, that its materials were accumulated in water
+whither they had been washed from the land which then existed. The
+ripple-marks show that the water in which the beds of sand were
+deposited was shallow, for in such water only are ripple-marks made.
+<a name="FNanchor_1_1" id="FNanchor_1_1"> </a> <a href="#Footnote_1_1" class="fnanchor">[1]</a>
+Once developed on the surface of the sand they may be preserved by
+burial under new deposits, just as ripple-marks on sandy shores are now
+being buried and preserved.</p>
+
+<p>The conglomerate beds of the formation corroborate the conclusions to
+which the composition and structure of the sandstone point. The
+water-worn shapes of the pebbles and stones show
+<span class="pagenum"> <a name="Page_11" id="Page_11">[Pg 11]</a> </span>
+that they were accumulated in water, while their size shows that the water must have
+been shallow, for stones of such sizes are handled only by water of such
+slight depth that waves or strong currents are effective at the bottom.
+Furthermore, the large bowlders show that the source of supply
+(quartzite) must have been close at hand, and that therefore land
+composed of this rock must have existed not far from the places where
+the conglomerate is found.</p>
+
+<p>The fossils likewise are the fossils of aquatic life. Not only this, but
+they are the fossils of animals which lived in salt water. The presence
+of salt water, that is, the sea, in this region when the sand of the
+sandstone was accumulating, makes the wide extent of the formation
+rational.</p>
+
+<p>From the constitution and structure of the sandstone, it is therefore
+inferred that it accumulated in shallow sea water, and that, in the
+vicinity of Devil's lake, there were land masses (islands) of quartzite
+which furnished the pebbles and bowlders found in the conglomerate beds
+at the base of the formation.</p>
+
+<p>This being the origin of the sandstone, it is clear that the layers
+which now appear on opposite sides of valleys must once have been
+continuous across the depressions; for the sand accumulated in shallow
+water is never deposited so as to leave valleys between ridges. It is
+deposited in beds which are continuous over considerable areas.</p>
+
+<p>Within the area under consideration, limestone is much less widely
+distributed than sandstone. Thin beds of it alternate with layers of
+sandstone in the upper portion of the Potsdam formation, and more
+massive beds lie above the sandstone on some of the higher elevations of
+the plain about the quartzite ridge. This is especially true in the
+southern and southwestern parts of the region shown on Plate
+<a href="images/i02.jpg">II</a>. The
+limestone immediately overlying the sandstone is the <i>Lower Magnesian</i>
+limestone.</p>
+
+<p>The beds of limestone, like those of the sandstone beneath, are
+horizontal or nearly so, and the upper formation lies conformably on the
+lower. The limestone does not contain water-worn
+<span class="pagenum"> <a name="Page_12" id="Page_12">[Pg 12]</a> </span>
+pebbles, and the surfaces of its layers are rarely if ever ripple-marked; yet the
+arrangement of the rock in distinct layers which carry fossils of marine
+animals shows that the limestone, like the sandstone beneath, was laid
+down in the sea. The bearing of this origin of the limestone on the
+development of the present valleys is the same as that of the sandstone.</p>
+
+<p> <i>Origin of the topography.</i>&mdash;The topography of the plain surrounding the
+quartzite ridges, especially that part lying west of Devil's lake, is
+then an erosion topography, developed by running water. Its chief
+characteristic is that every depression leads to a lower one, and that
+the form of the elevations, hills or ridges, is determined by the
+valleys. The valleys were made; the hills and ridges left. If the
+material carried away by the streams could be returned, the valleys
+would be filled to the level of the ridges which bound them. Were this
+done, the restored surface would be essentially flat. It is the
+sculpturing of such a plain, chiefly by running water, which has given
+rise to the present topography.</p>
+
+<p>In the development of this topography the more resistant limestone has
+served as a capping, tending to preserve the hills and ridges. Thus many
+of the hills, especially in the southwest portion of the area shown in
+Plate <a href="images/i02.jpg">II</a>, are found to have caps of the Lower
+Magnesian formation. Such hills usually have flat tops and steep or even
+precipitous slopes down to the base of the capping limestone, while the
+sandstone below, weathering more readily, gives the lower portions of the
+hills a gentler slope.</p>
+
+<p>The elevations of the hills and ridges above the axes of the valleys or,
+in other words, the relief of the plain is, on the average, about 300
+feet, only a few of the more prominent hills exceeding that figure.</p>
+
+<p>The topography east of the line between Kilbourn City and Prairie du Sac
+is not of the unmodified erosion type, as is made evident by marshes,
+ponds and lakes. The departure from the erosion type is due to a mantle
+of glacial drift which masks the topography of the bedded rock beneath.
+Its nature, and the topographic modifications which it has produced, will be
+more fully considered in a later part of this report (p. <a href="#Page_85">85</a>).
+<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IV.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/i04.jpg" width="300" height="111" alt="" />
+</div>
+<p class="center indent">
+The Lower Narrows of the Baraboo from a point on the South range.<br />
+<a href="images/i04.jpg">See larger image</a> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_13" id="Page_13">[Pg 13]</a> </span> <br /> </p>
+
+<h4>II. THE QUARTZITE RIDGES.</h4>
+
+<p> <i>Topography.</i>&mdash;The South or main quartzite range, about 23 miles in
+length and one to four miles in width, rises 500 feet to 800 feet above
+the surrounding sandstone plain. Its slopes are generally too steep for
+cultivation, and are clothed for the most part with a heavy growth of
+timber, the banks of forest being broken here and there by cultivated
+fields, or by the purple grey of the rock escarpments too steep for
+trees to gain a foothold. With the possible exception of the Blue mounds
+southwest of Madison, this quartzite range is the most obtrusive
+topographic feature of southern Wisconsin.</p>
+
+<p>As approached from the south, one of the striking features of the range
+is its nearly even crest. Extending for miles in an east-west direction,
+its summit gives a sky-line of long and gentle curves, in which the
+highest points are but little above the lowest. Viewed from the north,
+the evenness of the crest is not less distinct, but from this side it is
+seen to be interrupted by a notable break or notch at Devil's lake
+(Plates <a href="images/i05.jpg">V</a> and
+<a href="images/i37.jpg">XXXVII</a>). The pass across the range makes a right-angled
+turn in crossing the range, and for this reason is not seen from the
+south.</p>
+
+<p>The North or lesser quartzite range lying north of Baraboo is both
+narrower and lower than the south range, and its crest is frequently
+interrupted by notches or passes, some of which are wide. Near its
+eastern end occurs the striking gap known as the <i>Lower narrows</i> (Plate
+<a href="images/i04.jpg">IV</a>) through which the Baraboo river escapes to the northward, flowing
+thence to the Wisconsin. At this narrows the quartzite bluffs rise
+abruptly 500 feet above the river. At <i>a</i> and <i>b</i>, Plate
+<a href="images/i02.jpg">II</a>, there are
+similar though smaller breaks in the range, also occupied by streams.
+The connection between the passes and streams is therefore close.</p>
+
+<p>There are many small valleys in the sides of the quartzite ranges
+(especially the South range) which do not extend back
+<span class="pagenum"> <a name="Page_14" id="Page_14">[Pg 14]</a> </span>
+to their crests, and therefore do not occasion passes across them. The narrow valleys at
+<i>a</i> and <i>b</i> in Plate <a href="images/i37.jpg">XXXVII</a>, known as Parfrey's and Dorward's glens,
+respectively, are singularly beautiful gorges, and merit mention as well
+from the scenic as from the geologic point of view. Wider valleys, the
+heads of which do not reach the crest, occur on the flanks of the main
+range (as at <i>d</i> and <i>e</i>, Plate <a href="images/i02.jpg">II</a>) at many points. One such valley
+occurs east of the north end of the lake (<i>x</i>, Plate <a href="images/i37.jpg">XXXVII</a>), another
+west of the south end (<i>y</i>, Plate <a href="images/i37.jpg">XXXVII</a>), another on the north face of
+the west bluff west of the north end of the lake and between the East
+and West Sauk roads, and still others at greater distances from the lake
+in both directions. It is manifest that if the valleys were extended
+headward in the direction of their axes, they would interrupt the even
+crest. Many of these valleys, unlike the glens mentioned above, are very
+wide in proportion to their length. In some of these capacious valleys
+there are beds of Potsdam sandstone, showing that the valleys existed
+before the sand of the sandstone was deposited.</p>
+
+<p> <i>The structure and constitution of the ridges.</i>&mdash;The quartzite of the
+ridges is nothing more nor less than altered sandstone. Its origin dates
+from that part of geological time known to geologists as the Upper
+Huronian period (see p. <a href="#Page_23">23</a>). The popular local belief that the quartzite
+is of igneous origin is without the slightest warrant. It appears to
+have had its basis in the notion that Devil's lake occupies an extinct
+volcanic crater. Were this the fact, igneous rock should be found about
+it.</p>
+
+<p>Quartzite is sandstone in which the intergranular spaces have been
+filled with silica (quartz) brought in and deposited by percolating
+water subsequent to the accumulation of the sand. The conversion of
+sandstone into quartzite is but a continuation of the process which
+converts sand into sandstone. The Potsdam or any other sandstone
+formation might be converted into quartzite by the same process, and it
+would then be a <i>metamorphic</i> rock.</p>
+
+<p>Like the sandstone, the quartzite is in layers. This is perhaps nowhere
+so distinctly shown on a large scale as in the bluffs at<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. V.</p>
+<div class="figcenter" style="width: 350px;">
+<img src="images/i05.jpg" width="350" height="118" alt="" />
+</div>
+<p class="center indent">
+The Notch in the South quartzite range, at Devil's Lake.<br />
+<a href="images/i05.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VI.</p>
+<div class="figcenter" style="width: 231px;">
+<img src="images/i06.jpg" width="231" height="200" alt="" />
+</div>
+<p class="center indent">
+The east bluff of Devil's lake, showing the dip of quartzite (to the
+left), and talus above and below the level where the beds are shown.<br />
+<a href="images/i06.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+
+<p> <span class="pagenum"> <a name="Page_15" id="Page_15">[Pg 15]</a> </span>
+Devil's lake, and at the east end of the Devil's nose. On the East bluff
+of the lake, the stratification is most distinctly seen from the middle
+of the lake, from which point the photograph reproduced in Plate
+<a href="images/i06.jpg">VI</a> was taken.</p>
+
+<p>Unlike the sandstone and limestone, the beds of quartzite are not
+horizontal. The departure from horizontality, technically known as the
+<i>dip</i>, varies from point to point (Fig. <a href="images/fig04.jpg">4</a>). In the East bluff of the
+lake as shown in Plate <a href="images/i06.jpg">VI</a>, the dip is about 14° to the north. At the
+Upper and Lower narrows of the Baraboo (<i>b</i> and <i>c</i>, Plate
+<a href="images/i02.jpg">II</a>) the beds
+are essentially vertical, that is, they have a dip of about 90°. Between
+these extremes, many intermediate angles have been noted. Plate
+<a href="images/i07.jpg">VII</a>
+represents a view near Ablemans, in the Upper narrows, where the nearly
+vertical beds of quartzite are well exposed.</p>
+
+<p>The position of the beds in the quartzite is not always easy of
+recognition. The difficulty is occasioned by the presence of numerous
+cleavage planes developed in the rock after its conversion into
+quartzite. Some of these secondary cleavage planes are so regular and so
+nearly parallel to one another as to be easily confused with the bedding
+planes. This is especially liable to make determinations of the dip
+difficult, since the true bedding was often obscured when the cleavage
+was developed.</p>
+
+<p>In spite of the difficulties, the original stratification can usually be
+determined where there are good exposures of the rock. At some points
+the surfaces of the layers carry ripple marks, and where they are
+present, they serve as a ready means of identifying the bedding planes,
+even though the strata are now on edge. Layers of small pebbles are
+sometimes found. They were horizontal when the sands of the quartzite
+were accumulating, and where they are found they are sufficient to
+indicate the original position of the beds.</p>
+
+<p>Aside from the position of the beds, there is abundant evidence of
+dynamic action
+<a name="FNanchor_1_2" id="FNanchor_1_2"> </a> <a href="#Footnote_1_2" class="fnanchor">[2]</a>
+in the quartzite. Along the railway at Devil's lake,
+half a mile south of the Cliff House, thin <br /> <br /> <br />
+<span class="pagenum"> <a name="Page_16" id="Page_16">[Pg 16]</a> </span> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig04.jpg" width="400" height="60" alt="" />
+</div>
+<p class="center caption">
+Fig. 4. -- Diagram made by plotting the different dips now
+at hand along a section from A to B, Plate <a href="images/i02.jpg">II</a> and connecting
+them so as to show the structure indicated by the known data. The full
+lines, oblique or vertical, represent the beds of quartzite. The
+continuous line above them represents the present surface of the
+quartzite, while the dotted lines suggest the continuation of the beds
+which completed the great folds of which the present exposures appear to
+be remnants.<br />
+<a href="images/fig04.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig05.jpg" width="400" height="58" alt="" />
+</div>
+<p class="center indent">
+Fig. 5. -- A diagrammatic section showing the relation of
+the sandstone to the quartzite.<br />
+<a href="images/fig05.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VII.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i07.jpg" width="200" height="266" alt="" />
+</div>
+<p class="center indent">
+The East Bluff at the Upper Narrows of the Baraboo near Ablemans,
+showing the vertical position of the beds of quartzite. In the lower
+right-hand corner, above the bridge, appears some of the breccia
+ mentioned on p. <a href="#Page_18">18</a>.<br />
+<a href="images/i07.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VIII.</p>
+
+<div class="figcenter" style="width: 153px;">
+<img src="images/i08.jpg" width="153" height="200" alt="" />
+</div>
+<p class="center indent">
+Vertical shear zone in face of east bluff at Devil's lake.<br />
+<a href="images/i08.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_17" id="Page_17">[Pg 17]</a> </span>
+zones of schistose rock may be seen parallel to the bedding planes.
+These zones of schistose rock a few inches in thickness were developed
+from the quartzite by the slipping of the rock on either side. This
+slipping presumably occurred during the adjustment of the heavy beds of
+quartzite to their new positions, at the time of tilting and folding,
+for no thick series of rock can be folded without more or less slipping
+of the layers on one another. The slipping (adjustment) takes place
+along the weaker zones. Such zones of movement are sometimes known as
+<i>shear zones</i>, for the rock on the one side has been sheared (slipped)
+over that on the other.</p>
+
+<p>Near the shear zones parallel to the bedding planes, there is one
+distinct vertical shear zone (Plate <a href="images/i08.jpg">VIII</a>)
+three to four feet in width. It is exposed to a height of fully twenty-five
+feet. Along this zone the quartzite has been broken into angular fragments,
+and at places the crushing of the fragments has produced a "friction clay."
+Slipping along vertical zones would be no necessary part of folding, though
+it might accompany it. On the other hand, it might have preceded or followed the
+folding.</p>
+
+<p>Schistose structure probably does not always denote shearing, at least
+not the shearing which results from folding. Extreme pressure is likely
+to develop schistosity in rock, the cleavage planes being at right
+angles to the direction of pressure. It is not always possible to say
+how far the schistosity of rock at any given point is the result of
+shear, and how far the result of pressure without shear.</p>
+
+<p>Schistose structure which does not appear to have resulted from shear,
+at least not from the shear involved in folding, is well seen in the
+isolated quartzite mound about four miles southwest of Baraboo on the
+West Sauk road (<i>f</i>, Plate <a href="images/i02.jpg">II</a>). These
+quartzite schists are to be looked on as metamorphosed quartzite, just as
+quartzite is metamorphosed sandstone.</p>
+
+<p>At the Upper narrows of the Baraboo also (<i>b</i>, Plate
+<a href="images/i02.jpg">II</a>), evidence
+of dynamic action is patent. Movement along bedding planes with
+attendant development of quartz schist has occurred here as at the lake
+(Plate <a href="images/i09.jpg">IX</a>). Besides the schistose belts, a
+<span class="pagenum"> <a name="Page_18" id="Page_18">[Pg 18]</a> </span>
+wide zone of quartzite exposed in the bluffs at this locality has been crushed into angular
+fragments, and afterwards re-cemented by white quartz deposited from
+solution by percolating waters (Plate <a href="images/i10.jpg">X</a>). This quartzite is said to be
+brecciated. Within this zone there are spots where the fragments of
+quartzite are so well rounded as to simulate water-worn pebbles. Their
+forms appear to be the result of the wear of the fragments on one
+another during the movements which followed the crushing. Conglomerate
+originating in this way is <i>friction conglomerate</i> or <i>Reibungsbreccia</i>.</p>
+
+<p>The crushing of the rock in this zone probably took place while the beds
+were being folded; but the brecciated quartzite formed by the
+re-cementation of the fragments has itself been fractured and broken in
+such a manner as to show that the formation has suffered at least one
+dynamic movement since the development of the breccia. That these
+movements were separated by a considerable interval of time is shown by
+the fact that the re-cementation of the fragmental products of the first
+movement preceded the second.</p>
+
+<p>What has been said expresses the belief of geologists as to the origin
+of quartzite and quartz schists; but because of popular misconception on
+the point it may here be added that neither the changing of the
+sandstone into quartzite, nor the subsequent transformation of the
+quartzite to schist, was due primarily to heat. Heat was doubtless
+generated in the mechanical action involved in these changes, but it was
+subordinate in importance, as it was secondary in origin.</p>
+
+<p>Igneous rock is associated with the quartzite at a few points. At <i>g</i>
+and <i>h</i>, Plate <a href="images/i02.jpg">II</a> there are considerable masses of porphyry,
+sustaining such relations to the quartzite as to indicate that they were
+intruded into the sedimentary beds after the deposition of the latter.<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IX.</p>
+<div class="figcenter" style="width: 172px;">
+<img src="images/i09.jpg" width="172" height="250" alt="" />
+</div>
+<p class="center indent">
+A mass of quartzite <i>in situ</i>, in the road through the Upper Narrows
+near Ableman's. The bedding, which is nearly vertical, is indicated by
+the shading, while the secondary cleavage approaches horizontality.<br />
+<a href="images/i09.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. X.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i10.jpg" width="200" height="171" alt="" />
+</div>
+<p class="center indent">
+Brecciated quartzite near Ablemans in the Upper Narrows. The darker
+parts are quartzite, the lighter parts the cementing quartz.<br />
+<a href="images/i10.jpg">See larger image</a> <br /> </p>
+
+<p> <br /> <br /> <br />
+<span class="pagenum"> <a name="Page_19" id="Page_19">[Pg 19]</a> </span> </p>
+
+<h4>III. RELATIONS OF THE SANDSTONE OF THE PLAIN TO THE QUARTZITE OF THE
+RIDGES.</h4>
+
+<p>The horizontal beds of Potsdam sandstone may be traced up to the bases
+of the quartzite ranges, where they may frequently be seen to abut
+against the tilted beds of quartzite. Not only this, but isolated
+patches of sandstone lie on the truncated edges of the dipping beds of
+quartzite well up on the slopes, and even on the crest of the ridge
+itself. In the former position they may be seen on the East bluff at
+Devil's lake, where horizontal beds of conglomerate and sandstone rest
+on the layers of quartzite which dip 14° to the north.</p>
+
+<p>The stratigraphic relations of the two formations are shown in Fig. <a href="images/fig05.jpg">5</a>
+which represents a diagrammatic section from A to B, Plate <a href="images/i02.jpg">II</a>.
+Plate <a href="images/i11.jpg">XI</a>
+is reproduced from a photograph taken in the Upper narrows of the
+Baraboo near Ablemans, and shows the relations as they appear in the
+field. The quartzite layers are here on edge, and on them rest the
+horizontal beds of sandstone and conglomerate. Similar stratigraphic
+relations are shown at many other places. This is the relationship of
+<i>unconformity</i>.</p>
+
+<p>Such an unconformity as that between the sandstone and the quartzite of
+this region shows the following sequence of events: (1) the quartzite
+beds were folded and lifted above the sea in which the sand composing
+them was originally deposited; (2) a long period of erosion followed,
+during which the crests of the folds were worn off; (3) the land then
+sank, allowing the sea to again advance over the region; (4) while the
+sea was here, sand and gravel derived from the adjacent lands which
+remained unsubmerged, were deposited on its bottom. These sands became
+the Potsdam sandstone.</p>
+
+<p>This sequence of events means that between the deposition of the
+quartzite and the sandstone, the older formation was disturbed and
+eroded. Either of these events would have produced an unconformity; the
+two make it more pronounced. That the disturbance of the older formation
+took place before the later
+<span class="pagenum"> <a name="Page_20" id="Page_20">[Pg 20]</a> </span>
+sandstone was deposited is evident from the fact that the latter formation
+was not involved in the movements which disturbed the former.</p>
+
+<p>Although the sandstone appears in patches on the quartzite ranges, it is
+primarily the formation of the surrounding plains, occupying the broad
+valley between the ranges, and the territory surrounding them. The
+quartzite, on the other hand, is the formation of the ridges, though it
+outcrops at a few points in the plain. (Compare Plates <a href="images/i02.jpg">II</a> and
+<a href="images/i37.jpg">XXXVII</a>.) The striking topographic contrasts between
+the plains and the ridges is thus seen to be closely related to the rock formations
+involved. It is the hard and resistant quartzite which forms the ridges, and
+the less resistant sandstone which forms the lowlands about them.</p>
+
+<p>That quartzite underlies the sandstone of the plain is indicated by the
+occasional outcrops of the former rock on the plain, and from the fact
+that borings for deep wells have sometimes reached it where it is not
+exposed.</p>
+
+<p>The sandstone of the plain and the quartzite of the ridges are not
+everywhere exposed. A deep but variable covering of loose material or
+<i>mantle rock (drift</i>) is found throughout the eastern part of the area,
+but it does not extend far west of Baraboo. This mantle rock is so thick
+and so irregularly disposed that it has given origin to small hills and
+ridges. These elevations are superimposed on the erosion topography of
+the underlying rock, showing that the drift came into the region after
+the sandstone, limestone, and quartzite had their present relations, and
+essentially their present topography. Further consideration will be
+given to the drift in a later part of this report.<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XI.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i11.jpg" width="200" height="136" alt="" />
+</div>
+<p class="center indent">
+The northeast wall of the Upper Narrows, north of Ableman's, showing the
+horizontal Potsdam sandstone and conglomerate lying unconformably on the
+quartzite, the beds of which are vertical.<br />
+<a href="images/i11.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <br /> <br /> <br />
+<span class="pagenum"> <a name="Page_21" id="Page_21">[Pg 21]</a> </span> </p>
+<h1>PART II.</h1>
+
+<hr style="width: 45%;" />
+
+
+<h1>HISTORY OF THE TOPOGRAPHY.</h1>
+
+<p> <span class="pagenum"> <a name="Page_22" id="Page_22">[Pg 22]</a> </span> <br /> </p>
+
+<p>  <span class="pagenum"> <a name="Page_23" id="Page_23">[Pg 23]</a> </span> </p>
+
+<h2>CHAPTER II.</h2>
+<p> <br /> <br /> </p>
+
+<h4>OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS WHICH SHOW THEMSELVES AT
+THE SURFACE.</h4>
+
+<p> <br /> </p>
+
+<h4>I. THE PRE-CAMBRIAN HISTORY OF THE QUARTZITE.</h4>
+
+<p> <br /> <i>From loose sand to quartzite.</i>&mdash;To understand the geography of a region
+it is necessary to understand the nature of the materials, the sculpture
+of which has made the geography.</p>
+
+<p>It has already been indicated (p. <a href="#Page_14">14</a>) that the Huronian quartzite of
+which the most prominent elevations of this region are composed, was
+once loose sand. Even at the risk of repetition, the steps in its
+history are here recounted. The source of the sand was probably the
+still older rocks of the land in the northern part of Wisconsin. Brought
+down to the sea by rivers, or washed from the shores of the land by
+waves, the sand was deposited in horizontal or nearly horizontal beds at
+the bottom of the shallow water which then covered central and southern
+Wisconsin. Later, perhaps while it was still beneath the sea, the sand
+was converted into sandstone, the change being effected partly by
+compression which made the mass of sand more compact, but chiefly by the
+cementation of its constituent grains into a coherent mass. The water
+contained in the sand while consolidation was in progress, held in
+solution some slight amount of silica, the same material of which the
+grains of sand themselves are composed. Little by little this silica in
+solution was deposited on the surfaces of the sand grains, enlarging
+them, and at the same time binding them together. Thus the sand became
+sandstone. Continued deposition of silica between and around the grains
+finally filled the interstitial spaces, and when this process was
+completed, the sandstone had been converted
+<span class="pagenum"> <a name="Page_24" id="Page_24">[Pg 24]</a> </span>
+into quartzite. While quartzite is a metamorphic sandstone, it is not to be
+understood that sandstone cannot be metamorphosed in other ways.</p>
+
+<p> <i>Uplift and deformation. Dynamic metamorphism.</i>&mdash;After the deposition of
+the sands which later became the quartzite, the beds were uplifted and
+deformed, as their present positions and relations show (p. <a href="#Page_16">16</a>). It is
+not possible to say how far the process of transformation of sand into
+quartzite was carried while the formation was still beneath the shallow
+sea in which it was deposited. The sand may have been changed to
+sandstone, and the sandstone to quartzite, before the sea bottom was
+converted into land, while on the other hand, the formation may have
+been in any stage of change from sand to quartzite, when that event
+occurred. If the process of change was then incomplete, it may have been
+continued after the sea retired, by the percolating waters derived from
+the rainfall of the region.</p>
+
+<p>Either when first converted into land, or at some later time, the beds
+of rock were folded, and suffered such other changes as attend profound
+dynamic movements. The conversion of the sandstone into quartzite
+probably preceded the deformation, since many phenomena indicate that
+the rock was quartzite and not sandstone when the folding took place.
+For example, the crushing of the quartzite (now re-cemented into
+brecciated quartzite) at Ablemans probably dates from the orogenic
+movements which folded the quartzite, and the fractured bits of rock
+often have corners and edges so sharp as to show that the rock was
+thoroughly quartzitic when the crushing took place.</p>
+
+<p>The uplift and deformation of the beds was probably accomplished slowly,
+but the vertical and highly tilted strata show that the changes were
+profound (see Fig. <a href="images/fig04.jpg">4</a>).</p>
+
+<p>The dynamic metamorphism which accompanied this profound deformation has
+already been referred to (p. <a href="#Page_15">15</a>). The folding of the beds involved the
+slipping of some on others, and this resulted in the development of
+quartz schist along the lines of severest movement. Changes effected in
+the texture and structure of the rock under such conditions constitute <i>dynamic </i>
+<span class="pagenum"> <a name="Page_25" id="Page_25">[Pg 25]</a> </span>
+<i>metamorphism.</i> In general, the metamorphic changes effected by
+dynamic action are much more profound than those brought about in
+other ways, and most rocks which have been profoundly metamorphosed,
+were changed in this way. Dynamic action generates heat, but contrary to
+the popular notion, the heat involved in profound metamorphism is
+usually secondary, and the dynamic action fundamental.</p>
+
+<p>At the same time that quartz schist was locally developed from the
+quartzite, crushing probably occurred in other places. This is
+<i>demorphism</i>, rather than metamorphism.</p>
+
+<p> <i>Erosion of the quartzite.</i>&mdash;When the Huronian beds were raised to the
+estate of land, the processes of erosion immediately began to work on
+them. The heat and the cold, the plants and the animals, the winds, and
+especially the rain and the water which came from the melting of the
+snow, produced their appropriate effects. Under the influence of these
+agencies the surface of the rock was loosened by weathering, valleys
+were cut in it by running water, and wear and degradation went on at all
+points.</p>
+
+<p>The antagonistic processes of uplift and degradation went on for
+unnumbered centuries, long enough for even the slow processes involved
+to effect stupendous results. Degradation was continuous after the
+region became land, though uplift may not have been. On the whole,
+elevation exceeded degradation, for some parts of the quartzite finally
+came to stand high above the level of the sea,&mdash;the level to which all
+degradation tends.</p>
+
+<p>Fig. <a href="images/fig04.jpg">4</a> conveys some notion of the amount of rock which was
+removed from the quartzite folds about Baraboo during this long period
+of erosion. The south range would seem to represent the stub of one side
+of a great anticlinal fold, a large part of which (represented by the
+dotted lines) was carried away, while the north range may be the core of
+another fold, now exposed by erosion.</p>
+
+<p>Some idea of the geography of the quartzite at the close of this period
+of erosion may be gained by imagining the work of later times undone.
+The younger beds covering the quartzite
+<span class="pagenum"> <a name="Page_26" id="Page_26">[Pg 26]</a> </span>
+of the plains have a thickness varying from zero to several hundred feet,
+and effectually mask the irregularities of the surface of the subjacent quartzite.
+Could they be removed, the topography of the quartzite would be disclosed, and found
+to have much greater relief than the present surface; that is, the
+vertical distance between the crest of the quartzite ridge, and the
+surface of the quartzite under the surrounding lowlands, would be
+greater than that between the same crest and the surface of the
+sandstone. But even this does not give the full measure of the relief of
+the quartzite at the close of the long period of erosion which followed
+its uplift, for allowance must be made for the amount of erosion which
+the crests of the quartzite ranges have suffered since that time. The
+present surface therefore does not give an adequate conception of the
+irregularity of the surface at the close of the period of erosion which
+followed the uplift and deformation of the quartzite. So high were the
+crests of the quartzite ranges above their surroundings at that time,
+that they may well be thought of as mountainous. From this point of
+view, the quartzite ranges of today are the partially buried mountains
+of the pre-Potsdam land of south central Wisconsin.</p>
+
+<p>When the extreme hardness of the quartzite is remembered and also the
+extent of the erosion which affected it (Fig. <a href="images/fig04.jpg">4</a>)
+before the next succeeding formation was deposited, it is safe to conclude that the
+period of erosion was very long.</p>
+
+<p> <i>Thickness of the quartzite.</i>&mdash;The thickness of the quartzite is not
+known, even approximately. The great thickness in the south range suggested by the
+diagram (Fig. <a href="images/fig04.jpg">4</a>) may perhaps be an exaggeration.
+Faulting which has not been discovered may have occurred, causing repetition of beds
+at the surface (Fig. <a href="images/fig06.jpg">6</a>), and so an exaggerated
+appearance of thickness. After all allowances have been made, it is still evident
+that the thickness of the quartzite is very great.</p>
+
+<p>  <br /> <br /> <br /> <span class="pagenum"> <a name="Page_27" id="Page_27">[Pg 27]</a> </span> </p>
+<h4>II. THE HISTORY OF THE PALEOZOIC STRATA.</h4>
+
+<p> <i>The subsidence.</i>&mdash;Following the long period of erosion, the irregular
+and almost mountainous area of central Wisconsin was depressed
+sufficiently to submerge large areas which had been land. The subsidence
+was probably slow, and as the sea advanced from the south, it covered
+first the valleys and lowlands, and later the lower hills and ridges,
+while the higher hills and ridges of the quartzite stood as islands in
+the rising sea. Still later, the highest ridges of the region were
+themselves probably submerged.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig06.jpg" width="300" height="81" alt="" />
+</div>
+<p class="center indent">
+Fig. 6. -- A diagrammatic cross-section, showing how, by
+faulting, the apparent thickness of the quartzite would be increased.<br />
+<a href="images/fig06.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <i>The Potsdam sandstone (and conglomerate).</i>&mdash;So soon as the sea began to
+overspread the region, its bottom became the site of deposition, and the
+deposition continued as long as the submergence lasted. It is to the
+sediments deposited during the earlier part of this submergence that the
+name <i>Potsdam</i> is given.</p>
+
+<p>The sources of the sediments are not far to seek. As the former land was
+depressed beneath the sea, its surface was doubtless covered with the
+products of rock decay, consisting of earths, sands, small bits and
+larger masses of quartzite. These materials, or at least the finer
+parts, were handled by the waves of the shallow waters, for they were at
+first shallow, and assorted and re-distributed. Thus the residuary
+products on the submerged surface, were one source of sediments.</p>
+
+<p>From the shores also, so long as land areas remained, the waves derived
+sediments. These were composed in part of the weathered products of the
+rock, and in part of the undecomposed
+<span class="pagenum"> <a name="Page_28" id="Page_28">[Pg 28]</a> </span>
+rock against which the waves beat, after the loose materials had been worn away.
+These sediments derived from the shore were shifted, and finally mingled with those
+derived from the submerged surface.</p>
+
+<p>So long as any part of the older land remained above the water, its
+streams brought sediments to the sea. These also were shifted by the
+waves and shore currents, and finally deposited with the others on the
+eroded surface of the quartzite. Thus sediments derived in various ways,
+but inherently essentially similar, entered into the new formation.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig07.jpg" width="300" height="60" alt="" />
+</div>
+<p class="center indent">
+Fig. 7. -- Diagram to illustrate the theoretical disposition of sediments about an island.<br />
+<a href="images/fig07.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig08.jpg" width="300" height="57" alt="" />
+</div>
+<p class="center indent">
+Fig. 8. -- Same as Fig. <a href="images/fig07.jpg">7</a>, except that the land has been depressed.<br />
+<a href="images/fig08.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p>The first material to be deposited on the surface of the quartzite as it
+was submerged, was the coarsest part of the sediment. Of the sediment
+derived by the waves from the coasts, and brought down to the sea by
+rivers, the coarsest would at each stage be left nearest the shore,
+while the finer was carried progressively farther and farther from it.
+Thus at each stage the sand was deposited farther from the shore than
+the gravel, and the mud farther than the sand, where the water was so
+deep that the bottom was subject to little agitation by waves. The
+theoretical distribution of sediments about an island as it was
+depressed, is illustrated by the following diagrams, Figs.
+<a href="images/fig07.jpg">7</a> and <a href="images/fig08.jpg">8</a>. It
+will be seen that the surface of the quartzite is immediately overlain
+by conglomerate, but that the conglomerate near its top is younger than
+that near its base.</p>
+
+<p> <span class="pagenum"> <a name="Page_29" id="Page_29">[Pg 29]</a> </span>
+In conformity with this natural distribution of sediments, the basal
+beds of the Potsdam formation are often conglomeratic (Fig. <a href="images/fig09.jpg">9</a>,
+Plate <a href="#i03">III Fig. 2</a>, and Plate <a href="images/i25.jpg">XXV</a>).
+This may oftenest be seen near the quartzite ridges, for here only is the base of the formation
+commonly exposed. The pebbles and larger masses of the conglomerate are
+quartzite, like that of the subjacent beds, and demonstrate the source
+of at least some of the material of the younger formation. That the
+pebbles and bowlders are of quartzite is significant, for it shows that
+the older formation had been changed from sandstone to quartzite, before
+the deposition of the Potsdam sediments. The sand associated with the
+pebbles may well have come from the breaking up of the quartzite, though
+some of it may have been washed in from other sources by the waters in
+which the deposition took place.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/fig09.jpg" width="250" height="162" alt="" />
+</div>
+<p class="center indent">
+Fig. 9. -- Sketch showing relation of basal Potsdam
+conglomerate and sandstone to the quartzite, on the East bluff at
+Devil's lake, behind the Cliff house.<br />
+<a href="images/fig09.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>The basal conglomerate may be seen at many places, but nowhere about
+Devil's lake is it so well exposed as at Parfrey's glen (<i>a</i>, Plate
+<a href="images/i37.jpg">XXXVII</a>), where the rounded stones of which it is composed vary
+from pebbles, the size of a pea, to bowlders more than three feet in
+diameter. Other localities where the conglomerates may be seen to
+advantage are Dorward's glen (<i>b</i>, Plate <a href="images/i37.jpg">XXXVII</a>), the East bluff at
+Devil's lake just above the Cliff house, and at the Upper narrows of the
+Baraboo, above Ablemans.</p>
+
+<p> <span class="pagenum"> <a name="Page_30" id="Page_30">[Pg 30]</a> </span>
+While the base of the Potsdam is conglomeratic in many places, the main
+body of it is so generally sandstone that the formation as a whole is
+commonly known as the Potsdam sandstone.</p>
+
+<p>The first effect of the sedimentation which followed submergence was to
+even up the irregular surface of the quartzite, for the depressions in
+the surface were the first to be submerged, and the first to be filled.
+As the body of sediment thickened, it buried the lower hills and the
+lower parts of the higher ones. The extent to which the Potsdam
+formation buried the main ridge may never be known. It may have buried
+it completely, for as already stated (p. <a href="#Page_19">19</a>) patches of sandstone are
+found upon the main range. These patches make it clear that some
+formation younger than the quartzite once covered essentially all of the
+higher ridge. Other evidence to be adduced later, confirms this
+conclusion. It has, however, not been demonstrated that the high-level
+patches of sandstone are Potsdam.</p>
+
+<p>There is abundant evidence that the subsidence which let the Potsdam
+seas in over the eroded surface of the Huronian quartzite was gradual.
+One line of evidence is found in the cross-bedding of the sandstone
+(Plate <a href="images/i12.jpg">XII</a>) especially well exhibited in the Dalles of the Wisconsin.
+The beds of sandstone are essentially horizontal, but within the
+horizontal beds there are often secondary layers which depart many
+degrees from horizontality, the maximum being about 24°. Plates
+<a href="images/i27.jpg">XXVII</a> and <a href="images/i12.jpg">XII</a>
+give a better idea of the structure here referred to than verbal description can.</p>
+
+<p>The explanation of cross-bedding is to be found in the varying
+conditions under which sand was deposited. Cross-bedding denotes shallow
+water, where waves and shore currents were effective at the bottom where
+deposition is in progress. For a time, beds were deposited off shore at
+a certain angle, much as in the building of a delta (Fig. <a href="images/fig10.jpg">10</a>). Then by
+subsidence of the bottom, other layers with like structure were
+deposited over the first. By this sequence of events, the dip of the
+secondary layers should be toward the open water, and in this region
+their dip is<br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XII.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/i12.jpg" width="300" height="148" alt="" />
+</div>
+<p class="center indent">
+Steamboat rock -- an island in the Dalles of the Wisconsin.<br />
+<a href="images/i12.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_31" id="Page_31">[Pg 31]</a> </span>
+generally to the south. At any stage of deposition the waves engendered
+by storms were liable to erode the surface of the deposits already made,
+and new layers, discordant with those below, were likely to be laid down
+upon them. The subordinate layers of each deposit might dip in any
+direction. If this process were repeated many times during the
+submergence, the existing complexity would be explained.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig10.jpg" width="400" height="76" alt="" />
+</div>
+<p class="center indent">
+Fig. 10. -- A diagrammatic cross-section of a delta.<br />
+<a href="images/fig10.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>The maximum known thickness of the Potsdam sandstone in Wisconsin is
+about 1,000 feet, but its thickness in this region is much less. Where
+not capped by some younger formation, its upper surface has suffered
+extensive erosion, and the present thickness therefore falls short of
+the original. The figures given above may not be too great for the
+latter.</p>
+
+<p> <i>The Lower Magnesian limestone.</i>&mdash;The conditions of sedimentation
+finally changed in the area under consideration. When the sand of the
+sandstone was being deposited, adjacent lands were the source whence the
+sediments were chiefly derived. The evidence that the region was sinking
+while the sand was being deposited shows that the land masses which were
+supplying the sand, were becoming progressively smaller. Ultimately the
+sand ceased to be washed out to the region here described, either
+because the water became too deep
+<a name="FNanchor_1_3" id="FNanchor_1_3"> </a> <a href="#Footnote_1_3" class="fnanchor">[3]</a>,
+or because the source of supply
+was too distant. When these relations were brought about, the conditions
+were favorable for the deposition of sediments which were to become
+limestone. These sediments consisted chiefly of the shells of marine
+life, together with an unknown amount of lime carbonate precipitated
+from the waters of the sea. The limestone contains no coarse, and but
+little fine material derived from the land, and the surfaces of its layers
+<span class="pagenum"> <a name="Page_32" id="Page_32">[Pg 32]</a> </span>
+are rarely if ever ripple-marked. The materials of which it is
+made must therefore have been laid down in quiet waters which were
+essentially free from land-derived sediments. The depth of the water in
+which it was deposited was not, however, great, for the fossils are not
+the remains of animals which lived in abysmal depths.</p>
+
+<p>The deposition of limestone sediments following the deposition of the
+Potsdam sands, does not necessarily mean that there was more or
+different marine life while the younger formation was making, but only
+that the shells, etc., which before had been mingled with the sand,
+making fossiliferous sandstone, were now accumulated essentially free
+from land-derived sediment, and therefore made limestone.</p>
+
+<p>Like the sandstone beneath, the limestone formation has a wide
+distribution outside the area here under discussion, showing that
+conditions similar to those of central Wisconsin were widely distributed
+at this time.</p>
+
+<p>The beds of limestone are conformable on those of the sandstone, and the
+conformable relations of the two formations indicate that the deposition
+of the upper followed that of the lower, without interruption.</p>
+
+<p>The thickness of the Lower Magnesian limestone varies from less than 100
+to more than 200 feet, but in this region its thickness is nearer the
+lesser figure than the larger. The limestone is now present only in the
+eastern and southern parts of the area, though it originally covered the
+whole area.</p>
+
+<p> <i>The St. Peters sandstone.</i>&mdash;Overlying the Lower Magnesian limestone at
+a few points, are seen remnants of St. Peters sandstone. The constitution of this
+formation shows that conditions of sedimentation had again changed, so that
+sand was again deposited where the conditions had been favorable to the deposition
+of limestone but a short time before. This formation has been recognized at but two
+places (<i>d</i> and <i>e</i>) within the area shown on Plate
+<a href="images/i37.jpg">XXXVII</a>, but the relations at these
+two points are such as to lead to the conclusion that the formation may
+once have covered the entire region. This sandstone formation is very like
+<span class="pagenum"> <a name="Page_33" id="Page_33">[Pg 33]</a> </span>
+the sandstone below. Its materials doubtless came from the lands
+which then existed. The formation is relatively thin, ranging from
+somewhat below to somewhat above 100 feet.</p>
+
+<p>The change from the deposition of limestone sediments to sand may well
+have resulted from the shoaling of the waters, which allowed the sand to
+be carried farther from shore. Rise of the land may have accompanied the
+shoaling of the waters, and the higher lands would have furnished more
+and coarser sediments to the sea.</p>
+
+<div class="figright" style="width: 254px;">
+<img src="images/fig11.jpg" width="254" height="600" alt="Fig. 11. -- The geological formations of southern Wisconsin
+in the order of their occurrence. Not all of these are found about
+ Devil's lake." />
+<span class="caption">Fig. 11. -- The geological formations of southern Wisconsin
+in the order of their occurrence. Not all of these are found about
+ Devil's lake.</span>
+</div>
+
+<p> <i>Younger beds.</i>&mdash;That formations younger than the St. Peters sandstone
+once overlaid this part of Wisconsin is almost certain, though no
+remnants of them now exist. Evidence which cannot be here detailed
+<a name="FNanchor_1_4" id="FNanchor_1_4"> </a> <a href="#Footnote_1_4" class="fnanchor">[4]</a>
+indicates that sedimentation about the quartzite ridges went on not only
+until the irregularities of surface were evened up, but until even the
+highest peaks of the quartzite were buried, and that formations as high
+in the series as the Niagara limestone once overlay their crests. Before
+this condition was reached, the quartzite ridges had of course ceased to
+be islands, and at the same time had ceased to be a source of supply of
+sediments. The aggregate thickness of the Paleozoic beds in the region,
+as first deposited, was probably not less than 1,500 feet, and it may
+have been much more. This thickness would have buried the crests of the
+quartzite ridges under several hundred feet of sediment (see Fig.
+<a href="images/fig11.jpg">11</a>).</p>
+
+<p> <span class="pagenum"> <a name="Page_34" id="Page_34">[Pg 34]</a> </span>
+It is by no means certain that south central Wisconsin was continuously
+submerged while this thick series of beds was being deposited. Indeed,
+there is good reason to believe that there was at least one period of
+emergence, followed, after a considerable lapse of time, by
+re-submergence and renewed deposition, before the Paleozoic series of
+the region was complete. These movements, however, had little effect on
+the geography of the region.</p>
+
+<p>Finally the long period of submergence, during which several changes in
+sedimentation had taken place, came to an end, and the area under
+discussion was again converted into land.</p>
+
+<p> <i>Time involved.</i>&mdash;Though it cannot be reduced to numerical terms, the
+time involved in the deposition of these several formations of the
+Paleozoic must have been very long. It is probably to be reckoned in
+millions of years, rather than in denominations of a lower order.</p>
+
+<p> <i>Climatic conditions.</i>&mdash;Little is known concerning the climate of this
+long period of sedimentation. Theoretical considerations have usually
+been thought to lead to the conclusion that the climate during this part
+of the earth's history was uniform, moist, and warm; but the conclusion
+seems not to be so well founded as to command great confidence.</p>
+
+<p> <i>The uplift.</i>&mdash;After sedimentation had proceeded to some such extent as
+indicated, the sea again retired from central Wisconsin. This may have
+been because the sea bottom of this region rose, or because the sea
+bottom in other places was depressed, thus drawing off the water. The
+topography of this new land, like the topography of those portions of
+the sea bottom which are similarly situated, must have been for the most
+part level. Low swells and broad undulations may have existed, but no
+considerable prominences, and no sudden change of slope. The surface was
+probably so flat that it would have been regarded as a level surface had
+it been seen.</p>
+
+<p>The height to which the uplift carried the new land surface at the
+outset must ever remain a matter of conjecture. Some estimate may be
+made of the amount of uplift which the region
+<span class="pagenum"> <a name="Page_35" id="Page_35">[Pg 35]</a> </span>
+has suffered since the beginning of this uplift, but it is unknown how much
+took place at this time, and how much in later periods of geological history.</p>
+
+<p>The new land surface at once became the site of new activities. All
+processes of land erosion at once attacked the new surface, in the
+effort to carry its materials back to the sea. The sculpturing of this
+plain, which, with some interruption, has continued to the present day,
+has given the region the chief elements of its present topography. But
+before considering the special history of erosion in this region, it may
+be well to consider briefly the general principles and processes of land
+degradation.</p>
+
+
+<p> <br /> <br /> <br /> <br />
+<span class="pagenum"> <a name="Page_36" id="Page_36">[Pg 36]</a> </span> </p>
+<h2>CHAPTER III.</h2>
+<p> <br /> </p>
+
+<h4>GENERAL OUTLINE OF RAIN AND RIVER EROSION.</h4>
+
+
+<p> <i>Elements of erosion.</i>&mdash;The general process of subaerial erosion is
+divisible into the several sub-processes of weathering, transportation,
+and corrasion.
+<a name="FNanchor_1_5" id="FNanchor_1_5"> </a> <a href="#Footnote_1_5" class="fnanchor">[5]</a> </p>
+
+<p> <i>Weathering</i> is the term applied to all those processes which
+disintegrate and disrupt exposed surfaces of rock. It is accomplished
+chiefly by solution, changes in temperature, the wedge-work of ice and
+roots, the borings of animals, and such chemical changes as surface
+water and air effect. The products of weathering are transported by the
+direct action of gravity, by glaciers, by winds, and by running water.
+Of these the last is the most important.</p>
+
+<p> <i>Corrasion</i> is accomplished chiefly by the mechanical wear of streams,
+aided by the hard fragments such as sand, gravel and bowlders, which
+they carry. The solution effected by the waters of a stream may also be
+regarded as a part of corrasion. Under ordinary circumstances solution
+by streams is relatively unimportant, but where the rock is relatively
+soluble, and where conditions are not favorable for abrasion, solution
+may be more important than mechanical wear.</p>
+
+<p>So soon as sea bottom is raised to the estate of land, it is attacked by
+the several processes of degradation. The processes of weathering at
+once begin to loosen the material of the surface if it be solid; winds
+shift the finer particles about, and with the first shower
+transportation by running water begins. Weathering prepares the material
+for transportation and transportation leads to corrasion. Since the goal
+of all material transported by
+<span class="pagenum"> <a name="Page_37" id="Page_37">[Pg 37]</a> </span>
+running water is the sea, subaerial erosion means degradation of the surface.</p>
+
+<p> <i>Erosion without valleys.</i>&mdash;In the work of degradation the valley
+becomes the site of greatest activity, and in the following pages
+especial attention is given to the development of valleys and to the
+phases of topography to which their development leads.</p>
+
+<p>If a new land surface were to come into existence, composed of materials
+which were perfectly homogeneous, with slopes of absolute uniformity in
+all directions, and if the rain, the winds and all other surface
+agencies acted uniformly over the entire area, valleys would not be
+developed. That portion of the rainfall which was not evaporated and did
+not sink beneath the surface, would flow off the land in a sheet. The
+wear which it would effect would be equal in all directions from the
+center. If the angle of the slope were constant from center to shore, or
+if it increased shoreward, the wear effected by this sheet of water
+would be greatest at the shore, because here the sheet of flowing water
+would be deepest and swiftest, and therefore most effective in
+corrasion.</p>
+
+<p> <i>The beginning of a valley.</i>&mdash;But land masses as we know them do not
+have equal and uniform slopes to the sea in all directions, nor is the
+material over any considerable area perfectly homogeneous. Departure
+from these conditions, even in the smallest degree, would lead to very
+different results.</p>
+
+<p>That the surface of newly emerged land masses would, as a rule, not be
+rough, is evident from the fact that the bottom of the sea is usually
+rather smooth. Much of it indeed is so nearly plane that if the water
+were withdrawn, the eye would scarcely detect any departure from
+planeness. The topography of a land mass newly exposed either by its own
+elevation or by the withdrawal of the sea, would ordinarily be similar
+to that which would exist in the vicinity of Necedah and east of Camp
+Douglas, if the few lone hills were removed, and the very shallow
+valleys filled. Though such a surface would seem to be moderately
+uniform as to its slopes, and homogeneous as to its material,
+<span class="pagenum"> <a name="Page_38" id="Page_38">[Pg 38]</a> </span>
+neither the uniformity nor the homogeneity are perfect, and the rain water would
+not run off in sheets, and the wear would not be equal at all points.</p>
+
+<p>Let it be supposed that an area of shallow sea bottom is raised above
+the sea, and that the elevation proceeds until the land has an altitude
+of several hundred feet. So soon as it appears above the sea, the rain
+falling upon it begins to modify its surface. Some of the water
+evaporates at once, and has little effect on the surface; some of it
+sinks beneath the surface and finds its way underground to the sea; and
+some of it runs off over the surface and performs the work
+characteristic of streams. So far as concerns modifications of the
+surface, the run-off is the most important part.</p>
+
+<p>The run-off of the surface would tend to gather in the depressions of
+the surface, however slight they may be. This tendency is shown on
+almost every hillside during and after a considerable shower. The water
+concentrated in the depressions is in excess of that flowing over other
+parts of the surface, and therefore flows faster. Flowing faster, it
+erodes the surface over which it flows more rapidly, and as a result the
+initial depressions are deepened, and <i>washes</i> or <i>gullies</i> are
+started.</p>
+
+<p>Should the run-off not find irregularities of slope, it would, at the
+outset, fail of concentration; but should it find the material more
+easily eroded along certain lines than along others, the lines of easier
+wear would become the sites of greater erosion. This would lead to the
+development of gullies, that is, to irregularities of slope. Either
+inequality of slope or material may therefore determine the location of
+a gully, and one of these conditions is indispensable.</p>
+
+<p>Once started, each wash or gully becomes the cause of its own growth,
+for the gully developed by the water of one shower, determines greater
+concentration of water during the next. Greater concentration means
+faster flow, faster flow means more rapid wear, and this means
+corresponding enlargement of the depression through which the flow takes
+place. The enlargement effected by successive showers affects a gully in
+all dimensions.<br /> <br /> <br /> <br /> </p>
+
+<p> <a name="i13" id="i13"> </a> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIII.</p>
+
+<div class="imgspc">
+<div class="figmleft" style="width: 200px;">
+<img src="images/i13f1.jpg" width="200" height="187" alt="FIG. 1. A very young valley." />
+<span class="caption">FIG. 1. <br />A very young valley.</span>
+</div>
+
+<div class="figmright" style="width: 200px;">
+<img src="images/i13f2.jpg" width="200" height="195" alt="FIG. 2. A valley in a later stage of development." />
+<span class="caption">FIG. 2. <br />A valley in a later stage of development.</span>
+</div> </div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/i13f3.jpg" width="300" height="230" alt="" />
+</div>
+<p class="center indent">FIG. 3. <br />Young valleys.<br /> <br /> <br /> <br /> </p>
+
+
+<p> <span class="pagenum"> <a name="Page_39" id="Page_39">[Pg 39]</a> </span>
+The water coming in at its head carries the head back into the land
+(head erosion), thus lengthening the gully; the water coming in at its
+sides wears back the lateral slopes, thus widening it; and the water
+flowing along its bottom deepens it. Thus gullies grow to be ravines,
+and farther enlargement by the same processes converts ravines into
+valleys. A river valley therefore is often but a gully grown big.</p>
+
+<p> <i>The course of a valley.</i>&mdash;In the lengthening of a gully or valley
+headward, the growth will be in the direction of greatest wear. Thus in
+Plate <a href="#i13">XIII Fig. 1</a>, if the water coming in at the head of the gully
+effects most wear in the direction <i>a</i>, the head of the gully will
+advance in that direction; if there be most wear in the direction <i>b</i> or
+<i>c</i>, the head will advance toward one of these points. The direction of
+greatest wear will be determined either by the slope of the surface, or
+by the nature of the surface material. The slope may lead to the
+concentration of the entering waters along one line, and the surface
+material may be less resistant in one direction than in another. If
+these factors favor the same direction of head-growth, the lengthening
+will be more rapid than if but one is favorable. If there be more rapid
+growth along two lines, as <i>b</i> and <i>c</i>, Plate <a href="#i13">XIII Fig. 1</a>, than between
+them, two gullies may develop (Plate <a href="#i13">XIII Fig. 2</a>). The frequent and
+tortuous windings common to ravines and valleys are therefore to be
+explained by the inequalities of slope or material which affected the
+surface while the valley was developing.</p>
+
+<p> <i>Tributary valleys.</i>&mdash;Following out this simple conception of valley
+growth, we have to inquire how a valley system (a main valley and its
+tributaries) is developed. The conditions which determine the location
+and development of gullies in a new land surface, determine the location
+and development of tributary gullies. In flowing over the lateral slopes
+of a gully or ravine, the water finds either slope or surface material
+failing of uniformity. Both conditions lead to the concentration of the
+water along certain lines, and concentration of flow on the slope of an
+erosion depression, be it valley or gully, leads to the development
+<span class="pagenum"> <a name="Page_40" id="Page_40">[Pg 40]</a> </span>
+of a tributary depression. In its growth, the tributary repeats, in all
+essential respects, the history of its main. It is lengthened headward
+by water coming in at its upper end, is widened by side wash, and
+deepened by the downward cutting of the water which flows along its
+axis. The factors controlling its development are the same as those
+which controlled the valley to which it is tributary.</p>
+
+<p>There is one peculiarity of the courses of tributaries which deserves
+mention. Tributaries, as a rule, join their mains with an acute angle up
+stream. In general, new land surfaces, such as are now under
+consideration, slope toward the sea. If a tributary gully were to start
+back from its main at right angles, more water would come in on the side
+away from the shore, on account of the seaward slope of the land. This
+would be true of the head of the gully as well as of other portions, and
+the effect would be to turn the head more and more toward parallelism
+with the main valley. Local irregularities of surface may, and
+frequently do, interfere with these normal relations, so that the
+general course of a tributary is occasionally at right angles to its
+main. Still more rarely does the general course of a tributary make an
+acute angle with its main on the down stream side. Local irregularities
+of surface determine the windings of a tributary, so that their courses
+for longer or shorter distances may be in violation of the general rule
+(c, Fig. <a href="images/fig43.jpg">43</a>); but on the whole, the valleys of a system whose
+history has not been interrupted in a region where the surface material
+is not notably heterogeneous, follow the course indicated above. This is
+shown by nearly every drainage system on the Atlantic Coastal plain
+which represents more nearly than any other portion of our continent,
+the conditions here under consideration. Fig. <a href="images/fig12.jpg">12</a> represents the drainage
+system of the Mullica river in southern New Jersey and is a type of the
+Coastal plain river system.</p>
+
+<p> <i>How a valley gets a stream.</i>&mdash;Valleys may become somewhat deep and long
+and wide without possessing permanent streams, though from their
+inception they have <i>temporary</i> streams, the water for which is
+furnished by showers or melting snow. Yet
+<span class="pagenum"> <a name="Page_41" id="Page_41">[Pg 41]</a> </span>
+sooner or later, valleys come to have permanent streams. How are they acquired? Does the valley find
+the stream or the stream the valley? For the answer to these questions,
+a brief digression will be helpful.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig12.jpg" width="300" height="248" alt="" />
+</div>
+<p class="center indent">
+Fig. 12. -- A typical river system of the Coastal type.<br />
+<a href="images/fig12.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p>In cultivated regions, wells are of frequent occurrence. In a flat
+region of uniform structure, the depth at which well water may be
+obtained is essentially constant at all points. If holes (wells 1 and 2,
+Fig. <a href="images/fig13.jpg">13</a>) be excavated below this level, water seeps into them, and in a
+series of wells the water stands at a nearly common level. This means
+that the sub-structure is full of water up to that level. These
+relations are illustrated by Fig. <a href="images/fig13.jpg">13</a>. The diagram represents a vertical
+section through a flat region from the surface (<i>s s</i>) down below the
+bottom of wells. The water stands at the same level in the two cells (1
+and 2), and the plane through them, at the surface of the water, is the
+<i>ground water level</i>. If in such a surface a valley were to be cut until its
+<span class="pagenum"> <a name="Page_42" id="Page_42">[Pg 42]</a> </span>
+bottom was below the ground water level, the water would seep into
+it, as it does into the wells; and if the amount were sufficient, a
+permanent stream would be established. This is illustrated in Fig. <a href="images/fig13.jpg">13</a>.
+The line A A represents the ground water level, and the level at which
+the water stands in the wells, under ordinary circumstances. The bottom
+of the valley is below the level of the ground water, and the water
+seeps into it from either side. Its tendency is to fill the valley to
+the level A A. But instead of accumulating in the open valley as it does
+in the enclosed wells, it flows away, and the ground water level on
+either hand is drawn down.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/fig13.jpg" width="600" height="102" alt="" />
+</div>
+<p class="center indent">Fig. 13. -- Diagram illustrating the relations of ground
+water to streams.<br /> <br /> <br /> </p>
+
+<p>The level of the ground water fluctuates. It is depressed when the
+season is dry (A' A'), and raised when precipitation is abundant (A''
+A''). When it is raised, the water in the wells rises, and the stream in
+the valley is swollen. When it falls, the ground water surface is
+depressed, and the water in the wells becomes lower. If the water
+surface sinks below the bottom of the wells, the wells "go dry;" if
+below the bottom of the valley, the valley becomes for the time being, a
+"dry run." When a well is below the lowest ground-water level its supply
+of water never fails, and when the valley is sufficiently below the same
+level, its stream does not cease to flow, even in periods of drought. On
+account of the free evaporation in the open valley, the valley
+depression must be somewhat below the level necessary for a well, in
+order that the flow may be constant.</p>
+
+<p>It will be seen that <i>intermittent</i> streams, that is, streams which flow
+in wet seasons and fail in dry, are intermediate between streams which
+flow after showers only, and those which flow without interruption. In
+the figure the stream would become dry if the ground water level sank to
+A' A'.</p>
+
+<p> <span class="pagenum"> <a name="Page_43" id="Page_43">[Pg 43]</a> </span>
+It is to be noted that a permanent stream does not normally precede its
+valley, but that the valley, developed through gully-hood and
+ravine-hood to valley-hood by means of the temporary streams supplied by
+the run-off of occasional showers, <i>finds a stream</i>, just as diggers of
+wells find water. The case is not altered if the stream be fed by
+springs, for the valley finds the spring, as truly as the well-digger
+finds a "vein" of water.</p>
+
+<p> <i>Limits of a valley.</i>&mdash;So soon as a valley acquires a permanent stream,
+its development goes on without the interruption to which it was subject
+while the stream was intermittent. The permanent stream, like the
+temporary one which preceded it, tends to deepen and widen its valley,
+and, under certain conditions, to lengthen it as well. The means by
+which these enlargements are affected are the same as before. There are
+limits, however, in length, depth, and width, beyond which a valley may
+not go. No stream can cut below the level of the water into which it
+flows, and it can cut to that level only at its outlet. Up stream from
+that point, a gentle gradient will be established over which the water
+will flow without cutting. In this condition the stream is <i>at grade</i>.
+Its channel has reached baselevel, that is, the level to which the
+stream can wear its bed. This grade is, however, not necessarily
+permanent, for what was <i>baselevel</i> for a small stream in an early stage
+of its development, is not necessarily baselevel for the larger stream
+which succeeds it at a later time.</p>
+
+<p>Weathering, wash, and lateral corrasion of the stream continue to widen
+the valley after it has reached baselevel. The bluffs of valleys are
+thus forced to recede, and the valley is widened at the expense of the
+upland. Two valleys widening on opposite sides of a divide, narrow the
+divide between them, and may ultimately wear it out. When this is
+accomplished, the two valleys become one. The limit to which a valley
+may widen on either side is therefore its neighboring valley, and since,
+after two valleys have become one by the elimination of the ridge
+between them, there are still valleys on either hand, the final result
+of the widening of all valleys must be to reduce
+<span class="pagenum"> <a name="Page_44" id="Page_44">[Pg 44]</a> </span>
+all the area which they drain to baselevel. As this process goes forward, the upper flat
+into which the valleys were cut is being restricted in area, while the
+lower flats developed by the streams in the valley bottoms are being
+enlarged. Thus the lower flats grow at the expense of the higher.</p>
+
+<p>There are also limits in length which a valley may not exceed. The head
+of any valley may recede until some other valley is reached. The
+recession may not stop even there, for if, on opposite sides of a
+divide, erosion is unequal, as between <span class="smcap">1a</span> and
+<span class="smcap">1b</span>, Fig. <a href="images/fig14.jpg">14</a>, the divide
+will be moved toward the side of less rapid erosion, and it will cease
+to recede only when erosion on the two sides becomes equal (<span class="smcap">4a</span> <i>and</i>
+<span class="smcap">4b</span>). In homogeneous material this will be when the slopes on the two
+sides are equal.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig14.jpg" width="500" height="98" alt="" />
+</div>
+<p class="center indent">Fig. 14. -- Diagram showing the shifting of a divide. The
+slopes 1A and 1B are unequal. The steeper slope is worn more rapidly and
+the divide is shifted from 1 to 4, where the two slopes become equal and
+the migration of the divide ceases.<br /> <br /> <br /> </p>
+
+<p>It should be noted that the lengthening of a valley headward is not
+normally the work of the permanent stream, for the permanent stream
+begins some distance below the head of the valley. At the head,
+therefore, erosion goes on as at the beginning, even after a permanent
+stream is acquired.</p>
+
+<p>Under certain circumstances, the valley may be lengthened at its
+debouchure. If the detritus carried by it is deposited at its mouth, or
+if the sea bottom beyond that point rise, the land may be extended
+seaward, and over this extension the stream will find its way. Thus at
+their lower, as well as at their upper ends, both the stream and its
+valley may be lengthened.</p>
+
+<p> <i>A cycle of erosion.</i>&mdash;If, along the borders of a new-born land mass, a
+series of valleys were developed, essentially parallel to one another,
+they would constitute depressions separated by elevations, representing
+the original surface not yet notably affected<br /> <br /> <br /> </p>
+
+<p> <a name="i14" id="i14"> </a> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIV.</p>
+
+<div class="imgspc">
+<div class="figmleft" style="width: 200px;">
+<img src="images/i14f1.jpg" width="200" height="152" alt="FIG. 1. The same valleys
+ as shown in Plate XIII Fig. 3, in a later stage of development." />
+<span class="caption">FIG. 1. <br />The same valleys as shown in Plate
+<a href="#i13">XIII Fig. 3</a>, in a later stage of development.<br /></span>
+<a href="images/i14f1.jpg">See larger image</a> <br />
+</div>
+
+<div class="figmright" style="width: 200px;">
+<img src="images/i14f2.jpg" width="200" height="152" alt="FIG. 2. Same valleys as
+ shown in Fig. 1, in a still later stage of development." />
+<span class="caption">FIG. 2. <br /> Same valleys as shown in Fig. 1, in a still later stage of
+ development.<br /> </span>
+<a href="images/i14f2.jpg">See larger image</a> <br />
+</div> </div>
+
+<p> <span class="pagenum"> <a name="Page_45" id="Page_45">[Pg 45]</a> </span>
+by erosion (see Plate <a href="#i14">XIV Fig. 1</a>). These inter-valley areas might at
+first be wide or narrow, but in process of time they would necessarily
+become narrow, for, once, a valley is started, all the water which
+enters it from either side helps to wear back its slopes, and the
+wearing back of the slopes means the widening of the valleys on the one
+hand and the narrowing of the inter-valley ridges on the other. Not only
+would the water running over the slopes of a valley wear back its walls,
+but many other processes conspire to the same end. The wetting and
+drying, the freezing and the thawing, the roots of plants and the
+borings of animals, all tend to loosen the material on the slopes or
+walls of the valleys, and gravity helps the loosened material to
+descend. Once in the valley bottom, the running water is likely to carry
+it off, landing it finally in the sea. Thus the growth of the valley is
+not the result of running water alone, though this is the most important
+single factor in the process.</p>
+
+<p>Even if valleys developed no tributaries, they would, in the course of
+time, widen to such an extent as to nearly obliterate the intervening
+ridges. The surface, however, would not easily be reduced to perfect
+flatness. For a long time at least there would remain something of slope
+from the central axis of the former inter-stream ridge, toward the
+streams on either hand; but if the process of erosion went on for a
+sufficiently long period of time, the inter-stream ridge would be
+brought very low, and the result would be an essentially flat surface
+between the streams, much below the level of the old one.</p>
+
+<p>The first valleys which started on the land surface (see Plate
+<a href="#i13">XIII Fig. 3</a>) would be almost sure to develop numerous
+tributaries. Into tributary valleys water would flow from their sides and from their
+heads, and as a result they would widen and deepen and lengthen just as
+their mains had done before them. By lengthening headward they would
+work back from their mains some part, or even all of the way across the
+divides separating the main valleys. By this process, the tributaries
+cut the divides between the main streams into shorter cross-ridges. With
+the development of tributary valleys there would be many lines of
+drainage instead of two, working at the area between two main
+<span class="pagenum"> <a name="Page_46" id="Page_46">[Pg 46]</a> </span>
+streams. The result would be that the surface would be brought low much more
+rapidly, for it is clear that many valleys within the area between the
+main streams, widening at the same time, would diminish the aggregate
+area of the upland much more rapidly than two alone could do.</p>
+
+<p>The same thing is made clear in another way. It will be seen (Plate
+<a href="#i14">XIV Figs. 1 and 2</a>) that the tributaries would presently
+dissect an area of uniform surface, tending to cut it into a series of short
+ridges or hills. In this way the amount of sloping surface is greatly increased,
+and as a result, every shower would have much more effect in washing
+loose materials down to lower levels, whence the streams could carry
+them to the sea.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig15.jpg" width="300" height="227" alt="" />
+</div>
+<p class="center indent">Fig. 15. -- Cross-sections showing various stages of
+erosion in one cycle.<br /> <br /> <br /> </p>
+
+
+<p>The successive stages in the process of lowering a surface are suggested
+by Fig. <a href="images/fig15.jpg">15</a>, which represents a series of cross-sections of a land mass
+in process of degradation. The uppermost section represents a level
+surface crossed by young valleys. The next lower represents the same
+surface at a later stage, when the<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XV.</p>
+<div class="figcenter" style="width: 300px;">
+<img src="images/i15.jpg" width="300" height="211" alt="" />
+</div>
+<p class="center indent">Diagram illustrating how a hard inclined layer of rock becomes a ridge
+in the process of degradation.<br />
+<a href="images/i15.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_47" id="Page_47">[Pg 47]</a> </span>
+valleys have grown larger, while the third and succeeding sections
+represent still later stages in the process of degradation. Plate <a href="#i13">XIII Fig. 3</a>,
+and Plate <a href="#i14">XIV Figs. 1 and 2</a>, represent in another way the
+successive stages of stream work in the general process of degradation.</p>
+
+<p>In this manner a series of rivers, operating for a sufficiently long
+period of time, might reduce even a high land mass to a low level,
+scarcely above the sea. The new level would be developed soonest near
+the sea, and the areas farthest from it would be the last&mdash;other things
+being equal&mdash;to be brought low. The time necessary for the development
+of such a surface is known as a <i>cycle of erosion</i>, and the resulting
+surface is a <i>base-level plain</i>, that is, a plain as near sea level as
+river erosion can bring it. At a stage shortly preceding the base-level
+stage the surface would be a <i>peneplain</i>. A peneplain, therefore, is a
+surface which has been brought toward, but not to base-level. Land
+surfaces are often spoken of as young or old in their erosion history
+according to the stage of advancement which has been made toward
+baseleveling. Thus the Colorado canyon, deep and impressive as it is,
+is, in terms of erosion, a young valley, for the river has done but a
+small part of the work which must be done in order to bring its basin to
+baselevel.</p>
+
+<p> <i>Effects of unequal hardness.</i>&mdash;The process of erosion thus sketched
+would ultimately bring the surface of the land down to base-level, and
+in case the material of the land were homogeneous, the last points to be
+reduced would be those most remote from the axes of the streams doing
+the work of leveling. But if the material of the land were of unequal
+hardness, those parts which were hardest would resist the action of
+erosion most effectively. The areas of softer rock would be brought low,
+and the outcrops of hard rock (Plate <a href="images/i15.jpg">XV</a>) would constitute ridges during
+the later stages of an erosion cycle. If there were bodies of hard rock,
+such as the Baraboo quartzite, surrounded by sandstone, such as the
+Potsdam, the sandstone on either hand would be worn down much more
+readily than the quartzite, and in the course of degradation the latter would
+<span class="pagenum"> <a name="Page_48" id="Page_48">[Pg 48]</a> </span>
+come to stand out prominently. The region in the vicinity of Devil's
+lake is in that stage of erosion in which the quartzite ridges are
+conspicuous (Plate <a href="images/i37.jpg">XXXVII</a>). The less resistant sandstone has been
+removed from about them, and erosion has not advanced so far since the
+isolation of the quartzite ridges as to greatly lower their crests. The
+harder strata are at a level where surface water can still work
+effectively, even though slowly, upon them, and in spite of their great
+resistance they will ultimately be brought down to the common level. It
+will be seen that, from the point of view of subaerial erosion, a
+base-level plain is the only land surface which is in a condition of
+approximate stability.</p>
+
+<p> <i>Falls and rapids.</i>&mdash;If in lowering its channel a stream crosses one
+layer of rock much harder than the next underlying, the deepening will
+go on more rapidly on the less resistant bed. Where the stream crosses
+from the harder to the less hard, the gradient is likely to become
+steep, and a rapids is formed. These conditions are suggested in Fig. <a href="images/fig16.jpg">16</a>
+which represents the successive profiles (<i>a b, a c, d e, f e, g e,</i> and
+<i>h e</i>) of a stream crossing from a harder to a softer formation. Below
+the point <i>a</i> the <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig16.jpg" width="500" height="53" alt="" />
+</div>
+<p class="center indent">Fig. 16. -- Diagram to illustrate the development of a
+ rapid and fall. The upper layer is harder than the strata below. The
+ successive profiles of the stream below the hard layer are represented
+ by the lines <i>a b, a c, d e, f e, g e,</i> and <i>h e</i>.<br />
+<a href="images/fig16.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>stream is flowing over rock which is easily eroded, while above that
+point its course is over a harder formation. Just below <i>a</i> (profile <i>a
+b</i>) the gradient has become so steep that there are <i>rapids</i>. Under
+these conditions, erosion is rapid just beyond the crossing of the hard
+layer, and the gradient becomes higher and higher. When the steep slope
+of the rapids approaches verticality, the rapids become a <i>fall</i>
+(profile <i>a c</i>).</p>
+
+<p>As the water falls over the precipitous face and strikes upon the softer
+rock below, part of it rebounds against the base of<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVI.</p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/i16.jpg" width="250" height="186" alt="" />
+</div>
+<p class="center indent">Skillett Falls, in the Potsdam formation, three miles southwest of
+Baraboo. The several small falls are occasioned by slight inequalities
+in the hardness of the layers.<br />
+<a href="images/i16.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_49" id="Page_49">[Pg 49]</a> </span>
+the vertical face (Fig. <a href="images/fig16.jpg">16</a>). The result of wear at this point is the
+undermining of the hard layer above, and sooner or later, portions of it
+will fall. This will occasion the recession of the fall (profile <i>d e</i>
+and <i>f e</i>). As the fall recedes, it grows less and less high. When the
+recession has reached the point <i>i</i>, or, in other words, when the
+gradient of the stream below the fall crosses the junction of the beds
+of unequal hardness, as it ultimately must, effective undermining
+ceases, and the end of the fall is at hand.</p>
+
+<p>When the effective undercutting ceases because the softer bed is no
+longer accessible, the point of maximum wear is transferred to the top
+of the hard bed just where the water begins to fall (<i>g</i>,
+Fig. <a href="images/fig16.jpg">16</a>). The
+wear here is no greater than before, though it is greater relatively.
+The relatively greater wear at this point destroys the verticality of
+the face, converting it into a steep slope. When this happens, the fall
+is a thing of the past, and rapids succeed. With continued flow the bed
+of the rapids becomes less and less steep, until it is finally reduced
+to the normal gradient of the stream (<i>h e</i>), when the rapids disappear.</p>
+
+<p>When thin layers of rock in a stream's course vary in hardness, softer
+beds alternating with harder ones, a series of falls such as shown in
+Plate <a href="images/i16.jpg">XVI</a>, may result. As they work up stream, these falls will be
+obliterated one by one. Thus it is seen that falls and rapids are not
+permanent features of the landscape. They belong to the younger period
+of a valley's history, rather than to the older. They are marks of
+topographic youth.</p>
+
+<p> <i>Narrows.</i>&mdash;Where a stream crosses a hard layer or ridge of rock lying
+between softer ones, the valley will not widen so rapidly in the hard
+rock as above and below. If the hard beds be vertical, so that their
+outcrop is not shifted as the degradation of the surface proceeds, a
+notable constriction of the valley results. Such a constriction is a
+<i>narrows</i>. The Upper and Lower narrows of the Baraboo (Plate
+<a href="images/i04.jpg">IV</a>)
+are good examples of the effect of hard rock on the widening of a
+valley.</p>
+
+<p> <span class="pagenum"> <a name="Page_50" id="Page_50">[Pg 50]</a> </span>
+<i>Erosion of folded strata.</i>&mdash;The processes of river erosion would not be
+essentially different in case the land mass upon which erosion operated
+were made of tilted and folded strata. The folds would, at the outset,
+determine the position of the drainage lines, for the main streams would
+flow in the troughs (synclines) between the folds (anticlines). Once
+developed, the streams would lower their beds, widen their valleys, and
+lengthen their courses, and in the long process of time they would bring
+the area drained nearly to sea-level, just as in the preceding case. It
+was under such conditions that the general processes of subaerial
+erosion operated in south central Wisconsin, after the uplift of the
+quartzite and before the deposition of the Potsdam sandstone. It was
+then that the principal features of the topography of the quartzite were
+developed.</p>
+
+<p>In regions of folded strata, certain beds are likely to be more
+resistant than others. Where harder beds alternate with softer, the
+former finally come to stand out as ridges, while the outcrops of the
+latter mark the sites of the valleys. Such alternations of beds of
+unequal resistance give rise to various peculiarities of drainage,
+particularly in the courses of tributaries. These peculiarities find no
+illustration in this region and are not here discussed.</p>
+
+<p> <i>Base-level plains and peneplains.</i>&mdash;It is important to notice that a
+plane surface (base-level) developed by streams could only be developed
+at elevations but slightly above the sea, that is, at levels at which
+running water ceases to be an effective agent of erosion; for so long as
+a stream is actively deepening its valley, its tendency is to roughen
+the area which it drains, not to make it smooth. The Colorado river,
+flowing through high land, makes a deep gorge. All the streams of the
+western plateaus have deep valleys, and the manifest result of their
+action is to roughen the surface; but given time enough, and the streams
+will have cut their beds to low gradients. Then, though deepening of the
+valleys will cease, widening will not, and inch by inch and shower by
+shower the elevated lands between<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVII.</p>
+<div class="figcenter" style="width: 300px;">
+<img src="images/i17.jpg" width="300" height="100" alt="" />
+</div>
+<p class="center indent">A group of mounds on the plain southwest from Camp Douglas. The
+base-level surface is well shown, and above it rise the remnants of the
+higher plain from which the lower was reduced.<br />
+<a href="images/i17.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVIII.</p>
+<div class="figcenter" style="width: 300px;">
+<img src="images/i18.jpg" width="300" height="165" alt="" />
+</div>
+<p class="center indent">Castle Rock near Camp Douglas. In this view the relation of the erosion
+remnant to the extensive base-leveled surface is well shown.<br />
+<a href="images/i18.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_51" id="Page_51">[Pg 51]</a> </span>
+the valleys will be reduced in area,
+and ultimately the whole will be brought down nearly to the level of the
+stream beds. This is illustrated by Fig. <a href="images/fig15.jpg">15</a>.</p>
+
+<p>It is important to notice further that if the original surface on which
+erosion began is level, there is no stage intermediate between the
+beginning and the end of an erosion cycle, when the surface is again
+level, or nearly so, though in the stage of a cycle next preceding the
+last&mdash;the peneplain stage (fourth profile, Fig. <a href="images/fig15.jpg">15</a>)&mdash;the surface
+approaches flatness. It is also important to notice that when streams
+have cut a land surface down to the level at which they cease to erode,
+that surface will still possess some slight slope, and that to seaward.</p>
+
+<p>No definite degree of slope can be fixed upon as marking a base-level.
+The angle of slope which would practically stop erosion in a region of
+slight rainfall would be great enough to allow of erosion if the
+precipitation were greater. All that can be said, therefore, is that the
+angle of slope must be low. The Mississippi has a fall of less than a
+foot per mile for some hundreds of miles above the gulf. A small stream
+in a similar situation would have ceased to lower its channel before so
+low a gradient was reached.</p>
+
+<p>The nearest approach to a base-leveled region within the area here under
+consideration is in the vicinity of Camp Douglas and Necedah (see Plate
+<a href="images/i01.jpg">I</a>). This is indeed one of the best examples of a base-leveled
+plain known. Here the broad plain, extending in some directions as far
+as the eye can reach, is as low as it could be reduced by the streams
+which developed it. The erosion cycle which produced the plain was,
+however, not completed, for above the plain rise a few conspicuous hills
+(Plates <a href="images/i17.jpg">XVII</a> and
+<a href="images/i18.jpg">XVIII</a>, and Fig.
+<a href="images/fig17.jpg">17</a>), and to the west of it lie the
+highlands marking the level from which the low plain was reduced.</p>
+
+<p>Where a region has been clearly base-leveled, isolated masses or ridges
+of resistant rock may still stand out conspicuously above it. The
+quartzite hill at Necedah is an example. Such hills are known as
+<i>monadnocks</i>. This name was taken from
+<span class="pagenum"> <a name="Page_52" id="Page_52">[Pg 52]</a> </span>
+Mount Monadnock which owes its origin to the removal of the surrounding less resistant beds. The name
+has now become generic. Many of the isolated hills on the peneplain east
+of Camp Douglas are perhaps due to superior resistance, though the rock
+of which they are composed belongs to the same formation as that which
+has been removed.<br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig17.jpg" width="300" height="101" alt="" />
+</div>
+<p class="center indent">Fig. 17. -- Sketch, looking northwest from Camp Douglas.<br />
+<a href="images/fig17.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<h4>CHARACTERISTICS OF VALLEYS AT VARIOUS STAGES OF DEVELOPMENT.</h4>
+
+<p>In the early stages of its development a depression made by erosion has
+steep lateral slopes, the exact character of which is determined by many
+considerations. Its normal cross-section is usually described as
+V-shaped (Fig. <a href="images/fig18.jpg">18</a>). In the early stages<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig18.jpg" width="300" height="81" alt="" />
+</div>
+<p class="center indent">Fig. 18. -- Diagrammatic cross-section of a young valley.<br />
+<a href="images/fig18.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>of its development, especially if in unconsolidated material, the slopes
+are normally convex inward. If cut in solid rock, the cross section may
+be the same, though many variations are likely to appear, due especially
+to the structure of the rock and to inequalities of hardness. If a
+stream be swift enough to carry
+<span class="pagenum"> <a name="Page_53" id="Page_53">[Pg 53]</a> </span>
+off not only all the detritus descending from its slopes, but to abrade its bed effectively besides, a
+steep-sided gorge develops. If it becomes deep, it is a canyon. For the
+development of a canyon, the material of the walls must be such as is
+capable of standing at a high angle. A canyon always indicates that the
+down-cutting of a stream keeps well ahead of the widening.</p>
+
+<p>Of young valleys in loose material (drift) there are many examples in
+the eastern portion of the area here described. Shallow canyons or
+gorges in rock are also found. The gorge of Skillett creek at and above
+the Pewit's nest about three miles southwest from Baraboo, the gorge of
+Dell creek two miles south of Kilbourn City, and the Dalles of the
+Wisconsin at Kilbourn City may serve as illustrations of this type of
+valley.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/fig19.jpg" width="350" height="75" alt="" />
+</div>
+<p class="center indent">Fig. 19. -- Diagrammatic profile of a young valley.<br />
+<a href="images/fig19.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>The profile of a valley at the stage of its development corresponding to
+the above section is represented diagrammatically by the curve <span class="smcap">a b</span> in
+Fig. <a href="images/fig19.jpg">19</a>. The sketch (Plate <a href="#i19">XIX Fig. 1</a>)
+represents a bird's-eye view of a valley in the same stage of development.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig20.jpg" width="300" height="40" alt="" />
+</div>
+<p class="center indent">Fig. 20. -- Diagrammatic cross-section of a valley at a
+stage corresponding with that shown in Plate <a href="#i19">XIX, Fig. 2.</a> <br /> <br /> <br /> </p>
+
+<p>At a stage of development later than that represented by the V-shaped
+cross-section, the corresponding section is U-shaped, as shown in Fig.
+<a href="images/fig20.jpg">20</a>. The same form is sketched in
+Plate <a href="#i19">XIX Fig. 2</a>. This represents a
+stage of development where detritus descending the slopes is not all
+carried away by the stream, and where the valley is being widened faster
+than it is deepened. Its
+<span class="pagenum"> <a name="Page_54" id="Page_54">[Pg 54]</a> </span>
+slopes are therefore becoming gentler. The profile of the valley at this stage
+would be much the same as that in the preceding, except that the gradient in
+the lower portion would be lower.</p>
+
+<p>Still later the cross section of the valley assumes the shape shown in
+Fig. <a href="images/fig21.jpg">21</a>, and in perspective the form sketched in
+Plate <a href="#i20">XX Fig. 1</a>. This
+transformation is effected partly by erosion, and partly by deposition
+in the valley. When a stream has cut its valley as low as conditions
+allow, it becomes sluggish. A sluggish stream is easily turned from side
+to side, and, directed against its banks, it may undercut them, causing
+them to recede at the point of undercutting. In its meanderings, it
+undercuts at various points at various times, and the aggregate result
+is the widening of the valley. By this process alone the stream would
+develop a flat grade. At the same time all the drainage which comes in
+at the sides tends to carry the walls of the valley farther from its
+axis.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig21.jpg" width="300" height="37" alt="" />
+</div>
+<p class="center indent">Fig. 21. -- Diagrammatic cross-section of a valley at a
+stage later than that shown in Fig. <a href="images/fig20.jpg">20</a>.<br /> <br /> <br /> </p>
+
+<p>A sluggish stream is also generally a depositing stream. Its deposits
+tend to aggrade (build up) the flat which its meanderings develop. When
+a valley bottom is built up, it becomes wider at the same time, for the
+valley is, as a rule, wider at any given level than at any lower one.
+Thus the U-shaped valley is finally converted into a valley with a flat
+bottom, the flat being due in large part to erosion, and in smaller part
+to deposition. Under exceptional circumstances the relative importance
+of these two factors may be reversed.</p>
+
+<p>It will be seen that the cross-section of a valley affords a clue to its
+age. A valley without a flat is young, and increasing age is indicated
+by increasing width. Valleys illustrating all stages of development are
+to be found in the Devil's lake region. The valley of Honey creek
+southwest of Devil's lake may be taken<br /> <br /> <br /> </p>
+
+<p> <a name="i19" id="i19"> </a> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIX.</p>
+
+<div class="imgspc2">
+<div class="figmleft" style="width: 200px;">
+<img src="images/i19f1.jpg" width="200" height="157" alt="FIG. 1. Sketch of a valley
+ at the stage of development corresponding to the cross section shown in Fig. 18." />
+<span class="caption">FIG. 1. <br />Sketch of a valley at the stage of development corresponding to the
+ cross section shown in Fig. <a href="images/fig18.jpg">18</a>.</span>
+</div>
+
+<div class="figmright" style="width: 200px;">
+<img src="images/i19f2.jpg" width="200" height="151" alt="FIG. 2. Sketch of a valley
+ at the stage of development corresponding to the cross section shown in Fig. 20." />
+<span class="caption">FIG. 2. <br />Sketch of a valley at the stage of development corresponding to the
+ cross section shown in Fig. <a href="images/fig20.jpg">20</a>.</span>
+</div> </div>
+
+<p> <a name="i20" id="i20"> </a> </p>
+
+<p class="center"> <br /> <br />WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XX.</p>
+
+<div class="imgspc">
+<div class="figmleft" style="width: 200px;">
+<img src="images/i20f1.jpg" width="200" height="149" alt="FIG. 1. Sketch of a part of a
+valley at the stage of development corresponding to the cross section shown in Fig. 21." />
+<span class="caption">FIG. 1. <br /> Sketch of a part of a valley at the stage of development corresponding
+to the cross section shown in Fig. <a href="images/fig21.jpg">21</a>.</span>
+</div>
+
+<div class="figmright" style="width: 200px;">
+<img src="images/i20f2.jpg" width="200" height="144" alt="FIG. 2. Sketch of a section of the Baraboo valley." />
+<span class="caption">FIG. 2. <br /> Sketch of a section of the Baraboo valley.</span>
+</div> </div>
+
+<p>as an illustration of a valley at an intermediate stage of development, while examples of old valleys are
+found in the flat country about Camp Douglas and Necedah.</p>
+
+<h4> <i>Transportation and Deposition.</i> </h4>
+
+<p> <span class="pagenum"> <a name="Page_55" id="Page_55">[Pg 55]</a> </span>
+Sediment is carried by streams in two ways: (1) by being rolled along
+the bottom, and (2) by being held in suspension. Dissolved mineral
+matter (which is not sediment) is also carried in the water. By means of
+that rolled along the bottom and carried in suspension, especially the
+former, the stream as already stated abrades its bed.</p>
+
+<p>The transporting power of a stream of given size varies with its
+velocity. Increase in the declivity or the volume of a stream increases
+its velocity and therefore its transportive power. The transportation
+effected by a stream is influenced (1) by its transporting power, and (2)
+by the size and amount of material available for carriage. Fine material
+is carried with a less expenditure of energy than an equal amount of
+coarse. With the same expenditure of energy therefore a stream can carry
+a greater amount of the former than of the latter.</p>
+
+<p>Since the transportation effected by a stream is dependent on its
+gradient, its size, and the size and amount of material available, it
+follows that when these conditions change so as to decrease the carrying
+power of the river, deposition will follow, if the stream was previously
+fully loaded. In other words, a stream will deposit when it becomes
+overloaded.</p>
+
+<p>Overloading may come about in the following ways: (1) By decrease in
+gradient, checking velocity and therefore carrying power; (2) by
+decrease in amount of water, which may result from evaporation,
+absorption, etc.; (3) by change in the shape of the channel, so that the
+friction of flow is increased, and therefore the force available for
+transportation lessened; (4) by lateral drainage bringing in more
+sediment than the main stream can carry; (5) by change in the character
+of the material to which the stream has access; for if it becomes finer,
+the coarse material previously carried will be dropped, and the fine
+taken; and (6) by the checking of velocity when a stream flows into a
+<span class="pagenum"> <a name="Page_56" id="Page_56">[Pg 56]</a> </span>
+body of standing water.</p>
+
+<p> <i>Topographic forms resulting from stream deposition.</i>&mdash;The topographic
+forms resulting from stream deposition are various. At the bottoms of
+steep slopes, temporary streams build <i>alluvial cones</i> or <i>fans</i>. Along
+its flood-plain portion, a stream deposits more or less sediment on its
+flats. The part played by deposition in building a river flat has
+already been alluded to. A depositing stream often wanders about in an
+apparently aimless way across its flood plain. At the bends in its
+course, cutting is often taking place on the outside of a curve while
+deposition is going on in the inside. The valley of the Baraboo
+illustrates this process of cutting and building. Plate <a href="#i20">XX Fig. 2</a> is
+based upon the features of the valley within the city of Baraboo.</p>
+
+<p>Besides depositing on its flood-plain, a stream often deposits in its
+channel. Any obstruction of a channel which checks the current of a
+loaded stream occasions deposition. In this way "bars" are formed. Once
+started, the bar increases in size, for it becomes an obstacle to flow,
+and so the cause of its own growth. It may be built up nearly to the
+surface of the stream, and in low water, it may become an island by the
+depression of the surface water. In some parts of its course, as about
+Merrimac, the Wisconsin river is marked by such islands at low water,
+and by a much larger number of bars.</p>
+
+<p>At their debouchures, streams give up their loads of sediment. Under
+favorable conditions deltas are built, but delta-building has not
+entered into the physical history of this region to any notable extent.
+<br /> <br /> </p>
+
+
+<h4> <i>Rejuvenation of Streams.</i> </h4>
+
+<p>After the development of a base-level plain, its surface would suffer
+little change (except that effected by underground water) so long as it
+maintained its position. But if, after its development, a base-level
+plain were elevated, the old surface in a new position would be subject
+to a new series of changes identical in kind with those which had gone
+<span class="pagenum"> <a name="Page_57" id="Page_57">[Pg 57]</a> </span>
+before. The elevation would give the established streams greater fall,
+and they would reassume the characteristics of youth. The greater fall
+would accelerate their velocities; the increased velocities would entail
+increased erosion; increased erosion would result in the deepening of
+the valleys, and the deepening of the valleys would lead to the
+roughening of the surface. But in the course of time, the <i>rejuvenated</i>
+streams would have cut their valleys as low as the new altitude of the
+land permitted, that is, to a new base-level. The process of deepening
+would then stop, and the limit of vertical relief which the streams were
+capable of developing, would be attained. But the valleys would not stop
+widening when they stopped deepening, and as they widened, the
+intervening divides would become narrower, and ultimately lower. In the
+course of time they would be destroyed, giving rise to a new level
+surface much below the old one, but developed in the same position which
+the old one occupied when it originated; that is, a position but little
+above sea level.</p>
+
+<p>If at some intermediate stage in the development of a second base-level
+plain, say at a time when the streams, rejuvenated by uplift, had
+brought half the elevated surface down to a new base-level, another
+uplift were to occur, the half completed cycle would be brought to an
+end, and a new one begun. The streams would again be quickened, and as a
+result they would promptly cut new and deeper channels in the bottoms of
+the great valleys which had already been developed. The topography which
+would result is suggested by the following diagram (Fig.
+<a href="images/fig22.jpg">22</a>)<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig22.jpg" width="500" height="57" alt="" />
+</div>
+<p class="center indent">Fig. 22. -- Diagram (cross-section), illustrating the
+topographic effect of rejuvenation by uplift.<br />
+<a href="images/fig22.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>which illustrates the cross-section which would be found after the
+following sequence of events: (1) The development of a base-level, <span class="smcap">a a</span>;
+(2) uplift, rejuvenation of the streams, and a new cycle of erosion
+<span class="pagenum"> <a name="Page_58" id="Page_58">[Pg 58]</a> </span>
+half completed, the new base-level being at <span class="smcap">b b</span>; (3) a second uplift,
+bringing the second (incomplete) cycle of erosion to a close, and by
+rejuvenating the streams, inaugurating the third cycle. As represented
+in the diagram, the third cycle has not progressed far, being
+represented only by the narrow valley <span class="smcap">c</span>. The base-level is now 2-2, and
+the valley represented in the diagram has not yet reached it.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig23.jpg" width="500" height="26" alt="" />
+</div>
+<p class="center indent">Fig. 23. -- Normal profile of a valley bottom in a
+ non-mountainous region.<br /> <br /> <br /> </p>
+
+<p>The rejuvenation of a stream shows itself in another way. The normal
+profile of a valley bottom in a non-mountainous region is a gentle
+curve, concave upward with gradient increasing from debouchure to
+source. Such a profile is shown in Fig. <a href="images/fig23.jpg">23</a>.
+Fig. <a href="images/fig24.jpg">24</a>, on the other hand,
+is the profile of a rejuvenated stream. The valley once had a profile
+similar to that shown in Fig. <a href="images/fig23.jpg">23</a>.
+Below <span class="smcap">b</span> its former continuation is
+marked by the dotted line <span class="smcap">b c</span>. Since rejuvenation the stream has
+deepened the lower part of its valley, and established there a profile
+in harmony with the new conditions. The upper end of the new curve has
+not yet reached beyond <span class="smcap">b</span>.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig24.jpg" width="500" height="71" alt=""/>
+</div>
+<p class="center indent">Fig. 24. -- Profile of a stream rejuvenated by uplift.<br />
+<a href="images/fig24.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<h4> <i>Underground Water.</i> </h4>
+
+<p>In what has preceded, reference has been made only to the results
+accomplished by the water which runs off over the surface. The water
+which sinks beneath it is, however, of no small importance in reducing a
+land surface. The enormous amount of mineral matter in solution in
+spring water bears witness to the efficiency of the ground water in
+<span class="pagenum"> <a name="Page_59" id="Page_59">[Pg 59]</a> </span>
+dissolving rock, for since the water did not contain the mineral matter
+when it entered the soil, it must have acquired it below the surface. By
+this means alone, areas of more soluble rock are lowered below those of
+less solubility. Furthermore, the water is still active as a solvent
+agent after a surface has been reduced to so low a gradient that the
+run-off ceases to erode mechanically.
+<span class="pagenum"> <a name="Page_60" id="Page_60">[Pg 60]</a> </span> </p>
+
+<p> <br /> <br /> <br /> </p>
+
+<h2>CHAPTER IV.</h2>
+<p> <br /> </p>
+
+<h4>EROSION AND THE DEVELOPMENT OF STRIKING SCENIC FEATURES.</h4>
+
+
+<p>The uplift following the period of Paleozoic deposition in south central
+Wisconsin, inaugurated a period of erosion which, with some
+interruptions, has continued to the present day. The processes of
+weathering began as soon as the surface was exposed to the weather, and
+corrasion by running water began with the first shower which fell upon
+it. The sediment worn from the land was carried back to the sea, there
+to be used in the building of still younger formations.</p>
+
+<p>The rate of erosion of a land surface depends in large measure upon its
+height. As a rule, it is eroded rapidly if high, and but slowly if low.</p>
+
+<p>It is not known whether the lands of central Wisconsin rose to slight or
+to great heights at the close of the period of Paleozoic sedimentation.
+It is therefore not known whether the erosion was at the outset rapid or
+slow. If the land of southern Wisconsin remained low for a time after
+the uplift which brought the Paleozoic sedimentation to a close,
+weathering would have exceeded transportation and corrasion. A large
+proportion of the rainfall would have sunk beneath the surface, and
+found its way to the sea by subterranean routes. Loosening of material
+by alternate wetting and drying, expansion and contraction, freezing and
+thawing, and by solution, might have gone on steadily, but so long as
+the land was low, there would have been little run-off, and that little
+would have flowed over a surface of gentle slopes, and transportation
+would have been at a minimum. On the whole, the degradation of the land
+under these conditions could not have advanced rapidly.</p>
+
+<p>If, on the other hand, the land was raised promptly to a considerable
+<span class="pagenum"> <a name="Page_61" id="Page_61">[Pg 61]</a> </span>
+height, erosion would have been vigorous at the outset. The surface
+waters would soon have developed valleys which the streams would have
+widened, deepened and lengthened. Both transportation and corrasion
+would have been active, and whatever material was prepared for
+transportation by weathering, and brought into the valleys by side-wash,
+would have been hurried on its way to the sea, and degradation would
+have proceeded rapidly.</p>
+
+<p> <i>Establishment of drainage.</i>&mdash;Valleys were developed in this new land
+surface according to the principles already set forth. Between the
+valleys there were divides, which became higher as the valleys became
+deeper, and narrower as the valleys widened. Ultimately the ridges were
+lowered, and many of them finally eliminated in the manner already
+outlined. The distance below the original surface and that at which the
+first series of new flats were developed is conjectural, but it would
+have depended on the height of the land. So far as can now be inferred,
+the new base-plain toward which the streams cut may have been 400 or 500
+feet below the crests of the quartzite ridges. It was at this level that
+the oldest base-plain of which this immediate region shows evidence, was
+developed.</p>
+
+<p>Had the quartzite ranges not been completely buried by the Paleozoic
+sediments, they would have appeared as ridges on the new land surface,
+and would have had a marked influence on the development of the drainage
+of the newly emerged surface. But as the ranges were probably completely
+buried, the drainage lines were established regardless of the position
+of the hard, but buried ridges. When in the process of degradation the
+quartzite surfaces were reached, the streams encountered a formation far
+more resistant than the surrounding sandstone and limestone. As the less
+resistant strata were worn away, the old quartzite ridges, long buried,
+again became prominent topographic features. In this condition they were
+"resurrected mountains."</p>
+
+<p>If, when erosion on the uplifted surface of Paleozoic rocks began, a
+valley had been located directly over the buried quartzite ridge, and
+<span class="pagenum"> <a name="Page_62" id="Page_62">[Pg 62]</a> </span>
+along its course, it would have been deepened normally until its bottom
+reached the crest of the hard formation. Then, instead of sinking its
+valley vertically downward into the quartzite, the stream would have
+shifted its channel down the slope of the range along the junction of
+the softer and harder rock (Fig. <a href="images/fig25.jpg">25</a>). Such changes occasioned by the
+nature and position of the rock concerned, are known as <i>adjustments</i>.
+<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig25.jpg" width="400" height="141" alt="" />
+</div>
+<p class="center indent">Fig. 25. -- Diagram illustrating the hypothetical case of a
+stream working down the slope of the quartzite range. The successive
+sections of the valley are suggested by the lines ae, be, ce and de.<br />
+<a href="images/fig25.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>Streams which crossed the quartzite ridges on the overlying strata might
+have held their courses even after their valleys were lowered to the
+level of the quartzite. Such streams would have developed narrows at the
+crossing of the quartzite. In so far as there were passes in the
+quartzite range before the deposition of the Paleozoic beds, they were
+filled during the long period of sedimentation, to be again cleared out
+during the subsequent period of erosion. The gap in the South range now
+occupied by the lake was a narrows in a valley which existed, though
+perhaps not to its present depth, before the Potsdam sandstone was
+deposited. It was filled when the sediments of that formation were laid
+down, to be again opened, and perhaps deepened, in the period of erosion
+which followed the deposition of the Paleozoic series.</p>
+
+<p>During the earliest period of erosion of which there is positive
+evidence, after the uplift of the Paleozoic beds, the softer formations
+about the quartzite were worn down to a level 400 or 500 feet below the
+crests of the South quartzite range. At this lower level, an approximate
+plain, a peneplain, was developed, the level of which is shown by
+<span class="pagenum"> <a name="Page_63" id="Page_63">[Pg 63]</a> </span>
+numerous hills, the summits of which now reach an elevation of from
+1,000 to 1,100 feet above the sea. At the time of its development, this
+peneplain was but little above sea level, for this is the only elevation
+at which running water can develop such a plain. Above the general level
+of this plain rose the quartzite ranges as elongate monadnocks (see p.
+<a href="#Page_52">52</a>),
+the highest parts of which were fully 500 feet above the plain. A few other
+points in the vicinity failed to be reduced to the level of the
+peneplain. The 1,320 foot hill (<i>d</i>, Plate <a href="images/i37.jpg">XXXVII</a>), one and
+one-half miles southeast of the Lower narrows, and Gibraltar Rock (<i>e</i>,
+same plate), two miles southeast of Merrimac, rose as prominences above
+it. It is possible that these crests are remnants of a base-level plain
+older than that referred to above. If while the quartzite remained much
+as now, the valleys in the sandstone below 1,000 or 1,100 feet were
+filled, the result would correspond in a general way to the surface
+which existed in this region when the first distinctly recognizable
+cycle of erosion was brought to a close. Above the undulating plain
+developed in the sandstone and limestone, the main quartzite ridge would
+have risen as a conspicuous ridge 400 to 500 feet.</p>
+
+<p>This cycle had not been completed, that is, the work of base-leveling
+had not been altogether accomplished, when the peneplain was elevated,
+and the cycle, though still incomplete, brought to a close. By the
+uplift, the streams were rejuvenated, and sunk their valleys into the
+elevated peneplain. Thus a new cycle of erosion was begun, and the
+uplifted peneplain was dissected by the quickened streams which sank
+their valleys promptly into the slightly resistant sandstone. At their
+new base-level, they ultimately developed new flats. This cycle of
+erosion appears to have advanced no farther than to the development of
+wide flats along the principal streams, such as the Wisconsin and the
+Baraboo, and narrow ones along the subordinate water courses, when it
+was interrupted. Along the main streams the new flats were at a level
+which is now from 800 to 900 feet above the sea, and 700 to 800 feet
+<span class="pagenum"> <a name="Page_64" id="Page_64">[Pg 64]</a> </span>
+below the South quartzite range. It was at this time that the plains
+about Camp Douglas and Necedah, already referred to, were developed.
+During this second incomplete cycle, the quartzite ranges, resisting
+erosion, came to stand up still more prominently than during the first.</p>
+
+<p>The interruption of this cycle was caused by the advent of the glacial
+period which disturbed the normal course of erosion. This period was
+accompanied and followed by slight changes of level which also had their
+influence on the streams. The consideration of the effects of glaciation
+and of subsequent river erosion are postponed, but it may be stated that
+within the area which was glaciated the post-glacial streams have been
+largely occupied in removing the drift deposited by the ice from the
+preglacial valleys, or in cutting new valleys in the drift. The streams
+outside the area of glaciation were less seriously disturbed.</p>
+
+<p>At levels other than those indicated, partial base-levels are suggested,
+and although less well marked in this region, they might, in the study
+of a broader area, bring out a much more complicated erosion history. As
+already suggested, one cycle may have preceded that the remnants of
+which now stand 1,000-1,100 feet above sea level, and another may have
+intervened between this and that marked by the 800 to 900 foot level.</p>
+
+<p>From the foregoing it is clear that the topography of the region is, on
+the whole, an erosion topography, save for certain details in its
+eastern portion. The valleys differ in form and in size, with their age,
+and with the nature of the material in which they are cut; while the
+hills and ridges differ with varying relations to the streams, and with
+the nature of the material of which they are composed. <br /> <br /> <br /> </p>
+
+
+<h4> <i>Striking Scenic Features.</i> <br /> <br /> </h4>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXI.</p>
+
+<div class="figcenter" style="width: 171px;">
+<img src="images/i21.jpg" width="171" height="200" alt="" />
+</div>
+<p class="center indent">Cleopatra's Needle. West Bluff of Devil's Lake.<br />
+<a href="images/i21.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXII.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i22.jpg" width="200" height="122" alt="" />
+</div>
+<p class="center indent">Turk's Head. West Bluff of Devil's Lake.<br />
+<a href="images/i22.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIII.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i23.jpg" width="200" height="129" alt="" />
+</div>
+<p class="center indent">Devil's Doorway. East of Devil's Lake.<br />
+<a href="images/i23.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_65" id="Page_65">[Pg 65]</a> </span>
+In a region so devoid of striking scenery as the central portion of the
+Mississippi basin, topographic features which would be passed without
+special notice in regions of greater relief, become the objects of interest.
+But in south central Wisconsin there are various features which would
+attract attention in any region where the scenery is not mountainous.</p>
+
+<p>On the bluffs at Devil's lake there are many minor features which are
+sure to attract the attention of visitors. Such are "Cleopatra's Needle"
+(Plate <a href="images/i21.jpg">XXI</a>), "Turk's Head"
+(Plate <a href="images/i22.jpg">XXII</a>), and the "Devil's Doorway"
+(Plate <a href="images/i23.jpg">XXIII</a>).</p>
+
+<p>These particular forms have resulted from the peculiar weathering of the
+quartzite. The rock is affected by several systems of vertical or nearly
+vertical joint planes (cracks), which divide the whole formation into a
+series of vertical columns. There are also horizontal and oblique planes
+of cleavage dividing the columns, so that the great quartzite pile may
+be said to be made up of a series of blocks, which are generally in
+contact with one another. The isolated pillars and columns which have
+received special names have been left as they now stand by the falling
+away of the blocks which once surrounded them. They themselves must soon
+follow. The great talus slopes at the base of the bluffs, such as those
+on the west side of the lake and on the East bluff near its southeast
+corner, Plate <a href="images/i24.jpg">XXIV</a>, are silent witnesses of
+the extent to which this process has already gone. The blocks of rock of
+which they are composed have been loosened by freezing water, by the roots
+of trees, and by expansion and contraction due to changing temperature,
+and have fallen from their former positions to those they now occupy.
+Their descent, effected by gravity directly, is, it will be noted, the
+first step in their journey to the sea, the final resting place of all
+products of land degradation.</p>
+
+<p> <i>The Baraboo bluffs.</i>&mdash;Nowhere in southern Wisconsin, or indeed in a
+large area adjacent to it, are there elevations which so nearly approach
+mountains as the ranges of quartzite in the vicinity of Baraboo and
+Devil's lake. So much has already been said of their history that there
+is need for little further description. Plate <a href="images/i04.jpg">IV</a> gives some idea of the
+appearance of the ranges. The history of the ranges, already outlined,
+<span class="pagenum"> <a name="Page_66" id="Page_66">[Pg 66]</a> </span>
+involves the following stages: (1) The deposition of the sands in
+Huronian time; (2) the change of the sand to sandstone and the sandstone
+to quartzite; (3) the uplift and deformation of the beds; (4) igneous
+intrusions, faulting, crushing, and shoaring, with the development of
+schists accompanying the deformation; (5) a prolonged period of erosion
+during which the folds of quartzite were largely worn away, though
+considerable ridges, the Huronian mountains of early Cambrian times,
+still remained high above their surroundings; (6) the submergence of the
+region, finally involving even the crests of the ridges of quartzite;
+(7) a protracted period of deposition during which the Potsdam sandstone
+and several later Paleozoic formations were laid down about, and finally
+over, the quartzite, burying the mountainous ridges; (8) the elevation
+of the Paleozoic sea-bottom, converting it into land; (9) a long period
+of erosion, during which the upper Paleozoic beds were removed, and the
+quartzite re-discovered. Being much harder than the Paleozoic rocks, the
+quartzite ridges again came to stand out as prominent ridges, as the
+surrounding beds of relatively slight resistance were worn away. They
+are "resurrected" mountains, though not with the full height which they
+had in pre-Cambrian time, for they are still partially buried by younger
+beds.</p>
+
+<p> <i>The narrows in the quartzite.</i>&mdash;There are four narrows or passes in the
+quartzite ridges, all of which are rather striking features. One of them
+is in the South range, one in the North range near its eastern end,
+while the others are in an isolated area of quartzite at Ablemans which
+is really a continuation of the North range. Two of these narrows are
+occupied by the Baraboo river, one by Narrows creek, and the fourth by
+Devil's lake.</p>
+
+<p>From Ablemans to a point several miles east of Baraboo, the Baraboo
+river flows through a capacious valley. Where it crosses the North
+range, six miles or more north of east of Baraboo, the broad valley is
+abruptly constricted to a narrow pass with precipitous sides, about 500
+feet high (c, Plate <a href="images/i37.jpg">XXXVII</a>). This constriction is the Lower narrows,
+conspicuous from many
+<span class="pagenum"> <a name="Page_67" id="Page_67">[Pg 67]</a> </span>
+<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIV.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i24.jpg" width="200" height="143" alt="" />
+</div>
+<p class="center indent">Talus slope on the east bluff of Devil's lake.<br />
+<a href="images/i24.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p>points on the South range, and from the plains to the north. Beyond the
+quartzite, the valley again opens out into a broad flat.</p>
+
+<p>Seen from a distance, the narrows has the appearance of an abrupt notch
+in the high ridge (Plate <a href="images/i04.jpg">IV</a>). Seen at closer range, the gap is
+still more impressive. It is in striking contrast with the other narrows
+in that there are no talus accumulations at the bases of the steep
+slopes, and in that the slopes are relatively smooth and altogether free
+from the curious details of sculpture seen in the other gaps where the
+slopes are equally steep.</p>
+
+<p>The Upper narrows of the Baraboo at Ablemans (b, Plate <a href="images/i02.jpg">II</a>) is in some
+ways similar to the Lower, though less conspicuous because less deep.
+Its slopes are more rugged, and piles of talus lie at their bases as at
+Devil's lake. This narrows also differs from the Lower in that the
+quartzite on one side is covered with Potsdam conglomerate, which
+overlies the truncated edges of the vertical layers of quartzite with
+unconformable contact. So clear an example of unconformity is not often
+seen. Potsdam sandstone is also seen to rest against the quartzite on
+either side of the narrows (Fig. <a href="images/fig26.jpg">26</a>), thus emphasizing the unconformity.
+The beauty and interest of this narrows is enhanced by the quartzite
+breccia (p. <a href="#Page_18">18</a>) which appears on its walls.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig26.jpg" width="400" height="94" alt="" />
+</div>
+<p class="center indent">Fig. 26. -- A generalized diagrammatic cross-section at the
+Upper narrows, to show the relation of the sandstone to the quartzite.<br />
+<a href="images/fig26.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>One and one-half miles west of Ablemans (<i>a</i>, Plate
+<a href="images/i02.jpg">II</a>) is the third pass in the north quartzite
+ridge. This pass is narrower than the others, and is occupied by Narrows
+creek. Its walls are nearly vertical and possess the same rugged beauty as
+those at Ablemans. As at the Upper narrows, the beds of quartzite here are
+essentially vertical. They are
+<span class="pagenum"> <a name="Page_68" id="Page_68">[Pg 68]</a> </span>
+indeed the continuation of the beds exposed at that place.</p>
+
+<p>The fourth narrows is across the South range (i, Plate <a href="images/i02.jpg">II</a>). It is not
+now occupied by a stream, though like the others it was cut by a stream,
+which was afterwards shut out from it. Because of its depth, 600 feet,
+and the ruggedness of its slopes, and because of its occupancy by the
+lake, this pass is the center of interest for the whole region. So much
+has already been said concerning it in other portions of this report
+that further description is here omitted. The manner in which the pass
+was robbed of its stream will be discussed later (p. <a href="#Page_138">138</a>).</p>
+
+<p>The history of these several narrows, up to the time of the glacial
+period may now be summarized. Since remnants of Potsdam sandstone are
+found in some of them, it is clear that they existed in pre-Cambrian time,
+<a name="FNanchor_1_6" id="FNanchor_1_6"> </a> <a href="#Footnote_1_6" class="fnanchor">[6]</a>
+and there is no reason to doubt that they are the work of the
+streams of those ancient days, working as streams now work. Following
+the pre-Cambrian period of erosion during which the notches were cut,
+came the submergence of the region, and the gaps were filled with sand
+and gravel, and finally the ridges themselves were buried. Uplift and a
+second period of erosion followed, during which the quartzite ranges
+were again exposed by the removal of the beds which overlay them, and
+the narrows cleaned out and deepened, and again occupied by streams.
+This condition of things lasted up to the time when the ice invaded the
+region.</p>
+
+<p> <i>Glens.</i>&mdash;No enumeration of the special scenic features of this region
+would be complete without mention of Parfrey's and Dorward's glens (<i>a</i>
+and <i>b</i>, Plate <a href="images/i37.jpg">XXXVII</a>, and Plate
+<a href="images/i25.jpg">XXV</a>). Attention has already been
+directed to them as illustrations of young valleys, and as places where
+the Potsdam conglomerate is well shown, but they are attractive from the
+scenic point of view. Their frequent mention in earlier parts of this
+report makes further reference to them at this point unnecessary.
+<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXV.</p>
+
+<div class="figcenter" style="width: 175px;">
+<img src="images/i25.jpg" width="175" height="168" alt="" />
+</div>
+<p class="center indent">In Dorward's Glen. The basal conglomerate of the Potsdam formation is
+shown at the lower right-hand corner, and is overlain by sandstone.
+(Photograph furnished by Mr. Wilfred Dorward).<br />
+<a href="images/i25.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVI.</p>
+
+<div class="figcenter" style="width: 163px;">
+<img src="images/i26.jpg" width="163" height="200" alt="" />
+</div>
+<p class="center indent">Natural bridge near Denzer.<br />
+<a href="images/i26.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVII.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i27.jpg" width="200" height="131" alt="" />
+</div>
+<p class="center indent">Navy Yard. Dalles of the Wisconsin.<br />
+<a href="images/i27.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_69" id="Page_69">[Pg 69]</a> </span>
+Pine Hollow (k, Plate <a href="images/i02.jpg">II</a>) is another attractive gorge on the south flank
+of the greater quartzite range. The rock at this point is especially
+well exposed. This gorge is beyond the drift-covered portion of the
+range, and therefore dates from the pre-glacial time.</p>
+
+<p>The Pewit's nest, about three miles southwest of Baraboo (m, Plate <a href="images/i02.jpg">II</a>),
+is another point of interest. Above the "nest," Skillett creek flows
+through a narrow and picturesque gorge in the Potsdam sandstone. The
+origin of this gorge is explained elsewhere (p. <a href="#Page_53">53</a>).</p>
+
+<p> <i>Natural Bridge.</i>&mdash;About two miles north and a little west of the
+village of Denzer (Sec. 17, T. 10 N., R. 5 E.), is a small natural
+bridge, which has resulted from the unequal weathering of the sandstone
+(see Plate <a href="images/i26.jpg">XXVI</a>). The "bridge" is curious, rather than beautiful or
+impressive.</p>
+
+<p> <i>The Dalles of the Wisconsin.</i>&mdash;The <i>dalles</i> is the term applied to a
+narrow canyon-like stretch of the Wisconsin valley seven miles in length, near Kilbourn
+City (see <a href="images/frontispiece.jpg">Frontispiece</a>). The depth of the gorge is
+from 50 to 100 feet. The part above the bridge at Kilbourn City is the
+"Upper dalles;" that below, the "Lower dalles." Within this stretch of
+the valley are perhaps the most picturesque features of the region.</p>
+
+<p>The sides of the gorge are nearly vertical much of the way, and at many
+points are so steep on both sides that landing would be impossible.
+Between these sandstone walls flows the deep and swift Wisconsin river.</p>
+
+<p>Such a rock gorge is in itself a thing of beauty, but in the dalles
+there are many minor features which enhance the charm of the whole.</p>
+
+<p>One of the features which deserves especial mention is the peculiar
+crenate form of the walls at the banks of the river. This is perhaps
+best seen in that part of the dalles known as the "Navy Yard." Plate
+<a href="images/i27.jpg">XXVII</a>. The sandstone is affected by a series of vertical cracks or
+joints. From weathering, the rock along these joints becomes softened,
+and the running water wears the softened rock at the joint planes more
+readily than other parts of its bank, and so develops a reëntrant at
+<span class="pagenum"> <a name="Page_70" id="Page_70">[Pg 70]</a> </span>
+these points. Rain water descending to the river finds and follows the
+joint planes, and thus widens the cracks. As a result of stream and rain
+and weathering, deep reëntrant angles are produced. The projections
+between are rounded off so that the banks of the stream have assumed the
+crenate form shown in Plate <a href="images/i28.jpg">XXVIII</a>, and
+<a href="images/frontispiece.jpg">Frontispiece</a>.</p>
+
+<p>When this process of weathering at the joints is carried sufficiently
+far, columns of rock become isolated, and stand out on the river bluffs
+as "chimneys" (Plate <a href="images/i28.jpg">XXVIII</a>). At a still later stage of development,
+decay of the rock along the joint planes may leave a large mass of rock
+completely isolated. "Steamboat rock" (Plate <a href="images/i12.jpg">XII</a>) and "Sugar
+bowl" (Plate <a href="images/i29.jpg">XXIX</a>) are examples of islands thus formed.</p>
+
+<p>The walls of sandstone weather in a peculiar manner at some points in
+the Lower dalles, as shown on Plate <a href="images/i30.jpg">XXX</a>. The little ridges stand out
+because they are harder and resist weathering better than the other
+parts. This is due in part at least to the presence of iron in the more
+resistant portions, cementing them more firmly. In the process of
+segregation, cementing materials are often distributed unequally.</p>
+
+<p>The effect of differences in hardness on erosion is also shown on a
+larger scale and in other ways. Perhaps the most striking illustration
+is <i>Stand rock</i> (Plate <a href="images/i31.jpg">XXXI</a>), but most of the innumerable and
+picturesque irregularities on the rock walls are to be accounted for by
+such differences.</p>
+
+<p>Minor valleys tributary to the Wisconsin, such as <i>Witch's gulch</i> and
+<i>Cold Water canyon</i> deserve mention, both because of their beauty, and
+because they illustrate a type of erosion at an early stage of valley
+development. In character they are comparable to the larger gorge to
+which they are tributary. In the downward cutting, which far exceeds the
+side wear in these tributary canyons, the water has excavated large bowl
+or jug-like forms. In Witch's gulch such forms are now being excavated.
+They are developed just below falls, where the water carrying debris,
+eddies, and the jugs or pot-holes are the result of the wear effected by
+the eddies. The "Devil's jug" and many similar hollows are thus explained.
+<br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVIII.</p>
+
+<div class="figcenter" style="width: 150px;">
+<img src="images/i28.jpg" width="150" height="227" alt="" />
+</div>
+<p class="center indent">Chimney Rock. Dalles of the Wisconsin. Cross-bedding well shown in
+foreground near bottom.<br />
+<a href="images/i28.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIX.</p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/i29.jpg" width="250" height="148" alt="" />
+</div>
+<p class="center indent">An Island in the Lower Dalles.<br />
+<a href="images/i29.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXX.</p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/i30.jpg" width="250" height="192" alt="" />
+</div>
+<p class="center indent">View in lower Dalles showing peculiar honeycomb weathering.<br />
+<a href="images/i30.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_71" id="Page_71">[Pg 71]</a> </span>
+<i>The mounds and castle rocks.</i>&mdash;In the vicinity of Camp Douglas and over
+a large area to the east, are still other striking topographic forms,
+which owe their origin to different conditions, though they were
+fashioned by the same forces. Here there are many "tower" or "castle"
+rocks, which rise to heights varying from 75 to 190 feet above the
+surrounding plain. They are remnants of beds which were once continuous
+over the low lands above which the hills now rise. In Plates <a href="images/i17.jpg">XVII</a> and
+<a href="images/i18.jpg">XVIII</a> the general character of these hills is shown. The rock of
+which they are composed is Potsdam sandstone, the same formation which
+underlies most of the area about Baraboo. The effect of the vertical
+joints and of horizontal layers of unequal hardness is well shown.
+Rains, winds, frosts, and roots are still working to compass the
+destruction of these picturesque hills, and the talus of sand bordering
+the "castle" is a reminder of the fate which awaits them. These hills
+are the more conspicuous and the more instructive since the plain out of
+which they rise is so flat. It is indeed one of the best examples of a
+base-level plain to be found on the continent.</p>
+
+<p>The crests of these hills reach an elevation of between 1,000 and 1,100
+feet. They appear to correspond with the level of the first peneplain
+recognized in the Devil's lake region. It was in the second cycle of
+erosion, when their surroundings were brought down to the new
+base-level, that these hills were left. West of Camp Douglas, there are
+still higher elevations, which seem to match Gibraltar rock (see p.
+<a href="#Page_63">63</a>).</p>
+
+<p>The Friendship "mounds" north of Kilbourn City, the castellated hills a
+few miles northwest of the same place, and Petenwell peak on the banks
+of the Wisconsin (Plate <a href="images/i32.jpg">XXXII</a>), are further
+examples of the same class of hills. All are of Potsdam sandstone.</p>
+
+<p>In addition to the "castle" rocks and base-level plain about Camp
+Douglas, other features should be mentioned. No other portion of the
+area touched upon in this report affords such fine examples of the
+<span class="pagenum"> <a name="Page_72" id="Page_72">[Pg 72]</a> </span>
+different types of erosion topography. In the base-level plain are found
+"old-age" valleys, broad and shallow, with the stream meandering in a
+wide flood-plain. Traveling up such a valley, the topography becomes
+younger and younger, and the various stages mentioned on p. <a href="#Page_46">46</a>, and
+suggested in Plate <a href="#i19">XIX Figs. 1 and 2</a>, and Plate
+<a href="#i20">XX Fig. 1</a>, are here illustrated.<br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXI.</p>
+
+<div class="figcenter" style="width: 150px;">
+<img src="images/i31.jpg" width="150" height="192" alt="" />
+</div>
+<p class="center indent">Stand Rock. Upper end of the Upper Dalles.<br />
+<a href="images/i31.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXII.</p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/i32.jpg" width="250" height="159" alt="" />
+</div>
+<p class="center indent">Pentenwell Peak.<br />
+<a href="images/i32.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_73" id="Page_73">[Pg 73]</a> </span> </p>
+
+
+<h2>CHAPTER V.</h2>
+
+<h4>THE GLACIAL PERIOD.</h4>
+
+
+<p>The eastern part of the area with which this report deals, is covered
+with a mantle of drift which, as already pointed out, has greatly
+modified the details of its topography. To the consideration of the
+drift and its history attention is now turned.</p>
+
+<p> <i>The drift.</i>&mdash;The drift consists of a body of clay, sand, gravel and
+bowlders, spread out as a cover of unequal thickness over the rock
+formations beneath. These various classes of material may be confusedly
+commingled, or they may be more or less distinctly separated from one
+another. When commingled, all may be in approximately equal proportions,
+or any one may predominate over any or all the others to any extent.</p>
+
+<p>It was long since recognized that the materials of the drift did not
+originate where they now lie, and that, in consequence, they sustain no
+genetic relationship to the strata on which they rest. Long before the
+drift received any special attention from geologists, it was well known
+that it had been transported from some other locality to that where it
+now occurs. The early conception was that it had been drifted into its
+present position from some outside source by water. It was this
+conception of its origin which gave it the name of <i>drift</i>. It is now
+known that the drift was deposited by glacier ice and the waters which
+arose from its melting, but the old name is still retained.</p>
+
+<p>Clearly to understand the origin of the drift, and the method by which
+it attained its present distribution, it may be well to consider some
+elementary facts and principles concerning climate and its effects, even
+at the risk of repeating what is already familiar.</p>
+
+<p> <span class="pagenum"> <a name="Page_74" id="Page_74">[Pg 74]</a> </span>
+<i>Snow fields and ice sheets.</i>&mdash;The temperature and the snowfall of a
+region may stand in such a relation to each other that the summer's heat
+may barely suffice to melt the winter's snow. If under these
+circumstances the annual temperature were to be reduced, or the fall of
+snow increased, the summer's heat would fail to melt all the winter's
+snow, and some portion of it would endure through the summer, and
+through successive summers, constituting a perennial snow-field. Were
+this process once inaugurated, the depth of the snow would increase from
+year to year. The area of the snow-field would be extended at the same
+time, since the snow-field would so far reduce the surrounding
+temperature as to increase the proportion of the annual precipitation
+which fell as snow. In the course of time, and under favorable
+conditions, the area of the snow-field would attain great dimensions,
+and the depth of the snow would become very great.</p>
+
+<p>As in the case of existing snow fields the lower part of the snow mass
+would eventually be converted into ice. Several factors would conspire
+to this end. 1. The pressure of the overlying snow would tend to
+compress the lower portion, and snow rendered sufficiently compact by
+compression would be regarded as ice. 2. Water arising from the melting
+of the surface snow by the sun's heat, would percolate through the
+superficial layers of snow, and, freezing below, take the form of ice.
+3. On standing, even without pressure or partial melting, snow appears
+to undergo changes of crystallization which render it more compact. In
+these and perhaps other ways, a snow-field becomes an ice-field, the
+snow being restricted to its surface.</p>
+
+<p>Eventually the increase in the depth of the snow and ice in a snow-field
+will give rise to new phenomena. Let a snow and ice field be assumed in
+which the depth of snow and ice is greatest at the center, with
+diminution toward its edges. The field of snow, if resting on a level
+base, would have some such cross-section as that represented in the
+diagram, Fig. <a href="images/fig27.jpg">27</a>.</p>
+
+<p>When the thickness of the ice has become considerable, it is evident
+that the pressure upon its lower and marginal parts will be great. We
+<span class="pagenum"> <a name="Page_75" id="Page_75">[Pg 75]</a> </span>
+are wont to think of ice as a brittle solid. If in its place there were
+some plastic substance which would yield to pressure, the weight of the
+ice would cause the marginal parts to extend themselves in all
+directions by a sort of flowing motion.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig27.jpg" width="300" height="40" alt="" />
+</div>
+<p class="center indent">Fig. 27. -- Diagrammatic cross-section of a field of ice
+and snow (C) resting on a level base A-B.<br />
+<a href="images/fig27.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>Under great pressure, many substances which otherwise appear to be
+solid, exhibit the characteristics of plastic bodies. Among the
+substances exhibiting this property, ice is perhaps best known. Brittle
+and resistant as it seems, it may yet be molded into almost any
+desirable form if subjected to sufficient pressure, steadily applied
+through long intervals of time. The changes of form thus produced in ice
+are brought about without visible fracture. Concerning the exact nature
+of the movement, physicists are not agreed; but the result appears to be
+essentially such as would be brought about if the ice were capable of
+flowing, with extreme slowness, under great pressure continuously
+applied.</p>
+
+<p>In the assumed ice-field, there are the conditions for great pressure
+and for its continuous application. If the ice be capable of moving as a
+plastic body, the weight of the ice would induce gradual movement
+outward from the center of the field, so that the area surrounding the
+region where the snow accumulated would gradually be encroached upon by
+the spreading of the ice. Observation shows that this is what takes
+place in every snow-field of sufficient depth. Motion thus brought about
+is glacier motion, and ice thus moving is glacier ice.</p>
+
+<p>Once in motion, two factors would determine the limit to which the ice
+would extend itself: (1) the rate at which it advances; and (2) the rate
+at which the advancing edge is wasted. The rate of advance would depend
+upon several conditions, one of which, in all cases, would be the
+pressure of the ice which started and which perpetuates the motion. If
+<span class="pagenum"> <a name="Page_76" id="Page_76">[Pg 76]</a> </span>
+the pressure be increased the ice will advance more rapidly, and if it
+advance more rapidly, it will advance farther before it is melted. Other
+things remaining constant, therefore, increase of pressure will cause
+the ice-sheet to extend itself farther from the center of motion.
+Increase of snowfall will increase the pressure of the snow and ice
+field by increasing its mass. If, therefore, the precipitation over a
+given snow-field be increased for a period of years, the ice-sheet's
+marginal motion will be accelerated, and its area enlarged. A decrease
+of precipitation, taken in connection with unchanged wastage would
+decrease the pressure of the ice and retard its movement. If, while the
+rate of advance diminished, the rate of wastage remained constant, the
+edge of the ice would recede, and the snow and ice field be contracted.</p>
+
+<p>The rate at which the edge of the advancing ice is wasted depends
+largely on the climate. If, while the rate of advance remains constant,
+the climate becomes warmer, melting will be more rapid, and the ratio
+between melting and advance will be increased. The edge of the ice will
+therefore recede. The same result will follow, if, while temperature
+remains constant, the atmosphere becomes drier, since this will increase
+wastage by evaporation. Were the climate to become warmer and drier at
+the same time, the rate of recession of the ice would be greater than if
+but one of these changes occurred.</p>
+
+<p>If, on the other hand, the temperature over and about the ice field be
+lowered, melting will be diminished, and if the rate of movement be
+constant, the edge of the ice will advance farther than under the
+earlier conditions of temperature, since it has more time to advance
+before it is melted. An increase in the humidity of the atmosphere,
+while the temperature remains constant, will produce the same result,
+since increased humidity of the atmosphere diminishes evaporation. A
+decrease of temperature, decreasing the melting, and an increase of
+humidity, decreasing the evaporation, would cause the ice to advance
+farther than either change alone, since both changes decrease the
+wastage. If, at the same time that conditions so change as to increase
+<span class="pagenum"> <a name="Page_77" id="Page_77">[Pg 77]</a> </span>
+the rate of movement of the ice, climatic conditions so change as to
+reduce the rate of waste, the advance of the ice before it is melted
+will be greater than where only one set of conditions is altered. If,
+instead of favoring advance, the two series of conditions conspire to
+cause the ice to recede, the recession will likewise be greater than
+when but one set of conditions is favorable thereto.</p>
+
+<p>Greenland affords an example of the conditions here described. A large
+part of the half million or more square miles which this body of land is
+estimated to contain, is covered by a vast sheet of snow and ice,
+thousands of feet in thickness. In this field of snow and ice, there is
+continuous though slow movement. The ice creeps slowly toward the
+borders of the island, advancing until it reaches a position where the
+climate is such as to waste (melt and evaporate) it as rapidly as it
+advances.</p>
+
+<p>The edge of the ice does not remain fixed in position. There is reason
+to believe that it alternately advances and retreats as the ratio
+between movement and waste increases or decreases. These oscillations in
+position are doubtless connected with climatic changes. When the ice
+edge retreats, it may be because the waste is increased, or because the
+snowfall is decreased, or both. In any case, when the ice edge recedes
+from the coast, it tends to recede until its edge reaches a position
+where the melting is less rapid than in its former position, and where
+the advance is counterbalanced by the waste. This represents a condition
+of equilibrium so far as the edge of the ice is concerned, and here the
+edge of the ice would remain so long as the conditions were unchanged.</p>
+
+<p>When for a period of years the rate of melting of the ice is diminished,
+or the snowfall increased, or both, the ice edge advances to a new line
+where melting is more rapid than at its former edge. The edge of the ice
+would tend to reach a position where waste and advance balance. Here its
+advance would cease, and here its edge would remain so long as climatic
+conditions were unchanged.</p>
+
+<p>If the conditions determining melting and flowage be continually
+<span class="pagenum"> <a name="Page_78" id="Page_78">[Pg 78]</a> </span>
+changing, the ice edge will not find a position of equilibrium, but will
+advance when the conditions are favorable for advance, and retreat when
+the conditions are reversed.</p>
+
+<p>Not only the edge of the ice in Greenland, but the ends of existing
+mountain glaciers as well, are subject to fluctuation, and are delicate
+indices of variations in the climate of the regions where they occur.</p>
+
+<p> <i>The North American ice sheet.</i>&mdash;In an area north of the eastern part of
+the United States and in another west of Hudson Bay it is believed that
+ice sheets similar to that which now covers Greenland began to
+accumulate at the beginning of the glacial period. From these areas as
+centers, the ice spread in all directions, partly as the result of
+accumulation, and partly as the result of movement induced by the weight
+of the ice itself.</p>
+
+<p>The ice sheets spreading from these centers came together south of
+Hudson's bay, and invaded the territory of the United States as a single
+sheet, which, at the time of its greatest development, covered a large
+part of our country (Plate <a href="images/i33.jpg">XXXIII</a>), its
+area being known by the extent of the drift which it left behind when it
+was melted. In the east, it buried the whole of New England, most of New
+York, and the northern parts of New Jersey and Pennsylvania. Farther west,
+the southern margin of the ice crossed the Ohio river in the vicinity of
+Cincinnati, and pushed out over the uplands a few miles south of the river.
+In Indiana, except at the extreme east, its margin fell considerably short
+of the Ohio; in Illinois it reached well toward that river, attaining here its
+most southerly latitude. West of the Mississippi, the line which marks
+the limit of its advance curves to the northward, and follows, in a
+general way, the course of the Missouri river. The total area of the
+North American ice sheet, at the time of its maximum development, has
+been estimated to have been about 4,000,000 square miles, or about ten
+times the estimated area of the present ice-field of Greenland.</p>
+
+<p>Within the general area covered by the ice, there is an area of several
+thousand square miles, mainly in southwestern Wisconsin, where there is
+no drift. The ice, for some reason, failed to cover this <i>driftless
+area</i> though it overwhelmed the territory on all sides.
+<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIII.</p>
+
+<div class="figcenter" style="width: 219px;">
+<img src="images/i33.jpg" width="219" height="300" alt="" />
+</div>
+<p class="center indent">The North American Ice Sheet, at the time of maximum development.<br />
+<a href="images/i33.jpg">See larger image</a> <br /> <br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIV.</p>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/i34.jpg" width="350" height="121" alt="" />
+</div>
+<p class="center indent">View from the north of the Owl's Head, a hill two miles north of east of
+Merrimac, which has been shaped by the ice. The side to the left is the
+stone side.<br />
+<a href="images/i34.jpg">See larger image</a> <br /> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_79" id="Page_79">[Pg 79]</a> </span> </p>
+
+<p>Plate <a href="images/i02.jpg">II</a> shows the limit of ice advance in the area here described. The
+region may have been affected by the ice of more than one glacial epoch,
+but the chief results now observable were effected during the last, and
+the others need not be considered. <br /> <br /> </p>
+
+
+<h4> <i>The Work of Glacier Ice.</i> </h4>
+
+<p>As the edge of an ice sheet, or as the end of a glacier, retreats, the
+land which it has previously covered is laid bare, and the effects which
+the passage of the ice produced may be seen. In some cases one may
+actually go back a short distance beneath the ice now in motion, and see
+its mode of work and the results it is effecting. The beds of living
+glaciers, and the beds which glaciers have recently abandoned, are found
+to present identical features. Because of their greater accessibility,
+the latter offer the better facilities for determining the effects of
+glaciation.</p>
+
+<p>The conspicuous phenomena of abandoned glacier beds fall into two
+classes, (1) those which pertain to the bed rock over which the ice
+moved, and (2) those which pertain to the drift left by the ice.</p>
+
+<p> <i>Erosive work of the ice.</i>&mdash;<i>Effect on topography.</i>&mdash;The leading
+features of the rock bed over which glacier ice has moved, are easily
+recognized. Its surface is generally smoothed and polished, and
+frequently marked by lines (striæ) or grooves, parallel to one another.
+An examination of the bottom of an active glacier discloses the method
+by which the polishing and scoring are accomplished.</p>
+
+<p>The lower surface of the ice is thickly set with a quantity of clay,
+sand, and stony material of various grades of coarseness. These earthy
+and stony materials in the base of the ice are the tools with which it
+works. Thus armed, the glacier ice moves slowly forward, resting down
+upon the surfaces over which it passes with the whole weight of its
+mass, and the grinding action between the stony layer at the base of the
+ice and the rock bed over which it moves, is effective. If the material
+in the bottom of the ice be fine, like clay, the rock bed is polished.
+<span class="pagenum"> <a name="Page_80" id="Page_80">[Pg 80]</a> </span>
+If coarser materials, harder than the bed-rock, be mingled with the
+fine, the rock bed of the glacier will be scratched as well as polished.
+If there are bowlders in the bottom of the ice they may cut grooves or
+gorges in the underlying rock. The grooves may subsequently be polished
+by the passage over and through them of ice carrying clay or other fine,
+earthy matter.</p>
+
+<p>All these phases of rock wear may be seen about the termini of receding
+glaciers, on territory which they have but recently abandoned. There can
+thus be no possible doubt as to the origin of the polishing, planing and
+scoring.</p>
+
+<p>There are other peculiarities, less easily defined, which characterize
+the surface of glacier beds. The wear effected is not confined to the
+mere marking of the surface over which it passes. If prominences of rock
+exist in its path, as is often the case, they oppose the movement of the
+ice, and receive a corresponding measure of abrasion from it. If they be
+sufficiently resistant they may force the ice to yield by passing over
+or around them; but if they be weak, they are likely to be destroyed.</p>
+
+<p>As the ice of the North American ice sheet advanced, seemingly more
+rigid when it encountered yielding bodies, and more yielding when it
+encountered resistant ones, it denuded the surface of its loose and
+movable materials, and carried them forward. This accumulation of earthy
+and stony debris in the bottom of the ice, gave it a rough and grinding
+lower surface, which enabled it to abrade the land over which it passed
+much more effectively than ice alone could have done. Every hill and
+every mound which the ice encountered contested its advance. Every
+sufficiently resistant elevation compelled the ice to pass around or
+over it; but even in these cases the ice left its marks upon the surface
+to which it yielded. The powerful pressure of pure ice, which is
+relatively soft, upon firm hills of rock, which are relatively hard,
+would effect little. The hills would wear the ice, but the effect of the
+ice on the hills would be slight. But where the ice is supplied with
+earthy and stony material derived from the rock itself, the case is
+different. Under these conditions, the ice, yielding only under great
+<span class="pagenum"> <a name="Page_81" id="Page_81">[Pg 81]</a> </span>
+pressure and as little as may be, rubs its rock-shod base over every
+opposing surface, and with greatest severity where it meets with
+greatest resistance. Its action may be compared to that of a huge
+"flexible-rasp" fitting down snugly over hills and valleys alike, and
+working under enormous pressure.</p>
+
+<p>The abrasion effected by a moving body of ice under such conditions
+would be great. Every inch of ice advance would be likely to be attended
+by loss to the surface of any obstacle over or around which it is
+compelled to move. The sharp summits of the hills, and all the angular
+rugosities of their surfaces would be filed off, and the hills smoothed
+down to such forms as will offer progressively less and less resistance.
+If the process of abrasion be continued long enough, the forms, even of
+the large hills, may be greatly altered, and their dimensions greatly
+reduced. Among the results of ice wear, therefore, will be a lowering of
+the hills, and a smoothing and softening of their contours, while their
+surfaces will bear the marks of the tools which fashioned them, and will
+be polished, striated or grooved, according to the nature of the
+material which the ice pressed down upon them during its passage. Figs.
+<a href="images/fig28.jpg">28</a> and <a href="images/fig29.jpg">29</a>
+show the topographic effects which ice is likely to produce by
+erosion. Plate <a href="images/i34.jpg">XXXIV</a> is a hill two miles northeast of Merrimac, which
+shows how perfectly the wear actually performed corresponds to that
+which might be inferred.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig28.jpg" width="400" height="74" alt="" />
+</div>
+<p class="center indent">Fig. 28. -- A hill before the ice passes over it.<br /> <br /> <br /> <br /> </p>
+
+<p>A rock hill was sometimes left without covering of drift after having
+been severely worn by the ice. Such a hill is known as a <i>roche
+moutonnée</i>. An example of this type of hill occurs three miles north of
+east of Baraboo at the point marked <i>z</i> on Plate <a href="images/i37.jpg">XXXVII</a>.
+<span class="pagenum"> <a name="Page_82" id="Page_82">[Pg 82]</a> </span>
+This hill, composed of quartzite, is less symmetrical than those shown
+in Figs. <a href="images/fig28.jpg">28</a> and <a href="images/fig29.jpg">29</a>.
+Its whole surface, not its stoss side only, has been
+smoothed and polished by the ice. This hill is the most accessible, the
+most easily designated, and, on the whole, the best example of a <i>roche
+moutonnée</i> in the region, though many other hills show something of the
+same form.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig29.jpg" width="400" height="124" alt="" />
+</div>
+<p class="center indent">Fig. 29. -- The same hill after it has been eroded by the
+ice. <i>A</i> the stoss side. <i>B</i> the lee side.<br /> <br /> <br /> </p>
+
+<p>It was not the hills alone which the moving ice affected. Where it
+encountered valleys in its course they likewise suffered modification.
+Where the course of a valley was parallel to the direction of the ice
+movement, the ice moved through it. The depth of moving ice is one of
+the determinants of its velocity, and because of the greater depth of
+ice in valleys, its motion here was more rapid than on the uplands
+above, and its abrading action more powerful. Under these conditions the
+valleys were deepened and widened.</p>
+
+<p>Where the courses of the valleys were transverse to the direction of ice
+movement, the case was different. The ice was too viscous to span the
+valleys, and therefore filled them. In this case it is evident that the
+greater depth of the ice in the valley will not accelerate its motion,
+since the ice in the valley-trough and that above it are in a measure
+opposed. If left to itself, the ice in the valley would tend to flow in
+the direction of the axis of the valley. But in the case under
+consideration, the ice which lies above the valley depression is in
+motion at right angles to the axis of the valley. Under these
+circumstances three cases might arise:</p>
+
+<p> <span class="pagenum"> <a name="Page_83" id="Page_83">[Pg 83]</a> </span>
+1. If the movement of the ice sheet over the valley were able to push
+the valley ice up the farther slope, and out on the opposite highland,
+this work would retard the movement of the upper ice, since the
+resistance to movement would be great. In this case, the thickness of
+the ice is not directly and simply a determinant of its velocity. Under
+these conditions the bottom of the valley would not suffer great
+erosion, since ice did not move along it; but that slope of the valley
+against which the ice movement was projected would suffer great wear
+(Fig. <a href="images/fig30.jpg">30</a>). The valley would therefore be widened, and the slope
+suffering greatest wear would be reduced to a lower angle. Shallow
+valleys, and those possessing gentle slopes, favor this phase of ice
+movement and valley wear.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig30.jpg" width="400" height="94" alt="" />
+</div>
+<p class="center indent">Fig. 30. -- Diagram showing effect on valley of ice moving
+transversely across it.<br /> <br /> <br /> </p>
+
+<p>2. The ice in the valley might become stationary, in which case it
+might serve as a bridge for the upper ice to cross on (Fig. <a href="images/fig31.jpg">31</a>). In this
+case also the total thickness of ice will not be a determinant of its
+velocity, for it is the thickness of the moving ice only, which
+influences the velocity. In this case the valley would not suffer much
+wear, so long as this condition of things continued. Valleys which have
+great depth relative to the thickness of the ice, and valleys whose
+slopes are steep, favor this phase of movement.</p>
+
+<p>3. In valleys whose courses are transverse to the direction of ice
+movement, transverse currents of ice may exist, following the direction
+of the valleys. If the thickness of the ice be much greater than the
+depth of the valley, if the valley be capacious, and if one end of it be
+open and much lower than the other, the ice filling it may move along
+its axis, while the upper ice continues in its original course at right
+<span class="pagenum"> <a name="Page_84" id="Page_84">[Pg 84]</a> </span>
+angles to the valley. In this case the valley would be deepened and
+widened, but this effect would be due to the movement along its course,
+rather than to that transverse to it.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig31.jpg" width="400" height="126" alt="" />
+</div>
+<p class="center indent">Fig. 31. -- Diagram to illustrate case where ice fills a
+valley (C) and the upper ice then moves on over the filling.<br /> <br /> <br /> </p>
+
+<p>If the course of a valley were oblique to the direction of ice movement,
+its effect on the movement of ice would be intermediate between that of
+valleys parallel to the direction of movement, and those at right angles
+to it.</p>
+
+<p>It follows from the foregoing that the corrasive effects of ice upon the
+surface over which it passed, were locally dependent on pre-existent
+topography, and its relation to the direction of ice movement. In
+general, the effort was to cut down prominences, thus tending to level
+the surface. But when it encountered valleys parallel to its movement
+they were deepened, thus locally increasing relief. Whether the
+reduction of the hills exceeded the deepening of the valleys, or whether
+the reverse was true, so far as corrasion alone is concerned, is
+uncertain. But whatever the effect of the erosive effect of ice action
+upon the total amount of relief, the effect upon the contours was to
+make them more gentle. Not only were the sharp hills rounded off, but
+even the valleys which were deepened were widened as well, and in the
+process their slopes became more gentle. A river-erosion topography,
+modified by the wearing (not the depositing) action of the ice, would be
+notably different from the original, by reason of its gentler slopes and
+softer contours (Figs. <a href="images/fig28.jpg">28</a> and
+<a href="images/fig29.jpg">29</a>).</p>
+
+<p> <span class="pagenum"> <a name="Page_85" id="Page_85">[Pg 85]</a> </span>
+<i>Deposition by the ice. Effect on topography.</i>&mdash;On melting, glacier ice
+leaves its bed covered with the debris which it gathered during its
+movement. Had this debris been equally distributed on and in and beneath
+the ice during its movement, and had the conditions of deposition been
+everywhere the same, the drift would constitute a mantle of uniform
+thickness over the underlying rock. Such a mantle of drift would not
+greatly alter the topography; it would simply raise the surface by an
+amount equal to the thickness of the drift, leaving elevations and
+depressions of the same magnitude as before, and sustaining the same
+relations to one another. But the drift carried by the ice, in whatever
+position, was not equally distributed during transportation, and the
+conditions under which it was deposited were not uniform, so that it
+produced more or less notable changes in the topography of the surface
+on which it was deposited.</p>
+
+<p>The unequal distribution of the drift is readily understood. The larger
+part of the drift transported by the ice was carried in its basal
+portion; but since the surface over which the ice passed was variable,
+it yielded a variable amount of debris to the ice. Where it was hilly,
+the friction between it and the ice was greater than where it was plain,
+and the ice carried away more load. From areas where the surface was
+overspread by a great depth of loose material favorably disposed for
+removal, more debris was taken than from areas where material in a
+condition to be readily transported was meager. Because of the
+topographic diversity and lithological heterogeneity of the surface of
+the country over which it passed, some portions of the ice carried much
+more drift than others, and when the ice finally melted, greater depths
+of drift were left in some places than in others. Not all of the
+material transported by the ice was carried forward until the ice
+melted. Some of it was probably carried but a short distance from its
+original position before it lodged. Drift was thus accumulating at some
+points beneath the ice during its onward motion. At such points the
+surface was being built up; at other points, abrasion was taking place,
+and the surface was being cut down. The drift mantle of any region does
+<span class="pagenum"> <a name="Page_86" id="Page_86">[Pg 86]</a> </span>
+not, therefore, represent simply the material which was on and in and
+beneath the ice of that place at the time of its melting, but it
+represents, in addition, all that lodged beneath the ice during its
+movement.</p>
+
+<p>The constant tendency was for the ice to carry a considerable part of
+its load forward toward its thinned edge, and there to leave it. It
+follows that if the edge of the ice remained constant in position for
+any considerable period of time, large quantities of drift would have
+accumulated under its marginal portion, giving rise to a belt of
+relatively thick drift. Other things being equal, the longer the time
+during which the position of the edge was stationary, the greater the
+accumulation of drift. Certain ridge-like belts where the drift is
+thicker than on either hand, are confidently believed to mark the
+position where the edge of the ice-sheet stood for considerable periods
+of time.</p>
+
+<p>Because of the unequal amounts of material carried by different parts of
+the ice, and because of the unequal and inconstant conditions of
+deposition under the body of the ice and its edge, the mantle of drift
+has a very variable thickness; and a mantle of drift of variable
+thickness cannot fail to modify the topography of the region it covers.
+The extent of the modification will depend on the extent of the
+variation. This amounts in the aggregate, to hundreds of feet. The
+continental ice sheet, therefore, modified the topography of the region
+it covered, not only by the wear it effected, but also by the deposits
+it made.</p>
+
+<p>In some places it chanced that the greater thicknesses of drift were
+left in the positions formerly marked by valleys. Locally the body of
+drift was so great that valleys were completely filled, and therefore
+completely obliterated as surface features. Less frequently, drift not
+only filled the valleys but rose even higher over their former positions
+than on either side. In other places the greater depths of drift,
+instead of being deposited in the valleys, were left on pre-glacial
+elevations, building them up to still greater heights. In short, the
+mantle of drift of unequal thickness was laid down upon the rock
+<span class="pagenum"> <a name="Page_87" id="Page_87">[Pg 87]</a> </span>
+surface in such a manner that the thicker parts sometimes rest on hills
+and ridges, sometimes on slopes, sometimes on plains, and sometimes in
+valleys.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig32.jpg" width="500" height="90" alt="" />
+</div>
+<p class="center indent">Fig. 32. -- Diagrammatic section showing relation of drift
+to underlying rock, where the drift is thick relative to the relief of
+the rock. <i>a</i> and <i>b</i> represent the location of post-glacial valleys.
+<br /> <br /> <br /> </p>
+
+<p>These relations are suggested by Figs. <a href="images/fig32.jpg">32</a>
+and <a href="images/fig33.jpg">33</a>. From them it will be
+seen that in regions where the thickness of the drift is great, relative
+to the relief of the underlying rock, the topography may be completely
+changed. Not only may some of the valleys be obliterated by being
+filled, but some of the hills may be obliterated by having the lower
+land between them built up to their level. In regions where the
+thickness of the drift is slight, relative to the relief of the rock
+beneath, the hills cannot be buried, and the valleys cannot be
+completely filled, so that the relative positions of the principal
+topographic features will remain much the same after the deposition of
+the drift, as before (Fig. <a href="images/fig33.jpg">33</a>).
+<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig33.jpg" width="500" height="108" alt="" />
+</div>
+<p class="center indent">Fig. 33. -- Diagrammatic section showing relation of drift
+ to underlying rock where the drift is thin relative to the relief of the
+ underlying rock.<br /> <br /> <br /> </p>
+
+<p>In case the pre-glacial valleys were filled and the hills buried, the
+new valleys which the surface waters will in time cut in the drift
+surface will have but little correspondence in position with those
+<span class="pagenum"> <a name="Page_88" id="Page_88">[Pg 88]</a> </span>
+which existed before the ice incursion. A new system of valleys, and
+therefore a new system of ridges and hills, will be developed, in some
+measure independent of the old. These relations are illustrated by Fig.
+<a href="images/fig32.jpg">32.</a> </p>
+
+<p>Inequalities in the thickness of drift lead to a still further
+modification of the surface. It frequently happened that in a plane or
+nearly plane region a slight thickness of drift was deposited at one
+point, while all about it much greater thicknesses were left. The area
+of thin drift would then constitute a depression, surrounded by a higher
+surface built up by the thicker deposits. Such depressions would at
+first have no outlets, and are therefore unlike the depressions shaped
+by rain and river erosion. The presence of depressions without outlets
+is one of the marks of a drift-covered (glaciated) country. In these
+depressions water may collect, forming lakes or ponds, or in some cases
+only marshes and bogs. <br /> <br /> <br /> <br /> </p>
+
+
+<h4>DIRECTION OF ICE MOVEMENT.</h4>
+
+<p>The direction in which glacier ice moved may be determined in various
+ways, even after the ice has disappeared. The shapes of the rock hills
+over which the ice passed (p. <a href="#Page_81">81</a>), the direction from which the
+materials of the drift came, and the course of the margin of the drift,
+all show that the ice of south central Wisconsin was moving in a general
+southwest direction. In the rock hills, this is shown by the greater
+wear of their northeast ("stoss") sides (Plate <a href="images/i34.jpg">XXXIV</a>). From the
+course of the drift margin, the general direction of movement may be
+inferred when it is remembered that the tendency of glacier ice on a
+plane surface is to move at right angles to its margin.</p>
+
+<p>For the exact determination of the direction of ice movement, recourse
+must be had to the striæ on the bed-rock. Were the striated rock surface
+perfectly plane, and were the striæ even lines, they would only tell
+that the ice was moving in one of two directions. But the rock surface
+is not usually perfectly plane, nor the striæ even lines, and between
+the two directions which lines alone might suggest, it is usually
+<span class="pagenum"> <a name="Page_89" id="Page_89">[Pg 89]</a> </span>
+possible to decide. The minor prominences and depressions in the rock
+surface were shaped according to the same principles that govern the
+shaping of hills (Fig. <a href="images/fig29.jpg">29</a>) and valleys
+(Fig. <a href="images/fig30.jpg">30</a>); that is, the stoss
+sides of the minor prominences, and the distal sides of small
+depressions suffered the more wear. With a good compass, the direction
+of the striæ may be measured to within a fraction of a degree, and thus
+the direction of ice movement in a particular place be definitely
+determined. The striæ which have been determined about Baraboo are shown
+on Plate <a href="images/i02.jpg">II</a>.</p>
+
+<p> <i>Effect of topography on movement.</i>&mdash;The effect of glaciation on
+topography has been sketched, but the topography in turn exerted an
+important influence on the direction of ice movement. The extreme degree
+of topographic influence is seen in mountain regions like the Alps,
+where most of the glaciers are confined strictly to the valleys.</p>
+
+<p>As an ice sheet invades a region, it advances first and farthest along
+the lines of least resistance. In a rough country with great relief,
+tongues or lobes of ice would push forward in the valleys, while the
+hills or other prominences would tend to hold back or divide the onward
+moving mass. The edge of an ice sheet in such a region would be
+irregular. The marginal lobes of ice occupying the valleys would be
+separated by re-entrant angles marking the sites of hills and ridges.</p>
+
+<p>If the ice crossed a plane surface above which rose a notable ridge or
+hill, the first effect of the hill would be to indent the ice. The ice
+would move forward on either side, and if its thickness became
+sufficiently great, the parts moving forward on either side would again
+unite beyond it. A hill thus surrounded by ice is a <i>nunatak</i>. Later, as
+the advancing mass of ice became thicker, it might completely cover the
+hill; but the thickness of ice passing over the hill would be less than
+that passing on either side by an amount equal to the height of the
+hill. It follows that as ice encounters an isolated elevation, three
+stages in its contest with the obstruction may be recognized: (1) the
+stage when the ridge or hill acts as a wedge, dividing the moving ice
+<span class="pagenum"> <a name="Page_90" id="Page_90">[Pg 90]</a> </span>
+into lobes, Fig. <a href="images/fig34.jpg">34</a>; (2) the nunatak stage, when the ice has pushed
+forward and reunited beyond the hill, Fig. <a href="images/fig35.jpg">35</a>; (3) the stage when the ice
+has become sufficiently deep to cover the hill.<br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig34.jpg" width="300" height="136" alt="" />
+</div>
+<p class="center indent">Fig. 34. -- Diagrammatic representation of the effect of a
+hill on the edge of the ice.<br /> <br /> <br /> </p>
+
+<p>After the ice has disappeared, the influence of the obstruction might be
+found in the disposition of the drift. If recession began during the
+first stage, that is, when the ice edge was separated into lobes, the
+margin of the drift should be lobate, and would loop back around the
+ridge from its advanced position on either side. If recession began
+during the second stage, that is, when the lobes had become confluent
+and completely surrounded the hill, a <i>driftless area</i> would appear in
+the midst of drift. If recession began during the third stage, that is,
+after the ice had moved on over the obstruction, the evidence of the
+sequence might be obliterated; but if the ice moved but a short distance
+beyond the hill, the thinner ice over the hill would have advanced less
+far than the thicker ice on either side (Fig. <a href="images/fig35.jpg">35</a>), and the margin of
+<span class="pagenum"> <a name="Page_91" id="Page_91">[Pg 91]</a> </span>
+the drift would show a re-entrant pointing back toward the hill, though
+not reaching it. All these conditions are illustrated in the Devil's
+lake region.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig35.jpg" width="300" height="245" alt="" />
+</div>
+<p class="center indent">Fig. 35. -- Same as Fig. <a href="images/fig34.jpg">34</a>,
+when the ice has advanced farther.<br /> <br /> <br /> <br /> <br /> </p>
+
+<h4> <i>Limit of the Ice.</i> </h4>
+
+<p>The region under description is partly covered with drift, and partly
+free from it. The limit of the ice, at the time of its maximum expansion
+is well defined at many points, and the nature and position of the drift
+limit are so unique as to merit attention (see Plates <a href="images/i02.jpg">II</a> and
+<a href="images/i37.jpg">XXXVII</a>). They illustrate many of the principles already
+discussed.</p>
+
+<p>The ice which covered the region was the western margin of the Green Bay
+lobe (Fig. <a href="images/fig36.jpg">36</a>) of the last continental ice sheet. Its limit in this
+region is marked by a ridge-like accumulation of drift, the <i>terminal
+moraine</i>, which here has a general north-south direction. The region
+<span class="pagenum"> <a name="Page_92" id="Page_92">[Pg 92]</a> </span>
+may have been affected by the ice of more than one epoch, but since the
+ice of the last epoch advanced as far to the west in this region as that
+of any earlier epoch, the moraine is on the border between the<br /> <br /> </p>
+
+<div class="figcenter" style="width: 250px;">
+<img src="images/fig36.jpg" width="250" height="291" alt="" />
+</div>
+<p class="center indent">Fig. 36. -- Map showing relations of lobes of ice during
+the Wisconsin ice epoch, to the driftless area.<br />
+<a href="images/fig36.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>glaciated country to the east, and the driftless area to the west
+(Plates <a href="images/i01.jpg">I</a> and
+<a href="images/i02.jpg">II</a>). That part of the moraine which lies west of the
+Wisconsin river follows a somewhat sinuous course from Kilbourn City to
+a point a short distance north of Prairie du Sac. The departures from
+<span class="pagenum"> <a name="Page_93" id="Page_93">[Pg 93]</a> </span>
+this general course are especially significant of the behavior of
+glacier ice.</p>
+
+<p>In the great depression between the quartzite ranges, the moraine bends
+westward, showing that the ice advanced farther on the lowlands than on
+the ridges. As the moraine of this low area approaches the south range,
+it curves to the east. At the point southwest of Baraboo where the
+easterly curve begins to show itself, the moraine lies at the north base
+of the quartzite range; but as it is traced eastward, it is found to lie
+higher and higher on the slope of the range, until it reaches the crest
+nearly seven miles from the point where the eastward course was assumed.
+At this point it crosses the range, and, once across the crest, it turns
+promptly to the westward on the lower land to the south. Here the ice
+advanced up the valley between the East bluff (east of the lake) and the
+Devil's nose (Plate <a href="images/i37.jpg">XXXVII</a>), again illustrating the fact that lowlands
+favor ice advance. The valley between the Devil's nose and the East
+bluff is a narrow one, and the ice advanced through it nearly to the
+present site of the lake. Meanwhile the restraining influence of the
+"nose" was making itself felt, and the margin of the ice curved back
+from the bottom of the bluff near Kirkland, to the top of the bluff at
+the end of the nose. Here the edge of the ice crossed the point of the
+nose, and after rounding it, turned abruptly to the west. Thence its
+edge lay along the south slope of the ridge, descending from the crest
+of the ridge at the nose, to the base of the ridge two miles farther
+west. Here the ice reached its limit on the lowland, and its edge, as
+marked by the moraine, turned southward, reaching the Wisconsin river
+about a mile and a half above Prairie du Sac.</p>
+
+<p>The course of the terminal moraine across the ridges is such as the
+margin of the ice would normally have when it advanced into a region of
+great relief. The great loop in the moraine with its eastern extremity
+at <i>k</i>, Plate <a href="images/i37.jpg">XXXVII</a>, is explained by the presence of the quartzite
+ridge which retarded the advancing ice while it moved forward on either
+side. The minor loop around the Devil's nose is explained in the same
+way. Both the
+<span class="pagenum"> <a name="Page_94" id="Page_94">[Pg 94]</a> </span>
+main loop, and the smaller one on the nose, illustrate
+the point made on p. <a href="#Page_89">89</a>.</p>
+
+<p>The narrow and curious loop at <i>m</i>, is of a slightly different origin,
+though in principle the same. It is in the lee of a high point in the
+quartzite ridge. The ice surmounted this point, and descended its
+western slope; but the thickness of the ice passing over the summit was
+so slight that it advanced but a short distance down the slope before
+its force was exhausted, while the thicker ice on either side advanced
+farther before it was melted. <br /> <br /> </p>
+
+
+<h4> <i>Glacial Deposits.</i> </h4>
+
+<p>Before especial reference is made to the drift of this particular
+region, it will be well to consider the character of drift deposits in
+general. When the ice of the continental glacier began its motion, it
+carried none of the stony and earthy debris which constitute the drift.
+These materials were derived from the surface over which the ice moved.</p>
+
+<p>From the method by which it was gathered, it is evident that the drift
+of any locality may contain fragments of rock of every variety which
+occurs along the route followed by the ice which reached that locality.
+Where the ice had moved far, and where there were frequent changes in
+the character of the rock constituting its bed, the variety of materials
+in the drift is great. The heterogeneity of the drift arising from the
+diverse nature of the rocks which contributed to it is <i>lithological
+heterogeneity</i>&mdash;a term which implies the commingling of materials
+derived from different rock formations. Thus it is common to find pieces
+of sandstone, limestone, quartzite, granite, gneiss, schist, etc.,
+intimately commingled in the drift, wherever the ice which produced it
+passed over formations of these several sorts of rock. Lithological
+heterogeneity is one of the notable characteristics of glacial
+formations.</p>
+
+<p>Another characteristic of the drift is its <i>physical heterogeneity</i>. As
+first gathered from the bed of moving ice, some of the<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXV.</p>
+
+<div class="figcenter" style="width: 200px;">
+<img src="images/i35.jpg" width="200" height="197" alt="" />
+</div>
+<p class="center indent">Cut in drift, showing its physical heterogeneity.<br />
+<a href="images/i35.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_95" id="Page_95">[Pg 95]</a> </span>
+materials of the drift were fine and some coarse. The tendency of the
+ice in all cases was to reduce its load to a still finer condition. Some
+of the softer materials, such as soft shale, were crushed or ground to
+powder, forming what is known in common parlance as clay. Clayey (fine)
+material is likewise produced by the grinding action of ice-carried
+bowlders upon the rock-bed, and upon one another. Other sorts of rock,
+such as soft sandstone, were reduced to the physical condition of sand,
+instead of clay, and from sand to bowlders all grades of coarseness and
+fineness are represented in the glacial drift.</p>
+
+<p>Since the ice does not assort the material which it carries, as water
+does, the clay, sand, gravel and bowlders will not, by the action of the
+ice, be separated from one another. They are therefore not stratified.
+As left by the ice, these physically heterogeneous materials are
+confusedly commingled. The finer parts constitute a matrix in which the
+coarser are embedded.</p>
+
+<p>Physical heterogeneity (Plate <a href="images/i35.jpg">XXXV</a>), therefore, is another
+characteristic of glacial drift. It is not to be understood that the
+proportions of these various physical elements, clay, sand, gravel, and
+bowlders, are constant. Locally any one of them may predominate over any
+or all the others to any extent.</p>
+
+<p>Since lithological and physical heterogeneity are characteristics of
+glacial drift, they together afford a criterion which is often of
+service in distinguishing glacial drift from other surface formations.
+It follows that this double heterogeneity constitutes a feature which
+can be utilized in determining the former extension of existing
+glaciers, as well as the former existence of glaciers where glaciers do
+not now exist.</p>
+
+<p>Another characteristic of glacial drift, and one which clearly
+distinguishes it from all other formations with which it might be
+confounded, is easily understood from its method of formation. If the
+ice in its motion holds down rock debris upon the rock surface over
+which it passes with such pressure as to polish and striate the
+bed-rock, the material carried will itself suffer wear comparable to
+that which it inflicts. Thus the stones, large and small, of glacial
+drift, will be smoothed and striated.</p>
+
+<p> <span class="pagenum"> <a name="Page_96" id="Page_96">[Pg 96]</a> </span>
+This sort of wear on the transported blocks of rock, is effected both by
+the bed-rock reacting on the bowlders transported over it, and by
+bowlders acting on one another in and under the ice. The wear of
+bowlders by bowlders is effected wherever adjacent ones are carried
+along at different rates. Since the rate of motion of the ice is
+different in different parts of the glacier, the mutual abrasion of
+transported materials is a process constantly in operation. A large
+proportion of the transported stone and blocks of rock may thus
+eventually become striated.</p>
+
+<p>From the nature of the wear to which the stones are subjected when
+carried in the base of the ice, it is easy to understand that their
+shapes must be different from those of water-worn materials. The latter
+are rolled over and over, and thus lose all their angles and assume a
+more or less rounded form. The former, held more or less firmly in the
+ice, and pressed against the underlying rock or rock debris as they are
+carried slowly forward, have their faces planed and striated. The
+planation and striation of a stone need not be confined to its under
+surface. On either side or above it other stones, moving at different
+rates, are made to abrade it, so that its top and sides may be planed
+and scored. If the ice-carried stones shift their positions, as they may
+under various circumstances, new faces will be worn. The new face thus
+planed off may meet those developed at an earlier time at sharp angles,
+altogether unlike anything which water-wear is capable of producing. The
+stone thus acted upon shows a surface bounded by planes and more or less
+beveled, instead of a rounded surface such as water wear produces. We
+find, then, in the shape of the bowlders and smaller stones of the
+drift, and in the markings upon their surfaces, additional criteria for
+the identification of glacier drift (Plate <a href="images/i36.jpg">XXXVI</a>).</p>
+
+<p>The characteristics of glacial drift, so far as concerns its
+constitution, may then be enumerated as, (1) its lithological, and (2)
+physical heterogeneity; (3) the shapes, and (4) the markings of the stones
+of the drift. In structure, the drift which is strictly glacial, is
+unstratified.</p>
+
+<p>In the broadest sense of the term, all deposits made by glacier<br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVI.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/i36.jpg" width="300" height="108" alt="" />
+</div>
+<p class="center indent">Glaciated stones, showing both form and striae. (Matz.)<br />
+<a href="images/i36.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_97" id="Page_97">[Pg 97]</a> </span>
+ice are <i>moraines</i>. Those made beneath the ice and back from its edge
+constitute the <i>ground moraine</i>, and are distinguished from the
+considerable marginal accumulations which, under certain conditions, are
+accumulated at or near the margin. These marginal accumulations are
+<i>terminal moraines</i>. Associated with the moraines which are the deposits
+of the ice directly, there are considerable bodies of stratified gravel
+and sand, the structure of which shows that they were laid down by
+water. This is to be especially noted, since lack of stratification is
+popularly supposed to be the especial mark of the formations to which
+the ice gave rise.</p>
+
+<p>These deposits of stratified drift lie partly beyond the terminal
+moraine, and partly within it. They often sustain very complicated
+relations both to the ground and terminal moraines.</p>
+
+<p>The drift as a whole is therefore partly stratified and partly
+unstratified. Structurally the two types are thoroughly distinct, but
+their relations are often most complex, both horizontally and
+vertically. A fuller consideration of these relations will be found on a
+later page. <br /> <br /> </p>
+
+
+<h4> <i>The Ground Moraine.</i> </h4>
+
+<p>The ground moraine constitutes the great body of the glacial drift.
+<i>Bowlder clay</i>, a term descriptive of its constitution in some places,
+and <i>till</i>, are other terms often applied to the ground moraine. The
+ground moraine consists of all the drift which lodged beneath the ice
+during its advance, all that was deposited back from its edge while its
+margin was farthest south, and most of that which was deposited while
+the ice was retreating. From this mode of origin it is readily seen that
+the ground moraine should be essentially as widespread as the ice
+itself. Locally, however, it failed of deposition. Since it constitutes
+the larger part of the drift, the characteristics already enumerated (p.
+<a href="#Page_95">95</a>) as belonging to drift in general are the
+characteristics of the till. Wherever obstacles to the progress of the ice
+lay in its path, there was a chance that these obstacles, rising somewhat into the
+<span class="pagenum"> <a name="Page_98" id="Page_98">[Pg 98]</a> </span>
+lower part of the ice, would constitute barriers against which debris in
+the lower part of the ice would lodge. It might happen also that the
+ice, under a given set of conditions favoring erosion, would gather a
+greater load of rock-debris than could be transported under the changed
+conditions into which its advance brought it. In this case, some part of
+the load would be dropped and over-ridden. Especially near the margin of
+the ice where its thickness was slight and diminishing, the ice must
+have found itself unable to carry forward the loads of debris which it
+had gathered farther back where its action was more vigorous. It will be
+readily seen that if not earlier deposited, all material gathered by the
+under surface of the ice would ultimately find itself at the edge of the
+glacier, for given time enough, ablation will waste all that part of the
+ice occupying the space between the original position of the debris, and
+the margin of the ice. Under the thinned margin of the ice, therefore,
+considerable accumulations of drift must have been taking place while
+the ice was advancing. While the edge of the ice sheet was advancing
+into territory before uninvaded, the material accumulated beneath its
+edge at one time, found itself much farther from the margin at another
+and later time. Under the more forcible ice action back from the margin,
+the earlier accumulations, made under the thin edge, were partially or
+wholly removed by the thicker ice of a later time, and carried down to
+or toward the new and more advanced margin. Here they were deposited, to
+be in turn disturbed and transported still farther by the farther
+advance of the ice.</p>
+
+<p>Since in its final retreat the margin of the ice must have stood at all
+points once covered by it, these submarginal accumulations of drift must
+have been made over the whole country once covered by the ice. The
+deposits of drift made beneath the marginal part of the ice during its
+retreat, would either cover the deposits made under the body of the ice
+at an earlier time, or be left alongside them. The constitution of the
+two phases of till, that deposited during the advance of the ice, and
+that deposited during its retreat, is essentially the same, and there
+is nothing in their relative positions to sharply differentiate them.
+<span class="pagenum"> <a name="Page_99" id="Page_99">[Pg 99]</a> </span>
+They are classed together as <i>subglacial till</i>.</p>
+
+<p>Subglacial till was under the pressure of the overlying ice. In keeping
+with these conditions of accumulation, the till often possesses a
+firmness suggestive of great compression. Where its constitution is
+clayey it is often remarkably tough. Where this is the case, the quality
+here referred to has given rise to the suggestive name "hard pan." Where
+the constitution of the till is sandy, rather than clayey, this firmness
+and toughness are less developed, or may be altogether wanting, since
+sand cannot be compressed into coherent masses like clay.</p>
+
+<p> <i>Constitution.</i>&mdash;The till is composed of the more or less comminuted
+materials derived from the land across which the ice passed. The soil
+and all the loose materials which covered the rock entered into its
+composition. Where the ice was thick and its action vigorous, it not
+only carried away the loose material which it found in its path, but,
+armed with this material, it abraded the underlying rock, wearing down
+its surface and detaching large and small blocks of rock from it. It
+follows that the constitution of the till at any point is dependent upon
+the nature of the soil and rock from which it was derived.</p>
+
+<p>If sandstone be the formation which has contributed most largely to the
+till, the matrix of the till will be sandy. Where limestone instead of
+sandstone made the leading contribution to it, the till has a more
+earthy or clayey matrix. Any sort of rock which may be very generally
+reduced to a fine state of division under the mechanical action of the
+ice, will give rise to clayey till.</p>
+
+<p>The nature and the number of the bowlders in the till, no less than the
+finer parts, depend on the character of the rock overridden. A hard and
+resistant rock, such as quartzite, will give rise to more bowlders in
+proportion to the total amount of material furnished to the ice, than
+will softer rock. Shale or soft sandstone, possessing relatively slight
+resistance, will be much more completely crushed. They will, therefore,
+yield proportionately fewer bowlders than harder formations, and more
+<span class="pagenum"> <a name="Page_100" id="Page_100">[Pg 100]</a> </span>
+of the finer constituents of till.</p>
+
+<p>The bowlders taken up by the ice as it advanced over one sort of rock
+and another, possessed different degrees of resistance. The softer ones
+were worn to smaller dimensions or crushed with relative ease and speed.
+Bowlders of soft rock are, therefore, not commonly found in any
+abundance at great distances from their sources. The harder ones yielded
+less readily to abrasion, and were carried much farther before being
+destroyed, though even such must have suffered constant reduction in
+size during their subglacial journey. In general it is true that
+bowlders in the till, near their parent formations, are larger and less
+worn than those which have been transported great distances.</p>
+
+<p>The ice which covered this region had come a great distance and had
+passed over rock formations of many kinds. The till therefore contains
+elements derived from various formations; that is, it is lithologically
+heterogeneous. This heterogeneity cannot fail to attract the attention
+of one examining any of the many exposures of drift about Baraboo at
+road gradings, or in the cuts along the railway. Among the stones in the
+drift at these exposures are limestone, sandstone, quartzite, diabase,
+gabbro, gneiss, granite, schist, and porphyry, together with pieces of
+flint and chert.</p>
+
+<p>Such an array may be found at any of the exposures within the immediate
+vicinity of Devil's lake. To the north, and a few miles to the south of
+the Baraboo ranges, the quartzite from these bluffs, and the porphyry
+from the point marked <i>h</i> in Plate <a href="images/i02.jpg">II</a> are
+wanting, though other varieties of porphyry are present. The ice moved in a general
+west-southwest direction in this region, and the quartzite in the drift,
+so far as derived from the local formation, is therefore restricted to a
+narrow belt.</p>
+
+<p>The physical heterogeneity may be seen at all exposures, and is
+illustrated in Plate <a href="images/i35.jpg">XXXV</a>. The larger stones of the drift are
+usually of some hard variety of rock. Near the Baraboo ranges, the local
+quartzite often predominates among the bowlders, and since such
+<span class="pagenum"> <a name="Page_101" id="Page_101">[Pg 101]</a> </span>
+bowlders have not been carried far, they are often little worn. Away
+from the ranges, the bowlders are generally of some crystalline rock,
+such as granite and diabase. Bowlders of these sorts of rock are from a
+much more distant source, and are usually well worn.</p>
+
+<p>In general the till of any locality is made up largely of material
+derived from the formations close at hand. This fact seems to afford
+sufficient warrant for the conclusion that a considerable amount of
+deposition must have gone on beneath the ice during its movement, even
+back from its margin. To take a concrete illustration, it would seem
+that the drift of southeastern Wisconsin should have had a larger
+contribution than it has of material derived from Canadian territory, if
+material once taken up by the ice was all or chiefly carried down to its
+thinned edge before deposition. The fact that so little of the drift
+came from these distant sources would seem to prove that a large part of
+the material moved by the ice, is moved a relatively short distance
+only. The ice must be conceived of as continually depositing parts of
+its load, and parts which it has carried but a short distance, as it
+takes up new material from the territory newly invaded.</p>
+
+<p>In keeping with the character of till in general, that about Devil's
+lake was derived largely from the sandstone, limestone and quartzite of
+the immediate vicinity, while a much smaller part of it came from more
+distant sources. This is especially noticeable in the fine material,
+which is made up mostly of the comminuted products of the local rock.</p>
+
+<p> <i>Topography.</i>&mdash;The topography of the ground moraine is in general the
+topography already described (p. <a href="#Page_85">85</a>) in considering the modification of
+preglacial topography effected by ice deposition. As left by the ice,
+its surface was undulating. The undulations did not take the form of
+hills and ridges with intervening valleys, but of swells and depressions
+standing in no orderly relationship to one another. Undrained
+depressions are found in the ground moraine, but they are, as a rule,
+broader and shallower than the "kettles" common to terminal moraines.</p>
+
+<p> <span class="pagenum"> <a name="Page_102" id="Page_102">[Pg 102]</a> </span>
+It is in the broad, shallow depressions of the ground moraine that many
+of the lakes and more of the marshes of southeastern Wisconsin are
+located.</p>
+
+<p>The rolling, undulating topography characteristic of ground moraines is
+well shown about the City of Baraboo and between that point and the
+lake, and at many less easily designated points about Merrimac.</p>
+
+<p>In thickness the ground moraine reaches at least 160 feet, though its
+average is much less&mdash;too little to obliterate the greater topographic
+features of the rock beneath. It is, however, responsible for many of
+the details of the surface. <br /> <br /> </p>
+
+
+<h4> <i>Terminal Moraines.</i> </h4>
+
+<p>The marginal portion of the ice sheet was more heavily loaded&mdash;certainly
+more heavily loaded relative to its thickness&mdash;than any other. Toward
+its margin the thinned ice was constantly losing its transportive power,
+and at its edge this power was altogether gone. Since the ice was
+continually bringing drift down to this position and leaving it there,
+the rate of drift accumulation must have been greater, on the average,
+beneath the edge of the ice than elsewhere.</p>
+
+<p>Whenever, at any stage in its history, the edge of the ice remained
+essentially constant in position for a long period of time, the
+corresponding submarginal accumulation of drift was great, and when the
+ice melted, the former site of the stationary edge would be marked by a
+broad ridge or belt of drift, thicker than that on either side. Such
+thickened belts of drift are <i>terminal moraines</i>. It will be seen that a
+terminal moraine does not necessarily mark the terminus of the ice at
+the time of its greatest advance, but rather its terminus at any time
+when its edge was stationary or nearly so.</p>
+
+<p>From the conditions of their development it will be seen that these
+submarginal moraines may be made up of materials identical with those
+which constitute the ground moraine, and such is often the case. But
+water arising from the melting of the ice, played a much more
+<span class="pagenum"> <a name="Page_103" id="Page_103">[Pg 103]</a> </span>
+important role at its margin than farther back beneath it. One result of
+its greater activity may be seen in the greater coarseness which
+generally characterizes the material of the terminal moraine as compared
+with that of the adjacent ground moraine. This is partly because the
+water carried away such of the finer constituents as it was able to
+transport, leaving the coarser behind. Further evidence of the great
+activity of water near the margin of the ice is to be seen in the
+relatively large amount of assorted and stratified sand and gravel
+associated with the terminal moraine.</p>
+
+<p>Such materials as were carried on the ice were dropped at its edge when
+the ice which bore them melted from beneath. If the surface of the ice
+carried many bowlders, many would be dropped along the line of its edge
+wherever it remained stationary for any considerable period of time. A
+terminal moraine therefore embraces (1) the thick belt of drift
+accumulated beneath the edge of the ice while it was stationary, or
+nearly so; and (2) such debris as was carried on the surface of the ice
+and dumped at its margin. In general the latter is relatively
+unimportant.</p>
+
+<p>At various stages in its final retreat, the ice made more or less
+protracted halts. These halting places are marked by marginal moraines
+of greater or less size, depending on the duration of the stop, and the
+amount of load carried.</p>
+
+<p>A terminal moraine is not the sharp and continuous ridge we are wont to
+think it. It is a belt of thick drift, rather than a ridge, though it is
+often somewhat ridge-like. In width, it varies from a fraction of a mile
+to several miles. In the region under consideration it is rarely more
+than fifty feet high, and rarely less than a half mile wide, and a ridge
+of this height and width is not a conspicuous topographic feature in a
+region where the relief is so great as that of the Devil's lake region.</p>
+
+<p> <i>Topography of terminal moraines.</i>&mdash;The most distinctive feature of a
+terminal moraine is not its ridge-like character, but its peculiar
+topography. In general, it is marked by depressions without outlets,
+associated with hillocks and short ridges comparable in dimensions to
+<span class="pagenum"> <a name="Page_104" id="Page_104">[Pg 104]</a> </span>
+the depressions. Both elevations and depressions are, as a rule, more
+abrupt than in the ground moraine. In the depressions there are many
+marshes, bogs, ponds and small lakes. The shapes and the abundance of
+round and roundish hills have locally given rise to such names as "The
+Knobs," "Short Hills," etc. Elsewhere the moraine has been named the
+"Kettle Range" from the number of kettle-like depressions in its
+surface. It is to be kept in mind that it is the association of the
+"knobs" and "kettles," rather than either feature alone, which is the
+distinctive mark of terminal moraine topography.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/fig37.jpg" width="350" height="123" alt="" />
+</div>
+<p class="center indent">Fig. 37. -- Sketch of terminal moraine topography, on the
+quartzite ridge east of Devil's lake. (Matz.)<br /> <br /> <br /> </p>
+
+<p>The manner in which the topography of terminal moraines was developed is
+worthy of note. In the first place, the various parts of the ice margin
+carried unequal amounts of debris. This alone would have caused the
+moraine of any region to have been of unequal height and width at
+different points. In the second place, the margin of the ice, while
+maintaining the same <i>general</i> position during the making of a moraine,
+was yet subject to many minor oscillations. It doubtless receded to some
+slight extent because of increased melting during the summer, to advance
+again during the winter. In its recession, the ice margin probably did
+not remain exactly parallel to its former position. If some parts
+receded more than others, the details of the line of its margin may have
+been much changed during a temporary retreat. When the ice again
+advanced, its margin may have again changed its form in some slight
+<span class="pagenum"> <a name="Page_105" id="Page_105">[Pg 105]</a> </span>
+measure, so as to be parallel neither with its former advanced position,
+nor with its position after its temporary retreat. With each successive
+oscillation of the edge, the details of the margin may have altered, and
+at each stage the marginal deposits corresponded with the edge. There
+might even be considerable changes in the edge of the ice without any
+general recession or advance, as existing glaciers show.</p>
+
+<p>It was probably true of the margin of the American ice sheet, as of
+existing glaciers, that there were periods of years when the edge of the
+ice receded, followed by like periods when it remained stationary or
+nearly so, and these in turn followed by periods of advance. During any
+advance, the deposits made during the period of recession would be
+overridden and disturbed or destroyed.</p>
+
+<p>If the ice were to retreat and advance repeatedly during a considerable
+period of time, always within narrow limits, and if during this
+oscillation the details of its margin were frequently changing, the
+result would be a complex or "tangle" of minor morainic ridges of
+variable heights and widths. Between and among the minor ridges there
+would be depressions of various sizes and shapes. Thus, it is conceived,
+many of the peculiar hillocks and hollows which characterize terminal
+moraines may have arisen.</p>
+
+<p>Some of the depressions probably arose in another way. When the edge of
+the ice retreated, considerable detached masses of ice might be left
+beyond the main body. This might be buried by gravel and sand washed out
+from the moraine. On melting, the former sites of such blocks of ice
+would be marked by "kettles." In the marginal accumulations of drift as
+first deposited, considerable quantities of ice were doubtless left.
+When this melted, the drift settled and the unequal settling may have
+given rise to some of the topographic irregularities of the drift.</p>
+
+<p> <i>The terminal moraine about Devil's lake.</i>&mdash;On the lower lands, the
+terminal moraine of the Devil's lake region has the features
+characteristic of terminal moraines in general. It is a belt of thick
+<span class="pagenum"> <a name="Page_106" id="Page_106">[Pg 106]</a> </span>
+drift varying in width from half a mile or less to three-quarters of a
+mile or more. Its surface is marked by numerous hills and short ridges,
+with intervening depressions or "kettles." Some of the depressions among
+the hills contain water, making ponds or marshes, though the rather
+loose texture of the drift of this region is not favorable to the
+retention of water. The moraine belt, as a whole, is higher than the
+land on either side. It is therefore somewhat ridge-like, and the small,
+short hills and ridges which mark its surface, are but constituent parts
+of the larger, broader ridge.</p>
+
+<p>Approached from the west, that is from the driftless side, the moraine
+on the lower lands is a somewhat prominent topographic feature, often
+appearing as a ridge thirty, forty or even fifty feet in height.
+Approached from the opposite direction, that is, from the ground
+moraine, it is notably less prominent, and its inner limit wherever
+located, is more or less arbitrary.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/fig38.jpg" width="400" height="143" alt="" />
+</div>
+<p class="center indent">Fig. 38. -- Cut through the terminal moraine just east of
+ Kirkland, partially diagrammatic.<br />
+<a href="images/fig38.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>A deep, fresh railway cut in the moraine southeast of Devil's lake
+illustrates its complexity of structure, a complexity which is probably
+no greater than that at many other points where exposures are not seen.
+The section is represented in Fig. <a href="images/fig38.jpg">38</a>.
+The stratified sand to the right retains even the ripple-marks which were developed when it was
+deposited. To the left, at the same level, there is a body of <i>till</i>
+(unstratified drift), over which is a bed of stoneless and apparently
+structureless clay. In a depression just above the clay with till both
+to the right and left, is a body of loam which possesses the
+<span class="pagenum"> <a name="Page_107" id="Page_107">[Pg 107]</a> </span>
+characteristics of normal loess. It also contains calcareous
+concretions, though no shells have been found. This occurrence of loess
+is the more noteworthy, since loess is rarely found in association with
+drift of the last glacial epoch.
+<a name="FNanchor_1_7" id="FNanchor_1_7"> </a> <a href="#Footnote_1_7" class="fnanchor">[7]</a> </p>
+
+<p> <i>The moraine on the main quartzite range.</i>&mdash;In tracing the moraine over
+the greater quartzite range, it is found to possess a unique feature in
+the form of a narrow but sharply defined ridge of drift, formed at the
+extreme margin of the ice at the time of its maximum advance. For fully
+eleven miles, with but one decided break, and two short stretches where
+its development is not strong, this unique marginal ridge separates the
+drift-covered country on the one hand, from the driftless area on the
+other. In its course the ridge lies now on slopes, and now on summits,
+but in both situations preserves its identity. Where it rests on a
+plain, or nearly plain surface, its width at base varies from six to
+fifteen rods, and its average height is from twenty to thirty feet. Its
+crest is narrow, often no more than a single rod. Where it lies on a
+slope, it is asymmetrical in cross section (see Fig. <a href="images/fig39.jpg">39</a>),
+the shorter slope having a vertical<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig39.jpg" width="300" height="127" alt="" />
+</div>
+<p class="center indent">Fig. 39. -- Diagrammatic cross-section of the marginal
+ridge as it occurs on the south slope of the Devil's Nose. The slope
+below, though glaciated, is nearly free from drift.<br /> <br /> <br /> </p>
+
+<p>range of ten to thirty-five feet, and its longer
+a range of forty to one hundred feet. This asymmetrical form persists
+throughout all that portion of the ridge which lies on an inclined
+surface, the slope of which does not correspond with the direction of
+the moraine. Where it lies on a flat surface, or an inclined surface
+<span class="pagenum"> <a name="Page_108" id="Page_108">[Pg 108]</a> </span>
+the slope of which corresponds in direction with the course of the ridge
+itself, its cross section is more nearly symmetrical (see Fig. <a href="images/fig40.jpg">40</a>). In
+all essential characteristics this marginal ridge corresponds with the
+<i>End-Moräne</i> of the Germans.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig40.jpg" width="300" height="72" alt="" />
+</div>
+<p class="center indent">Fig. 40. -- Diagrammatic cross-section of the marginal
+ridge as it appears when its base is not a sloping surface.<br /> <br /> <br /> </p>
+
+<p>For the sake of bringing out some of its especially significant
+features, the ridge may be traced in detail, commencing on the south
+side of the west range. Where the moraine leaves the lowlands south of
+the Devil's nose, and begins the ascent of the prominence, the marginal
+ridge first appears at about the 940-foot contour (<i>f</i>, Plate <a href="images/i37.jpg">XXXVII</a>).
+Though at first its development is not strong, few rods have been passed
+before its crest is fifteen to twenty feet above the driftless area
+immediately to the north (see Fig. <a href="images/fig39.jpg">39</a>) and from forty to one hundred
+feet above its base to the south, down the slope. In general the ridge
+becomes more distinct with increasing elevation, and except for two or
+three narrow post-glacial erosion breaks, is continuous to the very
+summit at the end of the nose (<i>g</i>). The ridge in fact constitutes the
+uppermost forty or forty-five feet of the crest of the nose, which is
+the highest point of the west range within the area shown on the map.
+Throughout the whole of this course the marginal ridge lies on the south
+slope of the nose, and has the asymmetrical cross section shown in Fig.
+<a href="images/fig39.jpg">39</a>. Above (north of) the ridge at most points not a bowlder of drift
+occurs. So sharply is its outer (north) margin defined, that at many
+points it is possible to locate it within the space of less than a yard.</p>
+
+<p>At the crest of the nose (<i>g</i>) the marginal ridge, without a break,
+swings northward, and in less than a quarter of a mile turns again to
+the west. Bearing to the north it presently reaches (at <i>h</i>) the edge of
+the precipitous bluff, bordering the<br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVII.</p>
+
+<div class="figcenter" style="width: 217px;">
+<img src="images/i37.jpg" width="217" height="300" alt="" />
+</div>
+<p class="center caption">Topographic map (contour interval 100 feet) of a small area about
+Devil's lake, taken from the Baraboo sheet of the United States
+ Geological Survey. Each contour line connects points of the same
+elevation, and the figures upon them give the heights above sea level.
+Where contour lines lie close together, they indicate steep slopes.<br />
+<a href="images/i37.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_109" id="Page_109">[Pg 109]</a> </span>
+great valley at the south end of the lake. Between the two arms of the
+loop thus formed, the surface of the nose is so nearly level that it
+could have offered no notable opposition to the progress of the ice, and
+yet it failed to be covered by it.</p>
+
+<p>In the great valley between the nose and the east bluff, the marginal
+ridge does not appear. In the bottom of the valley the moraine takes on
+its normal form, and the slopes of the quartzite ridges on either hand
+are much too steep to allow any body of drift, or loose material of any
+sort, to lodge on them.</p>
+
+<p>Ascending the east bluff a little east of the point where the drift
+ridge drops off the west bluff, the ridge is again found (at <i>i</i>) in
+characteristic development. For some distance it is located at the edge
+of the precipitous south face of the bluff. Farther on it bears to the
+north, and soon crosses a col (<i>j</i>) in the ridge, building it up many
+feet above the level of the bed-rock. From this point eastward for about
+three miles the marginal ridge is clearly defined, the slopes about
+equal on either side, and the crest as nearly even as the topography of
+the underlying surface permits. The topographic relations in this part
+of the course are shown in Fig. <a href="images/fig40.jpg">40</a>.</p>
+
+<p>At <i>k</i>, this marginal ridge attains its maximum elevation, 1,620 feet.
+At this great elevation, the ridge turns sharply to the northwest at an
+angle of more than 90°. Following this direction for little more than
+half a mile, it turns to the west. At some points in this vicinity the
+ridge assumes the normal morainic habit, but this is true for short
+distances only. Farther west, at <i>l</i>, it turns abruptly to the northeast
+and is sharply defined. It here loops about a narrow area less than
+sixty rods wide, and over half a mile in length, the sharpest loop in
+its whole course. The driftless tract enclosed by the arms of this loop
+is lower than the drift ridge on either hand. The ice on either side
+would need to have advanced no more than thirty rods to have covered the
+whole of it.</p>
+
+<p>From the minor loop just mentioned, the marginal ridge is continued
+westward, being well developed for about a mile and a half. At this
+point the moraine swings south to the north end of Devil's lake, loses
+the unique marginal ridge which has characterized its outer edge
+<span class="pagenum"> <a name="Page_110" id="Page_110">[Pg 110]</a> </span>
+across the quartzite range for so many miles, and assumes the topography
+normal to terminal moraines. At no other point in the United States, so
+far as known to the writers, is there so sharply marked a marginal ridge
+associated with the terminal moraine, for so long a distance.</p>
+
+<p>From Plate <a href="images/i02.jpg">II</a> it will be seen that the moraine as a whole makes a
+great loop to the eastward in crossing the quartzite range. From the
+detailed description just given of the course of the marginal ridge, it
+will be seen that it has three distinct loops; one on the Devil's nose
+(west of <i>g</i>, Plate <a href="images/i37.jpg">XXXVII</a>); one on the main ridge (west of <i>k</i>)
+and a minor one on the north side of the last (southwest of <i>m</i>). The
+first and third are but minor irregularities on the sides of the great
+loop, the head of which is at <i>k</i>.</p>
+
+<p>The significant fact in connection with these irregularities in the
+margin of the moraine is that each loop stands in a definite relation to
+a prominence. The meaning of this relation is at once patent. The great
+quartzite range was a barrier to the advance of the ice. Acting as a
+wedge, it caused a re-entrant in the advancing margin of the glacier.
+The extent and position of the re-entrant is shown by the course of the
+moraine in Plate <a href="images/i02.jpg">II</a>. Thus the great loop in the moraine, the head of
+which is at <i>k</i>, Plate <a href="images/i37.jpg">XXXVII</a>, was caused by the quartzite range itself.</p>
+
+<p>The minor loops on the sides of the major are to be explained on the
+same principle. Northeast of the minor loop on the north side of the
+larger one (<i>m</i>) there are two considerable hills, reaching an elevation
+of nearly 1,500 feet. Though the ice advancing from the east-northeast
+overrode them, they must have acted like a wedge, to divide it into
+lobes. The ice which reached their summits had spent its energy in so
+doing, and was unable to move forward down the slope ahead, and the
+thicker bodies of ice which passed on either side of them, failed to
+unite in their lee (compare Figs. <a href="images/fig34.jpg">34</a>
+and <a href="images/fig35.jpg">35</a>). The application of the
+same principle to the loop on the Devil's nose is evident.</p>
+
+<p> <i>Constitution of the marginal ridge.</i>&mdash;The material in the marginal
+ridge, as seen where erosion has exposed it, is till, abnormal, if at
+all, only in the large percentage of widely transported bowlders which
+<span class="pagenum"> <a name="Page_111" id="Page_111">[Pg 111]</a> </span>
+it contains. This is especially true of the surface, where in some
+places 90 per cent. of the large bowlders are of very distant origin,
+and that in spite of the fact that the ice which deposited them had just
+risen up over a steep slope of quartzite, which could easily have
+yielded abundant bowlders. In other places the proportion of foreign
+bowlders is small, no more than one in ten. In general, however,
+bowlders of distant origin predominate over those derived close at hand.</p>
+
+<p> <i>The slope of the upper surface of the ice at the margin.</i>&mdash;The marginal
+ridge on the south slope of Devil's nose leads to an inference of
+especial interest. Its course lies along the south slope of the nose,
+from its summit on the east to its base on the west. Throughout this
+course the ridge marks with exactness the position of the edge of the
+ice at the time of its maximum advance, and its crest must therefore
+represent the slope of the upper surface of the ice at its margin.</p>
+
+<p>The western end of the ridge (<i>f</i>, Plate <a href="images/i37.jpg">XXXVII</a>) has an altitude of 940
+feet, and its eastern end (<i>g</i>) is just above the 1,500-foot contour.
+The distance from the one point to the other is one and three-fourths
+miles, and the difference in elevation, 560 feet. These figures show
+that the slope of the ice along the south face of this bluff was about
+320 feet per mile. This, so far as known, is the first determination of
+the slope of the edge of the continental ice sheet <i>at its extreme
+margin</i>. It is to be especially noted that these figures are for the
+extreme edge of the ice only. The angle of slope back from the edge was
+doubtless much less. <br /> <br /> </p>
+
+
+<h4> <i>Stratified Drift.</i> </h4>
+
+<p>While it is true that glacier ice does not distinctly stratify the
+deposits which it makes, it is still true that a very large part of the
+drift for which the ice of the glacial period was directly or indirectly
+responsible is stratified. That this should be so is not strange when it
+is remembered that most of the ice was ultimately converted into running
+water, just as the glaciers of today are. The relatively small portion
+which disappeared by evaporation was probably more than counterbalanced,
+at least near the margin of the ice, by the rain which fell upon it.
+<span class="pagenum"> <a name="Page_112" id="Page_112">[Pg 112]</a> </span>
+It cannot be considered an exaggeration, therefore, to say that the
+total amount of water which operated on the drift, first and last, was
+hardly less than the total amount of the ice itself. The drift deposited
+by the marginal part of the ice was affected during its deposition, not
+only by the water which arose from the melting of the ice which did the
+depositing, but by much water which arose from the melting of the ice
+far back from the margin. The general mobility of the water, as
+contrasted with ice, allowed it to concentrate its activities along
+those lines which favored its motion, so that different portions of the
+drift were not affected equally by the water of the melting ice.</p>
+
+<p>All in all it will be seen that the water must have been a very
+important factor in the deposition of the drift, especially near the
+margin of the ice. But the ice sheet had a marginal belt throughout its
+whole history, and water must have been active and effective along this
+belt, not only during the decadence of the ice sheet, but during its
+growth as well. It is further to be noted that any region of drift stood
+good chance of being operated upon by the water after the ice had
+departed from it, so that in regions over which topography directed
+drainage after the withdrawal of the ice, the water had the last chance
+at the drift, and modified it in such a way and to such an extent as
+circumstances permitted.</p>
+
+<p> <i>Its origin.</i>&mdash;There are various ways in which stratified drift may
+arise in connection with glacier deposits. It may come into existence by
+the operation of water alone; or by the co-operation of ice and water.
+Where water alone was immediately responsible for the deposition of
+stratified drift, the water concerned may have owed its origin to the
+melting ice, or it may have existed independently of the ice in the form
+of lakes. When the source of the water was the melting ice, the water
+may have been running, when it was actively concerned in the deposition
+of stratified drift; or it may have been standing (glacial lakes and
+ponds), when it was passively concerned. When ice co-operated with water
+in the development of stratified drift the ice was generally a passive
+partner.</p>
+
+<p> <span class="pagenum"> <a name="Page_113" id="Page_113">[Pg 113]</a> </span>
+<i>Glacial drainage.</i>&mdash;The body of an ice sheet during any glacial period
+is probably melting more or less at some horizons all the time, and at
+all horizons some of the time. Most of the water which is produced at
+the surface during the summer sinks beneath it. Some of it may congeal
+before it sinks far, but much of it reaches the bottom of the ice
+without refreezing. It is probable that melting is much more nearly
+continuous in the body of a moving ice sheet than at its surface, and
+that some of the water thus produced sinks to the bottom of the ice
+without refreezing. At the base of the ice, so long as it is in
+movement, there is doubtless more or less melting, due both to friction
+and to the heat received by conduction from the earth below. Thus in the
+ice and under the ice there must have been more or less water in motion
+throughout essentially all the history of an ice sheet.</p>
+
+<p>If it be safe to base conclusions on the phenomena of existing glaciers,
+it may be assumed that the waters beneath the ice, and to a less extent
+the waters in the ice, organized themselves to a greater or less degree
+into streams. For longer or shorter distances these streams flowed in
+the ice or beneath it. Ultimately they escaped from its edge. The
+subglacial streams doubtless flowed, in part, in the valleys which
+affected the land surface beneath the ice, but they were probably not
+all in such positions.</p>
+
+<p>The courses of well-defined subglacial streams were tunnels. The bases
+of the tunnels were of rock or drift, while the sides and tops were of
+ice. It will be seen, therefore, that their courses need not have
+corresponded with the courses of the valleys beneath the ice. They may
+sometimes have followed lines more or less independent of topography,
+much as water may be forced over elevations in closed tubes. It is not
+to be inferred, however, that the subglacial streams were altogether
+independent of the sub-ice topography. The tunnels in which the water
+ran probably had too many leaks to allow the water to be forced up over
+great elevations. This, at least, must have been the case where the ice
+was thin or affected by crevasses. Under such circumstances the
+topography of the land surface must have been the controlling element
+<span class="pagenum"> <a name="Page_114" id="Page_114">[Pg 114]</a> </span>
+in determining the course of the subglacial drainage.</p>
+
+<p>When the streams issued from beneath the ice the conditions of flow were
+more or less radically changed, and from their point of issue they
+followed the usual laws governing river flow. If the streams entered
+static water as they issued from the ice, and this was true where the
+ice edge reached the sea or a lake, the static water modified the
+results which the flowing waters would otherwise have produced.</p>
+
+<p> <i>Stages in the history of an ice sheet.</i>&mdash;The history of an ice sheet
+which no longer exists involves at least two distinct stages. These are
+(1) the period of growth, and (2) the period of decadence. If the latter
+does not begin as soon as the former is complete, an intervening stage,
+representing the period of maximum ice extension, must be recognized. In
+the case of the ice sheets of the glacial period, each of these stages
+was probably more or less complex. The general period of growth of each
+ice sheet is believed to have been marked by temporary, but by more or
+less extensive intervals of decadence, while during the general period
+of decadence, it is probable that the ice was subject to temporary, but
+to more or less extensive intervals of recrudescence. For the sake of
+simplicity, the effects of these oscillations of the edge of the ice
+will be neglected at the outset, and the work of the water accompanying
+the two or three principal stages of an ice sheet's history will be
+outlined as if interruptions in the advance and in the retreat,
+respectively, had not occurred.</p>
+
+<p>As they now exist, the deposits of stratified drift made at the edge of
+the ice or beyond it during the period of its maximum extension present
+the simplest, and at the same time most sharply defined phenomena, and
+are therefore considered first.</p>
+
+<p> <br /> <br />
+<span class="pagenum"> <a name="Page_115" id="Page_115">[Pg 115]</a> </span> </p>
+
+<h4> <i>Deposits Made by Extraglacial Waters During the Maximum Extension of
+the Ice.</i> </h4>
+
+<p>The deposits made by the water at the time of the maximum extension of
+the ice and during its final retreat, were never disturbed by subsequent
+glacier action. So far as not destroyed by subsequent erosion, they
+still retain the form and structure which they had at the outset. Such
+drift deposits, because they lie at the surface, and because they are
+more or less distinct topographically as well as structurally, are
+better known than the stratified drift of other stages of an ice sheet's
+history. Of stratified drift made during the maximum extension of the
+ice, and during its final retreat, there are several types.</p>
+
+<p> <i>A. At the edge of ice, on land.</i>&mdash;If the subglacial streams flowed
+under "head," the pressure was relieved when they escaped from the ice.
+With this relief, there was diminution of velocity. With the diminution
+of velocity, deposition of load would be likely to take place. Since
+these changes would be likely to occur at the immediate edge of the ice,
+one class of stratified drift deposits would be made in this position,
+in immediate contact with the edge of the ice, and their form would be
+influenced by it. At the stationary margin of an ice sheet, therefore,
+at the time of its maximum advance, ice and water must have co-operated
+to bring into existence considerable quantities of stratified drift.</p>
+
+<p>The edge of the ice was probably ragged, as the ends of glaciers are
+today, and as the waters issued from beneath it, they must frequently
+have left considerable quantities of such debris as they were carrying,
+against its irregular margin, and in its re-entrant angles and marginal
+crevasses. When the ice against which this debris was first lodged
+melted, the marginal accumulations of gravel and sand often assumed the
+form of <i>kames</i>. A typical kame is a hill, hillock, or less commonly a
+short ridge of stratified drift; but several or many are often
+associated, giving rise to groups and areas of kames. Kames are often
+<span class="pagenum"> <a name="Page_116" id="Page_116">[Pg 116]</a> </span>
+associated with terminal moraines, a relation which emphasizes the fact
+of their marginal origin.</p>
+
+<p>So far as the superficial streams which flowed to the edge of the ice
+carried debris, this was subject to deposition as the streams descended
+from the ice. Such drift would tend to increase the body of marginal
+stratified drift from subglacial sources.</p>
+
+<p>Marginal accumulations of stratified drift, made by the co-operation of
+running water and ice, must have had their most extensive development,
+other things being equal, where the margin of the ice was longest in one
+position, and where the streams were heavily loaded. The deposits made
+by water at the edge of the ice differ from those of the next
+class&mdash;made beyond the edge of the ice&mdash;in that they were influenced in
+their disposition and present topography, by the presence of ice.</p>
+
+<p>In the Devil's lake region isolated and well-defined kames are not of
+common occurrence. There are, however, at many points hills which have
+something of a kame-like character. There is such a hill a mile
+southeast of the Court house at Baraboo, at the point marked <i>p</i>, Plate
+<a href="images/i37.jpg">XXXVII</a>. In this hill there are good exposures which show its structure.
+There are many hillocks of a general kame-like habit associated with the
+terminal moraine south of the main quartzite range, and north of the
+Wisconsin river. Many of them occur somewhat within the terminal moraine
+a few miles northwest of Merrimac.</p>
+
+<p> <i>B. Beyond the edge of the ice, on land.</i>&mdash;As the waters escaping from
+the ice flowed farther, deposits of stratified drift were made quite
+beyond the edge of the ice. The forms assumed by such deposits are
+various, and depended on various conditions. Where the waters issuing
+from the edge of the ice found themselves concentrated in valleys, and
+where they possessed sufficient load, and not too great velocity, they
+aggraded the valleys through which they flowed, developing fluvial
+plains of gravel and sand, which often extended far beyond the ice. Such
+fluvial plains of gravel and sand constitute the <i>valley trains</i> which
+extend beyond the unstratified glacial drift in many of the valleys of
+<span class="pagenum"> <a name="Page_117" id="Page_117">[Pg 117]</a> </span>
+the United States. They are found especially in the valleys leading out
+from the stouter terminal moraines of late glacial age. From these
+moraines, the more extensive valley trains take their origin, thus
+emphasizing the fact that they are deposits made by water beyond a
+stationary ice margin. Valley trains have all the characteristics of
+alluvial plains built by rapid waters carrying heavy loads of detritus.
+Now and then their surfaces present slight variations from planeness,
+but they are minor. Like all plains of similar origin they decline
+gradually, and with diminishing gradient, down stream. They are of
+coarser material near their sources, and of finer material farther away.
+Valley trains constitute a distinct topographic as well as genetic type.</p>
+
+<p>A perfect example of a valley train does not occur within the region
+here discussed. There is such a train starting at the moraine where it
+crosses the Wisconsin river above Prairie du Sac, and extending down
+that valley to the Mississippi, but at its head this valley train is
+wide and has the appearance of an overwash plain, rather than a valley
+train. Farther from the moraine, however, it narrows, and assumes the
+normal characteristics of a valley train. It is the gravel and sand of
+this formation which underlies Sauk Prairie, and its topographic
+continuation to the westward.</p>
+
+<p>Where the subglacial streams did not follow subglacial valleys, they did
+not always find valleys when they issued from the ice. Under such
+circumstances, each heavily loaded stream coming out from beneath the
+ice must have tended to develop a plain of stratified material near its
+point of issue&mdash;a sort of alluvial fan. Where several such streams came
+out from beneath the ice near one another, their several plains, or
+fans, were likely to become continuous by lateral growth. Such border
+plains of stratified drift differ from valley trains particularly (1) in
+being much less elongate in the direction of drainage; (2) in being much
+more extended parallel to the margin of the ice; and (3) in not being
+confined to valleys. Such plains stood an especially good chance of
+development where the edge of the ice remained constant for a
+<span class="pagenum"> <a name="Page_118" id="Page_118">[Pg 118]</a> </span>
+considerable period of time, for it was under such conditions that the
+issuing waters had opportunity to do much work. Thus arose the type of
+stratified drift variously known as <i>overwash plains</i>, <i>outwash plains</i>,
+<i>morainic plains</i>, and <i>morainic aprons</i>. These plains sometimes skirt
+the moraine for many miles at a stretch.</p>
+
+<p>Overwash plains may sometimes depart from planeness by taking on some
+measure of undulation, of the sag and swell (kame) type, especially near
+their moraine edges. The same is often true of the heads of valley
+trains. The heads of valley trains and the inner edges of overwash
+plains, it is to be noted, occupy the general position in which kames
+are likely to be formed, and the undulations which often affect these
+parts of the trains and plains, respectively, are probably to be
+attributed to the influence of the ice itself. Valley trains and
+overwash plains, therefore, at their upper ends and edges respectively,
+may take on some of the features of kames. Indeed, either may head in a
+kame area.</p>
+
+<p>Good examples of overwash or outwash plains may be seen at various
+points in the vicinity of Baraboo. The plain west of the moraine just
+south of the main quartzite ridge has been referred to under valley
+trains. In Sauk Prairie, however, its characteristics are those of an
+outwash plain, rather than those of a valley train.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 550px;">
+<img src="images/fig41.jpg" width="550" height="82" alt="" />
+</div>
+<p class="center caption">Fig. 41. -- The morainic or outwash plain bordering the
+terminal moraine. The figure is diagrammatic, but represents, in cross
+section, the normal relation as seen south of the quartzite range at the
+east edge of Sauk Prairie, north of the Baraboo river and at some points
+ between the South range and the Baraboo.<br /> <br /> <br /> </p>
+
+<p>A good example of an outwash plain occurs southwest of Baraboo, flanking
+the moraine on the west (Fig. <a href="images/fig41.jpg">41</a>). Seen from the west, the moraine just
+north of the south quartzite range stands up as a conspicuous ridge
+twenty to forty feet above the morainic plain which abuts against it.
+Traced northward, the edge of the outwash plain, as it abuts against
+<span class="pagenum"> <a name="Page_119" id="Page_119">[Pg 119]</a> </span>
+the moraine, becomes higher, and in Section 4, Township 11 N., Range 6
+E., the moraine edge of the plain reaches the crest of the moraine (Fig.
+<a href="images/fig42.jpg">42</a>). From this point north to the Baraboo river the moraine scarcely
+rises above the edge of the outwash beyond.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 550px;">
+<img src="images/fig42.jpg" width="550" height="93" alt="" />
+</div>
+<p class="center indent">Fig. 42. -- The outwash plain is built up to the crest of
+the moraine. The figure is diagrammatic, but this relation is seen at
+the point marked <i>W</i>, Plate <a href="images/i02.jpg">II</a>.<br /> <br /> <br /> </p>
+
+<p>North of the Baraboo river the moraine is again distinct and the
+overwash plain to the west well developed much of the way from the
+Baraboo to Kilbourn City. A portion of it is known as Webster's Prairie.</p>
+
+<p>Locally, the outwash plains of this region have been much dissected by
+erosion since their deposition, and are now affected by many small
+valleys. In composition these plains are nearly everywhere gravel and
+sand, the coarser material being nearer the moraine. The loose material
+is in places covered by a layer of loam several feet deep, which greatly
+improves the character of the soil. This is especially true of Sauk
+Prairie, one of the richest agricultural tracts in the state.</p>
+
+<p>When the waters issuing from the edge of the ice were sluggish, whether
+they were in valleys or not, the materials which they carried and
+deposited were fine instead of coarse, giving rise to deposits of silt,
+or clay, instead of sand or gravel.</p>
+
+<p>At many points near the edge of the ice during its maximum stage of
+advance, there probably issued small quantities of water not in the form
+of well-defined streams, bearing small quantities of detritus. These
+small quantities of water, with their correspondingly small loads, were
+unable to develop considerable plains of stratified drift, but produced
+small patches instead. Such patches have received no special
+designation.</p>
+
+<p>In the deposition of stratified drift beyond the edge of the ice, the
+<span class="pagenum"> <a name="Page_120" id="Page_120">[Pg 120]</a> </span>
+latter was concerned only in so far as its activity helped to supply the
+water with the necessary materials.</p>
+
+<p> <i>C. Deposits at and beyond the edge of the ice in standing water.</i>&mdash;The
+waters which issued from the edge of the ice sometimes met a different
+fate. The ice in its advance often moved up river valleys. When at the
+time of its maximum extension, it filled the lower part of a valley,
+leaving the upper part free, drainage through the valley stood good
+chance of being blocked. Where this happened a marginal valley lake was
+formed. Such a lake was formed in the valley of the Baraboo when the
+edge of the ice lay where the moraine now is (Plate <a href="images/i02.jpg">II</a>). The waters
+which were held back by the ice dam, reinforced by the drainage from the
+ice itself, soon developed a lake above the point of obstruction. This
+extinct lake may be named <i>Baraboo lake</i>. In this lake deposits of
+laminated clay were made. They are now exposed in the brick yards west
+of Baraboo, and in occasional gullies and road cuts in the flat
+bordering the river.</p>
+
+<p>At the point marked <i>s</i> (Plate <a href="images/i37.jpg">XXXVII</a>) there was, in glacial
+times, a small lake having an origin somewhat different from that of
+Baraboo lake (see p. <a href="#Page_133">133</a>). The former site of the lake is now marked by
+a notable flat. Excavations in the flat show that it is made up of
+stratified clay, silt, sand and gravel, to the depth of many
+feet,&mdash;locally more than sixty. These lacustrine deposits are well
+exposed in the road cuts near the northwest corner of the flat, and in
+washes at some other points. Plate <a href="images/i38.jpg">XXXVIII</a> shows some of the silt and
+clay, the laminæ of which are much distorted.</p>
+
+<p> <i>Deltas</i> must have been formed where well-defined streams entered the
+lakes, and <i>subaqueous overwash plains</i> where deltas became continuous
+by lateral growth. The accumulation of stratified drift along the
+ice-ward shores of such lakes must have been rapid, because of the
+abundant supply of detritus. These materials were probably shifted about
+more or less by waves and shore currents, and some of them may have been
+widely distributed. Out from the borders of such lakes, fine silts and
+clays must have been in process of deposition, at the same time that the
+coarse materials were being laid down nearer shore.<br /> <br /> <br /> <br /> </p>
+
+<p class="center">WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVIII.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/i38.jpg" width="300" height="239" alt="" />
+</div>
+<p class="center indent">Distorted laminae of silt and clay.<br />
+<a href="images/i38.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p> <span class="pagenum"> <a name="Page_121" id="Page_121">[Pg 121]</a> </span>
+Good examples of deltas and subaqueous overwash plains do not appear to
+exist in the region, although conditions for their development seem to
+have been present. Thus in the lake which occupied the valley of the
+Baraboo, conditions would seem to have been ideal for the development of
+such features; that is, the overwash plains previously described should,
+theoretically, have been subaqueous overwash plains; but if this be
+their character, their distinctive marks have been destroyed by
+subsequent erosion.</p>
+
+<p>During the maximum extension of an ice sheet, therefore, there was
+chance for the development, at its edge or beyond it, of the following
+types of stratified drift: (1) kames and kame belts, at the edge of the
+ice; (2) fluvial plains or valley trains, in virtual contact with the
+ice at their heads; (3) border plains or overwash plains, in virtual
+contact with the ice at their upper edges; (4) ill-defined patches of
+stratified drift, coarse or fine near the ice; (5) subaqueous overwash
+plains and deltas, formed either in the sea or lakes at or near the edge
+of the ice; (6) lacustrine and marine deposits of other sorts, the
+materials for which were furnished by the waters arising from the ice.
+So far as this region is concerned, all the deposits made in standing
+water were made in lakes. <br /> <br /> </p>
+
+<h4> <i>Deposits Made by Extraglacial Waters During the Retreat of the Ice.</i> </h4>
+
+<p>During the retreat of any ice sheet, disregarding oscillations of its
+edge, its margin withdrew step by step from the position of extreme
+advance to its center. When the process of dissolution was complete,
+each portion of the territory once covered by the ice, had at some stage
+in the dissolution, found itself in a marginal position. At all stages
+in its retreat the waters issuing from the edge of the ice were working
+in the manner already outlined in the preceding paragraphs. Two points
+of difference only need be especially noted. In the first place the
+deposits made by waters issuing from the retreating ice were laid down
+<span class="pagenum"> <a name="Page_122" id="Page_122">[Pg 122]</a> </span>
+on territory which the ice had occupied, and their subjacent stratum was
+often glacial drift. So far as this was the case, the stratified drift
+was super-morainic, not extra-morainic. In the second place the edge of
+the ice in retreat did not give rise to such sharply marked formations
+as the edge of the ice which was stationary. The processes which had
+given rise to valley trains, overwash plains, kames, etc., while the ice
+edge was stationary, were still in operation, but the line or zone of
+their activity (the edge of the ice) was continually retreating, so that
+the foregoing types, more or less dependent on a stationary edge, were
+rarely well developed. As the ice withdrew, therefore, it allowed to be
+spread over the surface it had earlier occupied, many incipient valley
+trains, overwash plains, and kames, and a multitude of ill-defined
+patches of stratified drift, thick and thin, coarse and fine. Wherever
+the ice halted in its retreat, these various types stood chance of
+better development.</p>
+
+<p>Such deposits did not cover all the surface discovered by the ice in its
+retreat, since the issuing waters, thanks to their great mobility,
+concentrated their activities along those lines which favored their
+motion. Nevertheless the aggregate area of the deposits made by water
+outside the ice as it retreated, was great.</p>
+
+<p>It is to be noted that it was not streams alone which were operative as
+the ice retreated. As its edge withdrew, lakes and ponds were
+continually being drained, as their outlets, hitherto choked by the ice,
+were opened, while others were coming into existence as the depressions
+in the surface just freed from ice, filled with water. Lacustrine
+deposits at the edge of the ice during its retreat were in all essential
+respects identical with those made in similar situations during its
+maximum extension.</p>
+
+<p>Disregarding oscillations of the ice edge at these stages, the deposits
+made by extraglacial waters during the maximum extension of an ice
+sheet, and during its retreat, were always left at the surface, so far
+as the work of that ice sheet was concerned. The stratified drift laid
+down by extraglacial waters in these stages of the last ice sheet which
+affected any region of our continent still remain at the surface in much
+the condition in which they were deposited, except for the erosion they
+<span class="pagenum"> <a name="Page_123" id="Page_123">[Pg 123]</a> </span>
+have since suffered. It is because of their position at the surface that
+the deposits referable to these stages of the last ice sheet of any
+given region have received most attention and are therefore most
+familiar. <br /> <br /> </p>
+
+
+<h4> <i>Deposits Made by Extraglacial Waters During the Advance of the Ice.</i> </h4>
+
+<p>During the advance of an ice sheet, if its edge forged steadily forward,
+the waters issuing from it, and flowing beyond, were effecting similar
+results. They were starting valley trains, overwash plains, kames, and
+small ill-defined patches of stratified drift which the ice did not
+allow them to complete before pushing over them, thus moving forward the
+zone of activity of extraglacial waters. Unlike the deposits made by the
+waters of the retreating ice, those made by the waters of the advancing
+stage were laid down on territory which had not been glaciated, or at
+least not by the ice sheet concerned in their deposition. If the ice
+halted in its advance, there was at such time and place opportunity for
+the better development of extraglacial stratified drift.</p>
+
+<p>Lakes as well as streams were concerned in the making of stratified beds
+of drift, during the advance of the ice. Marginal lakes were obliterated
+by having their basins filled with the advancing ice, which displaced
+the water. But new ones were formed, on the whole, as rapidly as their
+predecessors became extinct, so that lacustrine deposits were being made at
+intervals along the margin of the advancing ice.</p>
+
+<p>Deposits made in advance of a growing ice sheet, by waters issuing from
+it, were subsequently overridden by the ice, to the limit of its
+advance, and in the process, suffered destruction, modification, or
+burial, in whole or in part, so that now they rarely appear at the
+surface.
+<span class="pagenum"> <a name="Page_124" id="Page_124">[Pg 124]</a> </span> </p>
+
+<p> <br /> </p>
+<h4> <i>Deposits Made by Subglacial Streams.</i> </h4>
+
+<p>Before their issuance from beneath the ice, subglacial waters were not
+idle. Their activity was sometimes erosive, and at such times stratified
+deposits were not made. But where the sub-glacial streams found
+themselves overloaded, as seems frequently to have been the case, they
+made deposits along their lines of flow. Where such waters were not
+confined to definite channels, their deposits probably took on the form
+of irregular patches of silt, sand, or gravel; but where depositing
+streams were confined to definite channels, their deposits were
+correspondingly concentrated.</p>
+
+<p>When subglacial streams were confined to definite channels, the same may
+have been constant in position, or may have shifted more or less from
+side to side. Where the latter happened there was a tendency to the
+development of a belt or strip of stratified drift having a width equal
+to the extent of the lateral migrations of the under-ice stream. Where
+the channel of the subglacial stream remained fixed in position, the
+deposition was more concentrated, and the bed was built up. If the
+stream held its course for a long period of time, the measure of
+building may have been considerable. In so far as these channel deposits
+were made near the edge of the ice, during the time of its maximum
+extension or retreat, they were likely to remain undisturbed during its
+melting. The aggraded channels then came to stand out as ridges. These
+ridges of gravel and sand are known as <i>osars</i> or <i>eskers</i>. It is not to
+be inferred that eskers never originated in other ways, but it seems
+clear that this is one method, and probably the principal one, by which
+they came into existence. Eskers early attracted attention, partly
+because they are relatively rare, and partly because they are often
+rather striking topographic features. The essential conditions,
+therefore, for their formations, so far as they are the product of
+subglacial drainage, are (1) the confining of the subglacial streams to
+definite channels; and (2) a sufficient supply of detritus. One esker
+<span class="pagenum"> <a name="Page_125" id="Page_125">[Pg 125]</a> </span>
+only has been found in the region under consideration. It is located at
+the point marked <i>j</i>, Plate <a href="images/i02.jpg">II</a>, seven and one-half miles northeast of
+Merrimac and one and one-half miles south of Alloa (<i>g</i>, Plate <a href="images/i02.jpg">II</a>). The
+esker is fully a quarter of a mile long, about thirty feet high, and
+four rods wide at its base.</p>
+
+<p>Subglacial deposits of stratified drift were sometimes made on
+unstratified drift (till) already deposited by the ice before the
+location of the stream, and sometimes on the rock surfaces on which no
+covering of glacier drift had been spread.</p>
+
+<p>It is to be kept in mind that subglacial drainage was operative during
+the advance of an ice sheet, during its maximum extension, and during
+its retreat, and that during all these stages it was effecting its
+appropriate results. It will be readily seen, however, that all deposits
+made by subglacial waters, were subject to modification or destruction
+or burial, through the agency of the ice, and that those made during the
+advance of the ice were less likely to escape than those made during its
+maximum extension or retreat. <br /> <br /> <br /> </p>
+
+
+<h4>RELATIONS OF STRATIFIED TO UNSTRATIFIED DRIFT.</h4>
+
+<p>When it is remembered that extraglacial and subglacial waters were
+active at all stages of an ice sheet's history, giving rise, or tending
+to give rise to all the phases of stratified drift enumerated above;
+when it is remembered that the ice of several epochs affected much of
+the drift-covered country; and when it is remembered further that the
+edge of the ice both during advance and retreat was subject to
+oscillation, and that each advance was likely to bury the stratified
+drift last deposited, beneath unstratified, it will be seen that the
+stratified drift and the unstratified had abundant opportunity to be
+associated in all relationships and in all degrees of intimacy, and that
+the relations of the one class of drift to the other may come to be very
+complex.</p>
+
+<p>As a result of edge oscillation, it is evident that stratified drift may
+alternate with unstratified many times in a formation of drift
+<span class="pagenum"> <a name="Page_126" id="Page_126">[Pg 126]</a> </span>
+deposited during a single ice epoch, and that two beds of till,
+separated by a bed of stratified drift, do not necessarily represent two
+distinct glacial epochs. The extent of individual beds of stratified
+drift, either beneath the till or inter-bedded with it, may not be
+great, though their aggregate area and their aggregate volume is very
+considerable. It is to be borne in mind that the ice, in many places,
+doubtless destroyed all the stratified drift deposited in advance on the
+territory which it occupied later, and that in others it may have left
+only patches of once extensive sheets. This may help to explain why it
+so frequently happens that a section of drift at one point shows many
+layers of stratified drift, while another section close by, of equal
+depth, and in similar relationships, shows no stratified material
+whatsoever.</p>
+
+<p>Such deposits as were made by superglacial streams during the advance of
+the ice must likewise have been delivered on the land surface, but would
+have been subsequently destroyed or buried, becoming in the latter case,
+submorainic. This would be likely to be the fate of all such
+superglacial gravels as reached the edge of the ice up to the time of
+its maximum advance.</p>
+
+<p>Streams descending from the surface of the ice into crevasses also must
+have carried down sand and gravel where such materials existed on the
+ice. These deposits may have been made on the rock which underlies the
+drift, or they may have been made on stratified or unstratified drift
+already deposited. In either case they were liable to be covered by
+till, thus reaching an inter-till or sub-till position.</p>
+
+<p>Englacial streams probably do little depositing, but it is altogether
+conceivable that they might accumulate such trivial pockets of sand and
+gravel as are found not infrequently in the midst of till. The
+inter-till position would be the result of subsequent burial after the
+stratified material reached a resting place.</p>
+
+<p> <i>Complexity of relations.</i>&mdash;From the foregoing it becomes clear that
+there are diverse ways by which stratified drift, arising in connection
+with an ice sheet, may come to be interbedded with till, when due
+<span class="pagenum"> <a name="Page_127" id="Page_127">[Pg 127]</a> </span>
+recognition is made of all the halts and oscillations to which the edge
+of a continental glacier may have been subject during both its advance
+and retreat. <br /> <br /> </p>
+
+
+<h4>CLASSIFICATION OF STRATIFIED DRIFT ON THE BASIS OF POSITION.</h4>
+
+<p>In general the conditions and relations which theoretically should
+prevail are those which are actually found.</p>
+
+<p>On the basis of position stratified drift deposits may be classified as
+follows:</p>
+
+<p>1. <i>Extraglacial deposits</i>, made by the waters of any glacial epoch if
+they flowed and deposited beyond the farthest limit of the ice.</p>
+
+<p>2. <i>Supermorainic deposits</i>, made chiefly during the final retreat of
+the ice from the locality where they occur, but sometimes by
+extraglacial streams or lakes of a much later time. Locally too,
+stratified deposits of an early stage of a glacial epoch, lying on till,
+may have failed to be buried by the subsequent passage of the ice over
+them, and so remain at the surface. In origin, supermorainic deposits
+were for the most part extraglacial (including marginal), so far as the
+ice sheet calling them into existence was concerned. Less commonly they
+were subglacial, and failed to be covered, and less commonly still
+superglacial.</p>
+
+<p>3. <i>The submorainic (basal) deposits</i> were made chiefly by extraglacial
+waters in advance of the first ice which affected the region where they
+occur. They were subsequently overridden by the ice and buried by its
+deposits. Submorainic deposits, however, may have arisen in other ways.
+Subglacial waters may have made deposits of stratified drift on surfaces
+which had been covered by ice, but not by till, and such deposits may
+have been subsequently buried. The retreat of an ice sheet may have left
+rock surfaces free from till covering, on which the marginal waters of
+the ice may have made deposits of stratified drift. These may have been
+subsequently covered by till during a re-advance of the ice in the same
+epoch or in a succeeding one. Still again, the till left by one ice
+<span class="pagenum"> <a name="Page_128" id="Page_128">[Pg 128]</a> </span>
+sheet may have been exposed to erosion to such an extent as to have been
+completely worn away before the next ice advance, so that stratified
+deposits connected with a second or later advance may have been made on
+a driftless surface, and subsequently buried.</p>
+
+<p>4. <i>Intermorainic stratified drift</i> may have originated at the outset in
+all the ways in which supermorainic drift may originate. It may have
+become intermorainic by being buried in any one of the various ways in
+which the stratified drift may become submorainic. <br /> <br /> <br /> </p>
+
+
+<h4>CHANGES IN DRAINAGE EFFECTED BY THE ICE.</h4>
+
+<h4> <i>While the Ice Was on.</i> </h4>
+
+<p>As the continental ice sheet invaded a region, the valleys were filled
+and drainage was thereby seriously disturbed. Different streams were
+affected in different ways. Where the entire basin of a stream was
+covered by ice, the streams of that basin were, for the time being,
+obliterated. Where the valley of a stream was partially filled with ice,
+the valley depression was only partially obliterated, and the remaining
+portion became the scene of various activities. Where the ice covered
+the lower course of a stream but not the upper, the ice blocked the
+drainage, giving rise to a lake. Where the ice covered the upper course
+of a stream, but not its lower, the lower portion was flooded, and
+though the river held its position, it assumed a new phase of activity.
+Streams issuing from the ice usually carry great quantities of gravel
+and sand, and make deposits along their lower courses. Long continued
+glacial drainage usually results in a large measure of aggradation. This
+was true of the streams of the glacial period.</p>
+
+<p>Where a stream flowed parallel or approximately parallel to the edge of
+the advancing ice it was sometimes shifted in the direction in which the
+ice was moving, keeping parallel to the front of the ice. All of these
+<span class="pagenum"> <a name="Page_129" id="Page_129">[Pg 129]</a> </span>
+classes of changes took place in this region.</p>
+
+<p> <i>Wisconsin lake.</i>&mdash;Reference has already been made to certain lakes
+which existed in the region when the ice was there. The largest of these
+lakes was that which resulted from the blocking of the Wisconsin river.
+The ice crossed its present course at Kilbourn City, and its edge lay to
+the west of the river from that point to Prairie du Sac (see Plate <a href="images/i01.jpg">I</a>).
+The waters from the area now draining into the Wisconsin must either
+have found an avenue of escape beneath the ice, or have accumulated in a
+lake west of the edge of the ice. There is reason to believe that the
+latter was what happened, and that a great lake covered much of the low
+land west of the Wisconsin river above and below Kilbourn City. The
+extensive gravel beds on the north flank of the quartzite bluff at
+Necedah, and the water-worn pebbles of local origin on the slope of
+Petenwell peak (Plate <a href="images/i32.jpg">XXXII</a>), as well as the gravels at other points,
+are presumably the work of that lake. The waters in this lake, as in
+that in the Baraboo valley, probably rose until the lowest point in the
+rim of the basin was reached, and there they had their outlet. The
+position of this outlet has not been definitely determined, but it has
+been thought to be over the divide of the Black river.
+<a name="FNanchor_1_8" id="FNanchor_1_8"> </a> <a href="#Footnote_1_8" class="fnanchor">[8]</a>
+It is possible, so far as now known, that this lake was connected with that of
+the Baraboo valley. Until topographic maps of this region are made, the
+connections will not be easily determined.</p>
+
+<p>Even after the ice had retreated past the Wisconsin, opening up the
+present line of drainage, the lakes did not disappear at once, for the
+ice had left considerable deposits of drift in the Wisconsin valley.
+Thus at <span class="smcap">f</span>, Plates <a href="images/i02.jpg">II</a>
+and <a href="images/i37.jpg">XXXVII</a>, and perhaps at other
+points, the Wisconsin has made cuts of considerable depth in the drift.
+Were these cuts filled, as they must have been when the ice melted, the
+drainage would be ponded, the waters standing at the level of the dam.
+This drift obstruction at <span class="smcap">f</span> would therefore have prolonged the history
+<span class="pagenum"> <a name="Page_130" id="Page_130">[Pg 130]</a> </span>
+of the lake which had come into existence when the ice blocked the
+drainage of the Wisconsin. As the drift of the valley was removed the
+level of the lake sank and finally disappeared.</p>
+
+<p> <i>Baraboo lake.</i>&mdash;Another lake which existed in this region when the ice
+was here, occupied the valley of the Baraboo and its tributaries when
+the ice blocked the valley at Baraboo. This lake occupied not only the
+valley of the Baraboo, but extended up the lower course of every
+tributary, presumably rising until it found the lowest point in the rim
+of the drainage basin. The location of this point, and therefore the
+height of the lake when at its maximum, are not certainly known, though
+meager data on this point have been collected. At a point three miles
+southeast of Ablemans on the surface of a sandstone slope, water-worn
+gravel occurs, the pebbles of which were derived from the local rock. On
+the slope below the gravel, the surface is covered with loam which has a
+suggestion of stratification, while above it, the soil and subsoil
+appear to be the product of local rock decomposition. This water-worn
+gravel of local origin on a steep slope facing the valley, probably
+represents the work of the waves of this lake, perhaps when it stood at
+its maximum height. This gravel is about 125 feet (aneroid measurement)
+above the Baraboo river to the north.</p>
+
+<p>Further evidence of a shore line has been found at the point marked <span class="smcap">t</span>,
+Plate <a href="images/i02.jpg">II</a>. At this place water-worn gravel of the local rock occurs in
+much the same relationship as that already mentioned, and at the same
+elevation above the Baraboo river. At a point two and one-half miles
+southwest of Ablemans there is local water-worn gravel, with which is
+mingled glacial material (pieces of porphyry and diabase) which could
+have reached this point only by being carried thither by floating ice
+from the glacier. The level of this mixed local and glacial material is
+(according to aneroid measurement) approximately the same as that of the
+other localities.</p>
+
+<p>When the ice melted, an outlet was opened <i>via</i> the Lower narrows, and
+the water of the lake drained off to the Wisconsin by this route. Had
+<span class="pagenum"> <a name="Page_131" id="Page_131">[Pg 131]</a> </span>
+the ice left no drift, the lake would have been promptly drained when
+the ice melted; but the lake did not entirely disappear immediately
+after the ice retreated, for the drift which the ice left obstructed
+drainage to the east. The moraine, however, was not so high as the
+outlet of the lake while the ice was on, so that, as the ice retreated,
+the water flowed over the moraine to the east, and drew down the level
+of the lake to the level of the lowest point in the moraine. The
+postglacial cut through the moraine is about ninety feet deep.</p>
+
+<p>Besides being obstructed where crossed by the terminal moraine, the
+valley of the Baraboo was clogged to a less extent by drift deposits
+between the moraine and the Lower narrows. At one or two places near the
+City of Baraboo, such obstructions, now removed, appear to have existed.
+Just above the Lower narrows (<i>c</i>, Plate <a href="images/i37.jpg">XXXVII</a>) there is positive
+evidence that the valley was choked with drift. Here in subsequent time,
+the river has cut through the drift-filling of the preglacial valley,
+developing a passage about twenty rods wide and thirty-five feet deep.
+If this passage were filled with drift, reproducing the surface left by
+the ice, the broad valley above it would be flooded, producing a shallow
+lake.</p>
+
+<p>The retreat of the ice therefore left two well defined drift dams in the
+valley, one low one just above the Lower narrows, and a higher one, the
+moraine dam, just west of Baraboo. Disregarding the influence of the
+ice, and considering the Baraboo valley only, these two dams would have
+given rise to two lakes, the upper one behind the higher dam being
+deeper and broader, and covering a much larger area; the lower one
+behind the lower dam, being both small and shallow.</p>
+
+<p>Up to the time that the ice retreated past the Lower narrows, the waters
+of the upper and lower lakes were united, held up to a common level by
+the ice which blocked this pass. After the ice retreated past the Lower
+narrows, the level of the Baraboo lake did not sink promptly, for not
+until the ice had retreated past the site of the Wisconsin was the
+present drainage established. Meantime the waters of the Baraboo lake
+joined
+<span class="pagenum"> <a name="Page_132" id="Page_132">[Pg 132]</a> </span>
+those of Wisconsin lake (p. <a href="#Page_129">129</a>) through the Lower narrows. If
+the lakes had been before connected at some point farther west, this
+connection through the narrows would not have changed the level of
+either. If they were not before connected, and if the Wisconsin lake was
+lower than the Baraboo, this connection would have drawn down the level
+of the latter.</p>
+
+<p>Since the drainage from the Baraboo went to the Wisconsin, the Baraboo
+lake was not at first lowered below the level of the highest obstruction
+in the valley of the Wisconsin even after the ice had retreated beyond
+that stream. As the drift obstructions of the Wisconsin valley were
+lowered, the levels of all the lakes above were correspondingly brought
+down. When the level of the waters in these lakes was brought down to
+the level of the moraine dam above Baraboo, the one Baraboo lake of
+earlier times became two. The level of the upper of these two lakes was
+determined by the moraine above Baraboo, that of the lower by the
+highest obstruction below the moraine in either the Baraboo or Wisconsin
+valley. The drift obstructions in the Baraboo valley were probably
+removed about as fast as those in the Wisconsin, and since the
+obstructions were of drift, and the streams strong, the removal of the
+dams was probably rapid. Both the upper and lower Baraboo lakes, as well
+as the Wisconsin, had probably been reduced to small proportions, if not
+been completely drained, before the glacial period was at an end.</p>
+
+<p> <i>Devil's lake in glacial times.</i>&mdash;While the ice edge was stationary in
+its position of maximum advance, its position on the north side of the
+main quartzite range was just north of Devil's lake (Plate <a href="images/i37.jpg">XXXVII</a>).
+The high ridge of drift a few rods north of the shore is a well
+defined moraine, and is here more clearly marked than farther east or
+west, because it stands between lower lands on either side, instead of
+being banked against the quartzite ridge. North of the lake it rises
+about 75 feet above the water. When the ice edge lay in this position on
+the north side of the range, its front between the East bluff and the
+Devil's nose lay a half mile or so from the south end of the lake. In
+this position also there is a well defined moraine.</p>
+
+<p> <span class="pagenum"> <a name="Page_133" id="Page_133">[Pg 133]</a> </span>
+While the ice was at its maximum stand, it rose above these moraine
+ridges at either end of the lake. Between the ice at these two points
+there was then a notable basin, comparable to that of the present lake
+except that the barriers to the north and southeast were higher than
+now. The melting of the ice supplied abundant water, and the lake rose
+above its present level. The height which it attained is not known, but
+it is known to have risen at least 90 feet above its present level. This
+is indicated by the presence of a few drift bowlders on the West bluff
+of the lake at this height. They represent the work of a berg or bergs
+which at some stage floated out into the lake with bowlders attached.
+Bowlders dropped by bergs might be dropped at any level lower than the
+highest stand of the lake.</p>
+
+<p> <i>Other lakes.</i>&mdash;Another glacial lake on the East quartzite bluff has
+already (p. <a href="#Page_120">120</a>) been referred to. Like the Devil's lake in glacial
+time, its basin was an enclosure between the ice on the one hand, and
+the quartzite ridge on the other. The location of this lake is shown on
+Plate <a href="images/i37.jpg">XXXVII</a> (<i>s</i>). Here the edge of the ice, as shown by the position
+of the moraine, was affected by a re-entrant curve, the two ends of
+which rested against the quartzite ridge. Between the ice on the one
+hand and the quartzite ridge on the other, a small lake was formed. Its
+position is marked by a notable flat.</p>
+
+<p>With the exception of the north side, and a narrow opening at the
+northwest corner, the flat is surrounded by high lands. When the ice
+occupied the region, its edge held the position shown by the line
+marking the limit of its advance, and constituted an ice barrier to the north.
+<a name="FNanchor_1_9" id="FNanchor_1_9"> </a> <a href="#Footnote_1_9" class="fnanchor">[9]</a>
+The area of the flat was, therefore, almost shut in, the only
+outlet being a narrow one at <i>t</i>, Plate <a href="images/i37.jpg">XXXVII</a>. If the filling of
+stratified drift which underlies the flat were removed, the bottom of
+the area would be much lower than at present, and much lower than the
+outlet at <i>t</i>. It is therefore evident that when the ice had taken its
+position along the north side of the flat, an enclosed basin must have
+<span class="pagenum"> <a name="Page_134" id="Page_134">[Pg 134]</a> </span>
+existed, properly situated for receiving and holding water. Since this
+lake had but a short life and became extinct before the ice retreated,
+its history is here given.</p>
+
+<p>At first the lake had no outlet and the water rose to the level of the
+lowest point (<i>t</i>) in the rim of the basin, and thence overflowed to the
+west. Meanwhile the sediments borne in by the glacial drainage were
+being deposited in the lake in the form of a subaqueous overwash plain,
+the coarser parts being left near the shore, while the finer were
+carried further out. Continued drainage from the ice continued to bring
+sediment into the lake, and the subaqueous overwash plain extended its
+delta-like front farther and farther into the lake, until its basin was
+completely filled. With the filling of the basin the lake became
+extinct. The later drainage from the ice followed the line of the
+outlet, the level of which corresponds with the level of the filled lake
+basin. This little extinct lake is of interest as an example of a
+glacial lake which became extinct by having its basin filled during
+glacial times, by sediments washed out from the ice.</p>
+
+<p>Near the northwest corner of this flat, an exposure in the sediments of
+the old lake bed shows the curiously contorted layers of sand, silt, and
+clay represented in Plate <a href="images/i38.jpg">XXXVIII</a>. The layers shown in the
+figure are but a few feet below the level of the flat which marks the
+site of the lake. It will be seen that the contorted layers are between
+two series of horizontal ones. The material throughout the section is
+made up of fine-grained sands and clays, well assorted. That these
+particular layers should have been so much disturbed, while those below
+and above remained horizontal, is strange enough. The grounding of an
+iceberg on the surface before the overlying layers were deposited, the
+action of lake ice, or the effect of expansion and contraction due to
+freezing and thawing, may have been responsible for the singular
+phenomenon. Contorted laminæ are rather characteristic of the deposits
+of stratified drift.
+<span class="pagenum"> <a name="Page_135" id="Page_135">[Pg 135]</a> </span> </p>
+
+<p> <br /> </p>
+<h4> <i>After the Ice Had Disappeared.</i> </h4>
+
+<p>As has already been indicated (p. <a href="#Page_101">101</a>), the irregular deposition of
+glacial drift gave rise to many depressions without outlets in which
+surface waters collected after the ice had disappeared, forming ponds or
+lakes. So abundant are lakes and ponds and marshes in recently glaciated
+regions and so rare elsewhere, that they constitute one of the more
+easily recognized characteristics of a glaciated region.</p>
+
+<p>After the ice had melted, the mantle of drift which it left was
+sometimes so disposed as to completely obliterate preglacial valleys.
+More commonly it filled preglacial valleys at certain points only. In
+still other cases a valley was not filled completely at any point,
+though partially at many. In this last case, the partial fillings at
+various points constituted dams above which drainage was ponded, making
+lakes. If the dams were not high enough to throw the drainage out of the
+valley, the lakes would have their outlets over them. The drift dam
+being unconsolidated would be quickly cut down by the out-flowing water,
+and the lake level lowered. When the dam was removed or cut to its base,
+the lake disappeared and drainage followed its preglacial course.</p>
+
+<p>In case the valley was completely filled, or completely filled at
+points, the case was very different. The drainage on the drift surface
+was established with reference to the topography which obtained when the
+ice departed, and not with reference to the preglacial valleys. Wherever
+the preglacial valleys were completely filled, the postglacial drainage
+followed lines which were altogether independent of them. When
+preglacial valleys were filled by the drift in spots only, the
+postglacial streams followed them where they were not filled, only to
+leave them where the blocking occurred. In the former case the present
+drainage is through valleys which are preglacial in some places, and
+postglacial in others.</p>
+
+<p>Thus the drainage changes effected by the drift after the ice was gone,
+concerned both lakes and rivers. In this region there are several
+illustrations of these changes.</p>
+
+<p> <span class="pagenum"> <a name="Page_136" id="Page_136">[Pg 136]</a> </span>
+<i>Lakes.</i>&mdash;The lake basins of drift-covered regions are of various types.
+Some of them are altogether in drift, some partly in drift and partly in
+rock, and some wholly in rock. Basins in the drift were likely to be
+developed whenever heavy deposits surrounded thin ones. They are
+especially common in the depressions of terminal moraines.</p>
+
+<p>Another class of lake basins occurs in valleys, the basins being partly
+rock and partly drift. If a thick deposit of drift be made at one point
+in a valley, while above there is little or none, the thick deposit will
+form a dam, above which waters may accumulate, forming a pond or lake.
+Again, a ridge of drift may be deposited in the form of a curve with its
+ends against a rock-ridge, thus giving rise to a basin.</p>
+
+<p>In the course of time, the lakes and ponds in the depressions made or
+occasioned by the drift will be destroyed by drainage. Remembering how
+valleys develop (p. <a href="#Page_46">46</a>) it is readily understood that the heads of the
+valleys will sooner or later find the lakes, and drain them if their
+bottoms be not too low.</p>
+
+<p>Drainage is hostile to lakes in another way. Every stream which flows
+into a lake brings in more or less sediment. In the standing water this
+sediment is deposited, thus tending to fill the lake basin. Both by
+filling their basins and by lowering their outlets, rivers tend to the
+destruction of lakes, and given time enough, they will accomplish this
+result. In view of this double hostility of streams, it is not too much
+to say that "rivers are the mortal enemies of lakes."</p>
+
+<p>The destruction of lakes by streams is commonly a gradual process, and
+so it comes about that the abundance and the condition of the undrained
+areas in a drift-covered region is in some sense an index of the length
+of time, reckoned in terms of erosion, which has elapsed since the drift
+was deposited.</p>
+
+<p>In this region there were few lakes which lasted long after the ice
+disappeared. The basins of the Baraboo and Wisconsin lakes (p. <a href="#Page_129">129</a>) were
+partly of ice, and so soon as the ice disappeared, the basins were so
+nearly destroyed, and the drift dams that remained so easily eroded,
+that the lakes had but a brief history,&mdash;a history that was glacial,
+rather than postglacial.</p>
+
+<p> <span class="pagenum"> <a name="Page_137" id="Page_137">[Pg 137]</a> </span>
+The history of the little lake on the East quartzite bluff (p. <a href="#Page_133">133</a>) as
+already pointed out, came to an end while the ice was still present.</p>
+
+<p>The beds of at least two other extinct ponds or small lakes above the
+level of the Baraboo are known. These are at <i>v</i> and <i>w</i>, Plate <a href="images/i37.jpg">XXXVII</a>.
+They owed their origin to depressions in the drift, but the outflowing
+waters have lowered their outlets sufficiently to bring them to the
+condition of marshes. Both were small in area and neither was deep.</p>
+
+<p> <i>Existing lakes.</i>&mdash;Relatively few lakes now remain in this immediate
+region, though they are common in most of the country covered by the ice
+sheet which overspread this region. Devil's lake only is well known. The
+lake which stood in this position while the ice was on, has already been
+referred to (p. <a href="#Page_132">132</a>). After the ice had melted away, the drift which it
+had deposited still left an enclosure suitable for holding water. The
+history of this basin calls for special mention.</p>
+
+<p>At the north end of the lake, and again in the capacious valley leading
+east from its south end, there are massive terminal moraines. Followed
+southward, this valley though blocked by the moraine a half mile below
+the lake, leads off towards the Wisconsin river, and is probably the
+course of a large preglacial stream. Beyond the moraine, this valley is
+occupied by a small tributary to the Wisconsin which heads at the
+moraine. To the north of the lake, the head of a tributary of the
+Baraboo comes within eighty rods of the lake, but again the terminal
+moraine intervenes. From data derived from wells it is known that the
+drift both at the north and south ends of the lake extends many feet
+below the level of its water, and at the north end, the base of the
+drift is known to be at least fifty feet below the level of the bottom
+of the lake. The draining of Devil's lake to the Baraboo river is
+therefore prevented only by the drift dam at its northern end. It is
+nearly certain also, that, were the moraine dam at the south end of the
+lake removed, all the water would flow out to the Wisconsin, though the
+data for the demonstration of this conclusion are not to be had, as
+already stated (p. <a href="#Page_132">132</a>).</p>
+
+<p> <span class="pagenum"> <a name="Page_138" id="Page_138">[Pg 138]</a> </span>
+There can be no doubt that the gorge between the East and West bluffs
+was originally the work of a pre-Cambrian stream, though the depth of
+the pre-Cambrian valley may not have been so great as that of the
+present. Later, the valley, so far as then excavated, was filled with
+the Cambrian (Potsdam) sandstone, and re-excavated in post-Cambrian and
+preglacial time. Devil's lake then occupies an unfilled portion of an
+old river valley, isolated by great morainic dams from its surface
+continuations on either hand. Between the dams, water has accumulated
+and formed the lake. <br /> <br /> </p>
+
+
+<h4> <i>Changes in Streams.</i> </h4>
+
+<p>In almost every region covered by the ice, the streams which established
+themselves after its departure follow more or less anomalous courses.
+This region is no exception. Illustrations of changes which the
+deposition of the drift effected have already been given in one
+connection or another in this report.</p>
+
+<p> <i>Skillett creek.</i>&mdash;An illustration of the sort of change which drift
+effects is furnished by Skillett creek, a small stream tributary to the
+Baraboo, southwest of the city of that name. For some distance from its
+head (<i>a</i> to <i>b</i>, Fig. <a href="images/fig43.jpg">43</a>) its course is through a capacious preglacial
+valley. The lower part of this valley was filled with the water-laid
+drift of the overwash plain. On reaching the overwash plain the creek
+therefore shifted its course so as to follow the border of that plain,
+and along this route, irrespective of material, it has cut a new channel
+to the Baraboo. The postglacial portion of the valley (<i>b</i> to <i>c</i>) is
+everywhere narrow, and especially so where cut in sandstone.</p>
+
+<p>The course and relations of this stream suggest the following
+explanation: Before the ice came into the region, Skillett creek
+probably flowed in a general northeasterly direction to the Baraboo,
+through a valley comparable in size to the preglacial part of the
+present valley. As the ice advanced, the lower part of this valley was
+occupied by it, and the creek was compelled to seek a new course. The
+only course open to it was to the north, just west of the advancing ice,
+and, shifting westward as fast as the ice advanced, it abandoned
+<span class="pagenum"> <a name="Page_139" id="Page_139">[Pg 139]</a> </span>
+altogether its former lower course. Drainage from the ice then carried
+out and deposited beyond the same, great quantities of gravel and sand,
+making the overwash plain. This forced the stream still farther west,
+until it finally reached its present position across a sandstone ridge
+or plain, much higher than its former course. Into this sandstone it has
+since cut a notable gorge, a good illustration of a postglacial valley.
+The series of changes shown by this creek is illustrative of the changes
+undergone by streams in similar situations and relations all along the
+margin of the ice.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig43.jpg" width="300" height="289" alt="" />
+</div>
+<p class="center indent">Fig. 43. -- Skillett Creek, illustrating the points
+mentioned in the text.<br />
+<a href="images/fig43.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>The picturesque glens (Parfrey's and Dorward's) on the south face of the
+East bluff are the work of post-glacial streams. The preglacial valleys
+of this slope were obliterated by being filled during the glacial epoch.</p>
+
+<p> <i>The Wisconsin.</i>&mdash;The preglacial course of the Wisconsin river is not
+known in detail, but it was certainly different from the course which
+the stream now follows. On Plate <a href="images/i01.jpg">I</a> the relations of the present
+stream to the moraine (and former ice-front) may be seen.
+<a name="FNanchor_1_10" id="FNanchor_1_10"> </a> <a href="#Footnote_1_10" class="fnanchor">[10]</a>
+<span class="pagenum"> <a name="Page_140" id="Page_140">[Pg 140]</a> </span>
+As the ice approached it from the east, the preglacial valley within the area
+here under consideration was affected first by the overwash from the
+moraine, and later by the ice itself, from the latitude of Kilbourn City
+to Prairie du Sac.</p>
+
+<p>It has already been stated that the ice probably dammed the river, and
+that a lake was formed above Kilbourn City, reaching east to the ice and
+west over the lowland tributary to the river, the water rising till it
+found an outlet, perhaps down to the Black river valley.</p>
+
+<p>When the ice retreated, the old valley had been partly filled, and the
+lowest line of drainage did not everywhere correspond with it. Where the
+stream follows its old course, it flows through a wide capacious valley,
+but where it was displaced, it found a new course on the broad flat
+which bordered its preglacial course. Displacement of the stream
+occurred in the vicinity of Kilbourn City, and, forced to find a new
+line of flow west of its former course, the stream has cut a new channel
+in the sandstone. To this displacement of the river, and its subsequent
+cutting, we are indebted for the far-famed Dalles of the Wisconsin (p.
+<a href="#Page_69">69</a>). But not all the present route of the river through the dalles has
+been followed throughout the entire postglacial history of the stream.
+In Fig. <a href="images/fig44.jpg">44</a>, the depression <span class="smcap">a</span>, <span class="smcap">b</span>,
+<span class="smcap">c</span>, was formerly the course of the
+stream. The present course between <span class="smcap">d</span> and
+<span class="smcap">e</span> is therefore the youngest
+portion of the valley, and from its lesser width is known as the
+"narrows." During high water in the spring, the river still sends part
+of its waters southward by the older and longer route.</p>
+
+<p>The preglacial course of the Wisconsin south of the dalles has never
+been determined with certainty, but rational conjectures as to its
+position have been made.</p>
+
+<p>The great gap in the main quartzite range, a part of which is occupied
+by Devil's lake, was a narrows in a preglacial valley. The only streams
+in the region sufficiently large to be thought of as competent to
+<span class="pagenum"> <a name="Page_141" id="Page_141">[Pg 141]</a> </span>
+produce such a gorge are the Baraboo and the Wisconsin. If the Baraboo
+was the stream which flowed through this gorge in preglacial time, the
+comparable narrows in the north quartzite range&mdash;the Lower narrows of
+the Baraboo&mdash;is to be accounted for. The stream which occupied one of
+these gorges probably occupied the other, for they are in every way
+comparable except in that one has been modified by glacial action, while
+the other has not.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 178px;">
+<img src="images/fig44.jpg" width="178" height="300" alt="" />
+</div>
+<p class="center indent">Fig. 44. -- The Wisconsin valley near Kilbourn City.<br />
+<a href="images/fig44.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>The Baraboo river flows through a gorge&mdash;the Upper narrows&mdash;in the north
+quartzite range at Ablemans, nine miles west of Baraboo. This gorge is
+much narrower than either the Lower narrows or the Devil's lake gorge,
+suggesting the work of a lesser stream. It seems on the whole
+<span class="pagenum"> <a name="Page_142" id="Page_142">[Pg 142]</a> </span>
+probable, as suggested by Irving,
+<a name="FNanchor_1_11" id="FNanchor_1_11"> </a> <a href="#Footnote_1_11" class="fnanchor">[11]</a>
+that in preglacial time the
+Wisconsin river flowed south through what is now the Lower narrows of
+the Baraboo, thence through the Devil's lake gorge to its present valley
+to the south. If this be true, the Baraboo must at that time have joined
+this larger stream at some point east of the city of the same name.</p>
+
+<h4> <i>The Driftless Area.</i> </h4>
+
+<p>Reference has already been made to the fact that the western part of the
+area here described is driftless, and the line marking the limit of ice
+advance has been defined. Beyond this line, gravel and sand, carried
+beyond the ice by water, extends some distance to the west. But a large
+area in the southwestern part of the state is essentially free from
+drift, though it is crossed by two belts of valley drift (valley trains)
+along the Wisconsin and Mississippi rivers.</p>
+
+<p>The "driftless area" includes, besides the southwestern portion of
+Wisconsin, the adjoining corners of Minnesota, Iowa and Illinois. In the
+earlier epochs of the glacial period this area was completely surrounded
+by the ice, but in the last or <i>Wisconsin epoch</i> it was not surrounded,
+since the lobes did not come together south of it as in earlier times.
+(Compare Plate <a href="images/i38.jpg">XXXVIII</a> and Fig.
+<a href="images/fig36.jpg">36</a>.)</p>
+
+<p>Various suggestions have been made in the attempt to explain the
+driftless area. The following is perhaps the most satisfactory:
+<a name="FNanchor_1_12" id="FNanchor_1_12"> </a> <a href="#Footnote_1_12" class="fnanchor">[12]</a> </p>
+
+<p>The adjacent highlands of the upper peninsula of Michigan, are bordered
+on the north by the capacious valley of Lake Superior leading off to the
+west, while to the east lies the valley of Lake Michigan leading to the
+south. These lake valleys were presumably not so broad and deep in
+preglacial times as now, though perhaps even then considerable valleys.</p>
+
+
+<p> <span class="pagenum"> <a name="Page_143" id="Page_143">[Pg 143]</a> </span>
+When the ice sheet, moving in a general southward direction from the
+Canadian territory, reached these valleys, they led off two great
+tongues or lobes of ice, the one to the south through the Lake Michigan
+depression, the other to the south of west through the Lake Superior
+trough. (Fig. <a href="images/fig36.jpg">36</a>) The highland between the lake valleys conspired with
+the valleys to the same end. It acted as a wedge, diverting the ice to
+either side. It offered such resistance to the ice, that the thin and
+relatively feeble sheet which succeeded in surmounting it, did not
+advance far to the south before it was exhausted. On the other hand, the
+ice following the valleys of Lakes Superior and Michigan respectively,
+failed to come together south of the highland until the latitude of
+northern Iowa and Illinois was reached. The driftless area therefore
+lies south of the highlands, beyond the limit of the ice which
+surmounted it, and between the Superior and Michigan glacial lobes above
+their point of union. The great depressions, together with the
+intervening highland, are therefore believed to be responsible for the
+absence of glaciation in the driftless area. <br /> <br /> </p>
+
+
+<h4> <i>Contrast Between Glaciated and Unglaciated Areas.</i> </h4>
+
+<p>The glaciated and unglaciated areas differ notably in (1) topography, (2)
+drainage, and (3) mantle rock.</p>
+
+<p>1. <i>Topography.</i>&mdash;The driftless area has long been exposed to the
+processes of degradation. It has been cut into valleys and ridges by
+streams, and the ridges have been dissected into hills. The
+characteristic features of a topography fashioned by running water are
+such as to mark it clearly from surfaces fashioned by other agencies.
+Rivers end at the sea (or in lakes). Generally speaking, every point at
+the bottom of a river valley is higher than any other point in the
+bottom of the same valley nearer the sea, and lower than any other point
+correspondingly situated farther from the sea. This follows from the
+fact that rivers make their own valleys for the most part, and a river's
+course is necessarily downward. In a region of erosion topography
+therefore, tributary valleys lead down to their mains, secondary
+tributaries lead down to the first, and so on; or, to state the same
+<span class="pagenum"> <a name="Page_144" id="Page_144">[Pg 144]</a> </span>
+thing in reverse order, in every region where the surface configuration
+has been determined by rain and river erosion, every gully and every
+ravine descends to a valley. The smaller valleys descend to larger and
+lower ones, which in turn lead to those still larger and lower. The
+lowest valley of a system ends at the sea, so that the valley which
+joins the sea is the last member of the series of erosion channels of
+which the ravines and gullies are the first. It will thus be seen that
+all depressions in the surface, worn by rivers, lead to lower ones. The
+surface of a region sculptured by rivers is therefore marked by valleys,
+with intervening ridges and hills, the slopes of which descend to them.
+All topographic features are here determined by the water courses.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig45.jpg" width="300" height="196" alt="" />
+</div>
+<p class="center indent">Fig. 45. -- Drainage in the driftless area. The absence of
+ponds and marshes is to be noted.<br />
+<a href="images/fig45.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+
+<p>The relief features of the glaciated area, on the other hand, lack the
+systematic arrangement of those of the unglaciated territory, and stream
+valleys are not the controlling elements in the topography.</p>
+
+<p>2. <i>Drainage.</i>&mdash;The surface of the driftless area is well drained. Ponds
+and lakes are essentially absent, except where streams have been
+<span class="pagenum"> <a name="Page_145" id="Page_145">[Pg 145]</a> </span>
+obstructed by human agency. The drainage of the drift-covered area, on
+the other hand, is usually imperfect. Marshes, ponds and lakes are of
+common occurrence. These types are shown by the accompanying maps, Figs.
+<a href="images/fig45.jpg">45</a> and
+<a href="images/fig46.jpg">46</a>, the one from the driftless area, the other from the
+drift-covered.<br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig46.jpg" width="300" height="290" alt="" />
+</div>
+<p class="center indent">Fig. 46. -- Drainage in a glaciated region. Walworth and
+Waukesha counties, Wisconsin, showing abundance of marshes and lakes.<br />
+<a href="images/fig46.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+
+<p>3. <i>Mantle rock.</i>&mdash;The unglaciated surface is overspread to an average
+depth of several feet by a mantle of soil and earth which has resulted
+from the decomposition of the underlying rock. This earthy material
+sometimes contains fragments and even large masses of rock like that
+beneath. These fragments and masses escaped disintegration because of
+their greater resistance while the surrounding rock was destroyed. This
+mantle rock grades from fine material at the surface down through
+coarser, until the solid rock is reached, the upper surface of the rock
+being often ill-defined (Fig. <a href="images/fig47.jpg">47</a>). The thickness of the mantle is
+<span class="pagenum"> <a name="Page_146" id="Page_146">[Pg 146]</a> </span>
+approximately constant in like topographic situations where the
+underlying rock is uniform.</p>
+
+<p>The residual soils are made up chiefly of the insoluble parts of the
+rock from which they are derived, the soluble parts having been removed
+in the process of disintegration.<br /> <br /> <br /> <br /> </p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig47.jpg" width="500" height="69" alt="" />
+</div>
+<p class="center indent">Fig. 47. -- Section in a driftless area, showing relation
+of the mantle rock to the solid rock beneath.<br />
+<a href="images/fig47.jpg">See larger image</a> <br /> <br /> <br /> </p>
+
+<p>With these residuary soils of the driftless area, the mantle rock of
+glaciated tracts is in sharp contrast. Here, as already pointed out, the
+material is diverse, having come from various formations and from widely
+separated sources. It contains the soluble as well as the insoluble
+parts of the rock from which it was derived. In it there is no
+suggestion of uniformity in thickness, no regular gradation from fine to
+coarse from the surface downward. The average thickness of the drift is
+also much greater than that of the residual earths. Further, the contact
+between the drift and the underlying rock surface is usually a definite
+surface. (Compare Figs. <a href="images/fig32.jpg">32</a> and
+<a href="images/fig47.jpg">47</a>.) <br /> <br /> </p>
+
+
+<h4>POSTGLACIAL CHANGES.</h4>
+
+<p>Since the ice melted from the region, the changes in its geography have
+been slight. Small lakes and ponds have been drained, the streams whose
+valleys had been partly filled, have been re-excavating them, and
+erosion has been going on at all points in the slow way in which it
+normally proceeds. The most striking example of postglacial erosion is
+the dalles of the Wisconsin, and even this is but a small gorge for so
+large a stream. The slight amount of erosion which has been accomplished
+since the drift was deposited, indicates that the last retreat of the
+ice, measured in terms of geology and geography, was very recent. It has
+been estimated at 7,000 to 10,000 years, though too great confidence is
+not to be placed in this, or any other numerical estimate of
+post-glacial time.</p>
+
+<p> <br /> <br /> <br /> <br />  <br /> <br />
+<span class="pagenum"> <a name="Page_147" id="Page_147">[Pg 147]</a> </span> </p>
+
+<h2>Footnotes</h2>
+<p> <br /> </p>
+
+<div class="footnote">
+<a name="Footnote_1_1" id="Footnote_1_1"> </a> <a href="#FNanchor_1_1"> <span class="label">[1]</span> </a>
+Ripple marks are often seen on the surface of wind-blown
+sand, but the other features of this sandstone show that this was not
+its mode of accumulation. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_2" id="Footnote_1_2"> </a> <a href="#FNanchor_1_2"> <span class="label">[2]</span> </a>
+Irving: "The Baraboo Quartzite Ranges." Vol. II, Geology of
+Wisconsin, pp. 504-519. Van Hise: "Some Dynamic Phenomena Shown by the
+Baraboo Quartzite Ranges of Central Wisconsin." Jour. of Geol., Vol. I,
+pp. 347-355.<br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_3" id="Footnote_1_3"> </a> <a href="#FNanchor_1_3"> <span class="label">[3]</span> </a>
+A few hundred feet would suffice. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_4" id="Footnote_1_4"> </a> <a href="#FNanchor_1_4"> <span class="label">[4]</span> </a>
+Jour. of Geol., Vol. III (pp. 655-67). <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_5" id="Footnote_1_5"> </a> <a href="#FNanchor_1_5"> <span class="label">[5]</span> </a>
+There is an admirable exposition of this subject in Gilbert's "Henry Mountains." <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_6" id="Footnote_1_6"> </a> <a href="#FNanchor_1_6"> <span class="label">[6]</span> </a>
+It is not here asserted that these notches were as deep as
+now, in pre-Cambrian time. It is, however, certain that the quartzite
+was deeply eroded, previous to the deposition of the Potsdam sandstone. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_7" id="Footnote_1_7"> </a> <a href="#FNanchor_1_7"> <span class="label">[7]</span> </a>
+An account of loess in connection with the drift of the
+last glacial epoch is given in the <i>Journal of Geology</i>, Vol. IV, pp.
+929-987. For a general account of loess, see Sixth Annual Report of U.
+S. Geological Survey. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_8" id="Footnote_1_8"> </a> <a href="#FNanchor_1_8"> <span class="label">[8]</span> </a>
+Chamberlin: Geology of Wisconsin, Vol. 1. <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_9" id="Footnote_1_9"> </a> <a href="#FNanchor_1_9"> <span class="label">[9]</span> </a>
+The moraine line on the map represents the crest of the
+marginal ridge rather than its outer limit, which is slightly nearer the
+lake margin. Stratified drift of the nature of overwash also intervenes
+at points between the moraine and the lake border. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_10" id="Footnote_1_10"> </a> <a href="#FNanchor_1_10"> <span class="label">[10]</span> </a>
+The preglacial course was probably east of the present in the vicinity of Kilbourn City. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_11" id="Footnote_1_11"> </a> <a href="#FNanchor_1_11"> <span class="label">[11]</span> </a>
+Irving. Geology of Wisconsin, Vol. II. <br /> <br /> <br /> </div>
+
+<div class="footnote">
+<a name="Footnote_1_12" id="Footnote_1_12"> </a> <a href="#FNanchor_1_12"> <span class="label">[12]</span> </a>
+Chamberlin and Irving. Geology of Wisconsin, Vols. I and II. <br /> <br /> <br /> </div>
+<p> <br /> <br /> <br /> <br /> </p>
+
+
+<h2>INDEX.</h2>
+
+<hr style="width: 45%;" />
+
+<table border="0" summary="Index" width="60%">
+<tr>
+   <td class="tdr padbottom2" colspan="2">PAGES</td>
+</tr>
+<tr>
+   <td class="tdl">Ablemans</td>
+   <td class="tdr padbottom2"> <a href="#Page_66">66</a>,  <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Baraboo Lake</td>
+   <td class="tdr"> <a href="#Page_130">130</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Baraboo Quartzite ranges</td>
+   <td class="tdr"> <a href="#Page_2">2</a>, <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Constitution of</td>
+   <td class="tdr"> <a href="#Page_14">14</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Dynamic action in</td>
+   <td class="tdr"> <a href="#Page_15">15</a>, <a href="#Page_17">17</a>, <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1" colspan="2">Gaps in&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Devil's Lake Gap</td>
+   <td class="tdr"> <a href="#Page_3">3</a>, <a href="#Page_13">13</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Lower Narrows</td>
+   <td class="tdr"> <a href="#Page_5">5</a>, <a href="#Page_13">13</a>, <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Narrows Creek</td>
+   <td class="tdr"> <a href="#Page_66">66</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Upper Narrows</td>
+   <td class="tdr"> <a href="#Page_5">5</a>, <a href="#Page_10">10</a>, <a href="#Page_17">17</a>,
+             <a href="#Page_19">19</a>, <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Igneous rock in</td>
+   <td class="tdr"> <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Structure of</td>
+   <td class="tdr"> <a href="#Page_15">15</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography of</td>
+   <td class="tdr"> <a href="#Page_5">5</a>, <a href="#Page_13">13</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Base-level</td>
+   <td class="tdr"> <a href="#Page_47">47</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Base-level plains</td>
+   <td class="tdr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Bowlder clay</td>
+   <td class="tdr"> <a href="#Page_97">97</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Breccia</td>
+   <td class="tdr padbottom2"> <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Castle Rock</td>
+   <td class="tdr"> <a href="#Page_71">71</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Cleopatra's Needle</td>
+   <td class="tdr"> <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Cold Water Canyon</td>
+   <td class="tdr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Conglomerate</td>
+   <td class="tdr"> <a href="#Page_10">10</a>, <a href="#Page_28">28</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Basal (Potsdam)</td>
+   <td class="tdr"> <a href="#Page_29">29</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Corrasion</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Cross-bedding</td>
+   <td class="tdr"> <a href="#Page_30">30</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Cycle of erosion</td>
+   <td class="tdr padbottom2"> <a href="#Page_44">44</a>, <a href="#Page_47">47</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Dalles of the Wisconsin</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of</td>
+   <td class="tdr"> <a href="#Page_53">53</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Scenery of</td>
+   <td class="tdr"> <a href="#Page_69">69</a>, <a href="#Page_140">140</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Dell Creek</td>
+   <td class="tdr"> <a href="#Page_53">53</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Deltas</td>
+   <td class="tdr"> <a href="#Page_30">30</a>, <a href="#Page_56">56</a>, <a href="#Page_120">120</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Deposits&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">By extra-glacial waters</td>
+   <td class="tdr"> <a href="#Page_115">115-123</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">By ice</td>
+   <td class="tdr"> <a href="#Page_85">85</a>, <a href="#Page_94">94</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">By rivers</td>
+   <td class="tdr"> <a href="#Page_55">55</a>, <a href="#Page_56">56</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">By subglacial streams</td>
+   <td class="tdr"> <a href="#Page_124">124</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of drift classified</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl"> <span class="pagenum"> <a name="Page_148" id="Page_148">[Pg 148]</a> </span>
+             Devil's Doorway</td>
+   <td class="tdr"> <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Devil's Lake</td>
+   <td class="tdr"> <a href="#Page_132">132</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">History of</td>
+   <td class="tdr"> <a href="#Page_132">132</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">In glacial times</td>
+   <td class="tdr"> <a href="#Page_132">132</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Location</td>
+   <td class="tdr"> <a href="#Page_3">3</a>, <a href="#Page_9">9</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of</td>
+   <td class="tdr"> <a href="#Page_132">132</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Devil's Nose</td>
+   <td class="tdr"> <a href="#Page_5">5</a>, <a href="#Page_110">110</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Divides, Shifting of</td>
+   <td class="tdr"> <a href="#Page_44">44</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Dorward's Glen</td>
+   <td class="tdr"> <a href="#Page_10">10</a>, <a href="#Page_14">14</a>, <a href="#Page_29">29</a>,
+             <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Drift</td>
+   <td class="tdr"> <a href="#Page_73">73</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Characteristics of</td>
+   <td class="tdr"> <a href="#Page_96">96</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Constitution of</td>
+   <td class="tdr"> <a href="#Page_94">94</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Deposits classified</td>
+   <td class="tdr"> <a href="#Page_127">127</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Effect on topography</td>
+   <td class="tdr"> <a href="#Page_85">85</a>, <a href="#Page_88">88</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Relation of stratified to unstratified</td>
+   <td class="tdr"> <a href="#Page_125">125</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Stratified</td>
+   <td class="tdr"> <a href="#Page_111">111</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Topography of</td>
+   <td class="tdr"> <a href="#Page_101">101</a>, <a href="#Page_103">103</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Driftless area</td>
+   <td class="tdr"> <a href="#Page_79">79</a>, <a href="#Page_142">142</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Drainage&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Adjustment of</td>
+   <td class="tdr"> <a href="#Page_62">62</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Changes in, effected by the ice</td>
+   <td class="tdr"> <a href="#Page_128">128</a>, <a href="#Page_142">142</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Establishment of</td>
+   <td class="tdr"> <a href="#Page_61">61</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Glacial</td>
+   <td class="tdr"> <a href="#Page_113">113</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of drift-covered area</td>
+   <td class="tdr"> <a href="#Page_144">144</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of driftless area</td>
+   <td class="tdr"> <a href="#Page_144">144</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">Postglacial changes in</td>
+   <td class="tdr padbottom2"> <a href="#Page_146">146</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Endmoräne</td>
+   <td class="tdr"> <a href="#Page_108">108</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Erosion&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">By rain, and rivers, general outline of</td>
+   <td class="tdr"> <a href="#Page_36">36-58</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Elements of</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of folded strata</td>
+   <td class="tdr"> <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of rocks of unequal hardness</td>
+   <td class="tdr"> <a href="#Page_47">47</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of the quartzite</td>
+   <td class="tdr"> <a href="#Page_25">25</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Preglacial</td>
+   <td class="tdr"> <a href="#Page_60">60</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography</td>
+   <td class="tdr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Without valleys</td>
+   <td class="tdr"> <a href="#Page_37">37</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Eskers</td>
+   <td class="tdr padbottom2"> <a href="#Page_124">124</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Falls</td>
+   <td class="tdr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Fossils&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">In limestone</td>
+   <td class="tdr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">In sandstone</td>
+   <td class="tdr"> <a href="#Page_9">9</a>, <a href="#Page_11">11</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Friendship mounds</td>
+   <td class="tdr padbottom2"> <a href="#Page_71">71</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Geographic features, general</td>
+   <td class="tdr"> <a href="#Page_3">3-20</a> </td>
+</tr>
+<tr>
+   <td class="tdl"> <span class="pagenum"> <a name="Page_149" id="Page_149">[Pg 149]</a> </span>
+             Glacial drainage</td>
+   <td class="tdr"> <a href="#Page_113">113</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Glaciated area</td>
+   <td class="tdr"> <a href="#Page_78">78</a>, <a href="#Page_91">91</a>, <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Glacier ice&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Deposition by</td>
+   <td class="tdr"> <a href="#Page_85">85</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Direction of movement</td>
+   <td class="tdr"> <a href="#Page_88">88</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosive work of</td>
+   <td class="tdr"> <a href="#Page_79">79-84</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Formation of</td>
+   <td class="tdr"> <a href="#Page_74">74</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Movement of, affected by topography</td>
+   <td class="tdr"> <a href="#Page_89">89</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Glens</td>
+   <td class="tdr"> <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Green Bay lobe</td>
+   <td class="tdr"> <a href="#Page_91">91</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Gibraltar rock</td>
+   <td class="tdr"> <a href="#Page_63">63</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Ground Moraine&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Constitution of</td>
+   <td class="tdr"> <a href="#Page_99">99</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Location of</td>
+   <td class="tdr"> <a href="#Page_97">97</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography of</td>
+   <td class="tdr"> <a href="#Page_101">101</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Groundwater level</td>
+   <td class="tdr padbottom2"> <a href="#Page_41">41</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Ice sheets&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Formation of</td>
+   <td class="tdr"> <a href="#Page_74">74</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">History of</td>
+   <td class="tdr"> <a href="#Page_114">114</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Movement of</td>
+   <td class="tdr"> <a href="#Page_75">75</a>, <a href="#Page_88">88</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">North American ice sheet</td>
+   <td class="tdr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Igneous rock</td>
+   <td class="tdr"> <a href="#Page_18">18</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Intermittent streams</td>
+   <td class="tdr padbottom2"> <a href="#Page_42">42</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Kames</td>
+   <td class="tdr padbottom2"> <a href="#Page_115">115</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Lakes&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Wisconsin Lake</td>
+   <td class="tdr"> <a href="#Page_129">129</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Baraboo Lake</td>
+   <td class="tdr"> <a href="#Page_130">130</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Devil's Lake</td>
+   <td class="tdr"> <a href="#Page_3">3</a>, <a href="#Page_9">9</a>, <a href="#Page_132">132</a>,
+             <a href="#Page_137">137</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Limestone, see Lower Magnesian.</td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Lower Magnesian limestone&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Fossils of</td>
+   <td class="tdr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">History of</td>
+   <td class="tdr"> <a href="#Page_31">31-32</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Occurrence of</td>
+   <td class="tdr"> <a href="#Page_11">11</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of</td>
+   <td class="tdr"> <a href="#Page_11">11</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Position of</td>
+   <td class="tdr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Structure of</td>
+   <td class="tdr"> <a href="#Page_8">8</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Lower Narrows</td>
+   <td class="tdr padbottom2"> <a href="#Page_5">5</a>, <a href="#Page_13">13</a>, <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Mantle rock</td>
+   <td class="tdr"> <a href="#Page_20">20</a>, <a href="#Page_144">144</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Metamorphism</td>
+   <td class="tdr"> <a href="#Page_14">14</a>, <a href="#Page_24">24</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Monadnocks</td>
+   <td class="tdr"> <a href="#Page_51">51</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Moraines (see terminal moraine and ground moraine).</td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Morainic aprons</td>
+   <td class="tdr padbottom2"> <a href="#Page_119">119</a> </td>
+</tr>
+<tr>
+   <td class="tdl"> <span class="pagenum"> <a name="Page_150" id="Page_150">[Pg 150]</a> </span>
+             Narrows</td>
+   <td class="tdr"> <a href="#Page_49">49</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">In quartzite</td>
+   <td class="tdr"> <a href="#Page_66">66</a>, <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Natural bridge</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Navy Yard</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Niagara limestone</td>
+   <td class="tdr"> <a href="#Page_33">33</a> </td>
+</tr>
+<tr>
+   <td class="tdl">North American ice sheet</td>
+   <td class="tdr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Nunatak</td>
+   <td class="tdr padbottom2"> <a href="#Page_89">89</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Osars (see Eskers).</td>
+</tr>
+<tr>
+   <td class="tdl">Outwash plains</td>
+   <td class="tdr"> <a href="#Page_118">118</a>, <a href="#Page_120">120</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Overwash plains</td>
+   <td class="tdr padbottom2"> <a href="#Page_118">118</a>, <a href="#Page_120">120</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Parfrey's Glen</td>
+   <td class="tdr"> <a href="#Page_10">10</a>, <a href="#Page_14">14</a>, <a href="#Page_29">29</a>,
+             <a href="#Page_68">68</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Peneplain</td>
+   <td class="tdr"> <a href="#Page_47">47</a>, <a href="#Page_50">50</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Pewit's nest</td>
+   <td class="tdr"> <a href="#Page_9">9</a>, <a href="#Page_53">53</a>, <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Pine Hollow</td>
+   <td class="tdr"> <a href="#Page_69">69</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Postglacial changes</td>
+   <td class="tdr"> <a href="#Page_146">146</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Potsdam sandstone&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Fossils of</td>
+   <td class="tdr"> <a href="#Page_9">9</a>, <a href="#Page_11">11</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">History of</td>
+   <td class="tdr"> <a href="#Page_27">27-31</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of</td>
+   <td class="tdr"> <a href="#Page_9">9-11</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Relation to quartzite</td>
+   <td class="tdr"> <a href="#Page_19">19</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1 padbottom2">Structure of</td>
+   <td class="tdr padbottom2"> <a href="#Page_8">8</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Quartzite (see also Baraboo quartzite ranges)&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Dynamic Metamorphism of</td>
+   <td class="tdr"> <a href="#Page_24">24</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosion of</td>
+   <td class="tdr"> <a href="#Page_25">25</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Origin of</td>
+   <td class="tdr"> <a href="#Page_23">23</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Submergence of</td>
+   <td class="tdr"> <a href="#Page_27">27</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Thickness of</td>
+   <td class="tdr"> <a href="#Page_26">26</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Uplift of</td>
+   <td class="tdr"> <a href="#Page_24">24</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Rapids</td>
+   <td class="tdr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Rejuvenation of streams</td>
+   <td class="tdr"> <a href="#Page_56">56</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Ripple marks</td>
+   <td class="tdr"> <a href="#Page_9">9</a>, <a href="#Page_15">15</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Roches mountennée</td>
+   <td class="tdr padbottom2"> <a href="#Page_81">81</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Sandstone (see Potsdam and St. Peters).</td>
+</tr>
+<tr>
+   <td class="tdl">Sauk Prarie</td>
+   <td class="tdr"> <a href="#Page_117">117</a>, <a href="#Page_118">118</a>, <a href="#Page_119">119</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Skillett Creek</td>
+   <td class="tdr"> <a href="#Page_8">8</a>, <a href="#Page_53">53</a>, <a href="#Page_138">138</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Slope of upper surface of ice</td>
+   <td class="tdr"> <a href="#Page_111">111</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Snow fields</td>
+   <td class="tdr"> <a href="#Page_74">74</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Soil</td>
+   <td class="tdr"> <a href="#Page_7">7</a>, <a href="#Page_144">144</a>, <a href="#Page_146">146</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Stand rock</td>
+   <td class="tdr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Steamboat rock</td>
+   <td class="tdr"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdl">St. Peter's sandstone</td>
+   <td class="tdr"> <a href="#Page_32">32</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Stratified drift</td>
+   <td class="tdr"> <a href="#Page_111">111-112</a>, <a href="#Page_125">125</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Streams, changes in</td>
+   <td class="tdr"> <a href="#Page_138">138</a> </td>
+</tr>
+<tr>
+   <td class="tdl"> <span class="pagenum"> <a name="Page_151" id="Page_151">[Pg 151]</a> </span>
+             Subaqueous overwash plains</td>
+   <td class="tdr"> <a href="#Page_120">120</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Subglacial till (ground moraines)</td>
+   <td class="tdr"> <a href="#Page_99">99</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Sugar Bowl</td>
+   <td class="tdr padbottom2"> <a href="#Page_70">70</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Talus slopes</td>
+   <td class="tdr"> <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Terminal moraines&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Across the United States</td>
+   <td class="tdr"> <a href="#Page_78">78</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Development of</td>
+   <td class="tdr"> <a href="#Page_102">102</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">In Devil's Lake region</td>
+   <td class="tdr"> <a href="#Page_105">105</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Boundaries of</td>
+   <td class="tdr"> <a href="#Page_106">106</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Location of</td>
+   <td class="tdr"> <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_108">108</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">On the main quartzite range</td>
+   <td class="tdr"> <a href="#Page_107">107</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft2">Width of</td>
+   <td class="tdr"> <a href="#Page_106">106</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Topography of</td>
+   <td class="tdr"> <a href="#Page_103">103</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Till</td>
+   <td class="tdr"> <a href="#Page_97">97</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Topography&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Effect of, on ice movement</td>
+   <td class="tdr"> <a href="#Page_89">89</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Erosion topography</td>
+   <td class="tdr"> <a href="#Page_12">12</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of drift-covered country</td>
+   <td class="tdr"> <a href="#Page_8">8</a>, <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of driftless area</td>
+   <td class="tdr"> <a href="#Page_6">6</a>, <a href="#Page_7">7</a>, <a href="#Page_12">12</a>,
+             <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of plain surrounding quartzite ridge</td>
+   <td class="tdr"> <a href="#Page_6">6</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Of quartzite ridges</td>
+   <td class="tdr"> <a href="#Page_5">5</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Transportation by streams</td>
+   <td class="tdr"> <a href="#Page_55">55</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Tributary valleys</td>
+   <td class="tdr"> <a href="#Page_39">39</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Turk's Head</td>
+   <td class="tdr padbottom2"> <a href="#Page_65">65</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Unconformity</td>
+   <td class="tdr"> <a href="#Page_19">19</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Underground water</td>
+   <td class="tdr"> <a href="#Page_58">58</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Unglaciated areas</td>
+   <td class="tdr"> <a href="#Page_79">79</a>, <a href="#Page_142">142</a>, <a href="#Page_143">143</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Unstratified drift</td>
+   <td class="tdr"> <a href="#Page_99">99</a>, <a href="#Page_102">102</a>, <a href="#Page_125">125</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Upper Narrows</td>
+   <td class="tdr padbottom2"> <a href="#Page_5">5</a>, <a href="#Page_10">10</a>, <a href="#Page_17">17</a>,
+             <a href="#Page_19">19</a>, <a href="#Page_67">67</a> </td>
+</tr>
+<tr>
+   <td class="tdl" colspan="2">Valley, the&mdash;</td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Beginning of</td>
+   <td class="tdr"> <a href="#Page_37">37</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Characteristics of, at various stages</td>
+   <td class="tdr"> <a href="#Page_52">52-54</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Course of</td>
+   <td class="tdr"> <a href="#Page_39">39</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">How a valley gets a stream</td>
+   <td class="tdr"> <a href="#Page_40">40</a> </td>
+</tr>
+<tr>
+   <td class="tdl padleft1">Limits of</td>
+   <td class="tdr"> <a href="#Page_43">43</a> </td>
+</tr>
+<tr>
+   <td class="tdl padbottom2">Valley trains</td>
+   <td class="tdr padbottom2"> <a href="#Page_116">116</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Waterfalls</td>
+   <td class="tdr"> <a href="#Page_48">48</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Weathering</td>
+   <td class="tdr"> <a href="#Page_36">36</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Webster's Prarie</td>
+   <td class="tdr"> <a href="#Page_119">119</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Wisconsin Lake</td>
+   <td class="tdr"> <a href="#Page_129">129</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Wisconsin River</td>
+   <td class="tdr"> <a href="#Page_139">139</a> </td>
+</tr>
+<tr>
+   <td class="tdl">Witch's Gulch</td>
+   <td class="tdr"> <a href="#Page_70">70</a> </td>
+</tr>
+</table>
+
+
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of The Geography of the Region about
+Devils Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+*** END OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+***** This file should be named 38148-h.htm or 38148-h.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/3/8/1/4/38148/
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+Updated editions will replace the previous one--the old editions
+will be renamed.
+
+Creating the works from public domain print editions means that no
+one owns a United States copyright in these works, so the Foundation
+(and you!) can copy and distribute it in the United States without
+permission and without paying copyright royalties.  Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark.  Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission.  If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy.  You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research.  They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks.  Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License (available with this file or online at
+http://gutenberg.org/license).
+
+
+Section 1.  General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A.  By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement.  If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B.  "Project Gutenberg" is a registered trademark.  It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement.  There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement.  See
+paragraph 1.C below.  There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works.  See paragraph 1.E below.
+
+1.C.  The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works.  Nearly all the individual works in the
+collection are in the public domain in the United States.  If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed.  Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work.  You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D.  The copyright laws of the place where you are located also govern
+what you can do with this work.  Copyright laws in most countries are in
+a constant state of change.  If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work.  The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E.  Unless you have removed all references to Project Gutenberg:
+
+1.E.1.  The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+1.E.2.  If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges.  If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3.  If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder.  Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4.  Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5.  Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6.  You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form.  However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form.  Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7.  Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8.  You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+     the use of Project Gutenberg-tm works calculated using the method
+     you already use to calculate your applicable taxes.  The fee is
+     owed to the owner of the Project Gutenberg-tm trademark, but he
+     has agreed to donate royalties under this paragraph to the
+     Project Gutenberg Literary Archive Foundation.  Royalty payments
+     must be paid within 60 days following each date on which you
+     prepare (or are legally required to prepare) your periodic tax
+     returns.  Royalty payments should be clearly marked as such and
+     sent to the Project Gutenberg Literary Archive Foundation at the
+     address specified in Section 4, "Information about donations to
+     the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+     you in writing (or by e-mail) within 30 days of receipt that s/he
+     does not agree to the terms of the full Project Gutenberg-tm
+     License.  You must require such a user to return or
+     destroy all copies of the works possessed in a physical medium
+     and discontinue all use of and all access to other copies of
+     Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+     money paid for a work or a replacement copy, if a defect in the
+     electronic work is discovered and reported to you within 90 days
+     of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+     distribution of Project Gutenberg-tm works.
+
+1.E.9.  If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark.  Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1.  Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection.  Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2.  LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees.  YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3.  LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from.  If you
+received the work on a physical medium, you must return the medium with
+your written explanation.  The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund.  If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund.  If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4.  Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5.  Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law.  The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6.  INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section  2.  Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers.  It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need, are critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come.  In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation web page at http://www.pglaf.org.
+
+
+Section 3.  Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service.  The Foundation's EIN or federal tax identification
+number is 64-6221541.  Its 501(c)(3) letter is posted at
+http://pglaf.org/fundraising.  Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations.  Its business office is located at
+809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
+business@pglaf.org.  Email contact links and up to date contact
+information can be found at the Foundation's web site and official
+page at http://pglaf.org
+
+For additional contact information:
+     Dr. Gregory B. Newby
+     Chief Executive and Director
+     gbnewby@pglaf.org
+
+
+Section 4.  Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment.  Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States.  Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements.  We do not solicit donations in locations
+where we have not received written confirmation of compliance.  To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit http://pglaf.org
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States.  U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses.  Donations are accepted in a number of other
+ways including checks, online payments and credit card donations.
+To donate, please visit: http://pglaf.org/donate
+
+
+Section 5.  General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart is the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone.  For thirty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included.  Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+
+Most people start at our Web site which has the main PG search facility:
+
+     http://www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
+
+
+</pre>
+
+</body>
+</html>
diff --git a/38148-h/images/fig01.jpg b/38148-h/images/fig01.jpg
new file mode 100644
index 0000000..605c189
--- /dev/null
+++ b/38148-h/images/fig01.jpg
diff --git a/38148-h/images/fig02.jpg b/38148-h/images/fig02.jpg
new file mode 100644
index 0000000..0fe8b24
--- /dev/null
+++ b/38148-h/images/fig02.jpg
diff --git a/38148-h/images/fig04.jpg b/38148-h/images/fig04.jpg
new file mode 100644
index 0000000..1d31abd
--- /dev/null
+++ b/38148-h/images/fig04.jpg
diff --git a/38148-h/images/fig05.jpg b/38148-h/images/fig05.jpg
new file mode 100644
index 0000000..f06fdc8
--- /dev/null
+++ b/38148-h/images/fig05.jpg
diff --git a/38148-h/images/fig06.jpg b/38148-h/images/fig06.jpg
new file mode 100644
index 0000000..fa2594f
--- /dev/null
+++ b/38148-h/images/fig06.jpg
diff --git a/38148-h/images/fig07.jpg b/38148-h/images/fig07.jpg
new file mode 100644
index 0000000..dbf77ee
--- /dev/null
+++ b/38148-h/images/fig07.jpg
diff --git a/38148-h/images/fig08.jpg b/38148-h/images/fig08.jpg
new file mode 100644
index 0000000..b032160
--- /dev/null
+++ b/38148-h/images/fig08.jpg
diff --git a/38148-h/images/fig09.jpg b/38148-h/images/fig09.jpg
new file mode 100644
index 0000000..b48c264
--- /dev/null
+++ b/38148-h/images/fig09.jpg
diff --git a/38148-h/images/fig10.jpg b/38148-h/images/fig10.jpg
new file mode 100644
index 0000000..86da253
--- /dev/null
+++ b/38148-h/images/fig10.jpg
diff --git a/38148-h/images/fig11.jpg b/38148-h/images/fig11.jpg
new file mode 100644
index 0000000..3544b47
--- /dev/null
+++ b/38148-h/images/fig11.jpg
diff --git a/38148-h/images/fig12.jpg b/38148-h/images/fig12.jpg
new file mode 100644
index 0000000..a0801a0
--- /dev/null
+++ b/38148-h/images/fig12.jpg
diff --git a/38148-h/images/fig13.jpg b/38148-h/images/fig13.jpg
new file mode 100644
index 0000000..191e941
--- /dev/null
+++ b/38148-h/images/fig13.jpg
diff --git a/38148-h/images/fig14.jpg b/38148-h/images/fig14.jpg
new file mode 100644
index 0000000..99fbc60
--- /dev/null
+++ b/38148-h/images/fig14.jpg
diff --git a/38148-h/images/fig15.jpg b/38148-h/images/fig15.jpg
new file mode 100644
index 0000000..72e22f0
--- /dev/null
+++ b/38148-h/images/fig15.jpg
diff --git a/38148-h/images/fig16.jpg b/38148-h/images/fig16.jpg
new file mode 100644
index 0000000..4dd0185
--- /dev/null
+++ b/38148-h/images/fig16.jpg
diff --git a/38148-h/images/fig17.jpg b/38148-h/images/fig17.jpg
new file mode 100644
index 0000000..325e5c3
--- /dev/null
+++ b/38148-h/images/fig17.jpg
diff --git a/38148-h/images/fig18.jpg b/38148-h/images/fig18.jpg
new file mode 100644
index 0000000..7f8778c
--- /dev/null
+++ b/38148-h/images/fig18.jpg
diff --git a/38148-h/images/fig19.jpg b/38148-h/images/fig19.jpg
new file mode 100644
index 0000000..6cec573
--- /dev/null
+++ b/38148-h/images/fig19.jpg
diff --git a/38148-h/images/fig20.jpg b/38148-h/images/fig20.jpg
new file mode 100644
index 0000000..66ac90d
--- /dev/null
+++ b/38148-h/images/fig20.jpg
diff --git a/38148-h/images/fig21.jpg b/38148-h/images/fig21.jpg
new file mode 100644
index 0000000..a881d08
--- /dev/null
+++ b/38148-h/images/fig21.jpg
diff --git a/38148-h/images/fig22.jpg b/38148-h/images/fig22.jpg
new file mode 100644
index 0000000..8ef860d
--- /dev/null
+++ b/38148-h/images/fig22.jpg
diff --git a/38148-h/images/fig23.jpg b/38148-h/images/fig23.jpg
new file mode 100644
index 0000000..e32529d
--- /dev/null
+++ b/38148-h/images/fig23.jpg
diff --git a/38148-h/images/fig24.jpg b/38148-h/images/fig24.jpg
new file mode 100644
index 0000000..9b03816
--- /dev/null
+++ b/38148-h/images/fig24.jpg
diff --git a/38148-h/images/fig25.jpg b/38148-h/images/fig25.jpg
new file mode 100644
index 0000000..df6847a
--- /dev/null
+++ b/38148-h/images/fig25.jpg
diff --git a/38148-h/images/fig26.jpg b/38148-h/images/fig26.jpg
new file mode 100644
index 0000000..307112e
--- /dev/null
+++ b/38148-h/images/fig26.jpg
diff --git a/38148-h/images/fig27.jpg b/38148-h/images/fig27.jpg
new file mode 100644
index 0000000..57ccce0
--- /dev/null
+++ b/38148-h/images/fig27.jpg
diff --git a/38148-h/images/fig28.jpg b/38148-h/images/fig28.jpg
new file mode 100644
index 0000000..8ebc4b4
--- /dev/null
+++ b/38148-h/images/fig28.jpg
diff --git a/38148-h/images/fig29.jpg b/38148-h/images/fig29.jpg
new file mode 100644
index 0000000..e8032b0
--- /dev/null
+++ b/38148-h/images/fig29.jpg
diff --git a/38148-h/images/fig30.jpg b/38148-h/images/fig30.jpg
new file mode 100644
index 0000000..a1df588
--- /dev/null
+++ b/38148-h/images/fig30.jpg
diff --git a/38148-h/images/fig31.jpg b/38148-h/images/fig31.jpg
new file mode 100644
index 0000000..816e5e7
--- /dev/null
+++ b/38148-h/images/fig31.jpg
diff --git a/38148-h/images/fig32.jpg b/38148-h/images/fig32.jpg
new file mode 100644
index 0000000..080bc67
--- /dev/null
+++ b/38148-h/images/fig32.jpg
diff --git a/38148-h/images/fig33.jpg b/38148-h/images/fig33.jpg
new file mode 100644
index 0000000..2c3e03d
--- /dev/null
+++ b/38148-h/images/fig33.jpg
diff --git a/38148-h/images/fig34.jpg b/38148-h/images/fig34.jpg
new file mode 100644
index 0000000..288ae07
--- /dev/null
+++ b/38148-h/images/fig34.jpg
diff --git a/38148-h/images/fig35.jpg b/38148-h/images/fig35.jpg
new file mode 100644
index 0000000..d798b4d
--- /dev/null
+++ b/38148-h/images/fig35.jpg
diff --git a/38148-h/images/fig36.jpg b/38148-h/images/fig36.jpg
new file mode 100644
index 0000000..97f6f6c
--- /dev/null
+++ b/38148-h/images/fig36.jpg
diff --git a/38148-h/images/fig37.jpg b/38148-h/images/fig37.jpg
new file mode 100644
index 0000000..1d531c2
--- /dev/null
+++ b/38148-h/images/fig37.jpg
diff --git a/38148-h/images/fig38.jpg b/38148-h/images/fig38.jpg
new file mode 100644
index 0000000..7345ee5
--- /dev/null
+++ b/38148-h/images/fig38.jpg
diff --git a/38148-h/images/fig39.jpg b/38148-h/images/fig39.jpg
new file mode 100644
index 0000000..56dca56
--- /dev/null
+++ b/38148-h/images/fig39.jpg
diff --git a/38148-h/images/fig40.jpg b/38148-h/images/fig40.jpg
new file mode 100644
index 0000000..a9cd58a
--- /dev/null
+++ b/38148-h/images/fig40.jpg
diff --git a/38148-h/images/fig41.jpg b/38148-h/images/fig41.jpg
new file mode 100644
index 0000000..4733847
--- /dev/null
+++ b/38148-h/images/fig41.jpg
diff --git a/38148-h/images/fig42.jpg b/38148-h/images/fig42.jpg
new file mode 100644
index 0000000..0b8e471
--- /dev/null
+++ b/38148-h/images/fig42.jpg
diff --git a/38148-h/images/fig43.jpg b/38148-h/images/fig43.jpg
new file mode 100644
index 0000000..073a1eb
--- /dev/null
+++ b/38148-h/images/fig43.jpg
diff --git a/38148-h/images/fig44.jpg b/38148-h/images/fig44.jpg
new file mode 100644
index 0000000..179b56b
--- /dev/null
+++ b/38148-h/images/fig44.jpg
diff --git a/38148-h/images/fig45.jpg b/38148-h/images/fig45.jpg
new file mode 100644
index 0000000..e546d44
--- /dev/null
+++ b/38148-h/images/fig45.jpg
diff --git a/38148-h/images/fig46.jpg b/38148-h/images/fig46.jpg
new file mode 100644
index 0000000..ceba8d5
--- /dev/null
+++ b/38148-h/images/fig46.jpg
diff --git a/38148-h/images/fig47.jpg b/38148-h/images/fig47.jpg
new file mode 100644
index 0000000..3ebbc89
--- /dev/null
+++ b/38148-h/images/fig47.jpg
diff --git a/38148-h/images/frontispiece.jpg b/38148-h/images/frontispiece.jpg
new file mode 100644
index 0000000..0658d56
--- /dev/null
+++ b/38148-h/images/frontispiece.jpg
diff --git a/38148-h/images/i01.jpg b/38148-h/images/i01.jpg
new file mode 100644
index 0000000..3bb0673
--- /dev/null
+++ b/38148-h/images/i01.jpg
diff --git a/38148-h/images/i02.jpg b/38148-h/images/i02.jpg
new file mode 100644
index 0000000..2ec1f42
--- /dev/null
+++ b/38148-h/images/i02.jpg
diff --git a/38148-h/images/i03f1.jpg b/38148-h/images/i03f1.jpg
new file mode 100644
index 0000000..fe93ee4
--- /dev/null
+++ b/38148-h/images/i03f1.jpg
diff --git a/38148-h/images/i03f2.jpg b/38148-h/images/i03f2.jpg
new file mode 100644
index 0000000..685e0a5
--- /dev/null
+++ b/38148-h/images/i03f2.jpg
diff --git a/38148-h/images/i04.jpg b/38148-h/images/i04.jpg
new file mode 100644
index 0000000..2fa1826
--- /dev/null
+++ b/38148-h/images/i04.jpg
diff --git a/38148-h/images/i05.jpg b/38148-h/images/i05.jpg
new file mode 100644
index 0000000..d48de3d
--- /dev/null
+++ b/38148-h/images/i05.jpg
diff --git a/38148-h/images/i06.jpg b/38148-h/images/i06.jpg
new file mode 100644
index 0000000..858cd1a
--- /dev/null
+++ b/38148-h/images/i06.jpg
diff --git a/38148-h/images/i07.jpg b/38148-h/images/i07.jpg
new file mode 100644
index 0000000..4e1b1a0
--- /dev/null
+++ b/38148-h/images/i07.jpg
diff --git a/38148-h/images/i08.jpg b/38148-h/images/i08.jpg
new file mode 100644
index 0000000..9059a9f
--- /dev/null
+++ b/38148-h/images/i08.jpg
diff --git a/38148-h/images/i09.jpg b/38148-h/images/i09.jpg
new file mode 100644
index 0000000..a58e185
--- /dev/null
+++ b/38148-h/images/i09.jpg
diff --git a/38148-h/images/i10.jpg b/38148-h/images/i10.jpg
new file mode 100644
index 0000000..619335f
--- /dev/null
+++ b/38148-h/images/i10.jpg
diff --git a/38148-h/images/i11.jpg b/38148-h/images/i11.jpg
new file mode 100644
index 0000000..9db2c18
--- /dev/null
+++ b/38148-h/images/i11.jpg
diff --git a/38148-h/images/i12.jpg b/38148-h/images/i12.jpg
new file mode 100644
index 0000000..c1f63cf
--- /dev/null
+++ b/38148-h/images/i12.jpg
diff --git a/38148-h/images/i13f1.jpg b/38148-h/images/i13f1.jpg
new file mode 100644
index 0000000..a6aa098
--- /dev/null
+++ b/38148-h/images/i13f1.jpg
diff --git a/38148-h/images/i13f2.jpg b/38148-h/images/i13f2.jpg
new file mode 100644
index 0000000..4faec50
--- /dev/null
+++ b/38148-h/images/i13f2.jpg
diff --git a/38148-h/images/i13f3.jpg b/38148-h/images/i13f3.jpg
new file mode 100644
index 0000000..5b5604e
--- /dev/null
+++ b/38148-h/images/i13f3.jpg
diff --git a/38148-h/images/i14f1.jpg b/38148-h/images/i14f1.jpg
new file mode 100644
index 0000000..31d96a6
--- /dev/null
+++ b/38148-h/images/i14f1.jpg
diff --git a/38148-h/images/i14f2.jpg b/38148-h/images/i14f2.jpg
new file mode 100644
index 0000000..3f76f19
--- /dev/null
+++ b/38148-h/images/i14f2.jpg
diff --git a/38148-h/images/i15.jpg b/38148-h/images/i15.jpg
new file mode 100644
index 0000000..21cf8e0
--- /dev/null
+++ b/38148-h/images/i15.jpg
diff --git a/38148-h/images/i16.jpg b/38148-h/images/i16.jpg
new file mode 100644
index 0000000..fadcf5c
--- /dev/null
+++ b/38148-h/images/i16.jpg
diff --git a/38148-h/images/i17.jpg b/38148-h/images/i17.jpg
new file mode 100644
index 0000000..e019101
--- /dev/null
+++ b/38148-h/images/i17.jpg
diff --git a/38148-h/images/i18.jpg b/38148-h/images/i18.jpg
new file mode 100644
index 0000000..2ced5ce
--- /dev/null
+++ b/38148-h/images/i18.jpg
diff --git a/38148-h/images/i19f1.jpg b/38148-h/images/i19f1.jpg
new file mode 100644
index 0000000..71bce5b
--- /dev/null
+++ b/38148-h/images/i19f1.jpg
diff --git a/38148-h/images/i19f2.jpg b/38148-h/images/i19f2.jpg
new file mode 100644
index 0000000..573bc26
--- /dev/null
+++ b/38148-h/images/i19f2.jpg
diff --git a/38148-h/images/i20f1.jpg b/38148-h/images/i20f1.jpg
new file mode 100644
index 0000000..c235c3f
--- /dev/null
+++ b/38148-h/images/i20f1.jpg
diff --git a/38148-h/images/i20f2.jpg b/38148-h/images/i20f2.jpg
new file mode 100644
index 0000000..566fc66
--- /dev/null
+++ b/38148-h/images/i20f2.jpg
diff --git a/38148-h/images/i21.jpg b/38148-h/images/i21.jpg
new file mode 100644
index 0000000..93ef3f3
--- /dev/null
+++ b/38148-h/images/i21.jpg
diff --git a/38148-h/images/i22.jpg b/38148-h/images/i22.jpg
new file mode 100644
index 0000000..a8f438c
--- /dev/null
+++ b/38148-h/images/i22.jpg
diff --git a/38148-h/images/i23.jpg b/38148-h/images/i23.jpg
new file mode 100644
index 0000000..4748c6e
--- /dev/null
+++ b/38148-h/images/i23.jpg
diff --git a/38148-h/images/i24.jpg b/38148-h/images/i24.jpg
new file mode 100644
index 0000000..9d2473f
--- /dev/null
+++ b/38148-h/images/i24.jpg
diff --git a/38148-h/images/i25.jpg b/38148-h/images/i25.jpg
new file mode 100644
index 0000000..3d87556
--- /dev/null
+++ b/38148-h/images/i25.jpg
diff --git a/38148-h/images/i26.jpg b/38148-h/images/i26.jpg
new file mode 100644
index 0000000..abe61ef
--- /dev/null
+++ b/38148-h/images/i26.jpg
diff --git a/38148-h/images/i27.jpg b/38148-h/images/i27.jpg
new file mode 100644
index 0000000..20af58c
--- /dev/null
+++ b/38148-h/images/i27.jpg
diff --git a/38148-h/images/i28.jpg b/38148-h/images/i28.jpg
new file mode 100644
index 0000000..7dde7ed
--- /dev/null
+++ b/38148-h/images/i28.jpg
diff --git a/38148-h/images/i29.jpg b/38148-h/images/i29.jpg
new file mode 100644
index 0000000..d94bc5b
--- /dev/null
+++ b/38148-h/images/i29.jpg
diff --git a/38148-h/images/i30.jpg b/38148-h/images/i30.jpg
new file mode 100644
index 0000000..d282500
--- /dev/null
+++ b/38148-h/images/i30.jpg
diff --git a/38148-h/images/i31.jpg b/38148-h/images/i31.jpg
new file mode 100644
index 0000000..1a7e129
--- /dev/null
+++ b/38148-h/images/i31.jpg
diff --git a/38148-h/images/i32.jpg b/38148-h/images/i32.jpg
new file mode 100644
index 0000000..b098d59
--- /dev/null
+++ b/38148-h/images/i32.jpg
diff --git a/38148-h/images/i33.jpg b/38148-h/images/i33.jpg
new file mode 100644
index 0000000..24ce5ef
--- /dev/null
+++ b/38148-h/images/i33.jpg
diff --git a/38148-h/images/i34.jpg b/38148-h/images/i34.jpg
new file mode 100644
index 0000000..4901caf
--- /dev/null
+++ b/38148-h/images/i34.jpg
diff --git a/38148-h/images/i35.jpg b/38148-h/images/i35.jpg
new file mode 100644
index 0000000..1790967
--- /dev/null
+++ b/38148-h/images/i35.jpg
diff --git a/38148-h/images/i36.jpg b/38148-h/images/i36.jpg
new file mode 100644
index 0000000..4dd6c42
--- /dev/null
+++ b/38148-h/images/i36.jpg
diff --git a/38148-h/images/i37.jpg b/38148-h/images/i37.jpg
new file mode 100644
index 0000000..8e61890
--- /dev/null
+++ b/38148-h/images/i37.jpg
diff --git a/38148-h/images/i38.jpg b/38148-h/images/i38.jpg
new file mode 100644
index 0000000..04cf5ce
--- /dev/null
+++ b/38148-h/images/i38.jpg
diff --git a/38148.txt b/38148.txt
new file mode 100644
index 0000000..11ac96b
--- /dev/null
+++ b/38148.txt
@@ -0,0 +1,6348 @@
+The Project Gutenberg EBook of The Geography of the Region about Devils
+Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Geography of the Region about Devils Lake and the Dalles of the Wisconsin
+
+Author: Rollin D. Salisbury
+        Wallace W. Atwood
+
+Release Date: November 27, 2011 [EBook #38148]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+
+
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+
+
+
+
+       Wisconsin Geological and Natural History Survey.
+
+E. A. BIRGE, Director.             C. R. VAN HISE, Consulting Geologist.
+BULLETIN NO. V.                                EDUCATIONAL SERIES NO. 1.
+
+
+
+
+                       THE GEOGRAPHY
+                          OF THE
+                  REGION ABOUT DEVIL'S LAKE
+                          AND THE
+                   DALLES OF THE WISCONSIN,
+            With Some Notes on Its Surface Geology.
+
+
+
+
+                            BY
+
+                 ROLLIN D. SALISBURY, A. M.,
+   _Professor of Geographic Geology, University of Chicago,_
+
+                           AND
+
+                 WALLACE W. ATWOOD, B. S.,
+       _Assistant in Geology, University of Chicago._
+
+
+                      MADISON, WIS.
+                 Published by the State.
+                          1900.
+
+
+       Wisconsin Geological and Natural History Survey.
+
+
+  -------------------------------------------------------------------
+
+
+                  BOARD OF COMMISSIONERS.
+
+
+  EDWARD SCOFIELD,
+     Governor of the State.
+
+  L. D. HARVEY,
+     State Superintendent of Public Instruction.
+
+  CHARLES K. ADAMS, President,
+     President of the University of Wisconsin.
+
+  EDWIN E. BRYANT, Vice-President,
+     President of the Commissioners of Fisheries.
+
+  CHARLES S. SLICHTER, Secretary,
+     President of the Wisconsin Academy of Sciences, Arts, and
+     Letters.
+
+  --------------------------------------------------------------
+
+  E. A. BIRGE, Director of the Survey.
+
+  C. R. VAN HISE, Consulting Geologist.
+
+  E. R. BUCKLEY, Assistant Geologist.
+     In charge of Economic Geology.
+
+  S. WEIDMAN, Assistant Geologist.
+     In charge of Geology of Wausau District.
+
+  L. S. SMITH, in charge of Hydrography.
+
+  S. V. PEPPEL, Chemist.
+
+  F. R. DENNISTON, Artist.
+
+
+[Illustration: THE DALLES OF THE WISCONSIN.]
+
+
+
+
+                             CONTENTS.
+
+      ---------------------------------------------------------
+
+
+     PART I. THE TOPOGRAPHY WITH SOME NOTES ON THE SURFACE GEOLOGY.
+
+
+                             CHAPTER I.
+
+                      GENERAL GEOGRAPHIC FEATURES
+
+
+     I. The Plain Surrounding the Quartzite Ridges.
+
+           Topography
+
+           Structure
+
+           Origin of the Sandstone and Limestone
+
+           Origin of the Topography
+
+
+    II. The Quartzite Ridges
+
+           Topography
+
+           The Structure and Constitution of the Ridges
+
+
+   III. Relations of the Sandstone of the
+          Plain to the Quartzite of the Ridges
+
+
+
+
+                   PART II. HISTORY OF THE TOPOGRAPHY.
+
+
+                             CHAPTER II.
+
+
+              OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS
+                  WHICH SHOW THEMSELVES AT THE SURFACE.
+
+
+    I. The Pre-Cambrian History of the Quartzite
+
+         From loose Sand to Quartzite
+
+         Uplift and Deformation. Dynamic Metamorphism
+
+         Erosion of the Quartzite
+
+         Thickness of the Quartzite
+
+
+  II. The History of the Paleozoic Strata
+
+         The Subsidence
+
+         The Potsdam Sandstone (and Conglomerate)
+
+         The Lower Magnesian Limestone
+
+         The St. Peters Sandstone
+
+         Younger Beds
+
+         Climatic Conditions
+
+         Time involved
+
+         The Uplift
+
+
+                             CHAPTER III.
+
+
+               GENERAL OUTLINE OF RAIN AND RIVER EROSION
+
+
+         Elements of Erosion
+
+         Weathering
+
+         Corrasion
+
+         Erosion without Valleys
+
+         The Beginning of a Valley
+
+         The Course of a Valley
+
+         Tributary Valleys
+
+         How a Valley gets a Stream
+
+         Limits of a Valley
+
+         A Cycle of Erosion
+
+         Effects of unequal Hardness
+
+         Falls and Rapids
+
+         Narrows
+
+         Erosion of folded Strata
+
+         Base-level Plains and Peneplains
+
+         Transportation and Deposition
+
+         Topographic Forms resulting from Stream Deposition
+
+         Rejuvenation of Streams
+
+         Underground Water
+
+
+                               CHAPTER IV.
+
+
+             EROSION AND THE DEVELOPMENT OF STRIKING SCENIC FEATURES
+
+
+         Establishment of Drainage
+
+         Striking scenic Features
+
+         The Baraboo Bluffs
+
+         The Narrows in the Quartzite
+
+         Glens
+
+         Natural Bridge
+
+         The Dalles of the Wisconsin
+
+         The Mounds and Castle Rocks
+
+
+                            CHAPTER V.
+
+
+                        THE GLACIAL PERIOD.
+
+
+         The Drift
+
+         Snow Fields and ice Sheets
+
+         The North American ice Sheets
+
+         The Work of glacier Ice
+
+         Erosive Work of Ice. Effect on Topography
+
+         Deposition by the Ice. Effect on Topography
+
+         Direction of ice Movement
+
+         Effect of Topography on Movement
+
+         Glacial Deposits
+
+         The ground Moraine
+
+         Constitution
+
+         Topography
+
+         Terminal Moraines
+
+         Topography of terminal Moraines
+
+         The terminal Moraine about Devil's Lake
+
+         The Moraine on the main Quartzite Range
+
+         Constitution of the marginal Ridge
+
+         The Slope of the upper Surface of the Ice at the Margin
+
+         Stratified Drift
+
+         Its Origin
+
+         Glacial Drainage
+
+         Stages in the History of an Ice Sheet
+
+    Deposits made by extraglacial Waters during the maximum Extension
+      of the Ice
+
+         At the Edge of the Ice, on Land
+
+         Beyond the Edge of the Ice, on Land
+
+         Deposits at and beyond the Edge of the Ice in standing Water
+
+   Deposits made by extraglacial Waters during the Retreat of the Ice
+
+   Deposits made by extraglacial Waters during the Advance of the Ice
+
+   Deposits made by subglacial Streams
+
+   Relations of stratified to unstratified Drift
+
+         Complexity of Relations
+
+   Classification of stratified Drift on the Basis of Position
+
+         Extraglacial Deposits
+
+         Supermorainic deposits
+
+         The submorainic (basal) Deposits
+
+         Intermorainic stratified Drift
+
+         Changes in Drainage effected by the Ice
+
+         While the Ice was on
+
+         Wisconsin Lake
+
+         Baraboo Lake
+
+         Devil's Lake in glacial Times
+
+         After the Ice had disappeared
+
+         Lakes
+
+         Existing Lakes
+
+         Changes in Streams
+
+         Skillett Creek
+
+         The Wisconsin
+
+         The Driftless Area
+
+         Contrast between glaciated and unglaciated Areas
+
+               Topography
+
+               Drainage
+
+               Mantle Rock
+
+
+
+
+                      LIST OF ILLUSTRATIONS.
+
+
+    ------------------------------------------------------------
+
+
+                              PLATES.
+
+
+        Plate
+
+Frontispiece.  The Dalles of the Wisconsin
+
+           I. General map of the Devil's Lake region
+
+          II. Local map of the Devil's Lake region
+
+         III. Fig. 1--Ripple marks on a slab of sandstone
+              Fig. 2--Piece of Potsdam conglomerate
+
+          IV. Lower Narrows of the Baraboo
+
+           V. Devil's Lake notch
+
+          VI. East bluff of Devil's Lake
+
+         VII. East bluff at the Upper Narrows of the Baraboo near Ableman's
+
+        VIII. Vertical shear zone face of east bluff at Devil's Lake
+
+          IX. Massive quartzite in situ in road through Upper Narrows near
+                Ableman's
+
+           X. Brecciated quartzite
+
+          XI. Northwest wall of the Upper Narrows
+
+         XII. Steamboat Rock
+
+        XIII. Fig. 1--A very young valley
+              Fig. 2--A valley at later stage of development
+              Fig. 3--Young valleys
+
+         XIV. Fig. 1--Same valleys as shown in Pl. XIII, Fig. 3,
+                        but at a later stage of development
+              Fig. 2--Same valleys as shown in Fig. 1 in later stage of
+                        development
+
+          XV. Diagram illustrating how a hard inclined layer of rock
+                becomes a ridge in the process of degradation
+
+         XVI. Skillett Falls
+
+        XVII. A group of mounds on the plain northwest from Camp Douglas
+
+       XVIII. Castle Rock near Camp Douglas
+
+         XIX. Fig. 1--Sketch of a young valley
+              Fig. 2--Same valleys as shown in Fig. 1 in later stage of
+                        development
+
+          XX. Fig. 1--Sketch of a part of a valley at a stage of
+                        development corresponding to the cross section
+                        shown in Figure 21
+              Fig. 2--Sketch of a section of the Baraboo valley
+
+         XXI. Cleopatra's Needle
+
+        XXII. Turk's Head
+
+       XXIII. Devil's Doorway
+
+        XXIV. Talus slope on east bluff of Devil's Lake
+
+         XXV. Dorward's Glen
+
+        XXVI. Natural Bridge near Denzer
+
+       XXVII. The Navy Yard
+
+      XXVIII. Chimney Rock
+
+        XXIX. An island in the Lower Dalles
+
+         XXX. View in Lower Dalles
+
+        XXXI. Stand Rock
+
+       XXXII. Petenwell Peak
+
+      XXXIII. North American ice sheet
+
+       XXXIV. Owl's Head
+
+        XXXV. Cut in glacial drift
+
+       XXXVI. Glaciated stones
+
+      XXXVII. Topographic map of a small area about Devil's Lake
+
+     XXXVIII. Distorted laminae of silt and clay
+
+
+
+
+                          FIGURES IN TEXT.
+
+
+  Figure
+
+   1. Profile across the Baraboo quartzite ranges through Baraboo
+
+   2. Profile across the Baraboo ranges through Merrimac
+
+   Transcriber's note: There is no figure 3.
+
+   4. Diagram showing the structure of the quartzite
+
+   5. Diagram showing the relation of the Potsdam sandstone to the Baraboo
+      quartzite
+
+   6. Diagram illustrating effect of faulting on outcrop
+
+   7. Diagram showing the disposition of sediments about an island
+
+   8. The same as 7 after subsidence
+
+   9. Diagram showing relation of Potsdam conglomerate to quartzite at
+      Devil's Lake
+
+  10. Cross section of a delta
+
+  11. The geological formations of southern Wisconsin
+
+  12. A typical river system
+
+  13. Diagram illustrating the relations of ground water to streams
+
+  14. Diagram illustrating the shifting of divides
+
+  15. Diagram showing topography at the various stages of an erosion cycle
+
+  16. Diagram illustrating the development of rapids and falls
+
+  17. Sketch looking northwest from Camp Douglas
+
+  18. Diagrammatic cross section of a young valley
+
+  19. Diagrammatic profile of a young valley
+
+  20. Diagrammatic cross section of a valley in a later stage of
+      development
+
+  21. The same at a still later stage
+
+  22. Diagram illustrating the topographic effect or rejuvenation of a
+      stream by uplift
+
+  23. Normal profile of a valley bottom
+
+  24. Profile of a stream rejuvenated by uplift
+
+  25. Diagram illustrating monoclinal shifting
+
+  26. Diagram showing the relation of the Potsdam sandstone to the
+      quartzite at the Upper Narrows
+
+  27. Diagrammatic cross section of a field of ice and snow
+
+  28. Shape of an erosion hill before glaciation
+
+  29. The same after glaciation
+
+  30. Diagram showing the effect of a valley on the movement of ice
+
+  31. The same under different conditions
+
+  32. Diagram showing the relation of drift to the underlying rock where
+      the drift is thick
+
+  33. The same where the drift is relatively thin
+
+  34. Diagrammatic representation of the effect of a hill on the edge of
+      the ice
+
+  35. The same at a later stage of the ice advance
+
+  36. Map showing the relation of the ice lobes during the Wisconsin epoch
+      of the glacial period
+
+  37. Sketch of the terminal moraine topography east of Devil's Lake
+
+  38. Cut through the terminal moraine east of Kirkland
+
+  39. Cross section of the marginal ridge of the moraine on the south
+      slope of the Devil's nose
+
+  40. Cross section of the marginal ridge of the moraine on the crest of
+      the quartzite range
+
+  41. Morainic outwash plain
+
+  42. The same in other relations
+
+  43. Skillett Creek and its peculiarities
+
+  44. The Wisconsin valley near Kilbourn city
+
+  45. Drainage in the driftless area
+
+  46. Drainage in the glaciated area
+
+  47. Section in the driftless region showing relation of the soil to the
+      solid rock beneath
+
+
+
+
+                             PART I.
+
+    ------------------------------------------------------------
+
+                         THE TOPOGRAPHY.
+
+               WITH SOME NOTES ON THE SURFACE GEOLOGY.
+
+
+
+
+       GEOGRAPHY AND SURFACE GEOLOGY OF THE DEVIL'S LAKE REGION.
+
+
+
+                           CHAPTER I.
+
+
+                  GENERAL GEOGRAPHIC FEATURES.
+
+
+This report has to do with the physical geography of the area in south
+central Wisconsin, shown on the accompanying sketch map, Plate I. The
+region is of especial interest, both because of its striking scenery,
+and because it illustrates clearly many of the principles involved in
+the evolution of the geography of land surfaces.
+
+Generally speaking, the region is an undulating plain, above which rise
+a few notable elevations, chief among which are the Baraboo quartzite
+ranges, marked by diagonal lines on Plates I and II. These elevations
+have often been described as two ranges. The South or main range lies
+three miles south of Baraboo, while the North or lesser range, which is
+far from continuous, lies just north of the city.
+
+The main range has a general east-west trend, and rises with bold and
+sometimes precipitous slopes 500 to 800 feet above its surroundings. A
+deep gap three or four miles south of Baraboo (Plates II, V, and
+XXXVII) divides the main range into an eastern and a western
+portion, known respectively as the _East and West bluffs_ or _ranges_.
+In the bottom of the gap lies Devil's lake (i, Plate II and Plate
+XXXVII), perhaps the most striking body of water of its size in the
+state, if not in the whole northern interior. A general notion of the
+topography of a small area in the immediate vicinity of the lake may be
+obtained from Plate XXXVII.
+
+The highest point in the range is about four miles east of the lake, and
+has an elevation of more than 1,600 feet above sea level, more than
+1,000 feet above Lake Michigan, and about 800 feet above the Baraboo
+valley at its northern base. The eastward extension of the west range
+(Plate XXXVII) lying south of the lake, and popularly known as the
+_Devil's nose_, reaches an elevation of a little more than 1,500 feet.
+
+The lesser or North quartzite range (Plate II) rises 300 feet to 500
+feet above its surroundings. It assumes considerable prominence at the
+Upper and Lower narrows of the Baraboo (b and c, Plate II, c, Plate
+XXXVII and Plate IV). The North range is not only lower than the
+South range, but its slopes are generally less steep, and, as Plate II
+shows, it is also less continuous. The lesser elevation and the gentler
+slopes make it far less conspicuous. About three miles southwest of
+Portage (Plate II) the North and South ranges join, and the elevation at
+the point of union is about 450 feet above the Wisconsin river a few
+miles to the east.
+
+The lower country above which these conspicuous ridges rise, has an
+average elevation of about 1,000 feet above the sea, and extends far
+beyond the borders of the area with which this report is concerned. The
+rock underlying it in the vicinity of Baraboo is chiefly sandstone, but
+there is much limestone farther east and south, in the area with which
+the Baraboo region is topographically continuous. Both the sandstone and
+limestone are much less resistant than the quartzite, and this
+difference has had much to do with the topography of the region.
+
+The distinctness of the quartzite ridges as topographic features is
+indicated in Plate XXXVII by the closeness of the contour lines on their
+slopes. The same features are shown in Figs. 1 and 2, which represent
+profiles along two north-south lines passing through Baraboo and
+Merrimac respectively.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. I.
+
+General map showing the location of the chief points mentioned in this
+report. The location of the area shown in Plate XXXVII, centering about
+Baraboo, is indicated.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. II.
+
+Map of Area considered in this Report.]
+
+[Illustration: Fig. 1.--Profile along a line extending due north and
+south from Baraboo across the north and south ranges. The dotted
+continuation northward, represents the extension of the profile beyond
+the topographic map, Plate XXXVII.]
+
+[Illustration: Fig. 2.--Profile north from Merrimac across the quartzite
+ranges. The dotted continuation northward represents the extension of
+the profile beyond the topographic map, Plate XXXVII.]
+
+
+         I. THE PLAIN SURROUNDING THE QUARTZITE RIDGES.
+
+_Topography._--As seen from the top of the quartzite ridges, the
+surrounding country appears to be an extensive plain, but at closer
+range it is seen to have considerable relief although there are
+extensive areas where the surface is nearly flat.
+
+The relief of the surface is of two somewhat different types. In some
+parts of the area, especially in the western part of the tract shown on
+Plate II, the surface is made up of a succession of ridges and valleys.
+The ridges may be broken by depressions at frequent intervals, but the
+valleys are nowhere similarly interrupted. It would rarely be possible
+to walk along a ridge or "divide" for many miles without descending into
+valleys; but once in a valley in any part of the area, it may be
+descended without interruption, until the Baraboo, the Wisconsin, the
+Mississippi, and finally the gulf is reached. In other words, the
+depressions are continuous, but the elevations are not. This is the
+first type of topography.
+
+Where this type of topography prevails its relation to drainage is
+evident at a glance. All the larger depressions are occupied by streams
+continuously, while the smaller ones contain running water during some
+part of the year. The relations of streams to the depressions, and the
+wear which the streams effect, whether they be permanent or temporary,
+suggest that running water is at least one of the agencies concerned in
+the making of valleys.
+
+An idea of the general arrangement of the valleys, as well as many
+suggestions concerning the evolution of the topography of the broken
+plain in which they lie might be gained by entering a valley at its
+head, and following it wherever it leads. At its head, the valley is
+relatively narrow, and its slopes descend promptly from either side in
+such a manner that a cross-section of the valley is V-shaped. In places,
+as west of Camp Douglas, the deep, steep-sided valleys are found to lead
+down and out from a tract of land so slightly rolling as to be well
+adapted to cultivation. Following down the valley, its progressive
+increase in width and depth is at once evident, and at the same time
+small tributary valleys come in from right and left. At no great
+distance from the heads of the valleys, streams are found in their
+bottoms.
+
+As the valleys increase in width and depth, and as the tributaries
+become more numerous and wider, the topography of which the valleys are
+a feature, becomes more and more broken. At first the tracts between the
+streams are in the form of ridges, wide if parallel valleys are distant
+from one another, and narrow if they are near. The ridges wind with the
+valleys which separate them. Whatever the width of the inter-stream
+ridges, it is clear that they must become narrower as the valleys
+between them become wider, and in following down a valley a point is
+reached, sooner or later, where the valleys, main and tributary, are of
+such size and so numerous that their slopes constitute a large part of
+the surface. Where this is true, and where the valleys are deep, the
+land is of little industrial value except for timber and grazing. When,
+in descending a valley system, this sort of topography is reached, the
+roads often follow either the valleys or the ridges, however indirect
+and crooked they may be. Where the ridges separating the valleys in such
+a region have considerable length, they are sometimes spoken of as "hog
+backs." Still farther down the valley system, tributary valleys of the
+second and lower orders cross the "hog backs," cutting them into hills.
+
+By the time this sort of topography is reached, a series of flats is
+found bordering the streams. These flats may occur on both sides of the
+stream, or on but one. The topography and the soil of these flats are
+such as to encourage agriculture, and the river flats or alluvial plains
+are among the choicest farming lands.
+
+With increasing distance from the heads of the valleys, these river
+plains are expanded, and may be widened so as to occupy the greater part
+of the surface. The intervening elevations are there relatively few and
+small. Their crests, however, often rise to the same level as that of
+the broader inter-stream areas farther up the valleys. The relations of
+the valleys and the high lands separating them, is such as to suggest
+that there are, generally speaking, two sets of flat surfaces, the
+higher one representing the upland in which the valleys lie, the lower
+one representing the alluvial plains of the streams. The two sets of
+flats are at once separated and connected by slopes. At the head of a
+drainage system, the upland flats predominate; in the lower courses, the
+river plains; in an intermediate stage, the slopes are more conspicuous
+than either upper or lower flat.
+
+Southwest from Devil's lake and northwest from Sauk City, in the valley
+of Honey creek, and again in the region southwest from Camp Douglas, the
+topography just described is well illustrated. In both these localities,
+as in all others where this type of topography prevails, the intimate
+relations of topography and drainage cannot fail to suggest that the
+streams which are today widening and deepening the valleys through which
+they flow, had much to do with their origin and development. This
+hypothesis, as applied to the region under consideration, may be tested
+by the study of the structure of the plain.
+
+The second type of topography affecting the plain about the quartzite
+ranges is found east of a line running from Kilbourn City to a point
+just north of Prairie du Sac. Though in its larger features the area
+east of this line resembles that to the west, its minor features are
+essentially different. Here there are many depressions which have no
+outlets, and marshes, ponds, and small lakes abound. Not only this, but
+many of the lesser elevations stand in no definite relation to valleys.
+The two types of topography make it clear that they were developed in
+different ways.
+
+_Structure._--Examination of the country surrounding the Baraboo ridges
+shows that its surface is underlaid at no great depth by horizontal or
+nearly horizontal beds of sandstone and limestone (see Plates XVI,
+XXVIII, and Frontispiece). These beds are frequently exposed on opposite
+sides of a valley, and in such positions the beds of one side are found
+to match those on the other. This is well shown along the narrow valley
+of Skillett creek just above the "Pewit's nest." Here the swift stream
+is rapidly deepening its channel, and it is clear that a few years
+hence, layers of sandstone which are now continuous beneath the bed of
+the creek will have been cut through, and their edges will appear on
+opposite sides of the valley just as higher layers do now. Here the most
+skeptical might be convinced that the layers of rock on either side of
+the narrow gorge were once continuous across it, and may see, at the
+same time, the means by which the separation was effected. Between the
+slight separation, here, where the valley is narrow, and the great
+separation where the valleys are wide, there are all gradations. The
+study of progressively wider valleys, commencing with such a gorge as
+that referred to, leaves no room for doubt that even the wide valleys,
+as well as the narrow ones, were cut out of the sandstone by running
+water.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. III.
+
+Illustration: FIG. 1.
+
+Ripple marks on a slab of Potsdam sandstone.
+
+Illustration: FIG. 2.
+
+Piece of Potsdam conglomerate. The larger pebbles are about three inches
+in diameter.]
+
+The same conclusion as to the origin of the valleys may be reached in
+another way. Either the beds of rock were formed with their present
+topography, or the valleys have been excavated in them since they were
+formed. Their mode of origin will therefore help to decide between these
+alternatives.
+
+_Origin of the sandstone and limestone._--The sandstone of the region,
+known as the Potsdam sandstone, consists of medium sized grains of
+sand, cemented together by siliceous, ferruginous, or calcareous cement.
+If the cement were removed, the sandstone would be reduced to sand, in
+all respect similar to that accumulating along the shores of seas and
+lakes today.
+
+The surfaces of the separate layers of sandstone are often distinctly
+ripple-marked (Fig. 1, Pl. III), and the character of the markings is
+identical in all essential respects with the ripples which affect the
+surface of the sand along the shores of Devil's lake, or sandy beaches
+elsewhere, at the present time. These ripple marks on the surfaces of
+the sandstone layers must have originated while the sand was movable,
+and therefore before it was cemented into sandstone.
+
+In the beds of sandstone, fossils of marine animals are found. Shells,
+or casts of shells of various sorts are common, as are also the tracks
+and burrowings of animals which had no shells. Among these latter signs
+of life may be mentioned the borings of worms. These borings are not now
+always hollow, but their fillings are often so unlike the surrounding
+rock, that they are still clearly marked. These worm borings, like the
+ripple marks, show that the sand was once loose.
+
+The basal beds of the sandstone are often conglomeratic. The
+conglomeratic layers are made up of water-worn pieces of quartzite,
+Plate III, Fig. 2, ranging in size from small pebbles to large bowlders.
+The interstices of the coarse material are filled by sand, and the whole
+cemented into solid rock. The conglomeratic phase of the sandstone may
+be seen to advantage at Parfrey's glen (a, Plate XXXVII) and Dorward's
+glen, (b, same plate) on the East bluff of Devil's lake above the Cliff
+House, and at the Upper narrows of the Baraboo, near Ablemans. It is
+also visible at numerous other less accessible and less easily
+designated places.
+
+From these several facts, viz.: the horizontal strata, the ripple-marks
+on the surfaces of the layers, the fossils, the character of the sand,
+and the water-worn pebbles and bowlders of the basal conglomerate,
+positive conclusions concerning the origin of the formation may be
+drawn.
+
+The arrangement in definite layers proves that the formation is
+sedimentary; that is, that its materials were accumulated in water
+whither they had been washed from the land which then existed. The
+ripple-marks show that the water in which the beds of sand were
+deposited was shallow, for in such water only are ripple-marks made.[1]
+Once developed on the surface of the sand they may be preserved by
+burial under new deposits, just as ripple-marks on sandy shores are now
+being buried and preserved.
+
+    [1] Ripple marks are often seen on the surface of wind-blown
+    sand, but the other features of this sandstone show that this
+    was not its mode of accumulation.
+
+The conglomerate beds of the formation corroborate the conclusions to
+which the composition and structure of the sandstone point. The
+water-worn shapes of the pebbles and stones show that they were
+accumulated in water, while their size shows that the water must have
+been shallow, for stones of such sizes are handled only by water of such
+slight depth that waves or strong currents are effective at the bottom.
+Furthermore, the large bowlders show that the source of supply
+(quartzite) must have been close at hand, and that therefore land
+composed of this rock must have existed not far from the places where
+the conglomerate is found.
+
+The fossils likewise are the fossils of aquatic life. Not only this, but
+they are the fossils of animals which lived in salt water. The presence
+of salt water, that is, the sea, in this region when the sand of the
+sandstone was accumulating, makes the wide extent of the formation
+rational.
+
+From the constitution and structure of the sandstone, it is therefore
+inferred that it accumulated in shallow sea water, and that, in the
+vicinity of Devil's lake, there were land masses (islands) of quartzite
+which furnished the pebbles and bowlders found in the conglomerate beds
+at the base of the formation.
+
+This being the origin of the sandstone, it is clear that the layers
+which now appear on opposite sides of valleys must once have been
+continuous across the depressions; for the sand accumulated in shallow
+water is never deposited so as to leave valleys between ridges. It is
+deposited in beds which are continuous over considerable areas.
+
+Within the area under consideration, limestone is much less widely
+distributed than sandstone. Thin beds of it alternate with layers of
+sandstone in the upper portion of the Potsdam formation, and more
+massive beds lie above the sandstone on some of the higher elevations of
+the plain about the quartzite ridge. This is especially true in the
+southern and southwestern parts of the region shown on Plate II. The
+limestone immediately overlying the sandstone is the _Lower Magnesian_
+limestone.
+
+The beds of limestone, like those of the sandstone beneath, are
+horizontal or nearly so, and the upper formation lies conformably on the
+lower. The limestone does not contain water-worn pebbles, and the
+surfaces of its layers are rarely if ever ripple-marked; yet the
+arrangement of the rock in distinct layers which carry fossils of marine
+animals shows that the limestone, like the sandstone beneath, was laid
+down in the sea. The bearing of this origin of the limestone on the
+development of the present valleys is the same as that of the sandstone.
+
+_Origin of the topography._--The topography of the plain surrounding the
+quartzite ridges, especially that part lying west of Devil's lake, is
+then an erosion topography, developed by running water. Its chief
+characteristic is that every depression leads to a lower one, and that
+the form of the elevations, hills or ridges, is determined by the
+valleys. The valleys were made; the hills and ridges left. If the
+material carried away by the streams could be returned, the valleys
+would be filled to the level of the ridges which bound them. Were this
+done, the restored surface would be essentially flat. It is the
+sculpturing of such a plain, chiefly by running water, which has given
+rise to the present topography.
+
+In the development of this topography the more resistant limestone has
+served as a capping, tending to preserve the hills and ridges. Thus many
+of the hills, especially in the southwest portion of the area shown in
+Plate II, are found to have caps of the Lower Magnesian formation. Such
+hills usually have flat tops and steep or even precipitous slopes down
+to the base of the capping limestone, while the sandstone below,
+weathering more readily, gives the lower portions of the hills a gentler
+slope.
+
+The elevations of the hills and ridges above the axes of the valleys or,
+in other words, the relief of the plain is, on the average, about 300
+feet, only a few of the more prominent hills exceeding that figure.
+
+The topography east of the line between Kilbourn City and Prairie du Sac
+is not of the unmodified erosion type, as is made evident by marshes,
+ponds and lakes. The departure from the erosion type is due to a mantle
+of glacial drift which masks the topography of the bedded rock beneath.
+Its nature, and the topographic modifications which it has produced, will
+be more fully considered in a later part of this report.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IV.
+
+The Lower Narrows of the Baraboo from a point on the South range.]
+
+
+                 II. THE QUARTZITE RIDGES.
+
+_Topography._--The South or main quartzite range, about 23 miles in
+length and one to four miles in width, rises 500 feet to 800 feet above
+the surrounding sandstone plain. Its slopes are generally too steep for
+cultivation, and are clothed for the most part with a heavy growth of
+timber, the banks of forest being broken here and there by cultivated
+fields, or by the purple grey of the rock escarpments too steep for
+trees to gain a foothold. With the possible exception of the Blue mounds
+southwest of Madison, this quartzite range is the most obtrusive
+topographic feature of southern Wisconsin.
+
+As approached from the south, one of the striking features of the range
+is its nearly even crest. Extending for miles in an east-west direction,
+its summit gives a sky-line of long and gentle curves, in which the
+highest points are but little above the lowest. Viewed from the north,
+the evenness of the crest is not less distinct, but from this side it is
+seen to be interrupted by a notable break or notch at Devil's lake
+(Plates V and XXXVII). The pass across the range makes a right-angled
+turn in crossing the range, and for this reason is not seen from the
+south.
+
+The North or lesser quartzite range lying north of Baraboo is both
+narrower and lower than the south range, and its crest is frequently
+interrupted by notches or passes, some of which are wide. Near its
+eastern end occurs the striking gap known as the _Lower narrows_ (Plate
+IV) through which the Baraboo river escapes to the northward, flowing
+thence to the Wisconsin. At this narrows the quartzite bluffs rise
+abruptly 500 feet above the river. At a and b, Plate II, there are
+similar though smaller breaks in the range, also occupied by streams.
+The connection between the passes and streams is therefore close.
+
+There are many small valleys in the sides of the quartzite ranges
+(especially the South range) which do not extend back to their crests,
+and therefore do not occasion passes across them. The narrow valleys at
+a and b in Plate XXXVII, known as Parfrey's and Dorward's glens,
+respectively, are singularly beautiful gorges, and merit mention as well
+from the scenic as from the geologic point of view. Wider valleys, the
+heads of which do not reach the crest, occur on the flanks of the main
+range (as at d and e, Plate II) at many points. One such valley
+occurs east of the north end of the lake (x, Plate XXXVII), another
+west of the south end (y, Plate XXXVII), another on the north face of
+the west bluff west of the north end of the lake and between the East
+and West Sauk roads, and still others at greater distances from the lake
+in both directions. It is manifest that if the valleys were extended
+headward in the direction of their axes, they would interrupt the even
+crest. Many of these valleys, unlike the glens mentioned above, are very
+wide in proportion to their length. In some of these capacious valleys
+there are beds of Potsdam sandstone, showing that the valleys existed
+before the sand of the sandstone was deposited.
+
+_The structure and constitution of the ridges._--The quartzite of the
+ridges is nothing more nor less than altered sandstone. Its origin dates
+from that part of geological time known to geologists as the Upper
+Huronian period. The popular local belief that the quartzite
+is of igneous origin is without the slightest warrant. It appears to
+have had its basis in the notion that Devil's lake occupies an extinct
+volcanic crater. Were this the fact, igneous rock should be found about
+it.
+
+Quartzite is sandstone in which the intergranular spaces have been
+filled with silica (quartz) brought in and deposited by percolating
+water subsequent to the accumulation of the sand. The conversion of
+sandstone into quartzite is but a continuation of the process which
+converts sand into sandstone. The Potsdam or any other sandstone
+formation might be converted into quartzite by the same process, and it
+would then be a _metamorphic_ rock.
+
+Like the sandstone, the quartzite is in layers. This is perhaps nowhere
+so distinctly shown on a large scale as in the bluffs at Devil's lake,
+and at the east end of the Devil's nose. On the East bluff of the lake,
+the stratification is most distinctly seen from the middle of the lake,
+from which point the photograph reproduced in Plate VI was taken.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. V.
+
+The Notch in the South quartzite range, at Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VI.
+
+The east bluff of Devil's lake, showing the dip of quartzite (to the
+left), and talus above and below the level where the beds are shown.]
+
+Unlike the sandstone and limestone, the beds of quartzite are not
+horizontal. The departure from horizontality, technically known as the
+_dip_, varies from point to point (Fig. 4). In the East bluff of the
+lake as shown in Plate VI, the dip is about 14 deg. to the north. At the
+Upper and Lower narrows of the Baraboo (b and c, Plate II) the beds
+are essentially vertical, that is, they have a dip of about 90 deg.. Between
+these extremes, many intermediate angles have been noted. Plate VII
+represents a view near Ablemans, in the Upper narrows, where the nearly
+vertical beds of quartzite are well exposed.
+
+The position of the beds in the quartzite is not always easy of
+recognition. The difficulty is occasioned by the presence of numerous
+cleavage planes developed in the rock after its conversion into
+quartzite. Some of these secondary cleavage planes are so regular and so
+nearly parallel to one another as to be easily confused with the bedding
+planes. This is especially liable to make determinations of the dip
+difficult, since the true bedding was often obscured when the cleavage
+was developed.
+
+In spite of the difficulties, the original stratification can usually be
+determined where there are good exposures of the rock. At some points
+the surfaces of the layers carry ripple marks, and where they are
+present, they serve as a ready means of identifying the bedding planes,
+even though the strata are now on edge. Layers of small pebbles are
+sometimes found. They were horizontal when the sands of the quartzite
+were accumulating, and where they are found they are sufficient to
+indicate the original position of the beds.
+
+Aside from the position of the beds, there is abundant evidence of
+dynamic action[2] in the quartzite. Along the railway at Devil's lake,
+half a mile south of the Cliff House, thin zones of schistose rock may
+be seen parallel to the bedding planes. These zones of schistose rock a
+few inches in thickness were developed from the quartzite by the
+slipping of the rock on either side. This slipping presumably occurred
+during the adjustment of the heavy beds of quartzite to their new
+positions, at the time of tilting and folding, for no thick series of
+rock can be folded without more or less slipping of the layers on one
+another. The slipping (adjustment) takes place along the weaker zones.
+Such zones of movement are sometimes known as _shear zones_, for the
+rock on the one side has been sheared (slipped) over that on the other.
+
+    [2] Irving: "The Baraboo Quartzite Ranges." Vol. II, Geology
+    of Wisconsin, pp. 504-519. Van Hise: "Some Dynamic Phenomena
+    Shown by the Baraboo Quartzite Ranges of Central Wisconsin."
+    Jour. of Geol., Vol. I, pp. 347-355.
+
+[Illustration: Fig. 4.--Diagram made by plotting the different dips now
+at hand along a section from A to B, Plate II, and connecting
+them so as to show the structure indicated by the known data. The full
+lines, oblique or vertical, represent the beds of quartzite. The
+continuous line above them represents the present surface of the
+quartzite, while the dotted lines suggest the continuation of the beds
+which completed the great folds of which the present exposures appear to
+be remnants.]
+
+[Illustration: Fig. 5.--A diagrammatic section showing the relation of
+the sandstone to the quartzite.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VII.
+
+The East Bluff at the Upper Narrows of the Baraboo near Ablemans,
+showing the vertical position of the beds of quartzite. In the lower
+right-hand corner, above the bridge, appears some breccia.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. VIII.
+
+Vertical shear zone in face of east bluff at Devil's lake.]
+
+Near the shear zones parallel to the bedding planes, there is one
+distinct vertical shear zone (Plate VIII) three to four feet in width.
+It is exposed to a height of fully twenty-five feet. Along this zone the
+quartzite has been broken into angular fragments, and at places the
+crushing of the fragments has produced a "friction clay." Slipping along
+vertical zones would be no necessary part of folding, though it might
+accompany it. On the other hand, it might have preceded or followed the
+folding.
+
+Schistose structure probably does not always denote shearing, at least
+not the shearing which results from folding. Extreme pressure is likely
+to develop schistosity in rock, the cleavage planes being at right
+angles to the direction of pressure. It is not always possible to say
+how far the schistosity of rock at any given point is the result of
+shear, and how far the result of pressure without shear.
+
+Schistose structure which does not appear to have resulted from shear,
+at least not from the shear involved in folding, is well seen in the
+isolated quartzite mound about four miles southwest of Baraboo on the
+West Sauk road (f, Plate II). These quartzite schists are to be looked
+on as metamorphosed quartzite, just as quartzite is metamorphosed
+sandstone.
+
+At the Upper narrows of the Baraboo also (b, Plate II), evidence
+of dynamic action is patent. Movement along bedding planes with
+attendant development of quartz schist has occurred here as at the lake
+(Plate IX). Besides the schistose belts, a wide zone of quartzite
+exposed in the bluffs at this locality has been crushed into angular
+fragments, and afterwards re-cemented by white quartz deposited from
+solution by percolating waters (Plate X). This quartzite is said to be
+brecciated. Within this zone there are spots where the fragments of
+quartzite are so well rounded as to simulate water-worn pebbles. Their
+forms appear to be the result of the wear of the fragments on one
+another during the movements which followed the crushing. Conglomerate
+originating in this way is _friction conglomerate_ or _Reibungsbreccia_.
+
+The crushing of the rock in this zone probably took place while the beds
+were being folded; but the brecciated quartzite formed by the
+re-cementation of the fragments has itself been fractured and broken in
+such a manner as to show that the formation has suffered at least one
+dynamic movement since the development of the breccia. That these
+movements were separated by a considerable interval of time is shown by
+the fact that the re-cementation of the fragmental products of the first
+movement preceded the second.
+
+What has been said expresses the belief of geologists as to the origin
+of quartzite and quartz schists; but because of popular misconception on
+the point it may here be added that neither the changing of the
+sandstone into quartzite, nor the subsequent transformation of the
+quartzite to schist, was due primarily to heat. Heat was doubtless
+generated in the mechanical action involved in these changes, but it was
+subordinate in importance, as it was secondary in origin.
+
+Igneous rock is associated with the quartzite at a few points. At g
+and h, Plate II there are considerable masses of porphyry,
+sustaining such relations to the quartzite as to indicate that they were
+intruded into the sedimentary beds after the deposition of the latter.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. IX.
+
+A mass of quartzite _in situ_, in the road through the Upper Narrows
+near Ableman's. The bedding, which is nearly vertical, is indicated by
+the shading, while the secondary cleavage approaches horizontality.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. X.
+
+Brecciated quartzite near Ablemans in the Upper Narrows. The darker
+parts are quartzite, the lighter parts the cementing quartz.]
+
+
+ III. RELATIONS OF THE SANDSTONE OF THE PLAIN TO THE QUARTZITE OF THE
+                            RIDGES.
+
+The horizontal beds of Potsdam sandstone may be traced up to the bases
+of the quartzite ranges, where they may frequently be seen to abut
+against the tilted beds of quartzite. Not only this, but isolated
+patches of sandstone lie on the truncated edges of the dipping beds of
+quartzite well up on the slopes, and even on the crest of the ridge
+itself. In the former position they may be seen on the East bluff at
+Devil's lake, where horizontal beds of conglomerate and sandstone rest
+on the layers of quartzite which dip 14 deg. to the north.
+
+The stratigraphic relations of the two formations are shown in Fig. 5
+which represents a diagrammatic section from A to B, Plate II. Plate XI
+is reproduced from a photograph taken in the Upper narrows of the
+Baraboo near Ablemans, and shows the relations as they appear in the
+field. The quartzite layers are here on edge, and on them rest the
+horizontal beds of sandstone and conglomerate. Similar stratigraphic
+relations are shown at many other places. This is the relationship of
+_unconformity_.
+
+Such an unconformity as that between the sandstone and the quartzite of
+this region shows the following sequence of events: (1) the quartzite
+beds were folded and lifted above the sea in which the sand composing
+them was originally deposited; (2) a long period of erosion followed,
+during which the crests of the folds were worn off; (3) the land then
+sank, allowing the sea to again advance over the region; (4) while the
+sea was here, sand and gravel derived from the adjacent lands which
+remained unsubmerged, were deposited on its bottom. These sands became
+the Potsdam sandstone.
+
+This sequence of events means that between the deposition of the
+quartzite and the sandstone, the older formation was disturbed and
+eroded. Either of these events would have produced an unconformity; the
+two make it more pronounced. That the disturbance of the older formation
+took place before the later sandstone was deposited is evident from the
+fact that the latter formation was not involved in the movements which
+disturbed the former.
+
+Although the sandstone appears in patches on the quartzite ranges, it is
+primarily the formation of the surrounding plains, occupying the broad
+valley between the ranges, and the territory surrounding them. The
+quartzite, on the other hand, is the formation of the ridges, though it
+outcrops at a few points in the plain. (Compare Plates II and XXXVII.)
+The striking topographic contrasts between the plains and the ridges is
+thus seen to be closely related to the rock formations involved. It is
+the hard and resistant quartzite which forms the ridges, and the less
+resistant sandstone which forms the lowlands about them.
+
+That quartzite underlies the sandstone of the plain is indicated by the
+occasional outcrops of the former rock on the plain, and from the fact
+that borings for deep wells have sometimes reached it where it is not
+exposed.
+
+The sandstone of the plain and the quartzite of the ridges are not
+everywhere exposed. A deep but variable covering of loose material or
+_mantle rock (drift)_ is found throughout the eastern part of the area,
+but it does not extend far west of Baraboo. This mantle rock is so thick
+and so irregularly disposed that it has given origin to small hills and
+ridges. These elevations are superimposed on the erosion topography of
+the underlying rock, showing that the drift came into the region after
+the sandstone, limestone, and quartzite had their present relations, and
+essentially their present topography. Further consideration will be
+given to the drift in a later part of this report.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XI.
+
+The northeast wall of the Upper Narrows, north of Ableman's, showing the
+horizontal Potsdam sandstone and conglomerate lying unconformably on the
+quartzite, the beds of which are vertical.]
+
+
+
+
+                            PART II.
+
+
+                   HISTORY OF THE TOPOGRAPHY.
+
+
+
+
+                          CHAPTER II.
+
+
+ OUTLINE OF THE HISTORY OF THE ROCK FORMATIONS WHICH SHOW THEMSELVES AT
+                         THE SURFACE.
+
+
+          I. THE PRE-CAMBRIAN HISTORY OF THE QUARTZITE.
+
+_From loose sand to quartzite._--To understand the geography of a region
+it is necessary to understand the nature of the materials, the sculpture
+of which has made the geography.
+
+It has already been indicated that the Huronian quartzite of
+which the most prominent elevations of this region are composed, was
+once loose sand. Even at the risk of repetition, the steps in its
+history are here recounted. The source of the sand was probably the
+still older rocks of the land in the northern part of Wisconsin. Brought
+down to the sea by rivers, or washed from the shores of the land by
+waves, the sand was deposited in horizontal or nearly horizontal beds at
+the bottom of the shallow water which then covered central and southern
+Wisconsin. Later, perhaps while it was still beneath the sea, the sand
+was converted into sandstone, the change being effected partly by
+compression which made the mass of sand more compact, but chiefly by the
+cementation of its constituent grains into a coherent mass. The water
+contained in the sand while consolidation was in progress, held in
+solution some slight amount of silica, the same material of which the
+grains of sand themselves are composed. Little by little this silica in
+solution was deposited on the surfaces of the sand grains, enlarging
+them, and at the same time binding them together. Thus the sand became
+sandstone. Continued deposition of silica between and around the grains
+finally filled the interstitial spaces, and when this process was
+completed, the sandstone had been converted into quartzite. While
+quartzite is a metamorphic sandstone, it is not to be understood that
+sandstone cannot be metamorphosed in other ways.
+
+_Uplift and deformation. Dynamic metamorphism._--After the deposition of
+the sands which later became the quartzite, the beds were uplifted and
+deformed, as their present positions and relations show. It is
+not possible to say how far the process of transformation of sand into
+quartzite was carried while the formation was still beneath the shallow
+sea in which it was deposited. The sand may have been changed to
+sandstone, and the sandstone to quartzite, before the sea bottom was
+converted into land, while on the other hand, the formation may have
+been in any stage of change from sand to quartzite, when that event
+occurred. If the process of change was then incomplete, it may have been
+continued after the sea retired, by the percolating waters derived from
+the rainfall of the region.
+
+Either when first converted into land, or at some later time, the beds
+of rock were folded, and suffered such other changes as attend profound
+dynamic movements. The conversion of the sandstone into quartzite
+probably preceded the deformation, since many phenomena indicate that
+the rock was quartzite and not sandstone when the folding took place.
+For example, the crushing of the quartzite (now re-cemented into
+brecciated quartzite) at Ablemans probably dates from the orogenic
+movements which folded the quartzite, and the fractured bits of rock
+often have corners and edges so sharp as to show that the rock was
+thoroughly quartzitic when the crushing took place.
+
+The uplift and deformation of the beds was probably accomplished slowly,
+but the vertical and highly tilted strata show that the changes were
+profound (see Fig. 4).
+
+The dynamic metamorphism which accompanied this profound deformation has
+already been referred to. The folding of the beds involved the
+slipping of some on others, and this resulted in the development of
+quartz schist along the lines of severest movement. Changes effected in
+the texture and structure of the rock under such conditions constitute
+_dynamic metamorphism_. In general, the metamorphic changes effected
+by dynamic action are much more profound than those brought about in
+other ways, and most rocks which have been profoundly metamorphosed,
+were changed in this way. Dynamic action generates heat, but contrary to
+the popular notion, the heat involved in profound metamorphism is
+usually secondary, and the dynamic action fundamental.
+
+At the same time that quartz schist was locally developed from the
+quartzite, crushing probably occurred in other places. This is
+_demorphism_, rather than metamorphism.
+
+_Erosion of the quartzite._--When the Huronian beds were raised to the
+estate of land, the processes of erosion immediately began to work on
+them. The heat and the cold, the plants and the animals, the winds, and
+especially the rain and the water which came from the melting of the
+snow, produced their appropriate effects. Under the influence of these
+agencies the surface of the rock was loosened by weathering, valleys
+were cut in it by running water, and wear and degradation went on at all
+points.
+
+The antagonistic processes of uplift and degradation went on for
+unnumbered centuries, long enough for even the slow processes involved
+to effect stupendous results. Degradation was continuous after the
+region became land, though uplift may not have been. On the whole,
+elevation exceeded degradation, for some parts of the quartzite finally
+came to stand high above the level of the sea,--the level to which all
+degradation tends.
+
+Fig. 4 conveys some notion of the amount of rock which was
+removed from the quartzite folds about Baraboo during this long period
+of erosion. The south range would seem to represent the stub of one side
+of a great anticlinal fold, a large part of which (represented by the
+dotted lines) was carried away, while the north range may be the core of
+another fold, now exposed by erosion.
+
+Some idea of the geography of the quartzite at the close of this period
+of erosion may be gained by imagining the work of later times undone.
+The younger beds covering the quartzite of the plains have a thickness
+varying from zero to several hundred feet, and effectually mask the
+irregularities of the surface of the subjacent quartzite. Could they be
+removed, the topography of the quartzite would be disclosed, and found
+to have much greater relief than the present surface; that is, the
+vertical distance between the crest of the quartzite ridge, and the
+surface of the quartzite under the surrounding lowlands, would be
+greater than that between the same crest and the surface of the
+sandstone. But even this does not give the full measure of the relief of
+the quartzite at the close of the long period of erosion which followed
+its uplift, for allowance must be made for the amount of erosion which
+the crests of the quartzite ranges have suffered since that time. The
+present surface therefore does not give an adequate conception of the
+irregularity of the surface at the close of the period of erosion which
+followed the uplift and deformation of the quartzite. So high were the
+crests of the quartzite ranges above their surroundings at that time,
+that they may well be thought of as mountainous. From this point of
+view, the quartzite ranges of today are the partially buried mountains
+of the pre-Potsdam land of south central Wisconsin.
+
+When the extreme hardness of the quartzite is remembered and also the
+extent of the erosion which affected it (Fig. 4) before the next
+succeeding formation was deposited, it is safe to conclude that the
+period of erosion was very long.
+
+_Thickness of the quartzite._--The thickness of the quartzite is not
+known, even approximately. The great thickness in the south range
+suggested by the diagram (Fig. 4) may perhaps be an exaggeration.
+Faulting which has not been discovered may have occurred, causing
+repetition of beds at the surface (Fig. 6), and so an exaggerated
+appearance of thickness. After all allowances have been made, it is
+still evident that the thickness of the quartzite is very great.
+
+
+             II. THE HISTORY OF THE PALEOZOIC STRATA.
+
+_The subsidence._--Following the long period of erosion, the irregular
+and almost mountainous area of central Wisconsin was depressed
+sufficiently to submerge large areas which had been land. The subsidence
+was probably slow, and as the sea advanced from the south, it covered
+first the valleys and lowlands, and later the lower hills and ridges,
+while the higher hills and ridges of the quartzite stood as islands in
+the rising sea. Still later, the highest ridges of the region were
+themselves probably submerged.
+
+[Illustration: Fig. 6.--A diagrammatic cross-section, showing how, by
+faulting, the apparent thickness of the quartzite would be increased.]
+
+_The Potsdam sandstone (and conglomerate)._--So soon as the sea began to
+overspread the region, its bottom became the site of deposition, and the
+deposition continued as long as the submergence lasted. It is to the
+sediments deposited during the earlier part of this submergence that the
+name _Potsdam_ is given.
+
+The sources of the sediments are not far to seek. As the former land was
+depressed beneath the sea, its surface was doubtless covered with the
+products of rock decay, consisting of earths, sands, small bits and
+larger masses of quartzite. These materials, or at least the finer
+parts, were handled by the waves of the shallow waters, for they were at
+first shallow, and assorted and re-distributed. Thus the residuary
+products on the submerged surface, were one source of sediments.
+
+From the shores also, so long as land areas remained, the waves derived
+sediments. These were composed in part of the weathered products of the
+rock, and in part of the undecomposed rock against which the waves
+beat, after the loose materials had been worn away. These sediments
+derived from the shore were shifted, and finally mingled with those
+derived from the submerged surface.
+
+So long as any part of the older land remained above the water, its
+streams brought sediments to the sea. These also were shifted by the
+waves and shore currents, and finally deposited with the others on the
+eroded surface of the quartzite. Thus sediments derived in various ways,
+but inherently essentially similar, entered into the new formation.
+
+[Illustration: Fig. 7.--Diagram to illustrate the theoretical
+disposition of sediments about an island.]
+
+[Illustration: Fig. 8.--Same as Fig. 7, except that the land has been
+depressed.]
+
+The first material to be deposited on the surface of the quartzite as it
+was submerged, was the coarsest part of the sediment. Of the sediment
+derived by the waves from the coasts, and brought down to the sea by
+rivers, the coarsest would at each stage be left nearest the shore,
+while the finer was carried progressively farther and farther from it.
+Thus at each stage the sand was deposited farther from the shore than
+the gravel, and the mud farther than the sand, where the water was so
+deep that the bottom was subject to little agitation by waves. The
+theoretical distribution of sediments about an island as it was
+depressed, is illustrated by the following diagrams, Figs. 7 and 8. It
+will be seen that the surface of the quartzite is immediately overlain
+by conglomerate, but that the conglomerate near its top is younger than
+that near its base.
+
+In conformity with this natural distribution of sediments, the basal
+beds of the Potsdam formation are often conglomeratic (Fig. 9, Plate
+III, Fig. 2, and Plate XXV). This may oftenest be seen near
+the quartzite ridges, for here only is the base of the formation
+commonly exposed. The pebbles and larger masses of the conglomerate are
+quartzite, like that of the subjacent beds, and demonstrate the source
+of at least some of the material of the younger formation. That the
+pebbles and bowlders are of quartzite is significant, for it shows that
+the older formation had been changed from sandstone to quartzite, before
+the deposition of the Potsdam sediments. The sand associated with the
+pebbles may well have come from the breaking up of the quartzite, though
+some of it may have been washed in from other sources by the waters in
+which the deposition took place.
+
+[Illustration: Fig. 9.--Sketch showing relation of basal Potsdam
+conglomerate and sandstone to the quartzite, on the East bluff at
+Devil's lake, behind the Cliff house.]
+
+The basal conglomerate may be seen at many places, but nowhere about
+Devil's lake is it so well exposed as at Parfrey's glen (a, Plate
+XXXVII), where the rounded stones of which it is composed vary
+from pebbles, the size of a pea, to bowlders more than three feet in
+diameter. Other localities where the conglomerates may be seen to
+advantage are Dorward's glen (b, Plate XXXVII), the East bluff at
+Devil's lake just above the Cliff house, and at the Upper narrows of the
+Baraboo, above Ablemans.
+
+While the base of the Potsdam is conglomeratic in many places, the main
+body of it is so generally sandstone that the formation as a whole is
+commonly known as the Potsdam sandstone.
+
+The first effect of the sedimentation which followed submergence was to
+even up the irregular surface of the quartzite, for the depressions in
+the surface were the first to be submerged, and the first to be filled.
+As the body of sediment thickened, it buried the lower hills and the
+lower parts of the higher ones. The extent to which the Potsdam
+formation buried the main ridge may never be known. It may have buried
+it completely, for as already stated patches of sandstone are
+found upon the main range. These patches make it clear that some
+formation younger than the quartzite once covered essentially all of the
+higher ridge. Other evidence to be adduced later, confirms this
+conclusion. It has, however, not been demonstrated that the high-level
+patches of sandstone are Potsdam.
+
+There is abundant evidence that the subsidence which let the Potsdam
+seas in over the eroded surface of the Huronian quartzite was gradual.
+One line of evidence is found in the cross-bedding of the sandstone
+(Plate XII) especially well exhibited in the Dalles of the Wisconsin.
+The beds of sandstone are essentially horizontal, but within the
+horizontal beds there are often secondary layers which depart many
+degrees from horizontality, the maximum being about 24 deg.. Plates XXVII
+and XII give a better idea of the structure here referred to than
+verbal description can.
+
+The explanation of cross-bedding is to be found in the varying
+conditions under which sand was deposited. Cross-bedding denotes shallow
+water, where waves and shore currents were effective at the bottom where
+deposition is in progress. For a time, beds were deposited off shore at
+a certain angle, much as in the building of a delta (Fig. 10). Then by
+subsidence of the bottom, other layers with like structure were
+deposited over the first. By this sequence of events, the dip of the
+secondary layers should be toward the open water, and in this region
+their dip is generally to the south. At any stage of deposition the waves
+engendered by storms were liable to erode the surface of the deposits
+already made, and new layers, discordant with those below, were likely
+to be laid down upon them. The subordinate layers of each deposit might
+dip in any direction. If this process were repeated many times during
+the submergence, the existing complexity would be explained.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XII.
+
+Steamboat rock,--an island in the Dalles of the Wisconsin.]
+
+[Illustration: Fig. 10.--A diagrammatic cross-section of a delta.]
+
+The maximum known thickness of the Potsdam sandstone in Wisconsin is
+about 1,000 feet, but its thickness in this region is much less. Where
+not capped by some younger formation, its upper surface has suffered
+extensive erosion, and the present thickness therefore falls short of
+the original. The figures given above may not be too great for the
+latter.
+
+_The Lower Magnesian limestone._--The conditions of sedimentation
+finally changed in the area under consideration. When the sand of the
+sandstone was being deposited, adjacent lands were the source whence the
+sediments were chiefly derived. The evidence that the region was sinking
+while the sand was being deposited shows that the land masses which were
+supplying the sand, were becoming progressively smaller. Ultimately the
+sand ceased to be washed out to the region here described, either
+because the water became too deep[3] or because the source of supply
+was too distant. When these relations were brought about, the conditions
+were favorable for the deposition of sediments which were to become
+limestone. These sediments consisted chiefly of the shells of marine
+life, together with an unknown amount of lime carbonate precipitated
+from the waters of the sea. The limestone contains no coarse, and but
+little fine material derived from the land, and the surfaces of its
+layers are rarely if ever ripple-marked. The materials of which it is
+made must therefore have been laid down in quiet waters which were
+essentially free from land-derived sediments. The depth of the water in
+which it was deposited was not, however, great, for the fossils are not
+the remains of animals which lived in abysmal depths.
+
+    [3] A few hundred feet would suffice.
+
+The deposition of limestone sediments following the deposition of the
+Potsdam sands, does not necessarily mean that there was more or
+different marine life while the younger formation was making, but only
+that the shells, etc., which before had been mingled with the sand,
+making fossiliferous sandstone, were now accumulated essentially free
+from land-derived sediment, and therefore made limestone.
+
+Like the sandstone beneath, the limestone formation has a wide
+distribution outside the area here under discussion, showing that
+conditions similar to those of central Wisconsin were widely distributed
+at this time.
+
+The beds of limestone are conformable on those of the sandstone, and the
+conformable relations of the two formations indicate that the deposition
+of the upper followed that of the lower, without interruption.
+
+The thickness of the Lower Magnesian limestone varies from less than 100
+to more than 200 feet, but in this region its thickness is nearer the
+lesser figure than the larger. The limestone is now present only in the
+eastern and southern parts of the area, though it originally covered the
+whole area.
+
+_The St. Peters sandstone._--Overlying the Lower Magnesian limestone at
+a few points, are seen remnants of St. Peters sandstone. The
+constitution of this formation shows that conditions of sedimentation
+had again changed, so that sand was again deposited where the conditions
+had been favorable to the deposition of limestone but a short time
+before. This formation has been recognized at but two places (d and
+e) within the area shown on Plate XXXVII, but the relations at these
+two points are such as to lead to the conclusion that the formation may
+once have covered the entire region. This sandstone formation is very
+like the sandstone below. Its materials doubtless came from the lands
+which then existed. The formation is relatively thin, ranging from
+somewhat below to somewhat above 100 feet.
+
+The change from the deposition of limestone sediments to sand may well
+have resulted from the shoaling of the waters, which allowed the sand to
+be carried farther from shore. Rise of the land may have accompanied the
+shoaling of the waters, and the higher lands would have furnished more
+and coarser sediments to the sea.
+
+_Younger beds._--That formations younger than the St. Peters sandstone
+once overlaid this part of Wisconsin is almost certain, though no
+remnants of them now exist. Evidence which cannot be here detailed[4]
+indicates that sedimentation about the quartzite ridges went on not only
+until the irregularities of surface were evened up, but until even the
+highest peaks of the quartzite were buried, and that formations as high
+in the series as the Niagara limestone once overlay their crests. Before
+this condition was reached, the quartzite ridges had of course ceased to
+be islands, and at the same time had ceased to be a source of supply of
+sediments. The aggregate thickness of the Paleozoic beds in the region,
+as first deposited, was probably not less than 1,500 feet, and it may
+have been much more. This thickness would have buried the crests of the
+quartzite ridges under several hundred feet of sediment (see Fig. 11).
+
+    [4] Jour. of Geol., Vol. III (pp. 655-67).
+
+[Illustration: Fig. 11.--The geological formations of southern Wisconsin
+in the order of their occurrence. Not all of these are found about
+Devil's lake.]
+
+It is by no means certain that south central Wisconsin was continuously
+submerged while this thick series of beds was being deposited. Indeed,
+there is good reason to believe that there was at least one period of
+emergence, followed, after a considerable lapse of time, by
+re-submergence and renewed deposition, before the Paleozoic series of
+the region was complete. These movements, however, had little effect on
+the geography of the region.
+
+Finally the long period of submergence, during which several changes in
+sedimentation had taken place, came to an end, and the area under
+discussion was again converted into land.
+
+_Time involved._--Though it cannot be reduced to numerical terms, the
+time involved in the deposition of these several formations of the
+Paleozoic must have been very long. It is probably to be reckoned in
+millions of years, rather than in denominations of a lower order.
+
+_Climatic conditions._--Little is known concerning the climate of this
+long period of sedimentation. Theoretical considerations have usually
+been thought to lead to the conclusion that the climate during this part
+of the earth's history was uniform, moist, and warm; but the conclusion
+seems not to be so well founded as to command great confidence.
+
+_The uplift._--After sedimentation had proceeded to some such extent as
+indicated, the sea again retired from central Wisconsin. This may have
+been because the sea bottom of this region rose, or because the sea
+bottom in other places was depressed, thus drawing off the water. The
+topography of this new land, like the topography of those portions of
+the sea bottom which are similarly situated, must have been for the most
+part level. Low swells and broad undulations may have existed, but no
+considerable prominences, and no sudden change of slope. The surface was
+probably so flat that it would have been regarded as a level surface had
+it been seen.
+
+The height to which the uplift carried the new land surface at the
+outset must ever remain a matter of conjecture. Some estimate may be
+made of the amount of uplift which the region has suffered since the
+beginning of this uplift, but it is unknown how much took place at this
+time, and how much in later periods of geological history.
+
+The new land surface at once became the site of new activities. All
+processes of land erosion at once attacked the new surface, in the
+effort to carry its materials back to the sea. The sculpturing of this
+plain, which, with some interruption, has continued to the present day,
+has given the region the chief elements of its present topography. But
+before considering the special history of erosion in this region, it may
+be well to consider briefly the general principles and processes of land
+degradation.
+
+
+                          CHAPTER III.
+
+
+           GENERAL OUTLINE OF RAIN AND RIVER EROSION.
+
+
+_Elements of erosion._--The general process of subaerial erosion is
+divisible into the several sub-processes of weathering, transportation,
+and corrasion.[5]
+
+    [5] There is an admirable exposition of this subject in
+    Gilbert's "Henry Mountains."
+
+_Weathering_ is the term applied to all those processes which
+disintegrate and disrupt exposed surfaces of rock. It is accomplished
+chiefly by solution, changes in temperature, the wedge-work of ice and
+roots, the borings of animals, and such chemical changes as surface
+water and air effect. The products of weathering are transported by the
+direct action of gravity, by glaciers, by winds, and by running water.
+Of these the last is the most important.
+
+_Corrasion_ is accomplished chiefly by the mechanical wear of streams,
+aided by the hard fragments such as sand, gravel and bowlders, which
+they carry. The solution effected by the waters of a stream may also be
+regarded as a part of corrasion. Under ordinary circumstances solution
+by streams is relatively unimportant, but where the rock is relatively
+soluble, and where conditions are not favorable for abrasion, solution
+may be more important than mechanical wear.
+
+So soon as sea bottom is raised to the estate of land, it is attacked by
+the several processes of degradation. The processes of weathering at
+once begin to loosen the material of the surface if it be solid; winds
+shift the finer particles about, and with the first shower
+transportation by running water begins. Weathering prepares the material
+for transportation and transportation leads to corrasion. Since the goal
+of all material transported by running water is the sea, subaerial
+erosion means degradation of the surface.
+
+_Erosion without valleys._--In the work of degradation the valley
+becomes the site of greatest activity, and in the following pages
+especial attention is given to the development of valleys and to the
+phases of topography to which their development leads.
+
+If a new land surface were to come into existence, composed of materials
+which were perfectly homogeneous, with slopes of absolute uniformity in
+all directions, and if the rain, the winds and all other surface
+agencies acted uniformly over the entire area, valleys would not be
+developed. That portion of the rainfall which was not evaporated and did
+not sink beneath the surface, would flow off the land in a sheet. The
+wear which it would effect would be equal in all directions from the
+center. If the angle of the slope were constant from center to shore, or
+if it increased shoreward, the wear effected by this sheet of water
+would be greatest at the shore, because here the sheet of flowing water
+would be deepest and swiftest, and therefore most effective in
+corrasion.
+
+_The beginning of a valley._--But land masses as we know them do not
+have equal and uniform slopes to the sea in all directions, nor is the
+material over any considerable area perfectly homogeneous. Departure
+from these conditions, even in the smallest degree, would lead to very
+different results.
+
+That the surface of newly emerged land masses would, as a rule, not be
+rough, is evident from the fact that the bottom of the sea is usually
+rather smooth. Much of it indeed is so nearly plane that if the water
+were withdrawn, the eye would scarcely detect any departure from
+planeness. The topography of a land mass newly exposed either by its own
+elevation or by the withdrawal of the sea, would ordinarily be similar
+to that which would exist in the vicinity of Necedah and east of Camp
+Douglas, if the few lone hills were removed, and the very shallow
+valleys filled. Though such a surface would seem to be moderately
+uniform as to its slopes, and homogeneous as to its material, neither
+the uniformity nor the homogeneity are perfect, and the rain water would
+not run off in sheets, and the wear would not be equal at all points.
+
+Let it be supposed that an area of shallow sea bottom is raised above
+the sea, and that the elevation proceeds until the land has an altitude
+of several hundred feet. So soon as it appears above the sea, the rain
+falling upon it begins to modify its surface. Some of the water
+evaporates at once, and has little effect on the surface; some of it
+sinks beneath the surface and finds its way underground to the sea; and
+some of it runs off over the surface and performs the work
+characteristic of streams. So far as concerns modifications of the
+surface, the run-off is the most important part.
+
+The run-off of the surface would tend to gather in the depressions of
+the surface, however slight they may be. This tendency is shown on
+almost every hillside during and after a considerable shower. The water
+concentrated in the depressions is in excess of that flowing over other
+parts of the surface, and therefore flows faster. Flowing faster, it
+erodes the surface over which it flows more rapidly, and as a result the
+initial depressions are deepened, and _washes_ or _gullies_ are started.
+
+Should the run-off not find irregularities of slope, it would, at the
+outset, fail of concentration; but should it find the material more
+easily eroded along certain lines than along others, the lines of easier
+wear would become the sites of greater erosion. This would lead to the
+development of gullies, that is, to irregularities of slope. Either
+inequality of slope or material may therefore determine the location of
+a gully, and one of these conditions is indispensable.
+
+Once started, each wash or gully becomes the cause of its own growth,
+for the gully developed by the water of one shower, determines greater
+concentration of water during the next. Greater concentration means
+faster flow, faster flow means more rapid wear, and this means
+corresponding enlargement of the depression through which the flow takes
+place. The enlargement effected by successive showers affects a gully in
+all dimensions. The water coming in at its head carries the head back
+into the land (head erosion), thus lengthening the gully; the water
+coming in at its sides wears back the lateral slopes, thus widening it;
+and the water flowing along its bottom deepens it. Thus gullies grow to
+be ravines, and farther enlargement by the same processes converts
+ravines into valleys. A river valley therefore is often but a gully
+grown big.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIII.
+
+FIG. 1.
+
+A very young valley.
+
+Illustration: FIG. 2.
+
+A valley in a later stage of development.
+
+Illustration: FIG. 3.
+
+Young valleys.]
+
+_The course of a valley._--In the lengthening of a gully or valley
+headward, the growth will be in the direction of greatest wear. Thus in
+Plate XIII, Fig. 1, if the water coming in at the head of the gully
+effects most wear in the direction a, the head of the gully will
+advance in that direction; if there be most wear in the direction b or
+c, the head will advance toward one of these points. The direction of
+greatest wear will be determined either by the slope of the surface, or
+by the nature of the surface material. The slope may lead to the
+concentration of the entering waters along one line, and the surface
+material may be less resistant in one direction than in another. If
+these factors favor the same direction of head-growth, the lengthening
+will be more rapid than if but one is favorable. If there be more rapid
+growth along two lines, as b and c, Plate XIII, Fig. 1, than between
+them, two gullies may develop (Plate XIII, Fig. 2). The frequent and
+tortuous windings common to ravines and valleys are therefore to be
+explained by the inequalities of slope or material which affected the
+surface while the valley was developing.
+
+_Tributary valleys._--Following out this simple conception of valley
+growth, we have to inquire how a valley system (a main valley and its
+tributaries) is developed. The conditions which determine the location
+and development of gullies in a new land surface, determine the location
+and development of tributary gullies. In flowing over the lateral slopes
+of a gully or ravine, the water finds either slope or surface material
+failing of uniformity. Both conditions lead to the concentration of the
+water along certain lines, and concentration of flow on the slope of an
+erosion depression, be it valley or gully, leads to the development of
+a tributary depression. In its growth, the tributary repeats, in all
+essential respects, the history of its main. It is lengthened headward
+by water coming in at its upper end, is widened by side wash, and
+deepened by the downward cutting of the water which flows along its
+axis. The factors controlling its development are the same as those
+which controlled the valley to which it is tributary.
+
+There is one peculiarity of the courses of tributaries which deserves
+mention. Tributaries, as a rule, join their mains with an acute angle up
+stream. In general, new land surfaces, such as are now under
+consideration, slope toward the sea. If a tributary gully were to start
+back from its main at right angles, more water would come in on the side
+away from the shore, on account of the seaward slope of the land. This
+would be true of the head of the gully as well as of other portions, and
+the effect would be to turn the head more and more toward parallelism
+with the main valley. Local irregularities of surface may, and
+frequently do, interfere with these normal relations, so that the
+general course of a tributary is occasionally at right angles to its
+main. Still more rarely does the general course of a tributary make an
+acute angle with its main on the down stream side. Local irregularities
+of surface determine the windings of a tributary, so that their courses
+for longer or shorter distances may be in violation of the general rule
+(c, Fig. 43); but on the whole, the valleys of a system whose
+history has not been interrupted in a region where the surface material
+is not notably heterogeneous, follow the course indicated above. This is
+shown by nearly every drainage system on the Atlantic Coastal plain
+which represents more nearly than any other portion of our continent,
+the conditions here under consideration. Fig. 12 represents the drainage
+system of the Mullica river in southern New Jersey and is a type of the
+Coastal plain river system.
+
+_How a valley gets a stream._--Valleys may become somewhat deep and long
+and wide without possessing permanent streams, though from their
+inception they have _temporary_ streams, the water for which is
+furnished by showers or melting snow. Yet sooner or later, valleys come
+to have permanent streams. How are they acquired? Does the valley find
+the stream or the stream the valley? For the answer to these questions,
+a brief digression will be helpful.
+
+[Illustration: Fig. 12.--A typical river system of the Coastal plain
+type.]
+
+In cultivated regions, wells are of frequent occurrence. In a flat
+region of uniform structure, the depth at which well water may be
+obtained is essentially constant at all points. If holes (wells 1 and 2,
+Fig. 13) be excavated below this level, water seeps into them, and in a
+series of wells the water stands at a nearly common level. This means
+that the sub-structure is full of water up to that level. These
+relations are illustrated by Fig. 13. The diagram represents a vertical
+section through a flat region from the surface (s s) down below the
+bottom of wells. The water stands at the same level in the two cells (1
+and 2), and the plane through them, at the surface of the water, is the
+_ground water level_. If in such a surface a valley were to be cut until
+its bottom was below the ground water level, the water would seep into
+it, as it does into the wells; and if the amount were sufficient, a
+permanent stream would be established. This is illustrated in Fig. 13.
+The line A A represents the ground water level, and the level at which
+the water stands in the wells, under ordinary circumstances. The bottom
+of the valley is below the level of the ground water, and the water
+seeps into it from either side. Its tendency is to fill the valley to
+the level A A. But instead of accumulating in the open valley as it does
+in the enclosed wells, it flows away, and the ground water level on
+either hand is drawn down.
+
+[Illustration: Fig. 13.--Diagram illustrating the relations of ground
+water to streams.]
+
+The level of the ground water fluctuates. It is depressed when the
+season is dry (A' A'), and raised when precipitation is abundant (A''
+A''). When it is raised, the water in the wells rises, and the stream in
+the valley is swollen. When it falls, the ground water surface is
+depressed, and the water in the wells becomes lower. If the water
+surface sinks below the bottom of the wells, the wells "go dry;" if
+below the bottom of the valley, the valley becomes for the time being, a
+"dry run." When a well is below the lowest ground-water level its supply
+of water never fails, and when the valley is sufficiently below the same
+level, its stream does not cease to flow, even in periods of drought. On
+account of the free evaporation in the open valley, the valley
+depression must be somewhat below the level necessary for a well, in
+order that the flow may be constant.
+
+It will be seen that _intermittent_ streams, that is, streams which flow
+in wet seasons and fail in dry, are intermediate between streams which
+flow after showers only, and those which flow without interruption. In
+the figure the stream would become dry if the ground water level sank to
+A' A'.
+
+It is to be noted that a permanent stream does not normally precede its
+valley, but that the valley, developed through gully-hood and
+ravine-hood to valley-hood by means of the temporary streams supplied by
+the run-off of occasional showers, _finds a stream_, just as diggers of
+wells find water. The case is not altered if the stream be fed by
+springs, for the valley finds the spring, as truly as the well-digger
+finds a "vein" of water.
+
+_Limits of a valley._--So soon as a valley acquires a permanent stream,
+its development goes on without the interruption to which it was subject
+while the stream was intermittent. The permanent stream, like the
+temporary one which preceded it, tends to deepen and widen its valley,
+and, under certain conditions, to lengthen it as well. The means by
+which these enlargements are affected are the same as before. There are
+limits, however, in length, depth, and width, beyond which a valley may
+not go. No stream can cut below the level of the water into which it
+flows, and it can cut to that level only at its outlet. Up stream from
+that point, a gentle gradient will be established over which the water
+will flow without cutting. In this condition the stream is _at grade_.
+Its channel has reached _baselevel_, that is, the level to which the
+stream can wear its bed. This grade is, however, not necessarily
+permanent, for what was baselevel for a small stream in an early stage
+of its development, is not necessarily baselevel for the larger stream
+which succeeds it at a later time.
+
+Weathering, wash, and lateral corrasion of the stream continue to widen
+the valley after it has reached baselevel. The bluffs of valleys are
+thus forced to recede, and the valley is widened at the expense of the
+upland. Two valleys widening on opposite sides of a divide, narrow the
+divide between them, and may ultimately wear it out. When this is
+accomplished, the two valleys become one. The limit to which a valley
+may widen on either side is therefore its neighboring valley, and since,
+after two valleys have become one by the elimination of the ridge
+between them, there are still valleys on either hand, the final result
+of the widening of all valleys must be to reduce all the area which
+they drain to baselevel. As this process goes forward, the upper flat
+into which the valleys were cut is being restricted in area, while the
+lower flats developed by the streams in the valley bottoms are being
+enlarged. Thus the lower flats grow at the expense of the higher.
+
+There are also limits in length which a valley may not exceed. The head
+of any valley may recede until some other valley is reached. The
+recession may not stop even there, for if, on opposite sides of a
+divide, erosion is unequal, as between 1A and 1B, Fig. 14, the divide
+will be moved toward the side of less rapid erosion, and it will cease
+to recede only when erosion on the two sides becomes equal (4A and
+4B). In homogeneous material this will be when the slopes on the two
+sides are equal.
+
+[Illustration: Fig. 14.--Diagram showing the shifting of a divide. The
+slopes 1A and 1B are unequal. The steeper slope is worn more rapidly and
+the divide is shifted from 1 to 4, where the two slopes become equal and
+the migration of the divide ceases.]
+
+It should be noted that the lengthening of a valley headward is not
+normally the work of the permanent stream, for the permanent stream
+begins some distance below the head of the valley. At the head,
+therefore, erosion goes on as at the beginning, even after a permanent
+stream is acquired.
+
+Under certain circumstances, the valley may be lengthened at its
+debouchure. If the detritus carried by it is deposited at its mouth, or
+if the sea bottom beyond that point rise, the land may be extended
+seaward, and over this extension the stream will find its way. Thus at
+their lower, as well as at their upper ends, both the stream and its
+valley may be lengthened.
+
+_A cycle of erosion._--If, along the borders of a new-born land mass, a
+series of valleys were developed, essentially parallel to one another,
+they would constitute depressions separated by elevations, representing
+the original surface not yet notably affected by erosion (see Plate XIV,
+Fig. 1). These inter-valley areas might at first be wide or narrow, but
+in process of time they would necessarily become narrow, for, once, a
+valley is started, all the water which enters it from either side helps
+to wear back its slopes, and the wearing back of the slopes means the
+widening of the valleys on the one hand and the narrowing of the
+inter-valley ridges on the other. Not only would the water running over
+the slopes of a valley wear back its walls, but many other processes
+conspire to the same end. The wetting and drying, the freezing and the
+thawing, the roots of plants and the borings of animals, all tend to
+loosen the material on the slopes or walls of the valleys, and gravity
+helps the loosened material to descend. Once in the valley bottom, the
+running water is likely to carry it off, landing it finally in the sea.
+Thus the growth of the valley is not the result of running water alone,
+though this is the most important single factor in the process.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIV.
+
+FIG. 1.
+
+The same valleys as shown in Plate XIII, Fig. 3, in a later stage of
+development.
+
+Illustration: FIG. 2.
+
+Same valleys as shown in Fig. 1, in a still later stage of
+development.]
+
+Even if valleys developed no tributaries, they would, in the course of
+time, widen to such an extent as to nearly obliterate the intervening
+ridges. The surface, however, would not easily be reduced to perfect
+flatness. For a long time at least there would remain something of slope
+from the central axis of the former inter-stream ridge, toward the
+streams on either hand; but if the process of erosion went on for a
+sufficiently long period of time, the inter-stream ridge would be
+brought very low, and the result would be an essentially flat surface
+between the streams, much below the level of the old one.
+
+The first valleys which started on the land surface (see Plate XIII,
+Fig. 3) would be almost sure to develop numerous tributaries. Into
+tributary valleys water would flow from their sides and from their
+heads, and as a result they would widen and deepen and lengthen just as
+their mains had done before them. By lengthening headward they would
+work back from their mains some part, or even all of the way across the
+divides separating the main valleys. By this process, the tributaries
+cut the divides between the main streams into shorter cross-ridges. With
+the development of tributary valleys there would be many lines of
+drainage instead of two, working at the area between two main streams.
+The result would be that the surface would be brought low much more
+rapidly, for it is clear that many valleys within the area between the
+main streams, widening at the same time, would diminish the aggregate
+area of the upland much more rapidly than two alone could do.
+
+The same thing is made clear in another way. It will be seen (Plate XIV,
+Figs. 1 and 2) that the tributaries would presently dissect an area of
+uniform surface, tending to cut it into a series of short ridges or
+hills. In this way the amount of sloping surface is greatly increased,
+and as a result, every shower would have much more effect in washing
+loose materials down to lower levels, whence the streams could carry
+them to the sea.
+
+[Illustration: Fig. 15.--Cross-sections showing various stages of
+erosion in one cycle.]
+
+The successive stages in the process of lowering a surface are suggested
+by Fig. 15, which represents a series of cross-sections of a land mass
+in process of degradation. The uppermost section represents a level
+surface crossed by young valleys. The next lower represents the same
+surface at a later stage, when the valleys have grown larger, while the
+third and succeeding sections represent still later stages in the
+process of degradation. Plate XIII, Fig. 3, and Plate XIV, Figs. 1 and
+2, represent in another way the successive stages of stream work in the
+general process of degradation.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XV.
+
+Diagram illustrating how a hard inclined layer of rock becomes a ridge
+in the process of degradation.]
+
+In this manner a series of rivers, operating for a sufficiently long
+period of time, might reduce even a high land mass to a low level,
+scarcely above the sea. The new level would be developed soonest near
+the sea, and the areas farthest from it would be the last--other things
+being equal--to be brought low. The time necessary for the development
+of such a surface is known as a _cycle of erosion_, and the resulting
+surface is a _base-level plain_, that is, a plain as near sea level as
+river erosion can bring it. At a stage shortly preceding the base-level
+stage the surface would be a _peneplain_. A peneplain, therefore, is a
+surface which has been brought toward, but not to base-level. Land
+surfaces are often spoken of as young or old in their erosion history
+according to the stage of advancement which has been made toward
+base-leveling. Thus the Colorado canyon, deep and impressive as it is,
+is, in terms of erosion, a young valley, for the river has done but a
+small part of the work which must be done in order to bring its basin to
+baselevel.
+
+_Effects of unequal hardness._--The process of erosion thus sketched
+would ultimately bring the surface of the land down to base-level, and
+in case the material of the land were homogeneous, the last points to be
+reduced would be those most remote from the axes of the streams doing
+the work of leveling. But if the material of the land were of unequal
+hardness, those parts which were hardest would resist the action of
+erosion most effectively. The areas of softer rock would be brought low,
+and the outcrops of hard rock (Plate XV) would constitute ridges during
+the later stages of an erosion cycle. If there were bodies of hard rock,
+such as the Baraboo quartzite, surrounded by sandstone, such as the
+Potsdam, the sandstone on either hand would be worn down much more
+readily than the quartzite, and in the course of degradation the latter
+would come to stand out prominently. The region in the vicinity of Devil's
+lake is in that stage of erosion in which the quartzite ridges are
+conspicuous (Plate XXXVII). The less resistant sandstone has been
+removed from about them, and erosion has not advanced so far since the
+isolation of the quartzite ridges as to greatly lower their crests. The
+harder strata are at a level where surface water can still work
+effectively, even though slowly, upon them, and in spite of their great
+resistance they will ultimately be brought down to the common level. It
+will be seen that, from the point of view of subaerial erosion, a
+base-level plain is the only land surface which is in a condition of
+approximate stability.
+
+_Falls and rapids._--If in lowering its channel a stream crosses one
+layer of rock much harder than the next underlying, the deepening will
+go on more rapidly on the less resistant bed. Where the stream crosses
+from the harder to the less hard, the gradient is likely to become
+steep, and a rapids is formed. These conditions are suggested in Fig. 16
+which represents the successive profiles (a b, a c, d e, f e, g e,
+and h e) of a stream crossing from a harder to a softer formation. Below
+the point a the stream is flowing over rock which is easily eroded, while
+above that point its course is over a harder formation. Just below a
+(profile a b) the gradient has become so steep that there are rapids.
+Under these conditions, erosion is rapid just beyond the crossing of the
+hard layer, and the gradient becomes higher and higher. When the steep
+slope of the rapids approaches verticality, the rapids become a _fall_
+(profile a c).
+
+[Illustration: Fig. 16.--Diagram to illustrate the development of a
+rapid and fall. The upper layer is harder than the strata below. The
+successive profiles of the stream below the hard layer are represented
+by the lines a b, a c, d e, f e, g e, and h e.]
+
+As the water falls over the precipitous face and strikes upon the softer
+rock below, part of it rebounds against the base of the vertical face
+(Fig. 16). The result of wear at this point is the undermining of the
+hard layer above, and sooner or later, portions of it will fall. This
+will occasion the recession of the fall (profile d e and f e). As the
+fall recedes, it grows less and less high. When the recession has
+reached the point i, or, in other words, when the gradient of the stream
+below the fall crosses the junction of the beds of unequal hardness, as
+it ultimately must, effective undermining ceases, and the end of the
+fall is at hand.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVI.
+
+Skillett Falls, in the Potsdam formation, three miles southwest of
+Baraboo. The several small falls are occasioned by slight inequalities
+in the hardness of the layers.]
+
+When the effective undercutting ceases because the softer bed is no
+longer accessible, the point of maximum wear is transferred to the top
+of the hard bed just where the water begins to fall (g, Fig. 16). The
+wear here is no greater than before, though it is greater relatively.
+The relatively greater wear at this point destroys the verticality of
+the face, converting it into a steep slope. When this happens, the fall
+is a thing of the past, and rapids succeed. With continued flow the bed
+of the rapids becomes less and less steep, until it is finally reduced
+to the normal gradient of the stream (h e), when the rapids disappear.
+
+When thin layers of rock in a stream's course vary in hardness, softer
+beds alternating with harder ones, a series of falls such as shown in
+Plate XVI, may result. As they work up stream, these falls will be
+obliterated one by one. Thus it is seen that falls and rapids are not
+permanent features of the landscape. They belong to the younger period
+of a valley's history, rather than to the older. They are marks of
+topographic youth.
+
+_Narrows._--Where a stream crosses a hard layer or ridge of rock lying
+between softer ones, the valley will not widen so rapidly in the hard
+rock as above and below. If the hard beds be vertical, so that their
+outcrop is not shifted as the degradation of the surface proceeds, a
+notable constriction of the valley results. Such a constriction is a
+_narrows_. The Upper and Lower narrows of the Baraboo (Plate IV)
+are good examples of the effect of hard rock on the widening of a
+valley.
+
+_Erosion of folded strata._--The processes of river erosion would not be
+essentially different in case the land mass upon which erosion operated
+were made of tilted and folded strata. The folds would, at the outset,
+determine the position of the drainage lines, for the main streams would
+flow in the troughs (synclines) between the folds (anticlines). Once
+developed, the streams would lower their beds, widen their valleys, and
+lengthen their courses, and in the long process of time they would bring
+the area drained nearly to sea-level, just as in the preceding case. It
+was under such conditions that the general processes of subaerial
+erosion operated in south central Wisconsin, after the uplift of the
+quartzite and before the deposition of the Potsdam sandstone. It was
+then that the principal features of the topography of the quartzite were
+developed.
+
+In regions of folded strata, certain beds are likely to be more
+resistant than others. Where harder beds alternate with softer, the
+former finally come to stand out as ridges, while the outcrops of the
+latter mark the sites of the valleys. Such alternations of beds of
+unequal resistance give rise to various peculiarities of drainage,
+particularly in the courses of tributaries. These peculiarities find no
+illustration in this region and are not here discussed.
+
+_Base-level plains and peneplains._--It is important to notice that a
+plane surface (base-level) developed by streams could only be developed
+at elevations but slightly above the sea, that is, at levels at which
+running water ceases to be an effective agent of erosion; for so long as
+a stream is actively deepening its valley, its tendency is to roughen
+the area which it drains, not to make it smooth. The Colorado river,
+flowing through high land, makes a deep gorge. All the streams of the
+western plateaus have deep valleys, and the manifest result of their
+action is to roughen the surface; but given time enough, and the streams
+will have cut their beds to low gradients. Then, though deepening of the
+valleys will cease, widening will not, and inch by inch and shower by
+shower the elevated lands between the valleys will be reduced in area,
+and ultimately the whole will be brought down nearly to the level of the
+stream beds. This is illustrated by Fig. 15.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVII.
+
+A group of mounds on the plain southwest from Camp Douglas. The
+base-level surface is well shown, and above it rise the remnants of the
+higher plain from which the lower was reduced.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XVIII.
+
+Castle Rock near Camp Douglas. In this view the relation of the erosion
+remnant to the extensive base-leveled surface is well shown.]
+
+It is important to notice further that if the original surface on which
+erosion began is level, there is no stage intermediate between the
+beginning and the end of an erosion cycle, when the surface is again
+level, or nearly so, though in the stage of a cycle next preceding the
+last--the peneplain stage (fourth profile, Fig. 15)--the surface
+approaches flatness. It is also important to notice that when streams
+have cut a land surface down to the level at which they cease to erode,
+that surface will still possess some slight slope, and that to seaward.
+
+No definite degree of slope can be fixed upon as marking a base-level.
+The angle of slope which would practically stop erosion in a region of
+slight rainfall would be great enough to allow of erosion if the
+precipitation were greater. All that can be said, therefore, is that the
+angle of slope must be low. The Mississippi has a fall of less than a
+foot per mile for some hundreds of miles above the gulf. A small stream
+in a similar situation would have ceased to lower its channel before so
+low a gradient was reached.
+
+The nearest approach to a base-leveled region within the area here under
+consideration is in the vicinity of Camp Douglas and Necedah (see Plate
+I). This is indeed one of the best examples of a base-leveled plain
+known. Here the broad plain, extending in some directions as far as the
+eye can reach, is as low as it could be reduced by the streams which
+developed it. The erosion cycle which produced the plain was, however,
+not completed, for above the plain rise a few conspicuous hills (Plates
+XVII and XVIII, and Fig. 17), and to the west of it lie the highlands
+marking the level from which the low plain was reduced.
+
+Where a region has been clearly base-leveled, isolated masses or ridges
+of resistant rock may still stand out conspicuously above it. The
+quartzite hill at Necedah is an example. Such hills are known as
+_monadnocks_. This name was taken from Mount Monadnock which owes its
+origin to the removal of the surrounding less resistant beds. The name
+has now become generic. Many of the isolated hills on the peneplain east
+of Camp Douglas are perhaps due to superior resistance, though the rock
+of which they are composed belongs to the same formation as that which
+has been removed.
+
+[Illustration: Fig. 17.--Sketch, looking northwest from Camp Douglas.]
+
+
+    CHARACTERISTICS OF VALLEYS AT VARIOUS STAGES OF DEVELOPMENT.
+
+In the early stages of its development a depression made by erosion has
+steep lateral slopes, the exact character of which is determined by many
+considerations. Its normal cross-section is usually described as
+V-shaped (Fig. 18). In the early stages of its development, especially
+if in unconsolidated material, the slopes are normally convex inward. If
+cut in solid rock, the cross section may be the same, though many
+variations are likely to appear, due especially to the structure of the
+rock and to inequalities of hardness. If a stream be swift enough to
+carry off not only all the detritus descending from its slopes, but to
+abrade its bed effectively besides, a steep-sided gorge develops. If it
+becomes deep, it is a canyon. For the development of a canyon, the
+material of the walls must be such as is capable of standing at a high
+angle. A canyon always indicates that the down-cutting of a stream keeps
+well ahead of the widening.
+
+[Illustration: Fig. 18.--Diagrammatic cross-section of a young valley.]
+
+Of young valleys in loose material (drift) there are many examples in
+the eastern portion of the area here described. Shallow canyons or
+gorges in rock are also found. The gorge of Skillett creek at and above
+the Pewit's nest about three miles southwest from Baraboo, the gorge of
+Dell creek two miles south of Kilbourn City, and the Dalles of the
+Wisconsin at Kilbourn City may serve as illustrations of this type of
+valley.
+
+[Illustration: Fig. 19.--Diagrammatic profile of a young valley.]
+
+The profile of a valley at the stage of its development corresponding to
+the above section is represented diagrammatically by the curve A B in
+Fig. 19. The sketch (Pl. XIX, Fig. 1) represents a bird's-eye view of a
+valley in the same stage of development.
+
+[Illustration: Fig. 20.--Diagrammatic cross-section of a valley at a
+stage corresponding with that shown in Plate XIX, Fig. 2.]
+
+At a stage of development later than that represented by the V-shaped
+cross-section, the corresponding section is U-shaped, as shown in Fig.
+20. The same form is sketched in Plate XIX, Fig. 2. This represents a
+stage of development where detritus descending the slopes is not all
+carried away by the stream, and where the valley is being widened faster
+than it is deepened. Its slopes are therefore becoming gentler. The
+profile of the valley at this stage would be much the same as that in
+the preceding, except that the gradient in the lower portion would be
+lower.
+
+Still later the cross section of the valley assumes the shape shown in
+Fig. 21, and in perspective the form sketched in Plate XX, Fig. 1. This
+transformation is effected partly by erosion, and partly by deposition
+in the valley. When a stream has cut its valley as low as conditions
+allow, it becomes sluggish. A sluggish stream is easily turned from side
+to side, and, directed against its banks, it may undercut them, causing
+them to recede at the point of undercutting. In its meanderings, it
+undercuts at various points at various times, and the aggregate result
+is the widening of the valley. By this process alone the stream would
+develop a flat grade. At the same time all the drainage which comes in
+at the sides tends to carry the walls of the valley farther from its
+axis.
+
+[Illustration: Fig. 21.--Diagrammatic cross-section of a valley at a
+stage later than that shown in Fig. 20.]
+
+A sluggish stream is also generally a depositing stream. Its deposits
+tend to aggrade (build up) the flat which its meanderings develop. When
+a valley bottom is built up, it becomes wider at the same time, for the
+valley is, as a rule, wider at any given level than at any lower one.
+Thus the U-shaped valley is finally converted into a valley with a flat
+bottom, the flat being due in large part to erosion, and in smaller part
+to deposition. Under exceptional circumstances the relative importance
+of these two factors may be reversed.
+
+It will be seen that the cross-section of a valley affords a clue to its
+age. A valley without a flat is young, and increasing age is indicated
+by increasing width. Valleys illustrating all stages of development are
+to be found in the Devil's lake region. The valley of Honey creek
+southwest of Devil's lake may be taken as an illustration of a valley at
+an intermediate stage of development, while examples of old valleys are
+found in the flat country about Camp Douglas and Necedah.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XIX.
+
+FIG. 1.
+
+Sketch of a valley at the stage of development corresponding to the
+cross section shown in Fig. 18.
+
+Illustration: FIG. 2.
+
+Sketch of a valley at the stage of development corresponding to the
+cross section shown in Fig. 20.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XX.
+
+FIG. 1.
+
+Sketch of a part of a valley at the stage of development corresponding
+to the cross section shown in Fig 21.
+
+Illustration: FIG. 2.
+
+Sketch of a section of the Baraboo valley.]
+
+
+               _Transportation and Deposition._
+
+Sediment is carried by streams in two ways: (1) by being rolled along
+the bottom, and (2) by being held in suspension. Dissolved mineral
+matter (which is not sediment) is also carried in the water. By means of
+that rolled along the bottom and carried in suspension, especially the
+former, the stream as already stated abrades its bed.
+
+The transporting power of a stream of given size varies with its
+velocity. Increase in the declivity or the volume of a stream increases
+its velocity and therefore its transportive power. The transportation
+effected by a stream is influenced (1) by its transporting power, and (2)
+by the size and amount of material available for carriage. Fine material
+is carried with a less expenditure of energy than an equal amount of
+coarse. With the same expenditure of energy therefore a stream can carry
+a greater amount of the former than of the latter.
+
+Since the transportation effected by a stream is dependent on its
+gradient, its size, and the size and amount of material available, it
+follows that when these conditions change so as to decrease the carrying
+power of the river, deposition will follow, if the stream was previously
+fully loaded. In other words, a stream will deposit when it becomes
+overloaded.
+
+Overloading may come about in the following ways: (1) By decrease in
+gradient, checking velocity and therefore carrying power; (2) by
+decrease in amount of water, which may result from evaporation,
+absorption, etc.; (3) by change in the shape of the channel, so that the
+friction of flow is increased, and therefore the force available for
+transportation lessened; (4) by lateral drainage bringing in more
+sediment than the main stream can carry; (5) by change in the character
+of the material to which the stream has access; for if it becomes finer,
+the coarse material previously carried will be dropped, and the fine
+taken; and (6) by the checking of velocity when a stream flows into a
+body of standing water.
+
+_Topographic forms resulting from stream deposition._--The topographic
+forms resulting from stream deposition are various. At the bottoms of
+steep slopes, temporary streams build _alluvial cones_ or _fans_. Along
+its flood-plain portion, a stream deposits more or less sediment on its
+flats. The part played by deposition in building a river flat has
+already been alluded to. A depositing stream often wanders about in an
+apparently aimless way across its flood plain. At the bends in its
+course, cutting is often taking place on the outside of a curve while
+deposition is going on in the inside. The valley of the Baraboo
+illustrates this process of cutting and building. Fig. 2, Plate XX, is
+based upon the features of the valley within the city of Baraboo.
+
+Besides depositing on its flood-plain, a stream often deposits in its
+channel. Any obstruction of a channel which checks the current of a
+loaded stream occasions deposition. In this way "bars" are formed. Once
+started, the bar increases in size, for it becomes an obstacle to flow,
+and so the cause of its own growth. It may be built up nearly to the
+surface of the stream, and in low water, it may become an island by the
+depression of the surface water. In some parts of its course, as about
+Merrimac, the Wisconsin river is marked by such islands at low water,
+and by a much larger number of bars.
+
+At their debouchures, streams give up their loads of sediment. Under
+favorable conditions deltas are built, but delta-building has not
+entered into the physical history of this region to any notable extent.
+
+
+                     _Rejuvenation of Streams._
+
+After the development of a base-level plain, its surface would suffer
+little change (except that effected by underground water) so long as it
+maintained its position. But if, after its development, a base-level
+plain were elevated, the old surface in a new position would be subject
+to a new series of changes identical in kind with those which had gone
+before. The elevation would give the established streams greater fall,
+and they would reassume the characteristics of youth. The greater fall
+would accelerate their velocities; the increased velocities would entail
+increased erosion; increased erosion would result in the deepening of
+the valleys, and the deepening of the valleys would lead to the
+roughening of the surface. But in the course of time, the _rejuvenated_
+streams would have cut their valleys as low as the new altitude of the
+land permitted, that is, to a new base-level. The process of deepening
+would then stop, and the limit of vertical relief which the streams were
+capable of developing, would be attained. But the valleys would not stop
+widening when they stopped deepening, and as they widened, the
+intervening divides would become narrower, and ultimately lower. In the
+course of time they would be destroyed, giving rise to a new level
+surface much below the old one, but developed in the same position which
+the old one occupied when it originated; that is, a position but little
+above sea level.
+
+If at some intermediate stage in the development of a second base-level
+plain, say at a time when the streams, rejuvenated by uplift, had
+brought half the elevated surface down to a new base-level, another
+uplift were to occur, the half completed cycle would be brought to an
+end, and a new one begun. The streams would again be quickened, and as a
+result they would promptly cut new and deeper channels in the bottoms of
+the great valleys which had already been developed. The topography which
+would result is suggested by the following diagram (Fig. 22) which
+illustrates the cross-section which would be found after the following
+sequence of events: (1) The development of a base-level, A A; (2)
+uplift, rejuvenation of the streams, and a new cycle of erosion half
+completed, the new base-level being at B B; (3) a second uplift,
+bringing the second (incomplete) cycle of erosion to a close, and by
+rejuvenating the streams, inaugurating the third cycle. As represented
+in the diagram, the third cycle has not progressed far, being
+represented only by the narrow valley C. The base-level is now 2-2, and
+the valley represented in the diagram has not yet reached it.
+
+[Illustration: Fig. 22.--Diagram (cross-section), illustrating the
+topographic effect of rejuvenation by uplift.]
+
+[Illustration: Fig. 23.--Normal profile of a valley bottom in a
+non-mountainous region.]
+
+The rejuvenation of a stream shows itself in another way. The normal
+profile of a valley bottom in a non-mountainous region is a gentle
+curve, concave upward with gradient increasing from debouchure to
+source. Such a profile is shown in Fig. 23. Fig. 24, on the other hand,
+is the profile of a rejuvenated stream. The valley once had a profile
+similar to that shown in Fig. 23. Below B its former continuation is
+marked by the dotted line B C. Since rejuvenation the stream has
+deepened the lower part of its valley, and established there a profile
+in harmony with the new conditions. The upper end of the new curve has
+not yet reached beyond B.
+
+[Illustration: Fig. 24.--Profile of a stream rejuvenated by uplift.]
+
+
+                       _Underground Water._
+
+In what has preceded, reference has been made only to the results
+accomplished by the water which runs off over the surface. The water
+which sinks beneath it is, however, of no small importance in reducing a
+land surface. The enormous amount of mineral matter in solution in
+spring water bears witness to the efficiency of the ground water in
+dissolving rock, for since the water did not contain the mineral matter
+when it entered the soil, it must have acquired it below the surface. By
+this means alone, areas of more soluble rock are lowered below those of
+less solubility. Furthermore, the water is still active as a solvent
+agent after a surface has been reduced to so low a gradient that the
+run-off ceases to erode mechanically.
+
+
+
+
+                            CHAPTER IV.
+
+
+        EROSION AND THE DEVELOPMENT OF STRIKING SCENIC FEATURES.
+
+
+The uplift following the period of Paleozoic deposition in south central
+Wisconsin, inaugurated a period of erosion which, with some
+interruptions, has continued to the present day. The processes of
+weathering began as soon as the surface was exposed to the weather, and
+corrasion by running water began with the first shower which fell upon
+it. The sediment worn from the land was carried back to the sea, there
+to be used in the building of still younger formations.
+
+The rate of erosion of a land surface depends in large measure upon its
+height. As a rule, it is eroded rapidly if high, and but slowly if low.
+
+It is not known whether the lands of central Wisconsin rose to slight or
+to great heights at the close of the period of Paleozoic sedimentation.
+It is therefore not known whether the erosion was at the outset rapid or
+slow. If the land of southern Wisconsin remained low for a time after
+the uplift which brought the Paleozoic sedimentation to a close,
+weathering would have exceeded transportation and corrasion. A large
+proportion of the rainfall would have sunk beneath the surface, and
+found its way to the sea by subterranean routes. Loosening of material
+by alternate wetting and drying, expansion and contraction, freezing and
+thawing, and by solution, might have gone on steadily, but so long as
+the land was low, there would have been little run-off, and that little
+would have flowed over a surface of gentle slopes, and transportation
+would have been at a minimum. On the whole, the degradation of the land
+under these conditions could not have advanced rapidly.
+
+If, on the other hand, the land was raised promptly to a considerable
+height, erosion would have been vigorous at the outset. The surface
+waters would soon have developed valleys which the streams would have
+widened, deepened and lengthened. Both transportation and corrasion
+would have been active, and whatever material was prepared for
+transportation by weathering, and brought into the valleys by side-wash,
+would have been hurried on its way to the sea, and degradation would
+have proceeded rapidly.
+
+_Establishment of drainage._--Valleys were developed in this new land
+surface according to the principles already set forth. Between the
+valleys there were divides, which became higher as the valleys became
+deeper, and narrower as the valleys widened. Ultimately the ridges were
+lowered, and many of them finally eliminated in the manner already
+outlined. The distance below the original surface and that at which the
+first series of new flats were developed is conjectural, but it would
+have depended on the height of the land. So far as can now be inferred,
+the new base-plain toward which the streams cut may have been 400 or 500
+feet below the crests of the quartzite ridges. It was at this level that
+the oldest base-plain of which this immediate region shows evidence, was
+developed.
+
+Had the quartzite ranges not been completely buried by the Paleozoic
+sediments, they would have appeared as ridges on the new land surface,
+and would have had a marked influence on the development of the drainage
+of the newly emerged surface. But as the ranges were probably completely
+buried, the drainage lines were established regardless of the position
+of the hard, but buried ridges. When in the process of degradation the
+quartzite surfaces were reached, the streams encountered a formation far
+more resistant than the surrounding sandstone and limestone. As the less
+resistant strata were worn away, the old quartzite ridges, long buried,
+again became prominent topographic features. In this condition they were
+"resurrected mountains."
+
+If, when erosion on the uplifted surface of Paleozoic rocks began, a
+valley had been located directly over the buried quartzite ridge, and
+along its course, it would have been deepened normally until its bottom
+reached the crest of the hard formation. Then, instead of sinking its
+valley vertically downward into the quartzite, the stream would have
+shifted its channel down the slope of the range along the junction of
+the softer and harder rock (Fig. 25). Such changes occasioned by the
+nature and position of the rock concerned, are known as _adjustments_.
+
+[Illustration: Fig. 25.--Diagram illustrating the hypothetical case of a
+stream working down the slope of the quartzite range. The successive
+sections of the valley are suggested by the lines ae, be, ce and de.]
+
+Streams which crossed the quartzite ridges on the overlying strata might
+have held their courses even after their valleys were lowered to the
+level of the quartzite. Such streams would have developed narrows at the
+crossing of the quartzite. In so far as there were passes in the
+quartzite range before the deposition of the Paleozoic beds, they were
+filled during the long period of sedimentation, to be again cleared out
+during the subsequent period of erosion. The gap in the South range now
+occupied by the lake was a narrows in a valley which existed, though
+perhaps not to its present depth, before the Potsdam sandstone was
+deposited. It was filled when the sediments of that formation were laid
+down, to be again opened, and perhaps deepened, in the period of erosion
+which followed the deposition of the Paleozoic series.
+
+During the earliest period of erosion of which there is positive
+evidence, after the uplift of the Paleozoic beds, the softer formations
+about the quartzite were worn down to a level 400 or 500 feet below the
+crests of the South quartzite range. At this lower level, an approximate
+plain, a peneplain, was developed, the level of which is shown by
+numerous hills, the summits of which now reach an elevation of from
+1,000 to 1,100 feet above the sea. At the time of its development, this
+peneplain was but little above sea level, for this is the only elevation
+at which running water can develop such a plain. Above the general level
+of this plain rose the quartzite ranges as elongate monadnocks, the
+highest parts of which were fully 500 feet above the plain. A few other
+points in the vicinity failed to be reduced to the level of the
+peneplain. The 1,320 foot hill (d, Plate XXXVII), one and one-half miles
+southeast of the Lower narrows, and Gibraltar Rock (e, same Plate), two
+miles southeast of Merrimac, rose as prominences above it. It is
+possible that these crests are remnants of a base-level plain older than
+that referred to above. If while the quartzite remained much as now, the
+valleys in the sandstone below 1,000 or 1,100 feet were filled, the
+result would correspond in a general way to the surface which existed in
+this region when the first distinctly recognizable cycle of erosion was
+brought to a close. Above the undulating plain developed in the
+sandstone and limestone, the main quartzite ridge would have risen as a
+conspicuous ridge 400 to 500 feet.
+
+This cycle had not been completed, that is, the work of base-leveling
+had not been altogether accomplished, when the peneplain was elevated,
+and the cycle, though still incomplete, brought to a close. By the
+uplift, the streams were rejuvenated, and sunk their valleys into the
+elevated peneplain. Thus a new cycle of erosion was begun, and the
+uplifted peneplain was dissected by the quickened streams which sank
+their valleys promptly into the slightly resistant sandstone. At their
+new base-level, they ultimately developed new flats. This cycle of
+erosion appears to have advanced no farther than to the development of
+wide flats along the principal streams, such as the Wisconsin and the
+Baraboo, and narrow ones along the subordinate water courses, when it
+was interrupted. Along the main streams the new flats were at a level
+which is now from 800 to 900 feet above the sea, and 700 to 800 feet
+below the South quartzite range. It was at this time that the plains
+about Camp Douglas and Necedah, already referred to, were developed.
+During this second incomplete cycle, the quartzite ranges, resisting
+erosion, came to stand up still more prominently than during the first.
+
+The interruption of this cycle was caused by the advent of the glacial
+period which disturbed the normal course of erosion. This period was
+accompanied and followed by slight changes of level which also had their
+influence on the streams. The consideration of the effects of glaciation
+and of subsequent river erosion are postponed, but it may be stated that
+within the area which was glaciated the post-glacial streams have been
+largely occupied in removing the drift deposited by the ice from the
+preglacial valleys, or in cutting new valleys in the drift. The streams
+outside the area of glaciation were less seriously disturbed.
+
+At levels other than those indicated, partial base-levels are suggested,
+and although less well marked in this region, they might, in the study
+of a broader area, bring out a much more complicated erosion history. As
+already suggested, one cycle may have preceded that the remnants of
+which now stand 1,000-1,100 feet above sea level, and another may have
+intervened between this and that marked by the 800 to 900 foot level.
+
+From the foregoing it is clear that the topography of the region is, on
+the whole, an erosion topography, save for certain details in its
+eastern portion. The valleys differ in form and in size, with their age,
+and with the nature of the material in which they are cut; while the
+hills and ridges differ with varying relations to the streams, and with
+the nature of the material of which they are composed.
+
+
+                   _Striking Scenic Features._
+
+In a region so devoid of striking scenery as the central portion of the
+Mississippi basin, topographic features which would be passed without
+special notice in regions of greater relief, become the objects of
+interest. But in south central Wisconsin there are various features
+which would attract attention in any region where the scenery is not
+mountainous.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXI.
+
+Cleopatra's Needle. West Bluff of Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXII.
+
+Turk's Head. West Bluff of Devil's Lake.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIII.
+
+Devil's Doorway. East of Devil's Lake.]
+
+On the bluffs at Devil's lake there are many minor features which are
+sure to attract the attention of visitors. Such are "Cleopatra's Needle"
+(Plate XXI), "Turk's Head" (Plate XXII), and the "Devil's Doorway"
+(Plate XXIII).
+
+These particular forms have resulted from the peculiar weathering of the
+quartzite. The rock is affected by several systems of vertical or nearly
+vertical joint planes (cracks), which divide the whole formation into a
+series of vertical columns. There are also horizontal and oblique planes
+of cleavage dividing the columns, so that the great quartzite pile may
+be said to be made up of a series of blocks, which are generally in
+contact with one another. The isolated pillars and columns which have
+received special names have been left as they now stand by the falling
+away of the blocks which once surrounded them. They themselves must soon
+follow. The great talus slopes at the base of the bluffs, such as those
+on the west side of the lake and on the East bluff near its southeast
+corner, Plate XXIV, are silent witnesses of the extent to which this
+process has already gone. The blocks of rock of which they are composed
+have been loosened by freezing water, by the roots of trees, and by
+expansion and contraction due to changing temperature, and have fallen
+from their former positions to those they now occupy. Their descent,
+effected by gravity directly, is, it will be noted, the first step in
+their journey to the sea, the final resting place of all products of
+land degradation.
+
+_The Baraboo bluffs._--Nowhere in southern Wisconsin, or indeed in a
+large area adjacent to it, are there elevations which so nearly approach
+mountains as the ranges of quartzite in the vicinity of Baraboo and
+Devil's lake. So much has already been said of their history that there
+is need for little further description. Plate IV gives some idea of the
+appearance of the ranges. The history of the ranges, already outlined,
+involves the following stages: (1) The deposition of the sands in
+Huronian time; (2) the change of the sand to sandstone and the sandstone
+to quartzite; (3) the uplift and deformation of the beds; (4) igneous
+intrusions, faulting, crushing, and shoaring, with the development of
+schists accompanying the deformation; (5) a prolonged period of erosion
+during which the folds of quartzite were largely worn away, though
+considerable ridges, the Huronian mountains of early Cambrian times,
+still remained high above their surroundings; (6) the submergence of the
+region, finally involving even the crests of the ridges of quartzite;
+(7) a protracted period of deposition during which the Potsdam sandstone
+and several later Paleozoic formations were laid down about, and finally
+over, the quartzite, burying the mountainous ridges; (8) the elevation
+of the Paleozoic sea-bottom, converting it into land; (9) a long period
+of erosion, during which the upper Paleozoic beds were removed, and the
+quartzite re-discovered. Being much harder than the Paleozoic rocks, the
+quartzite ridges again came to stand out as prominent ridges, as the
+surrounding beds of relatively slight resistance were worn away. They
+are "resurrected" mountains, though not with the full height which they
+had in pre-Cambrian time, for they are still partially buried by younger
+beds.
+
+_The narrows in the quartzite._--There are four narrows or passes in the
+quartzite ridges, all of which are rather striking features. One of them
+is in the South range, one in the North range near its eastern end,
+while the others are in an isolated area of quartzite at Ablemans which
+is really a continuation of the North range. Two of these narrows are
+occupied by the Baraboo river, one by Narrows creek, and the fourth by
+Devil's lake.
+
+From Ablemans to a point several miles east of Baraboo, the Baraboo
+river flows through a capacious valley. Where it crosses the North
+range, six miles or more north of east of Baraboo, the broad valley is
+abruptly constricted to a narrow pass with precipitous sides, about 500
+feet high (c, Plate XXXVII). This constriction is the Lower narrows,
+conspicuous from many points on the South range, and from the plains to
+the north. Beyond the quartzite, the valley again opens out into a broad
+flat.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIV.
+
+Talus slope on the east bluff of Devil's lake.]
+
+Seen from a distance, the narrows has the appearance of an abrupt notch
+in the high ridge (Plate IV). Seen at closer range, the gap is
+still more impressive. It is in striking contrast with the other narrows
+in that there are no talus accumulations at the bases of the steep
+slopes, and in that the slopes are relatively smooth and altogether free
+from the curious details of sculpture seen in the other gaps where the
+slopes are equally steep.
+
+The Upper narrows of the Baraboo at Ablemans (b, Plate II) is in some
+ways similar to the Lower, though less conspicuous because less deep.
+Its slopes are more rugged, and piles of talus lie at their bases as at
+Devil's lake. This narrows also differs from the Lower in that the
+quartzite on one side is covered with Potsdam conglomerate, which
+overlies the truncated edges of the vertical layers of quartzite with
+unconformable contact. So clear an example of unconformity is not often
+seen. Potsdam sandstone is also seen to rest against the quartzite on
+either side of the narrows (Fig. 26), thus emphasizing the unconformity.
+The beauty and interest of this narrows is enhanced by the quartzite
+breccia ( which appears on its walls.
+
+[Illustration: Fig. 26.--A generalized diagrammatic cross-section at the
+Upper narrows, to show the relation of the sandstone to the quartzite.]
+
+One and one-half miles west of Ablemans (a, Plate II) is the third
+pass in the north quartzite ridge. This pass is narrower than the
+others, and is occupied by Narrows creek. Its walls are nearly vertical
+and possess the same rugged beauty as those at Ablemans. As at the Upper
+narrows, the beds of quartzite here are essentially vertical. They are
+indeed the continuation of the beds exposed at that place.
+
+The fourth narrows is across the South range (i, Plate II). It is not
+now occupied by a stream, though like the others it was cut by a stream,
+which was afterwards shut out from it. Because of its depth, 600 feet,
+and the ruggedness of its slopes, and because of its occupancy by the
+lake, this pass is the center of interest for the whole region. So much
+has already been said concerning it in other portions of this report
+that further description is here omitted. The manner in which the pass
+was robbed of its stream will be discussed later.
+
+The history of these several narrows, up to the time of the glacial
+period may now be summarized. Since remnants of Potsdam sandstone are
+found in some of them, it is clear that they existed in pre-Cambrian
+time,[6] and there is no reason to doubt that they are the work of the
+streams of those ancient days, working as streams now work. Following
+the pre-Cambrian period of erosion during which the notches were cut,
+came the submergence of the region, and the gaps were filled with sand
+and gravel, and finally the ridges themselves were buried. Uplift and a
+second period of erosion followed, during which the quartzite ranges
+were again exposed by the removal of the beds which overlay them, and
+the narrows cleaned out and deepened, and again occupied by streams.
+This condition of things lasted up to the time when the ice invaded the
+region.
+
+    [6] It is not here asserted that these notches were as deep
+    as now, in pre-Cambrian time. It is, however, certain that
+    the quartzite was deeply eroded, previous to the deposition
+    of the Potsdam sandstone.
+
+_Glens._--No enumeration of the special scenic features of this region
+would be complete without mention of Parfrey's and Dorward's glens (a
+and b, Plate XXXVII, and Plate XXV). Attention has already been
+directed to them as illustrations of young valleys, and as places where
+the Potsdam conglomerate is well shown, but they are attractive from the
+scenic point of view. Their frequent mention in earlier parts of this
+report makes further reference to them at this point unnecessary.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXV.
+
+In Dorward's Glen. The basal conglomerate of the Potsdam formation is
+shown at the lower right-hand corner, and is overlain by sandstone.
+(Photograph furnished by Mr. Wilfred Dorward).]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVI.
+
+Natural bridge near Denzer.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVII.
+
+Navy Yard. Dalles of the Wisconsin.]
+
+Pine Hollow (k, Plate II) is another attractive gorge on the south flank
+of the greater quartzite range. The rock at this point is especially
+well exposed. This gorge is beyond the drift-covered portion of the
+range, and therefore dates from the pre-glacial time.
+
+The Pewit's nest, about three miles southwest of Baraboo (m, Plate II),
+is another point of interest. Above the "nest," Skillett creek flows
+through a narrow and picturesque gorge in the Potsdam sandstone. The
+origin of this gorge is explained elsewhere.
+
+_Natural Bridge._--About two miles north and a little west of the
+village of Denzer (Sec. 17, T. 10 N., R. 5 E.), is a small natural
+bridge, which has resulted from the unequal weathering of the sandstone
+(see Plate XXVI). The "bridge" is curious, rather than beautiful or
+impressive.
+
+_The Dalles of the Wisconsin._--The _dalles_ is the term applied to a
+narrow canyon-like stretch of the Wisconsin valley seven miles in
+length, near Kilbourn City (see frontispiece). The depth of the gorge is
+from 50 to 100 feet. The part above the bridge at Kilbourn City is the
+"Upper dalles;" that below, the "Lower dalles." Within this stretch of
+the valley are perhaps the most picturesque features of the region.
+
+The sides of the gorge are nearly vertical much of the way, and at many
+points are so steep on both sides that landing would be impossible.
+Between these sandstone walls flows the deep and swift Wisconsin river.
+
+Such a rock gorge is in itself a thing of beauty, but in the dalles
+there are many minor features which enhance the charm of the whole.
+
+One of the features which deserves especial mention is the peculiar
+crenate form of the walls at the banks of the river. This is perhaps
+best seen in that part of the dalles known as the "Navy Yard." Plate
+XXVII. The sandstone is affected by a series of vertical cracks or
+joints. From weathering, the rock along these joints becomes softened,
+and the running water wears the softened rock at the joint planes more
+readily than other parts of its bank, and so develops a reentrant at
+these points. Rain water descending to the river finds and follows the
+joint planes, and thus widens the cracks. As a result of stream and rain
+and weathering, deep reentrant angles are produced. The projections
+between are rounded off so that the banks of the stream have assumed the
+crenate form shown in Plate XXVIII, and Frontispiece.
+
+When this process of weathering at the joints is carried sufficiently
+far, columns of rock become isolated, and stand out on the river bluffs
+as "chimneys" (Plate XXVIII). At a still later stage of development,
+decay of the rock along the joint planes may leave a large mass of rock
+completely isolated. "Steamboat rock" (Plate XII) and "Sugar
+bowl" (Plate XXIX) are examples of islands thus formed.
+
+The walls of sandstone weather in a peculiar manner at some points in
+the Lower dalles, as shown on Plate XXX. The little ridges stand out
+because they are harder and resist weathering better than the other
+parts. This is due in part at least to the presence of iron in the more
+resistant portions, cementing them more firmly. In the process of
+segregation, cementing materials are often distributed unequally.
+
+The effect of differences in hardness on erosion is also shown on a
+larger scale and in other ways. Perhaps the most striking illustration
+is _Stand rock_ (Plate XXXI), but most of the innumerable and
+picturesque irregularities on the rock walls are to be accounted for by
+such differences.
+
+Minor valleys tributary to the Wisconsin, such as _Witch's gulch_ and
+_Cold Water canyon_ deserve mention, both because of their beauty, and
+because they illustrate a type of erosion at an early stage of valley
+development. In character they are comparable to the larger gorge to
+which they are tributary. In the downward cutting, which far exceeds the
+side wear in these tributary canyons, the water has excavated large bowl
+or jug-like forms. In Witch's gulch such forms are now being excavated.
+They are developed just below falls, where the water carrying debris,
+eddies, and the jugs or pot-holes are the result of the wear effected by
+the eddies. The "Devil's jug" and many similar hollows are thus
+explained.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXVIII.
+
+Chimney Rock. Dalles of the Wisconsin. Cross-bedding well shown in
+foreground near bottom.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXIX.
+
+An Island in the Lower Dalles.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXX.
+
+View in lower Dalles showing peculiar honeycomb weathering.]
+
+_The mounds and castle rocks._--In the vicinity of Camp Douglas and over
+a large area to the east, are still other striking topographic forms,
+which owe their origin to different conditions, though they were
+fashioned by the same forces. Here there are many "tower" or "castle"
+rocks, which rise to heights varying from 75 to 190 feet above the
+surrounding plain. They are remnants of beds which were once continuous
+over the low lands above which the hills now rise. In Plates XVII and
+XVIII the general character of these hills is shown. The rock of
+which they are composed is Potsdam sandstone, the same formation which
+underlies most of the area about Baraboo. The effect of the vertical
+joints and of horizontal layers of unequal hardness is well shown.
+Rains, winds, frosts, and roots are still working to compass the
+destruction of these picturesque hills, and the talus of sand bordering
+the "castle" is a reminder of the fate which awaits them. These hills
+are the more conspicuous and the more instructive since the plain out of
+which they rise is so flat. It is indeed one of the best examples of a
+base-level plain to be found on the continent.
+
+The crests of these hills reach an elevation of between 1,000 and 1,100
+feet. They appear to correspond with the level of the first peneplain
+recognized in the Devil's lake region. It was in the second cycle of
+erosion, when their surroundings were brought down to the new
+base-level, that these hills were left. West of Camp Douglas, there are
+still higher elevations, which seem to match Gibraltar rock.
+
+The Friendship "mounds" north of Kilbourn City, the castellated hills a
+few miles northwest of the same place, and Petenwell peak on the banks
+of the Wisconsin (Plate XXXII), are further examples of the same class
+of hills. All are of Potsdam sandstone.
+
+In addition to the "castle" rocks and base-level plain about Camp
+Douglas, other features should be mentioned. No other portion of the
+area touched upon in this report affords such fine examples of the
+different types of erosion topography. In the base-level plain are found
+"old-age" valleys, broad and shallow, with the stream meandering in a
+wide flood-plain. Traveling up such a valley, the topography becomes
+younger and younger, and the various stages mentioned earlier in the
+text, and suggested in Plate XIX, Figs. 1 and 2, and Plate XX, Fig. 1,
+are here illustrated.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXI.
+
+Stand Rock. Upper end of the Upper Dalles.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXII.
+
+Petenwell Peak.]
+
+
+                             CHAPTER V.
+
+
+                         THE GLACIAL PERIOD.
+
+
+The eastern part of the area with which this report deals, is covered
+with a mantle of drift which, as already pointed out, has greatly
+modified the details of its topography. To the consideration of the
+drift and its history attention is now turned.
+
+_The drift._--The drift consists of a body of clay, sand, gravel and
+bowlders, spread out as a cover of unequal thickness over the rock
+formations beneath. These various classes of material may be confusedly
+commingled, or they may be more or less distinctly separated from one
+another. When commingled, all may be in approximately equal proportions,
+or any one may predominate over any or all the others to any extent.
+
+It was long since recognized that the materials of the drift did not
+originate where they now lie, and that, in consequence, they sustain no
+genetic relationship to the strata on which they rest. Long before the
+drift received any special attention from geologists, it was well known
+that it had been transported from some other locality to that where it
+now occurs. The early conception was that it had been drifted into its
+present position from some outside source by water. It was this
+conception of its origin which gave it the name of _drift_. It is now
+known that the drift was deposited by glacier ice and the waters which
+arose from its melting, but the old name is still retained.
+
+Clearly to understand the origin of the drift, and the method by which
+it attained its present distribution, it may be well to consider some
+elementary facts and principles concerning climate and its effects, even
+at the risk of repeating what is already familiar.
+
+_Snow fields and ice sheets._--The temperature and the snowfall of a
+region may stand in such a relation to each other that the summer's heat
+may barely suffice to melt the winter's snow. If under these
+circumstances the annual temperature were to be reduced, or the fall of
+snow increased, the summer's heat would fail to melt all the winter's
+snow, and some portion of it would endure through the summer, and
+through successive summers, constituting a perennial snow-field. Were
+this process once inaugurated, the depth of the snow would increase from
+year to year. The area of the snow-field would be extended at the same
+time, since the snow-field would so far reduce the surrounding
+temperature as to increase the proportion of the annual precipitation
+which fell as snow. In the course of time, and under favorable
+conditions, the area of the snow-field would attain great dimensions,
+and the depth of the snow would become very great.
+
+As in the case of existing snow fields the lower part of the snow mass
+would eventually be converted into ice. Several factors would conspire
+to this end. 1. The pressure of the overlying snow would tend to
+compress the lower portion, and snow rendered sufficiently compact by
+compression would be regarded as ice. 2. Water arising from the melting
+of the surface snow by the sun's heat, would percolate through the
+superficial layers of snow, and, freezing below, take the form of ice.
+3. On standing, even without pressure or partial melting, snow appears
+to undergo changes of crystallization which render it more compact. In
+these and perhaps other ways, a snow-field becomes an ice-field, the
+snow being restricted to its surface.
+
+Eventually the increase in the depth of the snow and ice in a snow-field
+will give rise to new phenomena. Let a snow and ice field be assumed in
+which the depth of snow and ice is greatest at the center, with
+diminution toward its edges. The field of snow, if resting on a level
+base, would have some such cross-section as that represented in the
+diagram, Fig. 27.
+
+When the thickness of the ice has become considerable, it is evident
+that the pressure upon its lower and marginal parts will be great. We
+are wont to think of ice as a brittle solid. If in its place there were
+some plastic substance which would yield to pressure, the weight of the
+ice would cause the marginal parts to extend themselves in all
+directions by a sort of flowing motion.
+
+[Illustration: Fig. 27.--Diagrammatic cross-section of a field of ice
+and snow (c) resting on a level base A-B.]
+
+Under great pressure, many substances which otherwise appear to be
+solid, exhibit the characteristics of plastic bodies. Among the
+substances exhibiting this property, ice is perhaps best known. Brittle
+and resistant as it seems, it may yet be molded into almost any
+desirable form if subjected to sufficient pressure, steadily applied
+through long intervals of time. The changes of form thus produced in ice
+are brought about without visible fracture. Concerning the exact nature
+of the movement, physicists are not agreed; but the result appears to be
+essentially such as would be brought about if the ice were capable of
+flowing, with extreme slowness, under great pressure continuously
+applied.
+
+In the assumed ice-field, there are the conditions for great pressure
+and for its continuous application. If the ice be capable of moving as a
+plastic body, the weight of the ice would induce gradual movement
+outward from the center of the field, so that the area surrounding the
+region where the snow accumulated would gradually be encroached upon by
+the spreading of the ice. Observation shows that this is what takes
+place in every snow-field of sufficient depth. Motion thus brought about
+is glacier motion, and ice thus moving is glacier ice.
+
+Once in motion, two factors would determine the limit to which the ice
+would extend itself: (1) the rate at which it advances; and (2) the rate
+at which the advancing edge is wasted. The rate of advance would depend
+upon several conditions, one of which, in all cases, would be the
+pressure of the ice which started and which perpetuates the motion. If
+the pressure be increased the ice will advance more rapidly, and if it
+advance more rapidly, it will advance farther before it is melted. Other
+things remaining constant, therefore, increase of pressure will cause
+the ice-sheet to extend itself farther from the center of motion.
+Increase of snowfall will increase the pressure of the snow and ice
+field by increasing its mass. If, therefore, the precipitation over a
+given snow-field be increased for a period of years, the ice-sheet's
+marginal motion will be accelerated, and its area enlarged. A decrease
+of precipitation, taken in connection with unchanged wastage would
+decrease the pressure of the ice and retard its movement. If, while the
+rate of advance diminished, the rate of wastage remained constant, the
+edge of the ice would recede, and the snow and ice field be contracted.
+
+The rate at which the edge of the advancing ice is wasted depends
+largely on the climate. If, while the rate of advance remains constant,
+the climate becomes warmer, melting will be more rapid, and the ratio
+between melting and advance will be increased. The edge of the ice will
+therefore recede. The same result will follow, if, while temperature
+remains constant, the atmosphere becomes drier, since this will increase
+wastage by evaporation. Were the climate to become warmer and drier at
+the same time, the rate of recession of the ice would be greater than if
+but one of these changes occurred.
+
+If, on the other hand, the temperature over and about the ice field be
+lowered, melting will be diminished, and if the rate of movement be
+constant, the edge of the ice will advance farther than under the
+earlier conditions of temperature, since it has more time to advance
+before it is melted. An increase in the humidity of the atmosphere,
+while the temperature remains constant, will produce the same result,
+since increased humidity of the atmosphere diminishes evaporation. A
+decrease of temperature, decreasing the melting, and an increase of
+humidity, decreasing the evaporation, would cause the ice to advance
+farther than either change alone, since both changes decrease the
+wastage. If, at the same time that conditions so change as to increase
+the rate of movement of the ice, climatic conditions so change as to
+reduce the rate of waste, the advance of the ice before it is melted
+will be greater than where only one set of conditions is altered. If,
+instead of favoring advance, the two series of conditions conspire to
+cause the ice to recede, the recession will likewise be greater than
+when but one set of conditions is favorable thereto.
+
+Greenland affords an example of the conditions here described. A large
+part of the half million or more square miles which this body of land is
+estimated to contain, is covered by a vast sheet of snow and ice,
+thousands of feet in thickness. In this field of snow and ice, there is
+continuous though slow movement. The ice creeps slowly toward the
+borders of the island, advancing until it reaches a position where the
+climate is such as to waste (melt and evaporate) it as rapidly as it
+advances.
+
+The edge of the ice does not remain fixed in position. There is reason
+to believe that it alternately advances and retreats as the ratio
+between movement and waste increases or decreases. These oscillations in
+position are doubtless connected with climatic changes. When the ice
+edge retreats, it may be because the waste is increased, or because the
+snowfall is decreased, or both. In any case, when the ice edge recedes
+from the coast, it tends to recede until its edge reaches a position
+where the melting is less rapid than in its former position, and where
+the advance is counterbalanced by the waste. This represents a condition
+of equilibrium so far as the edge of the ice is concerned, and here the
+edge of the ice would remain so long as the conditions were unchanged.
+
+When for a period of years the rate of melting of the ice is diminished,
+or the snowfall increased, or both, the ice edge advances to a new line
+where melting is more rapid than at its former edge. The edge of the ice
+would tend to reach a position where waste and advance balance. Here its
+advance would cease, and here its edge would remain so long as climatic
+conditions were unchanged.
+
+If the conditions determining melting and flowage be continually
+changing, the ice edge will not find a position of equilibrium, but will
+advance when the conditions are favorable for advance, and retreat when
+the conditions are reversed.
+
+Not only the edge of the ice in Greenland, but the ends of existing
+mountain glaciers as well, are subject to fluctuation, and are delicate
+indices of variations in the climate of the regions where they occur.
+
+_The North American ice sheet._--In an area north of the eastern part of
+the United States and in another west of Hudson Bay it is believed that
+ice sheets similar to that which now covers Greenland began to
+accumulate at the beginning of the glacial period. From these areas as
+centers, the ice spread in all directions, partly as the result of
+accumulation, and partly as the result of movement induced by the weight
+of the ice itself.
+
+The ice sheets spreading from these centers came together south of
+Hudson's bay, and invaded the territory of the United States as a single
+sheet, which, at the time of its greatest development, covered a large
+part of our country (Plate XXXIII), its area being known by the extent
+of the drift which it left behind when it was melted. In the east, it
+buried the whole of New England, most of New York, and the northern
+parts of New Jersey and Pennsylvania. Farther west, the southern margin
+of the ice crossed the Ohio river in the vicinity of Cincinnati, and
+pushed out over the uplands a few miles south of the river. In Indiana,
+except at the extreme east, its margin fell considerably short of the
+Ohio; in Illinois it reached well toward that river, attaining here its
+most southerly latitude. West of the Mississippi, the line which marks
+the limit of its advance curves to the northward, and follows, in a
+general way, the course of the Missouri river. The total area of the
+North American ice sheet, at the time of its maximum development, has
+been estimated to have been about 4,000,000 square miles, or about ten
+times the estimated area of the present ice-field of Greenland.
+
+Within the general area covered by the ice, there is an area of several
+thousand square miles, mainly in southwestern Wisconsin, where there is
+no drift. The ice, for some reason, failed to cover this _driftless
+area_ though it overwhelmed the territory on all sides.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIII.
+
+The North American Ice Sheet, at the time of maximum development.]
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXIV.
+
+View from the north of the Owl's Head, a hill two miles north of east of
+Merrimac, which has been shaped by the ice. The side to the left is the
+stone side.]
+
+Plate II shows the limit of ice advance in the area here described. The
+region may have been affected by the ice of more than one glacial epoch,
+but the chief results now observable were effected during the last, and
+the others need not be considered.
+
+
+                    _The Work of Glacier Ice._
+
+As the edge of an ice sheet, or as the end of a glacier, retreats, the
+land which it has previously covered is laid bare, and the effects which
+the passage of the ice produced may be seen. In some cases one may
+actually go back a short distance beneath the ice now in motion, and see
+its mode of work and the results it is effecting. The beds of living
+glaciers, and the beds which glaciers have recently abandoned, are found
+to present identical features. Because of their greater accessibility,
+the latter offer the better facilities for determining the effects of
+glaciation.
+
+The conspicuous phenomena of abandoned glacier beds fall into two
+classes, (1) those which pertain to the bed rock over which the ice
+moved, and (2) those which pertain to the drift left by the ice.
+
+_Erosive work of the ice._--_Effect on topography._--The leading
+features of the rock bed over which glacier ice has moved, are easily
+recognized. Its surface is generally smoothed and polished, and
+frequently marked by lines (striae) or grooves, parallel to one another.
+An examination of the bottom of an active glacier discloses the method
+by which the polishing and scoring are accomplished.
+
+The lower surface of the ice is thickly set with a quantity of clay,
+sand, and stony material of various grades of coarseness. These earthy
+and stony materials in the base of the ice are the tools with which it
+works. Thus armed, the glacier ice moves slowly forward, resting down
+upon the surfaces over which it passes with the whole weight of its
+mass, and the grinding action between the stony layer at the base of the
+ice and the rock bed over which it moves, is effective. If the material
+in the bottom of the ice be fine, like clay, the rock bed is polished.
+If coarser materials, harder than the bed-rock, be mingled with the
+fine, the rock bed of the glacier will be scratched as well as polished.
+If there are bowlders in the bottom of the ice they may cut grooves or
+gorges in the underlying rock. The grooves may subsequently be polished
+by the passage over and through them of ice carrying clay or other fine,
+earthy matter.
+
+All these phases of rock wear may be seen about the termini of receding
+glaciers, on territory which they have but recently abandoned. There can
+thus be no possible doubt as to the origin of the polishing, planing and
+scoring.
+
+There are other peculiarities, less easily defined, which characterize
+the surface of glacier beds. The wear effected is not confined to the
+mere marking of the surface over which it passes. If prominences of rock
+exist in its path, as is often the case, they oppose the movement of the
+ice, and receive a corresponding measure of abrasion from it. If they be
+sufficiently resistant they may force the ice to yield by passing over
+or around them; but if they be weak, they are likely to be destroyed.
+
+As the ice of the North American ice sheet advanced, seemingly more
+rigid when it encountered yielding bodies, and more yielding when it
+encountered resistant ones, it denuded the surface of its loose and
+movable materials, and carried them forward. This accumulation of earthy
+and stony debris in the bottom of the ice, gave it a rough and grinding
+lower surface, which enabled it to abrade the land over which it passed
+much more effectively than ice alone could have done. Every hill and
+every mound which the ice encountered contested its advance. Every
+sufficiently resistant elevation compelled the ice to pass around or
+over it; but even in these cases the ice left its marks upon the surface
+to which it yielded. The powerful pressure of pure ice, which is
+relatively soft, upon firm hills of rock, which are relatively hard,
+would effect little. The hills would wear the ice, but the effect of the
+ice on the hills would be slight. But where the ice is supplied with
+earthy and stony material derived from the rock itself, the case is
+different. Under these conditions, the ice, yielding only under great
+pressure and as little as may be, rubs its rock-shod base over every
+opposing surface, and with greatest severity where it meets with
+greatest resistance. Its action may be compared to that of a huge
+"flexible-rasp" fitting down snugly over hills and valleys alike, and
+working under enormous pressure.
+
+The abrasion effected by a moving body of ice under such conditions
+would be great. Every inch of ice advance would be likely to be attended
+by loss to the surface of any obstacle over or around which it is
+compelled to move. The sharp summits of the hills, and all the angular
+rugosities of their surfaces would be filed off, and the hills smoothed
+down to such forms as will offer progressively less and less resistance.
+If the process of abrasion be continued long enough, the forms, even of
+the large hills, may be greatly altered, and their dimensions greatly
+reduced. Among the results of ice wear, therefore, will be a lowering of
+the hills, and a smoothing and softening of their contours, while their
+surfaces will bear the marks of the tools which fashioned them, and will
+be polished, striated or grooved, according to the nature of the
+material which the ice pressed down upon them during its passage. Figs.
+28 and 29 show the topographic effects which ice is likely to produce by
+erosion. Plate XXXIV is a hill two miles northeast of Merrimac, which
+shows how perfectly the wear actually performed corresponds to that
+which might be inferred.
+
+[Illustration: Fig. 28.--A hill before the ice passes over it.]
+
+A rock hill was sometimes left without covering of drift after having
+been severely worn by the ice. Such a hill is known as a _roche
+moutonnee_. An example of this type of hill occurs three miles north of
+east of Baraboo at the point marked z on Plate XXXVII. This hill,
+composed of quartzite, is less symmetrical than those shown in Figs. 28
+and 29. Its whole surface, not its stoss side only, has been smoothed
+and polished by the ice. This hill is the most accessible, the most
+easily designated, and, on the whole, the best example of a _roche
+moutonnee_ in the region, though many other hills show something of the
+same form.
+
+[Illustration: Fig. 29.--The same hill after it has been eroded by the
+ice. A the stoss side. B the lee side.]
+
+It was not the hills alone which the moving ice affected. Where it
+encountered valleys in its course they likewise suffered modification.
+Where the course of a valley was parallel to the direction of the ice
+movement, the ice moved through it. The depth of moving ice is one of
+the determinants of its velocity, and because of the greater depth of
+ice in valleys, its motion here was more rapid than on the uplands
+above, and its abrading action more powerful. Under these conditions the
+valleys were deepened and widened.
+
+Where the courses of the valleys were transverse to the direction of ice
+movement, the case was different. The ice was too viscous to span the
+valleys, and therefore filled them. In this case it is evident that the
+greater depth of the ice in the valley will not accelerate its motion,
+since the ice in the valley-trough and that above it are in a measure
+opposed. If left to itself, the ice in the valley would tend to flow in
+the direction of the axis of the valley. But in the case under
+consideration, the ice which lies above the valley depression is in
+motion at right angles to the axis of the valley. Under these
+circumstances three cases might arise:
+
+(1) If the movement of the ice sheet over the valley were able to push
+the valley ice up the farther slope, and out on the opposite highland,
+this work would retard the movement of the upper ice, since the
+resistance to movement would be great. In this case, the thickness of
+the ice is not directly and simply a determinant of its velocity. Under
+these conditions the bottom of the valley would not suffer great
+erosion, since ice did not move along it; but that slope of the valley
+against which the ice movement was projected would suffer great wear
+(Fig. 30). The valley would therefore be widened, and the slope
+suffering greatest wear would be reduced to a lower angle. Shallow
+valleys, and those possessing gentle slopes, favor this phase of ice
+movement and valley wear.
+
+[Illustration: Fig. 30.--Diagram showing effect on valley of ice moving
+transversely across it.]
+
+(2) The ice in the valley might become stationary, in which case it
+might serve as a bridge for the upper ice to cross on (Fig. 31). In this
+case also the total thickness of ice will not be a determinant of its
+velocity, for it is the thickness of the moving ice only, which
+influences the velocity. In this case the valley would not suffer much
+wear, so long as this condition of things continued. Valleys which have
+great depth relative to the thickness of the ice, and valleys whose
+slopes are steep, favor this phase of movement.
+
+(3) In valleys whose courses are transverse to the direction of ice
+movement, transverse currents of ice may exist, following the direction
+of the valleys. If the thickness of the ice be much greater than the
+depth of the valley, if the valley be capacious, and if one end of it be
+open and much lower than the other, the ice filling it may move along
+its axis, while the upper ice continues in its original course at right
+angles to the valley. In this case the valley would be deepened and
+widened, but this effect would be due to the movement along its course,
+rather than to that transverse to it.
+
+[Illustration: Fig. 31--Diagram to illustrate case where ice fills a
+valley (C) and the upper ice then moves on over the filling.]
+
+If the course of a valley were oblique to the direction of ice movement,
+its effect on the movement of ice would be intermediate between that of
+valleys parallel to the direction of movement, and those at right angles
+to it.
+
+It follows from the foregoing that the corrasive effects of ice upon the
+surface over which it passed, were locally dependent on pre-existent
+topography, and its relation to the direction of ice movement. In
+general, the effort was to cut down prominences, thus tending to level
+the surface. But when it encountered valleys parallel to its movement
+they were deepened, thus locally increasing relief. Whether the
+reduction of the hills exceeded the deepening of the valleys, or whether
+the reverse was true, so far as corrasion alone is concerned, is
+uncertain. But whatever the effect of the erosive effect of ice action
+upon the total amount of relief, the effect upon the contours was to
+make them more gentle. Not only were the sharp hills rounded off, but
+even the valleys which were deepened were widened as well, and in the
+process their slopes became more gentle. A river-erosion topography,
+modified by the wearing (not the depositing) action of the ice, would be
+notably different from the original, by reason of its gentler slopes and
+softer contours (Figs. 28 and 29).
+
+_Deposition by the ice. Effect on topography._--On melting, glacier ice
+leaves its bed covered with the debris which it gathered during its
+movement. Had this debris been equally distributed on and in and beneath
+the ice during its movement, and had the conditions of deposition been
+everywhere the same, the drift would constitute a mantle of uniform
+thickness over the underlying rock. Such a mantle of drift would not
+greatly alter the topography; it would simply raise the surface by an
+amount equal to the thickness of the drift, leaving elevations and
+depressions of the same magnitude as before, and sustaining the same
+relations to one another. But the drift carried by the ice, in whatever
+position, was not equally distributed during transportation, and the
+conditions under which it was deposited were not uniform, so that it
+produced more or less notable changes in the topography of the surface
+on which it was deposited.
+
+The unequal distribution of the drift is readily understood. The larger
+part of the drift transported by the ice was carried in its basal
+portion; but since the surface over which the ice passed was variable,
+it yielded a variable amount of debris to the ice. Where it was hilly,
+the friction between it and the ice was greater than where it was plain,
+and the ice carried away more load. From areas where the surface was
+overspread by a great depth of loose material favorably disposed for
+removal, more debris was taken than from areas where material in a
+condition to be readily transported was meager. Because of the
+topographic diversity and lithological heterogeneity of the surface of
+the country over which it passed, some portions of the ice carried much
+more drift than others, and when the ice finally melted, greater depths
+of drift were left in some places than in others. Not all of the
+material transported by the ice was carried forward until the ice
+melted. Some of it was probably carried but a short distance from its
+original position before it lodged. Drift was thus accumulating at some
+points beneath the ice during its onward motion. At such points the
+surface was being built up; at other points, abrasion was taking place,
+and the surface was being cut down. The drift mantle of any region does
+not, therefore, represent simply the material which was on and in and
+beneath the ice of that place at the time of its melting, but it
+represents, in addition, all that lodged beneath the ice during its
+movement.
+
+The constant tendency was for the ice to carry a considerable part of
+its load forward toward its thinned edge, and there to leave it. It
+follows that if the edge of the ice remained constant in position for
+any considerable period of time, large quantities of drift would have
+accumulated under its marginal portion, giving rise to a belt of
+relatively thick drift. Other things being equal, the longer the time
+during which the position of the edge was stationary, the greater the
+accumulation of drift. Certain ridge-like belts where the drift is
+thicker than on either hand, are confidently believed to mark the
+position where the edge of the ice-sheet stood for considerable periods
+of time.
+
+Because of the unequal amounts of material carried by different parts of
+the ice, and because of the unequal and inconstant conditions of
+deposition under the body of the ice and its edge, the mantle of drift
+has a very variable thickness; and a mantle of drift of variable
+thickness cannot fail to modify the topography of the region it covers.
+The extent of the modification will depend on the extent of the
+variation. This amounts in the aggregate, to hundreds of feet. The
+continental ice sheet, therefore, modified the topography of the region
+it covered, not only by the wear it effected, but also by the deposits
+it made.
+
+In some places it chanced that the greater thicknesses of drift were
+left in the positions formerly marked by valleys. Locally the body of
+drift was so great that valleys were completely filled, and therefore
+completely obliterated as surface features. Less frequently, drift not
+only filled the valleys but rose even higher over their former positions
+than on either side. In other places the greater depths of drift,
+instead of being deposited in the valleys, were left on pre-glacial
+elevations, building them up to still greater heights. In short, the
+mantle of drift of unequal thickness was laid down upon the rock
+surface in such a manner that the thicker parts sometimes rest on hills
+and ridges, sometimes on slopes, sometimes on plains, and sometimes in
+valleys.
+
+[Illustration: Fig. 32.--Diagrammatic section showing relation of drift
+to underlying rock, where the drift is thick relative to the relief of
+the rock. a and b represent the location of post-glacial valleys.]
+
+These relations are suggested by Figs. 32 and 33. From them it will be
+seen that in regions where the thickness of the drift is great, relative
+to the relief of the underlying rock, the topography may be completely
+changed. Not only may some of the valleys be obliterated by being
+filled, but some of the hills may be obliterated by having the lower
+land between them built up to their level. In regions where the
+thickness of the drift is slight, relative to the relief of the rock
+beneath, the hills cannot be buried, and the valleys cannot be
+completely filled, so that the relative positions of the principal
+topographic features will remain much the same after the deposition of
+the drift, as before (Fig. 33).
+
+[Illustration: Fig. 33.--Diagrammatic section showing relation of drift
+to underlying rock where the drift is thin relative to the relief of the
+underlying rock.]
+
+In case the pre-glacial valleys were filled and the hills buried, the
+new valleys which the surface waters will in time cut in the drift
+surface will have but little correspondence in position with those
+which existed before the ice incursion. A new system of valleys, and
+therefore a new system of ridges and hills, will be developed, in some
+measure independent of the old. These relations are illustrated by Fig.
+32.
+
+Inequalities in the thickness of drift lead to a still further
+modification of the surface. It frequently happened that in a plane or
+nearly plane region a slight thickness of drift was deposited at one
+point, while all about it much greater thicknesses were left. The area
+of thin drift would then constitute a depression, surrounded by a higher
+surface built up by the thicker deposits. Such depressions would at
+first have no outlets, and are therefore unlike the depressions shaped
+by rain and river erosion. The presence of depressions without outlets
+is one of the marks of a drift-covered (glaciated) country. In these
+depressions water may collect, forming lakes or ponds, or in some cases
+only marshes and bogs.
+
+
+                   DIRECTION OF ICE MOVEMENT.
+
+The direction in which glacier ice moved may be determined in various
+ways, even after the ice has disappeared. The shapes of the rock hills
+over which the ice passed, the direction from which the materials of the
+drift came, and the course of the margin of the drift, all show that the
+ice of south central Wisconsin was moving in a general southwest
+direction. In the rock hills, this is shown by the greater wear of their
+northeast ("stoss") sides (Plate XXXIV). From the course of the drift
+margin, the general direction of movement may be inferred when it is
+remembered that the tendency of glacier ice on a plane surface is to
+move at right angles to its margin.
+
+For the exact determination of the direction of ice movement, recourse
+must be had to the striae on the bed-rock. Were the striated rock surface
+perfectly plane, and were the striae even lines, they would only tell
+that the ice was moving in one of two directions. But the rock surface
+is not usually perfectly plane, nor the striae even lines, and between
+the two directions which lines alone might suggest, it is usually
+possible to decide. The minor prominences and depressions in the rock
+surface were shaped according to the same principles that govern the
+shaping of hills (Fig. 29) and valleys (Fig. 30); that is, the stoss
+sides of the minor prominences, and the distal sides of small
+depressions suffered the more wear. With a good compass, the direction
+of the striae may be measured to within a fraction of a degree, and thus
+the direction of ice movement in a particular place be definitely
+determined. The striae which have been determined about Baraboo are shown
+on Plate II.
+
+_Effect of topography on movement._--The effect of glaciation on
+topography has been sketched, but the topography in turn exerted an
+important influence on the direction of ice movement. The extreme degree
+of topographic influence is seen in mountain regions like the Alps,
+where most of the glaciers are confined strictly to the valleys.
+
+As an ice sheet invades a region, it advances first and farthest along
+the lines of least resistance. In a rough country with great relief,
+tongues or lobes of ice would push forward in the valleys, while the
+hills or other prominences would tend to hold back or divide the onward
+moving mass. The edge of an ice sheet in such a region would be
+irregular. The marginal lobes of ice occupying the valleys would be
+separated by re-entrant angles marking the sites of hills and ridges.
+
+If the ice crossed a plane surface above which rose a notable ridge or
+hill, the first effect of the hill would be to indent the ice. The ice
+would move forward on either side, and if its thickness became
+sufficiently great, the parts moving forward on either side would again
+unite beyond it. A hill thus surrounded by ice is a nunatak. Later, as
+the advancing mass of ice became thicker, it might completely cover the
+hill; but the thickness of ice passing over the hill would be less than
+that passing on either side by an amount equal to the height of the
+hill. It follows that as ice encounters an isolated elevation, three
+stages in its contest with the obstruction may be recognized: (1) the
+stage when the ridge or hill acts as a wedge, dividing the moving ice
+into lobes, Fig. 34; (2) the nunatak stage, when the ice has pushed
+forward and reunited beyond the hill, Fig. 35; (3) the stage when the ice
+has become sufficiently deep to cover the hill.
+
+[Illustration: Fig. 34.--Diagrammatic representation of the effect of a
+hill on the edge of the ice.]
+
+After the ice has disappeared, the influence of the obstruction might be
+found in the disposition of the drift. If recession began during the
+first stage, that is, when the ice edge was separated into lobes, the
+margin of the drift should be lobate, and would loop back around the
+ridge from its advanced position on either side. If recession began
+during the second stage, that is, when the lobes had become confluent
+and completely surrounded the hill, a _driftless area_ would appear in
+the midst of drift. If recession began during the third stage, that is,
+after the ice had moved on over the obstruction, the evidence of the
+sequence might be obliterated; but if the ice moved but a short distance
+beyond the hill, the thinner ice over the hill would have advanced less
+far than the thicker ice on either side (Fig. 35), and the margin of
+the drift would show a re-entrant pointing back toward the hill, though
+not reaching it. All these conditions are illustrated in the Devil's
+lake region.
+
+[Illustration: Fig. 35.--Same as Fig. 34, when the ice has advanced
+farther.]
+
+
+                      _Limit of the Ice._
+
+The region under description is partly covered with drift, and partly
+free from it. The limit of the ice, at the time of its maximum expansion
+is well defined at many points, and the nature and position of the drift
+limit are so unique as to merit attention (see Plates II and XXXVII).
+They illustrate many of the principles already discussed.
+
+The ice which covered the region was the western margin of the Green Bay
+lobe (Fig. 36) of the last continental ice sheet. Its limit in this
+region is marked by a ridge-like accumulation of drift, the _terminal
+moraine_, which here has a general north-south direction. The region
+may have been affected by the ice of more than one epoch, but since the
+ice of the last epoch advanced as far to the west in this region as that
+of any earlier epoch, the moraine is on the border between the glaciated
+country to the east, and the driftless area to the west (Plates I and
+II). That part of the moraine which lies west of the Wisconsin river
+follows a somewhat sinuous course from Kilbourn City to a point a short
+distance north of Prairie du Sac. The departures from this general
+course are especially significant of the behavior of glacier ice.
+
+[Illustration: Fig. 36.--Map showing relations of lobes of ice during
+the Wisconsin ice epoch, to the driftless area.]
+
+In the great depression between the quartzite ranges, the moraine bends
+westward, showing that the ice advanced farther on the lowlands than on
+the ridges. As the moraine of this low area approaches the south range,
+it curves to the east. At the point southwest of Baraboo where the
+easterly curve begins to show itself, the moraine lies at the north base
+of the quartzite range; but as it is traced eastward, it is found to lie
+higher and higher on the slope of the range, until it reaches the crest
+nearly seven miles from the point where the eastward course was assumed.
+At this point it crosses the range, and, once across the crest, it turns
+promptly to the westward on the lower land to the south. Here the ice
+advanced up the valley between the East bluff (east of the lake) and the
+Devil's nose (Plate XXXVII), again illustrating the fact that lowlands
+favor ice advance. The valley between the Devil's nose and the East
+bluff is a narrow one, and the ice advanced through it nearly to the
+present site of the lake. Meanwhile the restraining influence of the
+"nose" was making itself felt, and the margin of the ice curved back
+from the bottom of the bluff near Kirkland, to the top of the bluff at
+the end of the nose. Here the edge of the ice crossed the point of the
+nose, and after rounding it, turned abruptly to the west. Thence its
+edge lay along the south slope of the ridge, descending from the crest
+of the ridge at the nose, to the base of the ridge two miles farther
+west. Here the ice reached its limit on the lowland, and its edge, as
+marked by the moraine, turned southward, reaching the Wisconsin river
+about a mile and a half above Prairie du Sac.
+
+The course of the terminal moraine across the ridges is such as the
+margin of the ice would normally have when it advanced into a region of
+great relief. The great loop in the moraine with its eastern extremity
+at k, Plate XXXVII, is explained by the presence of the quartzite
+ridge which retarded the advancing ice while it moved forward on either
+side. The minor loop around the Devil's nose is explained in the same
+way. Both the main loop, and the smaller one on the nose, illustrate
+the point made earlier in the text.
+
+The narrow and curious loop at m, is of a slightly different origin,
+though in principle the same. It is in the lee of a high point in the
+quartzite ridge. The ice surmounted this point, and descended its
+western slope; but the thickness of the ice passing over the summit was
+so slight that it advanced but a short distance down the slope before
+its force was exhausted, while the thicker ice on either side advanced
+farther before it was melted.
+
+
+                     _Glacial Deposits._
+
+Before especial reference is made to the drift of this particular
+region, it will be well to consider the character of drift deposits in
+general. When the ice of the continental glacier began its motion, it
+carried none of the stony and earthy debris which constitute the drift.
+These materials were derived from the surface over which the ice moved.
+
+From the method by which it was gathered, it is evident that the drift
+of any locality may contain fragments of rock of every variety which
+occurs along the route followed by the ice which reached that locality.
+Where the ice had moved far, and where there were frequent changes in
+the character of the rock constituting its bed, the variety of materials
+in the drift is great. The heterogeneity of the drift arising from the
+diverse nature of the rocks which contributed to it is _lithological
+heterogeneity_--a term which implies the commingling of materials
+derived from different rock formations. Thus it is common to find pieces
+of sandstone, limestone, quartzite, granite, gneiss, schist, etc.,
+intimately commingled in the drift, wherever the ice which produced it
+passed over formations of these several sorts of rock. Lithological
+heterogeneity is one of the notable characteristics of glacial
+formations.
+
+Another characteristic of the drift is its _physical heterogeneity_. As
+first gathered from the bed of moving ice, some of the materials of the
+drift were fine and some coarse. The tendency of the ice in all cases
+was to reduce its load to a still finer condition. Some of the softer
+materials, such as soft shale, were crushed or ground to powder, forming
+what is known in common parlance as clay. Clayey (fine) material is
+likewise produced by the grinding action of ice-carried bowlders upon
+the rock-bed, and upon one another. Other sorts of rock, such as soft
+sandstone, were reduced to the physical condition of sand, instead of
+clay, and from sand to bowlders all grades of coarseness and fineness
+are represented in the glacial drift.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXV.
+
+Cut in drift, showing its physical heterogeneity.]
+
+Since the ice does not assort the material which it carries, as water
+does, the clay, sand, gravel and bowlders will not, by the action of the
+ice, be separated from one another. They are therefore not stratified.
+As left by the ice, these physically heterogeneous materials are
+confusedly commingled. The finer parts constitute a matrix in which the
+coarser are embedded.
+
+Physical heterogeneity (Plate XXXV), therefore, is another
+characteristic of glacial drift. It is not to be understood that the
+proportions of these various physical elements, clay, sand, gravel, and
+bowlders, are constant. Locally any one of them may predominate over any
+or all the others to any extent.
+
+Since lithological and physical heterogeneity are characteristics of
+glacial drift, they together afford a criterion which is often of
+service in distinguishing glacial drift from other surface formations.
+It follows that this double heterogeneity constitutes a feature which
+can be utilized in determining the former extension of existing
+glaciers, as well as the former existence of glaciers where glaciers do
+not now exist.
+
+Another characteristic of glacial drift, and one which clearly
+distinguishes it from all other formations with which it might be
+confounded, is easily understood from its method of formation. If the
+ice in its motion holds down rock debris upon the rock surface over
+which it passes with such pressure as to polish and striate the
+bed-rock, the material carried will itself suffer wear comparable to
+that which it inflicts. Thus the stones, large and small, of glacial
+drift, will be smoothed and striated. This sort of wear on the
+transported blocks of rock, is effected both by the bed-rock reacting on
+the bowlders transported over it, and by bowlders acting on one another
+in and under the ice. The wear of bowlders by bowlders is effected
+wherever adjacent ones are carried along at different rates. Since the
+rate of motion of the ice is different in different parts of the
+glacier, the mutual abrasion of transported materials is a process
+constantly in operation. A large proportion of the transported stone and
+blocks of rock may thus eventually become striated.
+
+From the nature of the wear to which the stones are subjected when
+carried in the base of the ice, it is easy to understand that their
+shapes must be different from those of water-worn materials. The latter
+are rolled over and over, and thus lose all their angles and assume a
+more or less rounded form. The former, held more or less firmly in the
+ice, and pressed against the underlying rock or rock debris as they are
+carried slowly forward, have their faces planed and striated. The
+planation and striation of a stone need not be confined to its under
+surface. On either side or above it other stones, moving at different
+rates, are made to abrade it, so that its top and sides may be planed
+and scored. If the ice-carried stones shift their positions, as they may
+under various circumstances, new faces will be worn. The new face thus
+planed off may meet those developed at an earlier time at sharp angles,
+altogether unlike anything which water-wear is capable of producing. The
+stone thus acted upon shows a surface bounded by planes and more or less
+beveled, instead of a rounded surface such as water wear produces. We
+find, then, in the shape of the bowlders and smaller stones of the
+drift, and in the markings upon their surfaces, additional criteria for
+the identification of glacier drift (Plate XXXVI).
+
+The characteristics of glacial drift, so far as concerns its
+constitution, may then be enumerated as, (1) its lithological, and (2)
+physical heterogeneity; (3) the shapes, and (4) the markings of the stones
+of the drift. In structure, the drift which is strictly glacial, is
+unstratified.
+
+In the broadest sense of the term, all deposits made by glacier ice are
+_moraines_. Those made beneath the ice and back from its edge constitute
+the _ground moraine_, and are distinguished from the considerable
+marginal accumulations which, under certain conditions, are accumulated
+at or near the margin. These marginal accumulations are _terminal
+moraines_. Associated with the moraines which are the deposits of the
+ice directly, there are considerable bodies of stratified gravel and
+sand, the structure of which shows that they were laid down by water.
+This is to be especially noted, since lack of stratification is
+popularly supposed to be the especial mark of the formations to which
+the ice gave rise.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVI.
+
+Glaciated stones, showing both form and striae. (Matz.)]
+
+These deposits of stratified drift lie partly beyond the terminal
+moraine, and partly within it. They often sustain very complicated
+relations both to the ground and terminal moraines.
+
+The drift as a whole is therefore partly stratified and partly
+unstratified. Structurally the two types are thoroughly distinct, but
+their relations are often most complex, both horizontally and
+vertically. A fuller consideration of these relations will be found on a
+later page.
+
+
+                      _The Ground Moraine._
+
+The ground moraine constitutes the great body of the glacial drift.
+_Bowlder clay_, a term descriptive of its constitution in some places,
+and _till_, are other terms often applied to the ground moraine. The
+ground moraine consists of all the drift which lodged beneath the ice
+during its advance, all that was deposited back from its edge while its
+margin was farthest south, and most of that which was deposited while
+the ice was retreating. From this mode of origin it is readily seen that
+the ground moraine should be essentially as widespread as the ice
+itself. Locally, however, it failed of deposition. Since it constitutes
+the larger part of the drift, the characteristics already enumerated
+as belonging to drift in general are the characteristics of the
+till. Wherever obstacles to the progress of the ice lay in its path,
+there was a chance that these obstacles, rising somewhat into the
+lower part of the ice, would constitute barriers against which debris in
+the lower part of the ice would lodge. It might happen also that the
+ice, under a given set of conditions favoring erosion, would gather a
+greater load of rock-debris than could be transported under the changed
+conditions into which its advance brought it. In this case, some part of
+the load would be dropped and over-ridden. Especially near the margin of
+the ice where its thickness was slight and diminishing, the ice must
+have found itself unable to carry forward the loads of debris which it
+had gathered farther back where its action was more vigorous. It will be
+readily seen that if not earlier deposited, all material gathered by the
+under surface of the ice would ultimately find itself at the edge of the
+glacier, for given time enough, ablation will waste all that part of the
+ice occupying the space between the original position of the debris, and
+the margin of the ice. Under the thinned margin of the ice, therefore,
+considerable accumulations of drift must have been taking place while
+the ice was advancing. While the edge of the ice sheet was advancing
+into territory before uninvaded, the material accumulated beneath its
+edge at one time, found itself much farther from the margin at another
+and later time. Under the more forcible ice action back from the margin,
+the earlier accumulations, made under the thin edge, were partially or
+wholly removed by the thicker ice of a later time, and carried down to
+or toward the new and more advanced margin. Here they were deposited, to
+be in turn disturbed and transported still farther by the farther
+advance of the ice.
+
+Since in its final retreat the margin of the ice must have stood at all
+points once covered by it, these submarginal accumulations of drift must
+have been made over the whole country once covered by the ice. The
+deposits of drift made beneath the marginal part of the ice during its
+retreat, would either cover the deposits made under the body of the ice
+at an earlier time, or be left alongside them. The constitution of the
+two phases of till, that deposited during the advance of the ice, and
+that deposited during its retreat, is essentially the same, and there
+is nothing in their relative positions to sharply differentiate them.
+They are classed together as _subglacial till_.
+
+Subglacial till was under the pressure of the overlying ice. In keeping
+with these conditions of accumulation, the till often possesses a
+firmness suggestive of great compression. Where its constitution is
+clayey it is often remarkably tough. Where this is the case, the quality
+here referred to has given rise to the suggestive name "hard pan." Where
+the constitution of the till is sandy, rather than clayey, this firmness
+and toughness are less developed, or may be altogether wanting, since
+sand cannot be compressed into coherent masses like clay.
+
+_Constitution._--The till is composed of the more or less comminuted
+materials derived from the land across which the ice passed. The soil
+and all the loose materials which covered the rock entered into its
+composition. Where the ice was thick and its action vigorous, it not
+only carried away the loose material which it found in its path, but,
+armed with this material, it abraded the underlying rock, wearing down
+its surface and detaching large and small blocks of rock from it. It
+follows that the constitution of the till at any point is dependent upon
+the nature of the soil and rock from which it was derived.
+
+If sandstone be the formation which has contributed most largely to the
+till, the matrix of the till will be sandy. Where limestone instead of
+sandstone made the leading contribution to it, the till has a more
+earthy or clayey matrix. Any sort of rock which may be very generally
+reduced to a fine state of division under the mechanical action of the
+ice, will give rise to clayey till.
+
+The nature and the number of the bowlders in the till, no less than the
+finer parts, depend on the character of the rock overridden. A hard and
+resistant rock, such as quartzite, will give rise to more bowlders in
+proportion to the total amount of material furnished to the ice, than
+will softer rock. Shale or soft sandstone, possessing relatively slight
+resistance, will be much more completely crushed. They will, therefore,
+yield proportionately fewer bowlders than harder formations, and more
+of the finer constituents of till.
+
+The bowlders taken up by the ice as it advanced over one sort of rock
+and another, possessed different degrees of resistance. The softer ones
+were worn to smaller dimensions or crushed with relative ease and speed.
+Bowlders of soft rock are, therefore, not commonly found in any
+abundance at great distances from their sources. The harder ones yielded
+less readily to abrasion, and were carried much farther before being
+destroyed, though even such must have suffered constant reduction in
+size during their subglacial journey. In general it is true that
+bowlders in the till, near their parent formations, are larger and less
+worn than those which have been transported great distances.
+
+The ice which covered this region had come a great distance and had
+passed over rock formations of many kinds. The till therefore contains
+elements derived from various formations; that is, it is lithologically
+heterogeneous. This heterogeneity cannot fail to attract the attention
+of one examining any of the many exposures of drift about Baraboo at
+road gradings, or in the cuts along the railway. Among the stones in the
+drift at these exposures are limestone, sandstone, quartzite, diabase,
+gabbro, gneiss, granite, schist, and porphyry, together with pieces of
+flint and chert.
+
+Such an array may be found at any of the exposures within the immediate
+vicinity of Devil's lake. To the north, and a few miles to the south of
+the Baraboo ranges, the quartzite from these bluffs, and the porphyry
+from the point marked h in Plate II, are wanting, though other
+varieties of porphyry are present. The ice moved in a general
+west-southwest direction in this region, and the quartzite in the drift,
+so far as derived from the local formation, is therefore restricted to a
+narrow belt.
+
+The physical heterogeneity may be seen at all exposures, and is
+illustrated in Plate XXXV. The larger stones of the drift are
+usually of some hard variety of rock. Near the Baraboo ranges, the local
+quartzite often predominates among the bowlders, and since such
+bowlders have not been carried far, they are often little worn. Away
+from the ranges, the bowlders are generally of some crystalline rock,
+such as granite and diabase. Bowlders of these sorts of rock are from a
+much more distant source, and are usually well worn.
+
+In general the till of any locality is made up largely of material
+derived from the formations close at hand. This fact seems to afford
+sufficient warrant for the conclusion that a considerable amount of
+deposition must have gone on beneath the ice during its movement, even
+back from its margin. To take a concrete illustration, it would seem
+that the drift of southeastern Wisconsin should have had a larger
+contribution than it has of material derived from Canadian territory, if
+material once taken up by the ice was all or chiefly carried down to its
+thinned edge before deposition. The fact that so little of the drift
+came from these distant sources would seem to prove that a large part of
+the material moved by the ice, is moved a relatively short distance
+only. The ice must be conceived of as continually depositing parts of
+its load, and parts which it has carried but a short distance, as it
+takes up new material from the territory newly invaded.
+
+In keeping with the character of till in general, that about Devil's
+lake was derived largely from the sandstone, limestone and quartzite of
+the immediate vicinity, while a much smaller part of it came from more
+distant sources. This is especially noticeable in the fine material,
+which is made up mostly of the comminuted products of the local rock.
+
+_Topography._--The topography of the ground moraine is in general the
+topography already described in considering the modification of
+preglacial topography effected by ice deposition. As left by the ice,
+its surface was undulating. The undulations did not take the form of
+hills and ridges with intervening valleys, but of swells and depressions
+standing in no orderly relationship to one another. Undrained
+depressions are found in the ground moraine, but they are, as a rule,
+broader and shallower than the "kettles" common to terminal moraines.
+
+It is in the broad, shallow depressions of the ground moraine that many
+of the lakes and more of the marshes of southeastern Wisconsin are
+located.
+
+The rolling, undulating topography characteristic of ground moraines is
+well shown about the City of Baraboo and between that point and the
+lake, and at many less easily designated points about Merrimac.
+
+In thickness the ground moraine reaches at least 160 feet, though its
+average is much less--too little to obliterate the greater topographic
+features of the rock beneath. It is, however, responsible for many of
+the details of the surface.
+
+
+                    _Terminal Moraines._
+
+The marginal portion of the ice sheet was more heavily loaded--certainly
+more heavily loaded relative to its thickness--than any other. Toward
+its margin the thinned ice was constantly losing its transportive power,
+and at its edge this power was altogether gone. Since the ice was
+continually bringing drift down to this position and leaving it there,
+the rate of drift accumulation must have been greater, on the average,
+beneath the edge of the ice than elsewhere.
+
+Whenever, at any stage in its history, the edge of the ice remained
+essentially constant in position for a long period of time, the
+corresponding submarginal accumulation of drift was great, and when the
+ice melted, the former site of the stationary edge would be marked by a
+broad ridge or belt of drift, thicker than that on either side. Such
+thickened belts of drift are _terminal moraines_. It will be seen that a
+terminal moraine does not necessarily mark the terminus of the ice at
+the time of its greatest advance, but rather its terminus at any time
+when its edge was stationary or nearly so.
+
+From the conditions of their development it will be seen that these
+submarginal moraines may be made up of materials identical with those
+which constitute the ground moraine, and such is often the case. But
+water arising from the melting of the ice, played a much more
+important role at its margin than farther back beneath it. One result of
+its greater activity may be seen in the greater coarseness which
+generally characterizes the material of the terminal moraine as compared
+with that of the adjacent ground moraine. This is partly because the
+water carried away such of the finer constituents as it was able to
+transport, leaving the coarser behind. Further evidence of the great
+activity of water near the margin of the ice is to be seen in the
+relatively large amount of assorted and stratified sand and gravel
+associated with the terminal moraine.
+
+Such materials as were carried on the ice were dropped at its edge when
+the ice which bore them melted from beneath. If the surface of the ice
+carried many bowlders, many would be dropped along the line of its edge
+wherever it remained stationary for any considerable period of time. A
+terminal moraine therefore embraces (1) the thick belt of drift
+accumulated beneath the edge of the ice while it was stationary, or
+nearly so; and (2) such debris as was carried on the surface of the ice
+and dumped at its margin. In general the latter is relatively
+unimportant.
+
+At various stages in its final retreat, the ice made more or less
+protracted halts. These halting places are marked by marginal moraines
+of greater or less size, depending on the duration of the stop, and the
+amount of load carried.
+
+A terminal moraine is not the sharp and continuous ridge we are wont to
+think it. It is a belt of thick drift, rather than a ridge, though it is
+often somewhat ridge-like. In width, it varies from a fraction of a mile
+to several miles. In the region under consideration it is rarely more
+than fifty feet high, and rarely less than a half mile wide, and a ridge
+of this height and width is not a conspicuous topographic feature in a
+region where the relief is so great as that of the Devil's lake region.
+
+_Topography of terminal moraines._--The most distinctive feature of a
+terminal moraine is not its ridge-like character, but its peculiar
+topography. In general, it is marked by depressions without outlets,
+associated with hillocks and short ridges comparable in dimensions to
+the depressions. Both elevations and depressions are, as a rule, more
+abrupt than in the ground moraine. In the depressions there are many
+marshes, bogs, ponds and small lakes. The shapes and the abundance of
+round and roundish hills have locally given rise to such names as "The
+Knobs," "Short Hills," etc. Elsewhere the moraine has been named the
+"Kettle Range" from the number of kettle-like depressions in its
+surface. It is to be kept in mind that it is the association of the
+"knobs" and "kettles," rather than either feature alone, which is the
+distinctive mark of terminal moraine topography.
+
+[Illustration: Fig. 37.--Sketch of terminal moraine topography, on the
+quartzite ridge east of Devil's lake. (Matz.)]
+
+The manner in which the topography of terminal moraines was developed is
+worthy of note. In the first place, the various parts of the ice margin
+carried unequal amounts of debris. This alone would have caused the
+moraine of any region to have been of unequal height and width at
+different points. In the second place, the margin of the ice, while
+maintaining the same _general_ position during the making of a moraine,
+was yet subject to many minor oscillations. It doubtless receded to some
+slight extent because of increased melting during the summer, to advance
+again during the winter. In its recession, the ice margin probably did
+not remain exactly parallel to its former position. If some parts
+receded more than others, the details of the line of its margin may have
+been much changed during a temporary retreat. When the ice again
+advanced, its margin may have again changed its form in some slight
+measure, so as to be parallel neither with its former advanced position,
+nor with its position after its temporary retreat. With each successive
+oscillation of the edge, the details of the margin may have altered, and
+at each stage the marginal deposits corresponded with the edge. There
+might even be considerable changes in the edge of the ice without any
+general recession or advance, as existing glaciers show.
+
+It was probably true of the margin of the American ice sheet, as of
+existing glaciers, that there were periods of years when the edge of the
+ice receded, followed by like periods when it remained stationary or
+nearly so, and these in turn followed by periods of advance. During any
+advance, the deposits made during the period of recession would be
+overridden and disturbed or destroyed.
+
+If the ice were to retreat and advance repeatedly during a considerable
+period of time, always within narrow limits, and if during this
+oscillation the details of its margin were frequently changing, the
+result would be a complex or "tangle" of minor morainic ridges of
+variable heights and widths. Between and among the minor ridges there
+would be depressions of various sizes and shapes. Thus, it is conceived,
+many of the peculiar hillocks and hollows which characterize terminal
+moraines may have arisen.
+
+Some of the depressions probably arose in another way. When the edge of
+the ice retreated, considerable detached masses of ice might be left
+beyond the main body. This might be buried by gravel and sand washed out
+from the moraine. On melting, the former sites of such blocks of ice
+would be marked by "kettles." In the marginal accumulations of drift as
+first deposited, considerable quantities of ice were doubtless left.
+When this melted, the drift settled and the unequal settling may have
+given rise to some of the topographic irregularities of the drift.
+
+_The terminal moraine about Devil's lake._--On the lower lands, the
+terminal moraine of the Devil's lake region has the features
+characteristic of terminal moraines in general. It is a belt of thick
+drift varying in width from half a mile or less to three-quarters of a
+mile or more. Its surface is marked by numerous hills and short ridges,
+with intervening depressions or "kettles." Some of the depressions among
+the hills contain water, making ponds or marshes, though the rather
+loose texture of the drift of this region is not favorable to the
+retention of water. The moraine belt, as a whole, is higher than the
+land on either side. It is therefore somewhat ridge-like, and the small,
+short hills and ridges which mark its surface, are but constituent parts
+of the larger, broader ridge.
+
+Approached from the west, that is from the driftless side, the moraine
+on the lower lands is a somewhat prominent topographic feature, often
+appearing as a ridge thirty, forty or even fifty feet in height.
+Approached from the opposite direction, that is, from the ground
+moraine, it is notably less prominent, and its inner limit wherever
+located, is more or less arbitrary.
+
+[Illustration: Fig. 38.--Cut through the terminal moraine just east of
+Kirkland, partially diagrammatic.]
+
+A deep, fresh railway cut in the moraine southeast of Devil's lake
+illustrates its complexity of structure, a complexity which is probably
+no greater than that at many other points where exposures are not seen.
+The section is represented in Fig. 38. The stratified sand to the right
+retains even the ripple-marks which were developed when it was
+deposited. To the left, at the same level, there is a body of _till_
+(unstratified drift), over which is a bed of stoneless and apparently
+structureless clay. In a depression just above the clay with till both
+to the right and left, is a body of loam which possesses the
+characteristics of normal loess. It also contains calcareous
+concretions, though no shells have been found. This occurrence of loess
+is the more noteworthy, since loess is rarely found in association with
+drift of the last glacial epoch.[7]
+
+    [7] An account of loess in connection with the drift of the
+    last glacial epoch is given in the _Journal of Geology_, Vol.
+    IV, pp. 929-987. For a general account of loess, see Sixth
+    Annual Report of U.S. Geological Survey.
+
+_The moraine on the main quartzite range._--In tracing the moraine over
+the greater quartzite range, it is found to possess a unique feature in
+the form of a narrow but sharply defined ridge of drift, formed at the
+extreme margin of the ice at the time of its maximum advance. For fully
+eleven miles, with but one decided break, and two short stretches where
+its development is not strong, this unique marginal ridge separates the
+drift-covered country on the one hand, from the driftless area on the
+other. In its course the ridge lies now on slopes, and now on summits,
+but in both situations preserves its identity. Where it rests on a
+plain, or nearly plain surface, its width at base varies from six to
+fifteen rods, and its average height is from twenty to thirty feet. Its
+crest is narrow, often no more than a single rod. Where it lies on a
+slope, it is asymmetrical in cross section (see Fig. 39), the shorter
+slope having a vertical range of ten to thirty-five feet, and its longer
+a range of forty to one hundred feet. This asymmetrical form persists
+throughout all that portion of the ridge which lies on an inclined
+surface, the slope of which does not correspond with the direction of
+the moraine. Where it lies on a flat surface, or an inclined surface
+the slope of which corresponds in direction with the course of the ridge
+itself, its cross section is more nearly symmetrical (see Fig. 40). In
+all essential characteristics this marginal ridge corresponds with the
+_End-Moraene_ of the Germans.
+
+[Illustration: Fig. 39.--Diagrammatic cross-section of the marginal
+ridge as it occurs on the south slope of the Devil's Nose. The slope
+below, though glaciated, is nearly free from drift.]
+
+[Illustration: Fig. 40.--Diagrammatic cross-section of the marginal
+ridge as it appears when its base is not a sloping surface.]
+
+For the sake of bringing out some of its especially significant
+features, the ridge may be traced in detail, commencing on the south
+side of the west range. Where the moraine leaves the lowlands south of
+the Devil's nose, and begins the ascent of the prominence, the marginal
+ridge first appears at about the 940-foot contour (f, Plate XXXVII).
+Though at first its development is not strong, few rods have been passed
+before its crest is fifteen to twenty feet above the driftless area
+immediately to the north (see Fig. 39) and from forty to one hundred
+feet above its base to the south, down the slope. In general the ridge
+becomes more distinct with increasing elevation, and except for two or
+three narrow post-glacial erosion breaks, is continuous to the very
+summit at the end of the nose (g). The ridge in fact constitutes the
+uppermost forty or forty-five feet of the crest of the nose, which is
+the highest point of the west range within the area shown on the map.
+Throughout the whole of this course the marginal ridge lies on the south
+slope of the nose, and has the asymmetrical cross section shown in Fig.
+39. Above (north of) the ridge at most points not a bowlder of drift
+occurs. So sharply is its outer (north) margin defined, that at many
+points it is possible to locate it within the space of less than a yard.
+
+At the crest of the nose (g) the marginal ridge, without a break,
+swings northward, and in less than a quarter of a mile turns again to
+the west. Bearing to the north it presently reaches (at h) the edge of
+the precipitous bluff, bordering the great valley at the south end of
+the lake. Between the two arms of the loop thus formed, the surface of
+the nose is so nearly level that it could have offered no notable
+opposition to the progress of the ice, and yet it failed to be covered
+by it.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVII.
+
+Topographic map (contour interval 100 feet) of a small area about
+Devil's lake, taken from the Baraboo sheet of the United States
+Geological Survey. Each contour line connects points of the same
+elevation, and the figures upon them give the heights above sea level.
+Where contour lines lie close together, they indicate steep slopes.]
+
+In the great valley between the nose and the east bluff, the marginal
+ridge does not appear. In the bottom of the valley the moraine takes on
+its normal form, and the slopes of the quartzite ridges on either hand
+are much too steep to allow any body of drift, or loose material of any
+sort, to lodge on them.
+
+Ascending the east bluff a little east of the point where the drift
+ridge drops off the west bluff, the ridge is again found (at i) in
+characteristic development. For some distance it is located at the edge
+of the precipitous south face of the bluff. Farther on it bears to the
+north, and soon crosses a col (j) in the ridge, building it up many
+feet above the level of the bed-rock. From this point eastward for about
+three miles the marginal ridge is clearly defined, the slopes about
+equal on either side, and the crest as nearly even as the topography of
+the underlying surface permits. The topographic relations in this part
+of the course are shown in Fig. 40.
+
+At k, this marginal ridge attains its maximum elevation, 1,620 feet.
+At this great elevation, the ridge turns sharply to the northwest at an
+angle of more than 90 deg.. Following this direction for little more than
+half a mile, it turns to the west. At some points in this vicinity the
+ridge assumes the normal morainic habit, but this is true for short
+distances only. Farther west, at l, it turns abruptly to the northeast
+and is sharply defined. It here loops about a narrow area less than
+sixty rods wide, and over half a mile in length, the sharpest loop in
+its whole course. The driftless tract enclosed by the arms of this loop
+is lower than the drift ridge on either hand. The ice on either side
+would need to have advanced no more than thirty rods to have covered the
+whole of it.
+
+From the minor loop just mentioned, the marginal ridge is continued
+westward, being well developed for about a mile and a half. At this
+point the moraine swings south to the north end of Devil's lake, loses
+the unique marginal ridge which has characterized its outer edge
+across the quartzite range for so many miles, and assumes the topography
+normal to terminal moraines. At no other point in the United States, so
+far as known to the writers, is there so sharply marked a marginal ridge
+associated with the terminal moraine, for so long a distance.
+
+From Plate II it will be seen that the moraine as a whole makes a
+great loop to the eastward in crossing the quartzite range. From the
+detailed description just given of the course of the marginal ridge, it
+will be seen that it has three distinct loops; one on the Devil's nose
+(west of g, Plate XXXVII); one on the main ridge (west of k)
+and a minor one on the north side of the last (southwest of m). The
+first and third are but minor irregularities on the sides of the great
+loop, the head of which is at k.
+
+The significant fact in connection with these irregularities in the
+margin of the moraine is that each loop stands in a definite relation to
+a prominence. The meaning of this relation is at once patent. The great
+quartzite range was a barrier to the advance of the ice. Acting as a
+wedge, it caused a re-entrant in the advancing margin of the glacier.
+The extent and position of the re-entrant is shown by the course of the
+moraine in Plate II. Thus the great loop in the moraine, the head of
+which is at k, Plate XXXVII, was caused by the quartzite range itself.
+
+The minor loops on the sides of the major are to be explained on the
+same principle. Northeast of the minor loop on the north side of the
+larger one (m) there are two considerable hills, reaching an elevation
+of nearly 1,500 feet. Though the ice advancing from the east-northeast
+overrode them, they must have acted like a wedge, to divide it into
+lobes. The ice which reached their summits had spent its energy in so
+doing, and was unable to move forward down the slope ahead, and the
+thicker bodies of ice which passed on either side of them, failed to
+unite in their lee (compare Figs. 34 and 35). The application of the
+same principle to the loop on the Devil's nose is evident.
+
+_Constitution of the marginal ridge._--The material in the marginal
+ridge, as seen where erosion has exposed it, is till, abnormal, if at
+all, only in the large percentage of widely transported bowlders which
+it contains. This is especially true of the surface, where in some
+places 90 per cent. of the large bowlders are of very distant origin,
+and that in spite of the fact that the ice which deposited them had just
+risen up over a steep slope of quartzite, which could easily have
+yielded abundant bowlders. In other places the proportion of foreign
+bowlders is small, no more than one in ten. In general, however,
+bowlders of distant origin predominate over those derived close at hand.
+
+_The slope of the upper surface of the ice at the margin._--The marginal
+ridge on the south slope of Devil's nose leads to an inference of
+especial interest. Its course lies along the south slope of the nose,
+from its summit on the east to its base on the west. Throughout this
+course the ridge marks with exactness the position of the edge of the
+ice at the time of its maximum advance, and its crest must therefore
+represent the slope of the upper surface of the ice at its margin.
+
+The western end of the ridge (f, Plate XXXVII) has an altitude of 940
+feet, and its eastern end (g) is just above the 1,500-foot contour.
+The distance from the one point to the other is one and three-fourths
+miles, and the difference in elevation, 560 feet. These figures show
+that the slope of the ice along the south face of this bluff was about
+320 feet per mile. This, so far as known, is the first determination of
+the slope of the edge of the continental ice sheet _at its extreme
+margin_. It is to be especially noted that these figures are for the
+extreme edge of the ice only. The angle of slope back from the edge was
+doubtless much less.
+
+
+                      _Stratified Drift._
+
+While it is true that glacier ice does not distinctly stratify the
+deposits which it makes, it is still true that a very large part of the
+drift for which the ice of the glacial period was directly or indirectly
+responsible is stratified. That this should be so is not strange when it
+is remembered that most of the ice was ultimately converted into running
+water, just as the glaciers of today are. The relatively small portion
+which disappeared by evaporation was probably more than counterbalanced,
+at least near the margin of the ice, by the rain which fell upon it.
+
+It cannot be considered an exaggeration, therefore, to say that the
+total amount of water which operated on the drift, first and last, was
+hardly less than the total amount of the ice itself. The drift deposited
+by the marginal part of the ice was affected during its deposition, not
+only by the water which arose from the melting of the ice which did the
+depositing, but by much water which arose from the melting of the ice
+far back from the margin. The general mobility of the water, as
+contrasted with ice, allowed it to concentrate its activities along
+those lines which favored its motion, so that different portions of the
+drift were not affected equally by the water of the melting ice.
+
+All in all it will be seen that the water must have been a very
+important factor in the deposition of the drift, especially near the
+margin of the ice. But the ice sheet had a marginal belt throughout its
+whole history, and water must have been active and effective along this
+belt, not only during the decadence of the ice sheet, but during its
+growth as well. It is further to be noted that any region of drift stood
+good chance of being operated upon by the water after the ice had
+departed from it, so that in regions over which topography directed
+drainage after the withdrawal of the ice, the water had the last chance
+at the drift, and modified it in such a way and to such an extent as
+circumstances permitted.
+
+_Its origin._--There are various ways in which stratified drift may
+arise in connection with glacier deposits. It may come into existence by
+the operation of water alone; or by the co-operation of ice and water.
+Where water alone was immediately responsible for the deposition of
+stratified drift, the water concerned may have owed its origin to the
+melting ice, or it may have existed independently of the ice in the form
+of lakes. When the source of the water was the melting ice, the water
+may have been running, when it was actively concerned in the deposition
+of stratified drift; or it may have been standing (glacial lakes and
+ponds), when it was passively concerned. When ice co-operated with water
+in the development of stratified drift the ice was generally a passive
+partner.
+
+_Glacial drainage._--The body of an ice sheet during any glacial period
+is probably melting more or less at some horizons all the time, and at
+all horizons some of the time. Most of the water which is produced at
+the surface during the summer sinks beneath it. Some of it may congeal
+before it sinks far, but much of it reaches the bottom of the ice
+without refreezing. It is probable that melting is much more nearly
+continuous in the body of a moving ice sheet than at its surface, and
+that some of the water thus produced sinks to the bottom of the ice
+without refreezing. At the base of the ice, so long as it is in
+movement, there is doubtless more or less melting, due both to friction
+and to the heat received by conduction from the earth below. Thus in the
+ice and under the ice there must have been more or less water in motion
+throughout essentially all the history of an ice sheet.
+
+If it be safe to base conclusions on the phenomena of existing glaciers,
+it may be assumed that the waters beneath the ice, and to a less extent
+the waters in the ice, organized themselves to a greater or less degree
+into streams. For longer or shorter distances these streams flowed in
+the ice or beneath it. Ultimately they escaped from its edge. The
+subglacial streams doubtless flowed, in part, in the valleys which
+affected the land surface beneath the ice, but they were probably not
+all in such positions.
+
+The courses of well-defined subglacial streams were tunnels. The bases
+of the tunnels were of rock or drift, while the sides and tops were of
+ice. It will be seen, therefore, that their courses need not have
+corresponded with the courses of the valleys beneath the ice. They may
+sometimes have followed lines more or less independent of topography,
+much as water may be forced over elevations in closed tubes. It is not
+to be inferred, however, that the subglacial streams were altogether
+independent of the sub-ice topography. The tunnels in which the water
+ran probably had too many leaks to allow the water to be forced up over
+great elevations. This, at least, must have been the case where the ice
+was thin or affected by crevasses. Under such circumstances the
+topography of the land surface must have been the controlling element
+in determining the course of the subglacial drainage.
+
+When the streams issued from beneath the ice the conditions of flow were
+more or less radically changed, and from their point of issue they
+followed the usual laws governing river flow. If the streams entered
+static water as they issued from the ice, and this was true where the
+ice edge reached the sea or a lake, the static water modified the
+results which the flowing waters would otherwise have produced.
+
+_Stages in the history of an ice sheet._--The history of an ice sheet
+which no longer exists involves at least two distinct stages. These are
+(1) the period of growth, and (2) the period of decadence. If the latter
+does not begin as soon as the former is complete, an intervening stage,
+representing the period of maximum ice extension, must be recognized. In
+the case of the ice sheets of the glacial period, each of these stages
+was probably more or less complex. The general period of growth of each
+ice sheet is believed to have been marked by temporary, but by more or
+less extensive intervals of decadence, while during the general period
+of decadence, it is probable that the ice was subject to temporary, but
+to more or less extensive intervals of recrudescence. For the sake of
+simplicity, the effects of these oscillations of the edge of the ice
+will be neglected at the outset, and the work of the water accompanying
+the two or three principal stages of an ice sheet's history will be
+outlined as if interruptions in the advance and in the retreat,
+respectively, had not occurred.
+
+As they now exist, the deposits of stratified drift made at the edge of
+the ice or beyond it during the period of its maximum extension present
+the simplest, and at the same time most sharply defined phenomena, and
+are therefore considered first.
+
+
+ _Deposits Made by Extraglacial Waters During the Maximum Extension of
+                           the Ice._
+
+The deposits made by the water at the time of the maximum extension of
+the ice and during its final retreat, were never disturbed by subsequent
+glacier action. So far as not destroyed by subsequent erosion, they
+still retain the form and structure which they had at the outset. Such
+drift deposits, because they lie at the surface, and because they are
+more or less distinct topographically as well as structurally, are
+better known than the stratified drift of other stages of an ice sheet's
+history. Of stratified drift made during the maximum extension of the
+ice, and during its final retreat, there are several types.
+
+_A. At the edge of ice, on land._--If the subglacial streams flowed
+under "head," the pressure was relieved when they escaped from the ice.
+With this relief, there was diminution of velocity. With the diminution
+of velocity, deposition of load would be likely to take place. Since
+these changes would be likely to occur at the immediate edge of the ice,
+one class of stratified drift deposits would be made in this position,
+in immediate contact with the edge of the ice, and their form would be
+influenced by it. At the stationary margin of an ice sheet, therefore,
+at the time of its maximum advance, ice and water must have co-operated
+to bring into existence considerable quantities of stratified drift.
+
+The edge of the ice was probably ragged, as the ends of glaciers are
+today, and as the waters issued from beneath it, they must frequently
+have left considerable quantities of such debris as they were carrying,
+against its irregular margin, and in its re-entrant angles and marginal
+crevasses. When the ice against which this debris was first lodged
+melted, the marginal accumulations of gravel and sand often assumed the
+form of kames. A typical kame is a hill, hillock, or less commonly a
+short ridge of stratified drift; but several or many are often
+associated, giving rise to groups and areas of _kames_. Kames are often
+associated with terminal moraines, a relation which emphasizes the fact
+of their marginal origin.
+
+So far as the superficial streams which flowed to the edge of the ice
+carried debris, this was subject to deposition as the streams descended
+from the ice. Such drift would tend to increase the body of marginal
+stratified drift from subglacial sources.
+
+Marginal accumulations of stratified drift, made by the co-operation of
+running water and ice, must have had their most extensive development,
+other things being equal, where the margin of the ice was longest in one
+position, and where the streams were heavily loaded. The deposits made
+by water at the edge of the ice differ from those of the next
+class--made beyond the edge of the ice--in that they were influenced in
+their disposition and present topography, by the presence of ice.
+
+In the Devil's lake region isolated and well-defined kames are not of
+common occurrence. There are, however, at many points hills which have
+something of a kame-like character. There is such a hill a mile
+southeast of the Court house at Baraboo, at the point marked p, Plate
+XXXVII. In this hill there are good exposures which show its structure.
+There are many hillocks of a general kame-like habit associated with the
+terminal moraine south of the main quartzite range, and north of the
+Wisconsin river. Many of them occur somewhat within the terminal moraine
+a few miles northwest of Merrimac.
+
+_B. Beyond the edge of the ice, on land._--As the waters escaping from
+the ice flowed farther, deposits of stratified drift were made quite
+beyond the edge of the ice. The forms assumed by such deposits are
+various, and depended on various conditions. Where the waters issuing
+from the edge of the ice found themselves concentrated in valleys, and
+where they possessed sufficient load, and not too great velocity, they
+aggraded the valleys through which they flowed, developing fluvial
+plains of gravel and sand, which often extended far beyond the ice. Such
+fluvial plains of gravel and sand constitute the _valley trains_ which
+extend beyond the unstratified glacial drift in many of the valleys of
+the United States. They are found especially in the valleys leading out
+from the stouter terminal moraines of late glacial age. From these
+moraines, the more extensive valley trains take their origin, thus
+emphasizing the fact that they are deposits made by water beyond a
+stationary ice margin. Valley trains have all the characteristics of
+alluvial plains built by rapid waters carrying heavy loads of detritus.
+Now and then their surfaces present slight variations from planeness,
+but they are minor. Like all plains of similar origin they decline
+gradually, and with diminishing gradient, down stream. They are of
+coarser material near their sources, and of finer material farther away.
+Valley trains constitute a distinct topographic as well as genetic type.
+
+A perfect example of a valley train does not occur within the region
+here discussed. There is such a train starting at the moraine where it
+crosses the Wisconsin river above Prairie du Sac, and extending down
+that valley to the Mississippi, but at its head this valley train is
+wide and has the appearance of an overwash plain, rather than a valley
+train. Farther from the moraine, however, it narrows, and assumes the
+normal characteristics of a valley train. It is the gravel and sand of
+this formation which underlies Sauk Prairie, and its topographic
+continuation to the westward.
+
+Where the subglacial streams did not follow subglacial valleys, they did
+not always find valleys when they issued from the ice. Under such
+circumstances, each heavily loaded stream coming out from beneath the
+ice must have tended to develop a plain of stratified material near its
+point of issue--a sort of alluvial fan. Where several such streams came
+out from beneath the ice near one another, their several plains, or
+fans, were likely to become continuous by lateral growth. Such border
+plains of stratified drift differ from valley trains particularly (1) in
+being much less elongate in the direction of drainage; (2) in being much
+more extended parallel to the margin of the ice; and (3) in not being
+confined to valleys. Such plains stood an especially good chance of
+development where the edge of the ice remained constant for a
+considerable period of time, for it was under such conditions that the
+issuing waters had opportunity to do much work. Thus arose the type of
+stratified drift variously known as _overwash plains_, _outwash plains_,
+_morainic plains_, and _morainic aprons_. These plains sometimes skirt
+the moraine for many miles at a stretch.
+
+Overwash plains may sometimes depart from planeness by taking on some
+measure of undulation, of the sag and swell (kame) type, especially near
+their moraine edges. The same is often true of the heads of valley
+trains. The heads of valley trains and the inner edges of overwash
+plains, it is to be noted, occupy the general position in which kames
+are likely to be formed, and the undulations which often affect these
+parts of the trains and plains, respectively, are probably to be
+attributed to the influence of the ice itself. Valley trains and
+overwash plains, therefore, at their upper ends and edges respectively,
+may take on some of the features of kames. Indeed, either may head in a
+kame area.
+
+Good examples of overwash or outwash plains may be seen at various
+points in the vicinity of Baraboo. The plain west of the moraine just
+south of the main quartzite ridge has been referred to under valley
+trains. In Sauk Prairie, however, its characteristics are those of an
+outwash plain, rather than those of a valley train.
+
+[Illustration: Fig. 41.--The morainic or outwash plain bordering the
+terminal moraine. The figure is diagrammatic, but represents, in cross
+section, the normal relation as seen south of the quartzite range at the
+east edge of Sauk Prairie, north of the Baraboo river and at some points
+between the South range and the Baraboo.]
+
+A good example of an outwash plain occurs southwest of Baraboo, flanking
+the moraine on the west (Fig. 41). Seen from the west, the moraine just
+north of the south quartzite range stands up as a conspicuous ridge
+twenty to forty feet above the morainic plain which abuts against it.
+Traced northward, the edge of the outwash plain, as it abuts against
+the moraine, becomes higher, and in Section 4, Township 11 N., Range 6
+E., the moraine edge of the plain reaches the crest of the moraine (Fig.
+42). From this point north to the Baraboo river the moraine scarcely
+rises above the edge of the outwash beyond.
+
+[Illustration: Fig. 42.--The outwash plain is built up to the crest of
+the moraine. The figure is diagrammatic, but this relation is seen at
+the point marked W, Plate II.]
+
+North of the Baraboo river the moraine is again distinct and the
+overwash plain to the west well developed much of the way from the
+Baraboo to Kilbourn City. A portion of it is known as Webster's Prairie.
+
+Locally, the outwash plains of this region have been much dissected by
+erosion since their deposition, and are now affected by many small
+valleys. In composition these plains are nearly everywhere gravel and
+sand, the coarser material being nearer the moraine. The loose material
+is in places covered by a layer of loam several feet deep, which greatly
+improves the character of the soil. This is especially true of Sauk
+Prairie, one of the richest agricultural tracts in the state.
+
+When the waters issuing from the edge of the ice were sluggish, whether
+they were in valleys or not, the materials which they carried and
+deposited were fine instead of coarse, giving rise to deposits of silt,
+or clay, instead of sand or gravel.
+
+At many points near the edge of the ice during its maximum stage of
+advance, there probably issued small quantities of water not in the form
+of well-defined streams, bearing small quantities of detritus. These
+small quantities of water, with their correspondingly small loads, were
+unable to develop considerable plains of stratified drift, but produced
+small patches instead. Such patches have received no special
+designation.
+
+In the deposition of stratified drift beyond the edge of the ice, the
+latter was concerned only in so far as its activity helped to supply the
+water with the necessary materials.
+
+_C. Deposits at and beyond the edge of the ice in standing water._--The
+waters which issued from the edge of the ice sometimes met a different
+fate. The ice in its advance often moved up river valleys. When at the
+time of its maximum extension, it filled the lower part of a valley,
+leaving the upper part free, drainage through the valley stood good
+chance of being blocked. Where this happened a marginal valley lake was
+formed. Such a lake was formed in the valley of the Baraboo when the
+edge of the ice lay where the moraine now is (Plate II). The waters
+which were held back by the ice dam, reinforced by the drainage from the
+ice itself, soon developed a lake above the point of obstruction. This
+extinct lake may be named Baraboo lake. In this lake deposits of
+laminated clay were made. They are now exposed in the brick yards west
+of Baraboo, and in occasional gullies and road cuts in the flat
+bordering the river.
+
+At the point marked s (Plate XXXVII) there was, in glacial
+times, a small lake having an origin somewhat different from that of
+Baraboo lake. The former site of the lake is now marked by
+a notable flat. Excavations in the flat show that it is made up of
+stratified clay, silt, sand and gravel, to the depth of many
+feet,--locally more than sixty. These lacustrine deposits are well
+exposed in the road cuts near the northwest corner of the flat, and in
+washes at some other points. Plate XXXVIII shows some of the silt and
+clay, the laminae of which are much distorted.
+
+_Deltas_ must have been formed where well-defined streams entered the
+lakes, and _subaqueous overwash plains_ where deltas became continuous
+by lateral growth. The accumulation of stratified drift along the
+ice-ward shores of such lakes must have been rapid, because of the
+abundant supply of detritus. These materials were probably shifted about
+more or less by waves and shore currents, and some of them may have been
+widely distributed. Out from the borders of such lakes, fine silts and
+clays must have been in process of deposition, at the same time that the
+coarse materials were being laid down nearer shore.
+
+[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
+PL. XXXVIII.
+
+Distorted laminae of silt and clay.]
+
+Good examples of deltas and subaqueous overwash plains do not appear to
+exist in the region, although conditions for their development seem to
+have been present. Thus in the lake which occupied the valley of the
+Baraboo, conditions would seem to have been ideal for the development of
+such features; that is, the overwash plains previously described should,
+theoretically, have been subaqueous overwash plains; but if this be
+their character, their distinctive marks have been destroyed by
+subsequent erosion.
+
+During the maximum extension of an ice sheet, therefore, there was
+chance for the development, at its edge or beyond it, of the following
+types of stratified drift: (1) kames and kame belts, at the edge of the
+ice; (2) fluvial plains or valley trains, in virtual contact with the
+ice at their heads; (3) border plains or overwash plains, in virtual
+contact with the ice at their upper edges; (4) ill-defined patches of
+stratified drift, coarse or fine near the ice; (5) subaqueous overwash
+plains and deltas, formed either in the sea or lakes at or near the edge
+of the ice; (6) lacustrine and marine deposits of other sorts, the
+materials for which were furnished by the waters arising from the ice.
+So far as this region is concerned, all the deposits made in standing
+water were made in lakes.
+
+_Deposits Made by Extraglacial Waters During the Retreat of the Ice._
+
+During the retreat of any ice sheet, disregarding oscillations of its
+edge, its margin withdrew step by step from the position of extreme
+advance to its center. When the process of dissolution was complete,
+each portion of the territory once covered by the ice, had at some stage
+in the dissolution, found itself in a marginal position. At all stages
+in its retreat the waters issuing from the edge of the ice were working
+in the manner already outlined in the preceding paragraphs. Two points
+of difference only need be especially noted. In the first place the
+deposits made by waters issuing from the retreating ice were laid down
+on territory which the ice had occupied, and their subjacent stratum was
+often glacial drift. So far as this was the case, the stratified drift
+was super-morainic, not extra-morainic. In the second place the edge of
+the ice in retreat did not give rise to such sharply marked formations
+as the edge of the ice which was stationary. The processes which had
+given rise to valley trains, overwash plains, kames, etc., while the ice
+edge was stationary, were still in operation, but the line or zone of
+their activity (the edge of the ice) was continually retreating, so that
+the foregoing types, more or less dependent on a stationary edge, were
+rarely well developed. As the ice withdrew, therefore, it allowed to be
+spread over the surface it had earlier occupied, many incipient valley
+trains, overwash plains, and kames, and a multitude of ill-defined
+patches of stratified drift, thick and thin, coarse and fine. Wherever
+the ice halted in its retreat, these various types stood chance of
+better development.
+
+Such deposits did not cover all the surface discovered by the ice in its
+retreat, since the issuing waters, thanks to their great mobility,
+concentrated their activities along those lines which favored their
+motion. Nevertheless the aggregate area of the deposits made by water
+outside the ice as it retreated, was great.
+
+It is to be noted that it was not streams alone which were operative as
+the ice retreated. As its edge withdrew, lakes and ponds were
+continually being drained, as their outlets, hitherto choked by the ice,
+were opened, while others were coming into existence as the depressions
+in the surface just freed from ice, filled with water. Lacustrine
+deposits at the edge of the ice during its retreat were in all essential
+respects identical with those made in similar situations during its
+maximum extension.
+
+Disregarding oscillations of the ice edge at these stages, the deposits
+made by extraglacial waters during the maximum extension of an ice
+sheet, and during its retreat, were always left at the surface, so far
+as the work of that ice sheet was concerned. The stratified drift laid
+down by extraglacial waters in these stages of the last ice sheet which
+affected any region of our continent still remain at the surface in much
+the condition in which they were deposited, except for the erosion they
+have since suffered. It is because of their position at the surface that
+the deposits referable to these stages of the last ice sheet of any
+given region have received most attention and are therefore most
+familiar.
+
+
+ _Deposits Made by Extraglacial Waters During the Advance of the Ice._
+
+During the advance of an ice sheet, if its edge forged steadily forward,
+the waters issuing from it, and flowing beyond, were effecting similar
+results. They were starting valley trains, overwash plains, kames, and
+small ill-defined patches of stratified drift which the ice did not
+allow them to complete before pushing over them, thus moving forward the
+zone of activity of extraglacial waters. Unlike the deposits made by the
+waters of the retreating ice, those made by the waters of the advancing
+stage were laid down on territory which had not been glaciated, or at
+least not by the ice sheet concerned in their deposition. If the ice
+halted in its advance, there was at such time and place opportunity for
+the better development of extraglacial stratified drift.
+
+Lakes as well as streams were concerned in the making of stratified beds
+of drift, during the advance of the ice. Marginal lakes were obliterated
+by having their basins filled with the advancing ice, which displaced
+the water. But new ones were formed, on the whole, as rapidly as their
+predecessors became extinct, so that lacustrine deposits were making at
+intervals along the margin of the advancing ice.
+
+Deposits made in advance of a growing ice sheet, by waters issuing from
+it, were subsequently overridden by the ice, to the limit of its
+advance, and in the process, suffered destruction, modification, or
+burial, in whole or in part, so that now they rarely appear at the
+surface.
+
+
+              _Deposits Made by Subglacial Streams._
+
+Before their issuance from beneath the ice, subglacial waters were not
+idle. Their activity was sometimes erosive, and at such times stratified
+deposits were not made. But where the sub-glacial streams found
+themselves overloaded, as seems frequently to have been the case, they
+made deposits along their lines of flow. Where such waters were not
+confined to definite channels, their deposits probably took on the form
+of irregular patches of silt, sand, or gravel; but where depositing
+streams were confined to definite channels, their deposits were
+correspondingly concentrated.
+
+When subglacial streams were confined to definite channels, the same may
+have been constant in position, or may have shifted more or less from
+side to side. Where the latter happened there was a tendency to the
+development of a belt or strip of stratified drift having a width equal
+to the extent of the lateral migrations of the under-ice stream. Where
+the channel of the subglacial stream remained fixed in position, the
+deposition was more concentrated, and the bed was built up. If the
+stream held its course for a long period of time, the measure of
+building may have been considerable. In so far as these channel deposits
+were made near the edge of the ice, during the time of its maximum
+extension or retreat, they were likely to remain undisturbed during its
+melting. The aggraded channels then came to stand out as ridges. These
+ridges of gravel and sand are known as osars or eskers. It is not to
+be inferred that eskers never originated in other ways, but it seems
+clear that this is one method, and probably the principal one, by which
+they came into existence. Eskers early attracted attention, partly
+because they are relatively rare, and partly because they are often
+rather striking topographic features. The essential conditions,
+therefore, for their formations, so far as they are the product of
+subglacial drainage, are (1) the confining of the subglacial streams to
+definite channels; and (2) a sufficient supply of detritus. One esker
+only has been found in the region under consideration. It is located at
+the point marked j, Plate II, seven and one-half miles northeast of
+Merrimac and one and one-half miles south of Alloa (g, Plate II). The
+esker is fully a quarter of a mile long, about thirty feet high, and
+four rods wide at its base.
+
+Subglacial deposits of stratified drift were sometimes made on
+unstratified drift (till) already deposited by the ice before the
+location of the stream, and sometimes on the rock surfaces on which no
+covering of glacier drift had been spread.
+
+It is to be kept in mind that subglacial drainage was operative during
+the advance of an ice sheet, during its maximum extension, and during
+its retreat, and that during all these stages it was effecting its
+appropriate results. It will be readily seen, however, that all deposits
+made by subglacial waters, were subject to modification or destruction
+or burial, through the agency of the ice, and that those made during the
+advance of the ice were less likely to escape than those made during its
+maximum extension or retreat.
+
+
+           RELATIONS OF STRATIFIED TO UNSTRATIFIED DRIFT.
+
+When it is remembered that extraglacial and subglacial waters were
+active at all stages of an ice sheet's history, giving rise, or tending
+to give rise to all the phases of stratified drift enumerated above;
+when it is remembered that the ice of several epochs affected much of
+the drift-covered country; and when it is remembered further that the
+edge of the ice both during advance and retreat was subject to
+oscillation, and that each advance was likely to bury the stratified
+drift last deposited, beneath unstratified, it will be seen that the
+stratified drift and the unstratified had abundant opportunity to be
+associated in all relationships and in all degrees of intimacy, and that
+the relations of the one class of drift to the other may come to be very
+complex.
+
+As a result of edge oscillation, it is evident that stratified drift may
+alternate with unstratified many times in a formation of drift
+deposited during a single ice epoch, and that two beds of till,
+separated by a bed of stratified drift, do not necessarily represent two
+distinct glacial epochs. The extent of individual beds of stratified
+drift, either beneath the till or inter-bedded with it, may not be
+great, though their aggregate area and their aggregate volume is very
+considerable. It is to be borne in mind that the ice, in many places,
+doubtless destroyed all the stratified drift deposited in advance on the
+territory which it occupied later, and that in others it may have left
+only patches of once extensive sheets. This may help to explain why it
+so frequently happens that a section of drift at one point shows many
+layers of stratified drift, while another section close by, of equal
+depth, and in similar relationships, shows no stratified material
+whatsoever.
+
+Such deposits as were made by superglacial streams during the advance of
+the ice must likewise have been delivered on the land surface, but would
+have been subsequently destroyed or buried, becoming in the latter case,
+submorainic. This would be likely to be the fate of all such
+superglacial gravels as reached the edge of the ice up to the time of
+its maximum advance.
+
+Streams descending from the surface of the ice into crevasses also must
+have carried down sand and gravel where such materials existed on the
+ice. These deposits may have been made on the rock which underlies the
+drift, or they may have been made on stratified or unstratified drift
+already deposited. In either case they were liable to be covered by
+till, thus reaching an inter-till or sub-till position.
+
+Englacial streams probably do little depositing, but it is altogether
+conceivable that they might accumulate such trivial pockets of sand and
+gravel as are found not infrequently in the midst of till. The
+inter-till position would be the result of subsequent burial after the
+stratified material reached a resting place.
+
+Complexity of relations.--From the foregoing it becomes clear that
+there are diverse ways by which stratified drift, arising in connection
+with an ice sheet, may come to be interbedded with till, when due
+recognition is made of all the halts and oscillations to which the edge
+of a continental glacier may have been subject during both its advance
+and retreat.
+
+
+     CLASSIFICATION OF STRATIFIED DRIFT ON THE BASIS OF POSITION.
+
+In general the conditions and relations which theoretically should
+prevail are those which are actually found.
+
+On the basis of position stratified drift deposits may be classified as
+follows:
+
+1. Extraglacial deposits, made by the waters of any glacial epoch if
+they flowed and deposited beyond the farthest limit of the ice.
+
+2. Supermorainic deposits, made chiefly during the final retreat of
+the ice from the locality where they occur, but sometimes by
+extraglacial streams or lakes of a much later time. Locally too,
+stratified deposits of an early stage of a glacial epoch, lying on till,
+may have failed to be buried by the subsequent passage of the ice over
+them, and so remain at the surface. In origin, supermorainic deposits
+were for the most part extraglacial (including marginal), so far as the
+ice sheet calling them into existence was concerned. Less commonly they
+were subglacial, and failed to be covered, and less commonly still
+superglacial.
+
+3. The submorainic (basal) deposits were made chiefly by extraglacial
+waters in advance of the first ice which affected the region where they
+occur. They were subsequently overridden by the ice and buried by its
+deposits. Submorainic deposits, however, may have arisen in other ways.
+Subglacial waters may have made deposits of stratified drift on surfaces
+which had been covered by ice, but not by till, and such deposits may
+have been subsequently buried. The retreat of an ice sheet may have left
+rock surfaces free from till covering, on which the marginal waters of
+the ice may have made deposits of stratified drift. These may have been
+subsequently covered by till during a re-advance of the ice in the same
+epoch or in a succeeding one. Still again, the till left by one ice
+sheet may have been exposed to erosion to such an extent as to have been
+completely worn away before the next ice advance, so that stratified
+deposits connected with a second or later advance may have been made on
+a driftless surface, and subsequently buried.
+
+4. Intermorainic stratified drift may have originated at the outset in
+all the ways in which supermorainic drift may originate. It may have
+become intermorainic by being buried in any one of the various ways in
+which the stratified drift may become submorainic.
+
+
+
+
+            CHANGES IN DRAINAGE EFFECTED BY THE ICE.
+
+
+                    _While the Ice Was on._
+
+As the continental ice sheet invaded a region, the valleys were filled
+and drainage was thereby seriously disturbed. Different streams were
+affected in different ways. Where the entire basin of a stream was
+covered by ice, the streams of that basin were, for the time being,
+obliterated. Where the valley of a stream was partially filled with ice,
+the valley depression was only partially obliterated, and the remaining
+portion became the scene of various activities. Where the ice covered
+the lower course of a stream but not the upper, the ice blocked the
+drainage, giving rise to a lake. Where the ice covered the upper course
+of a stream, but not its lower, the lower portion was flooded, and
+though the river held its position, it assumed a new phase of activity.
+Streams issuing from the ice usually carry great quantities of gravel
+and sand, and make deposits along their lower courses. Long continued
+glacial drainage usually results in a large measure of aggradation. This
+was true of the streams of the glacial period.
+
+Where a stream flowed parallel or approximately parallel to the edge of
+the advancing ice it was sometimes shifted in the direction in which the
+ice was moving, keeping parallel to the front of the ice. All of these
+classes of changes took place in this region.
+
+_Wisconsin lake._--Reference has already been made to certain lakes
+which existed in the region when the ice was there. The largest of these
+lakes was that which resulted from the blocking of the Wisconsin river.
+The ice crossed its present course at Kilbourn City, and its edge lay to
+the west of the river from that point to Prairie du Sac (see Plate I).
+The waters from the area now draining into the Wisconsin must either
+have found an avenue of escape beneath the ice, or have accumulated in a
+lake west of the edge of the ice. There is reason to believe that the
+latter was what happened, and that a great lake covered much of the low
+land west of the Wisconsin river above and below Kilbourn City. The
+extensive gravel beds on the north flank of the quartzite bluff at
+Necedah, and the water-worn pebbles of local origin on the slope of
+Petenwell peak (Plate XXXII), as well as the gravels at other points,
+are presumably the work of that lake. The waters in this lake, as in
+that in the Baraboo valley, probably rose until the lowest point in the
+rim of the basin was reached, and there they had their outlet. The
+position of this outlet has not been definitely determined, but it has
+been thought to be over the divide of the Black river.[8] It is
+possible, so far as now known, that this lake was connected with that of
+the Baraboo valley. Until topographic maps of this region are made, the
+connections will not be easily determined.
+
+    [8] Chamberlin: Geology of Wisconsin, Vol. 1.
+
+Even after the ice had retreated past the Wisconsin, opening up the
+present line of drainage, the lakes did not disappear at once, for the
+ice had left considerable deposits of drift in the Wisconsin valley.
+Thus at F, Plates II and XXXVII, and perhaps at other points, the
+Wisconsin has made cuts of considerable depth in the drift. Were these
+cuts filled, as they must have been when the ice melted, the drainage
+would be ponded, the waters standing at the level of the dam. This drift
+obstruction at F would therefore have prolonged the history of the lake
+which had come into existence when the ice blocked the drainage of the
+Wisconsin. As the drift of the valley was removed the level of the lake
+sank and finally disappeared.
+
+_Baraboo lake._--Another lake which existed in this region when the ice
+was here, occupied the valley of the Baraboo and its tributaries when
+the ice blocked the valley at Baraboo. This lake occupied not only the
+valley of the Baraboo, but extended up the lower course of every
+tributary, presumably rising until it found the lowest point in the rim
+of the drainage basin. The location of this point, and therefore the
+height of the lake when at its maximum, are not certainly known, though
+meager data on this point have been collected. At a point three miles
+southeast of Ablemans on the surface of a sandstone slope, water-worn
+gravel occurs, the pebbles of which were derived from the local rock. On
+the slope below the gravel, the surface is covered with loam which has a
+suggestion of stratification, while above it, the soil and subsoil
+appear to be the product of local rock decomposition. This water-worn
+gravel of local origin on a steep slope facing the valley, probably
+represents the work of the waves of this lake, perhaps when it stood at
+its maximum height. This gravel is about 125 feet (aneroid measurement)
+above the Baraboo river to the north.
+
+Further evidence of a shore line has been found at the point marked T,
+Plate II. At this place water-worn gravel of the local rock occurs in
+much the same relationship as that already mentioned, and at the same
+elevation above the Baraboo river. At a point two and one-half miles
+southwest of Ablemans there is local water-worn gravel, with which is
+mingled glacial material (pieces of porphyry and diabase) which could
+have reached this point only by being carried thither by floating ice
+from the glacier. The level of this mixed local and glacial material is
+(according to aneroid measurement) approximately the same as that of the
+other localities.
+
+When the ice melted, an outlet was opened _via_ the Lower narrows, and
+the water of the lake drained off to the Wisconsin by this route. Had
+the ice left no drift, the lake would have been promptly drained when
+the ice melted; but the lake did not entirely disappear immediately
+after the ice retreated, for the drift which the ice left obstructed
+drainage to the east. The moraine, however, was not so high as the
+outlet of the lake while the ice was on, so that, as the ice retreated,
+the water flowed over the moraine to the east, and drew down the level
+of the lake to the level of the lowest point in the moraine. The
+postglacial cut through the moraine is about ninety feet deep.
+
+Besides being obstructed where crossed by the terminal moraine, the
+valley of the Baraboo was clogged to a less extent by drift deposits
+between the moraine and the Lower narrows. At one or two places near the
+City of Baraboo, such obstructions, now removed, appear to have existed.
+Just above the Lower narrows (c, Plate XXXVII) there is positive
+evidence that the valley was choked with drift. Here in subsequent time,
+the river has cut through the drift-filling of the preglacial valley,
+developing a passage about twenty rods wide and thirty-five feet deep.
+If this passage were filled with drift, reproducing the surface left by
+the ice, the broad valley above it would be flooded, producing a shallow
+lake.
+
+The retreat of the ice therefore left two well defined drift dams in the
+valley, one low one just above the Lower narrows, and a higher one, the
+moraine dam, just west of Baraboo. Disregarding the influence of the
+ice, and considering the Baraboo valley only, these two dams would have
+given rise to two lakes, the upper one behind the higher dam being
+deeper and broader, and covering a much larger area; the lower one
+behind the lower dam, being both small and shallow.
+
+Up to the time that the ice retreated past the Lower narrows, the waters
+of the upper and lower lakes were united, held up to a common level by
+the ice which blocked this pass. After the ice retreated past the Lower
+narrows, the level of the Baraboo lake did not sink promptly, for not
+until the ice had retreated past the site of the Wisconsin was the
+present drainage established. Meantime the waters of the Baraboo lake
+joined those of Wisconsin lake through the Lower narrows. If
+the lakes had been before connected at some point farther west, this
+connection through the narrows would not have changed the level of
+either. If they were not before connected, and if the Wisconsin lake was
+lower than the Baraboo, this connection would have drawn down the level
+of the latter.
+
+Since the drainage from the Baraboo went to the Wisconsin, the Baraboo
+lake was not at first lowered below the level of the highest obstruction
+in the valley of the Wisconsin even after the ice had retreated beyond
+that stream. As the drift obstructions of the Wisconsin valley were
+lowered, the levels of all the lakes above were correspondingly brought
+down. When the level of the waters in these lakes was brought down to
+the level of the moraine dam above Baraboo, the one Baraboo lake of
+earlier times became two. The level of the upper of these two lakes was
+determined by the moraine above Baraboo, that of the lower by the
+highest obstruction below the moraine in either the Baraboo or Wisconsin
+valley. The drift obstructions in the Baraboo valley were probably
+removed about as fast as those in the Wisconsin, and since the
+obstructions were of drift, and the streams strong, the removal of the
+dams was probably rapid. Both the upper and lower Baraboo lakes, as well
+as the Wisconsin, had probably been reduced to small proportions, if not
+been completely drained, before the glacial period was at an end.
+
+_Devil's lake in glacial times._--While the ice edge was stationary in
+its position of maximum advance, its position on the north side of the
+main quartzite range was just north of Devil's lake (Plate XXXVII). The
+high ridge of drift a few rods north of the shore is a well defined
+moraine, and is here more clearly marked than farther east or west,
+because it stands between lower lands on either side, instead of being
+banked against the quartzite ridge. North of the lake it rises about 75
+feet above the water. When the ice edge lay in this position on the
+north side of the range, its front between the East bluff and the
+Devil's nose lay a half mile or so from the south end of the lake. In
+this position also there is a well defined moraine.
+
+While the ice was at its maximum stand, it rose above these moraine
+ridges at either end of the lake. Between the ice at these two points
+there was then a notable basin, comparable to that of the present lake
+except that the barriers to the north and southeast were higher than
+now. The melting of the ice supplied abundant water, and the lake rose
+above its present level. The height which it attained is not known, but
+it is known to have risen at least 90 feet above its present level. This
+is indicated by the presence of a few drift bowlders on the West bluff
+of the lake at this height. They represent the work of a berg or bergs
+which at some stage floated out into the lake with bowlders attached.
+Bowlders dropped by bergs might be dropped at any level lower than the
+highest stand of the lake.
+
+_Other lakes._--Another glacial lake on the East quartzite bluff has
+already been referred to. Like the Devil's lake in glacial
+time, its basin was an enclosure between the ice on the one hand, and
+the quartzite ridge on the other. The location of this lake is shown on
+Plate XXXVII (s). Here the edge of the ice, as shown by the position
+of the moraine, was affected by a re-entrant curve, the two ends of
+which rested against the quartzite ridge. Between the ice on the one
+hand and the quartzite ridge on the other, a small lake was formed. Its
+position is marked by a notable flat.
+
+With the exception of the north side, and a narrow opening at the
+northwest corner, the flat is surrounded by high lands. When the ice
+occupied the region, its edge held the position shown by the line
+marking the limit of its advance, and constituted an ice barrier to the
+north.[9] The area of the flat was, therefore, almost shut in, the only
+outlet being a narrow one at t, Plate XXXVII. If the filling of
+stratified drift which underlies the flat were removed, the bottom of
+the area would be much lower than at present, and much lower than the
+outlet at t. It is therefore evident that when the ice had taken its
+position along the north side of the flat, an enclosed basin must have
+existed, properly situated for receiving and holding water. Since this
+lake had but a short life and became extinct before the ice retreated,
+its history is here given.
+
+    [9] The moraine line on the map represents the crest of the
+    marginal ridge rather than its outer limit, which is slightly
+    nearer the lake margin. Stratified drift of the nature of
+    overwash also intervenes at points between the moraine and
+    the lake border.
+
+At first the lake had no outlet and the water rose to the level of the
+lowest point (t) in the rim of the basin, and thence overflowed to the
+west. Meanwhile the sediments borne in by the glacial drainage were
+being deposited in the lake in the form of a subaqueous overwash plain,
+the coarser parts being left near the shore, while the finer were
+carried further out. Continued drainage from the ice continued to bring
+sediment into the lake, and the subaqueous overwash plain extended its
+delta-like front farther and farther into the lake, until its basin was
+completely filled. With the filling of the basin the lake became
+extinct. The later drainage from the ice followed the line of the
+outlet, the level of which corresponds with the level of the filled lake
+basin. This little extinct lake is of interest as an example of a
+glacial lake which became extinct by having its basin filled during
+glacial times, by sediments washed out from the ice.
+
+Near the northwest corner of this flat, an exposure in the sediments of
+the old lake bed shows the curiously contorted layers of sand, silt, and
+clay represented in Plate XXXVIII. The layers shown in the
+figure are but a few feet below the level of the flat which marks the
+site of the lake. It will be seen that the contorted layers are between
+two series of horizontal ones. The material throughout the section is
+made up of fine-grained sands and clays, well assorted. That these
+particular layers should have been so much disturbed, while those below
+and above remained horizontal, is strange enough. The grounding of an
+iceberg on the surface before the overlying layers were deposited, the
+action of lake ice, or the effect of expansion and contraction due to
+freezing and thawing, may have been responsible for the singular
+phenomenon. Contorted laminae are rather characteristic of the deposits
+of stratified drift.
+
+
+                _After the Ice Had Disappeared._
+
+As has already been indicated, the irregular deposition of
+glacial drift gave rise to many depressions without outlets in which
+surface waters collected after the ice had disappeared, forming ponds or
+lakes. So abundant are lakes and ponds and marshes in recently glaciated
+regions and so rare elsewhere, that they constitute one of the more
+easily recognized characteristics of a glaciated region.
+
+After the ice had melted, the mantle of drift which it left was
+sometimes so disposed as to completely obliterate preglacial valleys.
+More commonly it filled preglacial valleys at certain points only. In
+still other cases a valley was not filled completely at any point,
+though partially at many. In this last case, the partial fillings at
+various points constituted dams above which drainage was ponded, making
+lakes. If the dams were not high enough to throw the drainage out of the
+valley, the lakes would have their outlets over them. The drift dam
+being unconsolidated would be quickly cut down by the outflowing water,
+and the lake level lowered. When the dam was removed or cut to its base,
+the lake disappeared and drainage followed its preglacial course.
+
+In case the valley was completely filled, or completely filled at
+points, the case was very different. The drainage on the drift surface
+was established with reference to the topography which obtained when the
+ice departed, and not with reference to the preglacial valleys. Wherever
+the preglacial valleys were completely filled, the postglacial drainage
+followed lines which were altogether independent of them. When
+preglacial valleys were filled by the drift in spots only, the
+postglacial streams followed them where they were not filled, only to
+leave them where the blocking occurred. In the former case the present
+drainage is through valleys which are preglacial in some places, and
+postglacial in others.
+
+Thus the drainage changes effected by the drift after the ice was gone,
+concerned both lakes and rivers. In this region there are several
+illustrations of these changes.
+
+_Lakes._--The lake basins of drift-covered regions are of various types.
+Some of them are altogether in drift, some partly in drift and partly in
+rock, and some wholly in rock. Basins in the drift were likely to be
+developed whenever heavy deposits surrounded thin ones. They are
+especially common in the depressions of terminal moraines.
+
+Another class of lake basins occurs in valleys, the basins being partly
+rock and partly drift. If a thick deposit of drift be made at one point
+in a valley, while above there is little or none, the thick deposit will
+form a dam, above which waters may accumulate, forming a pond or lake.
+Again, a ridge of drift may be deposited in the form of a curve with its
+ends against a rock-ridge, thus giving rise to a basin.
+
+In the course of time, the lakes and ponds in the depressions made or
+occasioned by the drift will be destroyed by drainage. Remembering how
+valleys develop it is readily understood that the heads of the
+valleys will sooner or later find the lakes, and drain them if their
+bottoms be not too low.
+
+Drainage is hostile to lakes in another way. Every stream which flows
+into a lake brings in more or less sediment. In the standing water this
+sediment is deposited, thus tending to fill the lake basin. Both by
+filling their basins and by lowering their outlets, rivers tend to the
+destruction of lakes, and given time enough, they will accomplish this
+result. In view of this double hostility of streams, it is not too much
+to say that "rivers are the mortal enemies of lakes."
+
+The destruction of lakes by streams is commonly a gradual process, and
+so it comes about that the abundance and the condition of the undrained
+areas in a drift-covered region is in some sense an index of the length
+of time, reckoned in terms of erosion, which has elapsed since the drift
+was deposited.
+
+In this region there were few lakes which lasted long after the ice
+disappeared. The basins of the Baraboo and Wisconsin lakes were
+partly of ice, and so soon as the ice disappeared, the basins were so
+nearly destroyed, and the drift dams that remained so easily eroded,
+that the lakes had but a brief history,--a history that was glacial,
+rather than postglacial.
+
+The history of the little lake on the East quartzite bluff as
+already pointed out, came to an end while the ice was still present.
+
+The beds of at least two other extinct ponds or small lakes above the
+level of the Baraboo are known. These are at v and w, Plate XXXVII.
+They owed their origin to depressions in the drift, but the outflowing
+waters have lowered their outlets sufficiently to bring them to the
+condition of marshes. Both were small in area and neither was deep.
+
+_Existing lakes._--Relatively few lakes now remain in this immediate
+region, though they are common in most of the country covered by the ice
+sheet which overspread this region. Devil's lake only is well known. The
+lake which stood in this position while the ice was on, has already been
+referred to. After the ice had melted away, the drift which it
+had deposited still left an enclosure suitable for holding water. The
+history of this basin calls for special mention.
+
+At the north end of the lake, and again in the capacious valley leading
+east from its south end, there are massive terminal moraines. Followed
+southward, this valley though blocked by the moraine a half mile below
+the lake, leads off towards the Wisconsin river, and is probably the
+course of a large preglacial stream. Beyond the moraine, this valley is
+occupied by a small tributary to the Wisconsin which heads at the
+moraine. To the north of the lake, the head of a tributary of the
+Baraboo comes within eighty rods of the lake, but again the terminal
+moraine intervenes. From data derived from wells it is known that the
+drift both at the north and south ends of the lake extends many feet
+below the level of its water, and at the north end, the base of the
+drift is known to be at least fifty feet below the level of the bottom
+of the lake. The draining of Devil's lake to the Baraboo river is
+therefore prevented only by the drift dam at its northern end. It is
+nearly certain also, that, were the moraine dam at the south end of the
+lake removed, all the water would flow out to the Wisconsin, though the
+data for the demonstration of this conclusion are not to be had, as
+already stated.
+
+There can be no doubt that the gorge between the East and West bluffs
+was originally the work of a pre-Cambrian stream, though the depth of
+the pre-Cambrian valley may not have been so great as that of the
+present. Later, the valley, so far as then excavated, was filled with
+the Cambrian (Potsdam) sandstone, and re-excavated in post-Cambrian and
+preglacial time. Devil's lake then occupies an unfilled portion of an
+old river valley, isolated by great morainic dams from its surface
+continuations on either hand. Between the dams, water has accumulated
+and formed the lake.
+
+
+                     _Changes in Streams._
+
+In almost every region covered by the ice, the streams which established
+themselves after its departure follow more or less anomalous courses.
+This region is no exception. Illustrations of changes which the
+deposition of the drift effected have already been given in one
+connection or another in this report.
+
+_Skillett creek._--An illustration of the sort of change which drift
+effects is furnished by Skillett creek, a small stream tributary to the
+Baraboo, southwest of the city of that name. For some distance from its
+head (a to b, Fig. 43) its course is through a capacious preglacial
+valley. The lower part of this valley was filled with the water-laid
+drift of the overwash plain. On reaching the overwash plain the creek
+therefore shifted its course so as to follow the border of that plain,
+and along this route, irrespective of material, it has cut a new channel
+to the Baraboo. The postglacial portion of the valley (b to c) is
+everywhere narrow, and especially so where cut in sandstone.
+
+The course and relations of this stream suggest the following
+explanation: Before the ice came into the region, Skillett creek
+probably flowed in a general northeasterly direction to the Baraboo,
+through a valley comparable in size to the preglacial part of the
+present valley. As the ice advanced, the lower part of this valley was
+occupied by it, and the creek was compelled to seek a new course. The
+only course open to it was to the north, just west of the advancing ice,
+and, shifting westward as fast as the ice advanced, it abandoned
+
+altogether its former lower course. Drainage from the ice then carried
+out and deposited beyond the same, great quantities of gravel and sand,
+making the overwash plain. This forced the stream still farther west,
+until it finally reached its present position across a sandstone ridge
+or plain, much higher than its former course. Into this sandstone it has
+since cut a notable gorge, a good illustration of a postglacial valley.
+The series of changes shown by this creek is illustrative of the changes
+undergone by streams in similar situations and relations all along the
+margin of the ice.
+
+[Illustration: Fig. 43.--Skillett Creek, illustrating the points
+mentioned in the text.]
+
+The picturesque glens (Parfrey's and Dorward's) on the south face of the
+East bluff are the work of post-glacial streams. The preglacial valleys
+of this slope were obliterated by being filled during the glacial epoch.
+
+_The Wisconsin._--The preglacial course of the Wisconsin river is not
+known in detail, but it was certainly different from the course which
+the stream now follows. On Plate I the relations of the present stream
+to the moraine (and former ice-front) may be seen.[10] As the ice
+approached it from the east, the preglacial valley within the area here
+under consideration was affected first by the overwash from the moraine,
+and later by the ice itself, from the latitude of Kilbourn City to
+Prairie du Sac.
+
+    [10] The preglacial course was probably east of the present
+    in the vicinity of Kilbourn City.
+
+It has already been stated that the ice probably dammed the river, and
+that a lake was formed above Kilbourn City, reaching east to the ice and
+west over the lowland tributary to the river, the water rising till it
+found an outlet, perhaps down to the Black river valley.
+
+When the ice retreated, the old valley had been partly filled, and the
+lowest line of drainage did not everywhere correspond with it. Where the
+stream follows its old course, it flows through a wide capacious valley,
+but where it was displaced, it found a new course on the broad flat
+which bordered its preglacial course. Displacement of the stream
+occurred in the vicinity of Kilbourn City, and, forced to find a new
+line of flow west of its former course, the stream has cut a new channel
+in the sandstone. To this displacement of the river, and its subsequent
+cutting, we are indebted for the far-famed Dalles of the Wisconsin.
+But not all the present route of the river through the dalles has
+been followed throughout the entire postglacial history of the stream.
+In Fig. 44, the depression A, B, C, was formerly the course of the
+stream. The present course between D and E is therefore the youngest
+portion of the valley, and from its lesser width is known as the
+"narrows." During high water in the spring, the river still sends part
+of its waters southward by the older and longer route.
+
+The preglacial course of the Wisconsin south of the dalles has never
+been determined with certainty, but rational conjectures as to its
+position have been made.
+
+The great gap in the main quartzite range, a part of which is occupied
+by Devil's lake, was a narrows in a preglacial valley. The only streams
+in the region sufficiently large to be thought of as competent to
+produce such a gorge are the Baraboo and the Wisconsin. If the Baraboo
+was the stream which flowed through this gorge in preglacial time, the
+comparable narrows in the north quartzite range--the Lower narrows of
+the Baraboo--is to be accounted for. The stream which occupied one of
+these gorges probably occupied the other, for they are in every way
+comparable except in that one has been modified by glacial action, while
+the other has not.
+
+[Illustration: Fig. 44.--The Wisconsin valley near Kilbourn City.]
+
+The Baraboo river flows through a gorge--the Upper narrows--in the north
+quartzite range at Ablemans, nine miles west of Baraboo. This gorge is
+much narrower than either the Lower narrows or the Devil's lake gorge,
+suggesting the work of a lesser stream. It seems on the whole
+probable, as suggested by Irving,[11] that in preglacial time the
+Wisconsin river flowed south through what is now the Lower narrows of
+the Baraboo, thence through the Devil's lake gorge to its present valley
+to the south. If this be true, the Baraboo must at that time have joined
+this larger stream at some point east of the city of the same name.
+
+    [11] Irving. Geology of Wisconsin, Vol. II.
+
+
+                      _The Driftless Area._
+
+Reference has already been made to the fact that the western part of the
+area here described is driftless, and the line marking the limit of ice
+advance has been defined. Beyond this line, gravel and sand, carried
+beyond the ice by water, extends some distance to the west. But a large
+area in the southwestern part of the state is essentially free from
+drift, though it is crossed by two belts of valley drift (valley trains)
+along the Wisconsin and Mississippi rivers.
+
+The "driftless area" includes, besides the southwestern portion of
+Wisconsin, the adjoining corners of Minnesota, Iowa and Illinois. In the
+earlier epochs of the glacial period this area was completely surrounded
+by the ice, but in the last or Wisconsin epoch it was not surrounded,
+since the lobes did not come together south of it as in earlier times.
+(Compare Plate XXXIII and Fig. 36.)
+
+Various suggestions have been made in the attempt to explain the
+driftless area. The following is perhaps the most satisfactory:[12]
+
+    [12] Chamberlin and Irving. Geology of Wisconsin, Vols. I and
+    II.
+
+The adjacent highlands of the upper peninsula of Michigan, are bordered
+on the north by the capacious valley of Lake Superior leading off to the
+west, while to the east lies the valley of Lake Michigan leading to the
+south. These lake valleys were presumably not so broad and deep in
+preglacial times as now, though perhaps even then considerable valleys.
+
+When the ice sheet, moving in a general southward direction from the
+Canadian territory, reached these valleys, they led off two great
+tongues or lobes of ice, the one to the south through the Lake Michigan
+depression, the other to the south of west through the Lake Superior
+trough. (Fig. 36.) The highland between the lake valleys conspired with
+the valleys to the same end. It acted as a wedge, diverting the ice to
+either side. It offered such resistance to the ice, that the thin and
+relatively feeble sheet which succeeded in surmounting it, did not
+advance far to the south before it was exhausted. On the other hand, the
+ice following the valleys of Lakes Superior and Michigan respectively,
+failed to come together south of the highland until the latitude of
+northern Iowa and Illinois was reached. The driftless area therefore
+lies south of the highlands, beyond the limit of the ice which
+surmounted it, and between the Superior and Michigan glacial lobes above
+their point of union. The great depressions, together with the
+intervening highland, are therefore believed to be responsible for the
+absence of glaciation in the driftless area.
+
+
+        _Contrast Between Glaciated and Unglaciated Areas._
+
+The glaciated and unglaciated areas differ notably in (1) topography, (2)
+drainage, and (3) mantle rock.
+
+1. _Topography._--The driftless area has long been exposed to the
+processes of degradation. It has been cut into valleys and ridges by
+streams, and the ridges have been dissected into hills. The
+characteristic features of a topography fashioned by running water are
+such as to mark it clearly from surfaces fashioned by other agencies.
+Rivers end at the sea (or in lakes). Generally speaking, every point at
+the bottom of a river valley is higher than any other point in the
+bottom of the same valley nearer the sea, and lower than any other point
+correspondingly situated farther from the sea. This follows from the
+fact that rivers make their own valleys for the most part, and a river's
+course is necessarily downward. In a region of erosion topography
+therefore, tributary valleys lead down to their mains, secondary
+tributaries lead down to the first, and so on; or, to state the same
+thing in reverse order, in every region where the surface configuration
+has been determined by rain and river erosion, every gully and every
+ravine descends to a valley. The smaller valleys descend to larger and
+lower ones, which in turn lead to those still larger and lower. The
+lowest valley of a system ends at the sea, so that the valley which
+joins the sea is the last member of the series of erosion channels of
+which the ravines and gullies are the first. It will thus be seen that
+all depressions in the surface, worn by rivers, lead to lower ones. The
+surface of a region sculptured by rivers is therefore marked by valleys,
+with intervening ridges and hills, the slopes of which descend to them.
+All topographic features are here determined by the water courses.
+
+[Illustration: Fig. 45.--Drainage in the driftless area. The absence of
+ponds and marshes is to be noted.]
+
+The relief features of the glaciated area, on the other hand, lack the
+systematic arrangement of those of the unglaciated territory, and stream
+valleys are not the controlling elements in the topography.
+
+2. _Drainage._--The surface of the driftless area is well drained. Ponds
+and lakes are essentially absent, except where streams have been
+obstructed by human agency. The drainage of the drift-covered area, on
+the other hand, is usually imperfect. Marshes, ponds and lakes are of
+common occurrence. These types are shown by the accompanying maps, Figs.
+45 and 46, the one from the driftless area, the other from the
+drift-covered.
+
+[Illustration: Fig. 46.--Drainage in a glaciated region. Walworth and
+Waukesha counties, Wisconsin, showing abundance of marshes and lakes.]
+
+3. _Mantle rock._--The unglaciated surface is overspread to an average
+depth of several feet by a mantle of soil and earth which has resulted
+from the decomposition of the underlying rock. This earthy material
+sometimes contains fragments and even large masses of rock like that
+beneath. These fragments and masses escaped disintegration because of
+their greater resistance while the surrounding rock was destroyed. This
+mantle rock grades from fine material at the surface down through
+coarser, until the solid rock is reached, the upper surface of the rock
+being often ill-defined (Fig. 47). The thickness of the mantle is
+approximately constant in like topographic situations where the
+underlying rock is uniform.
+
+The residual soils are made up chiefly of the insoluble parts of the
+rock from which they are derived, the soluble parts having been removed
+in the process of disintegration.
+
+[Illustration: Fig. 47.--Section in a driftless area, showing relation
+of the mantle rock to the solid rock beneath.]
+
+With these residuary soils of the driftless area, the mantle rock of
+glaciated tracts is in sharp contrast. Here, as already pointed out, the
+material is diverse, having come from various formations and from widely
+separated sources. It contains the soluble as well as the insoluble
+parts of the rock from which it was derived. In it there is no
+suggestion of uniformity in thickness, no regular gradation from fine to
+coarse from the surface downward. The average thickness of the drift is
+also much greater than that of the residual earths. Further, the contact
+between the drift and the underlying rock surface is usually a definite
+surface. (Compare Figs. 32 and 47.)
+
+
+                       POSTGLACIAL CHANGES.
+
+Since the ice melted from the region, the changes in its geography have
+been slight. Small lakes and ponds have been drained, the streams whose
+valleys had been partly filled, have been re-excavating them, and
+erosion has been going on at all points in the slow way in which it
+normally proceeds. The most striking example of postglacial erosion is
+the dalles of the Wisconsin, and even this is but a small gorge for so
+large a stream. The slight amount of erosion which has been accomplished
+since the drift was deposited, indicates that the last retreat of the
+ice, measured in terms of geology and geography, was very recent. It has
+been estimated at 7,000 to 10,000 years, though too great confidence is
+not to be placed in this, or any other numerical estimate of
+post-glacial time.
+
+
+                               INDEX.
+
+           --------------------------------------------------
+                                                                PAGES
+
+
+   Ablemans                                                     66,67
+
+
+   Baraboo Lake                                                   130
+
+   Baraboo Quartzite ranges                                     2, 65
+
+      Constitution of                                              14
+
+      Dynamic action in                                    15, 17, 18
+
+      Gaps in--
+
+         Devil's Lake Gap                                       3, 13
+
+         Lower Narrows                                      5, 13, 67
+
+         Narrows Creek                                             66
+
+         Upper Narrows                              5, 10, 17, 19, 67
+
+      Igneous rock in                                              18
+
+      Structure of                                                 15
+
+      Topography of                                             5, 13
+
+   Base-level                                                      47
+
+   Base-level plains                                               50
+
+   Bowlder clay                                                    97
+
+   Breccia                                                         18
+
+
+   Castle Rock                                                     71
+
+   Cleopatra's Needle                                              65
+
+   Cold Water Canyon                                               70
+
+   Conglomerate                                                10, 28
+
+      Basal (Potsdam)                                              29
+
+   Corrasion                                                       36
+
+   Cross-bedding                                                   30
+
+   Cycle of erosion                                            44, 47
+
+
+   Dalles of the Wisconsin                                         69
+
+      Origin of                                                    53
+
+      Scenery of                                              69, 140
+
+   Dell Creek                                                      53
+
+   Deltas                                                 30, 56, 120
+
+   Deposits--
+
+      By extra-glacial waters                                 115-123
+
+      By ice                                                   85, 94
+
+      By rivers                                                55, 56
+
+      By subglacial streams                                       124
+
+      Of drift classified                                         127
+
+   Devil's Doorway                                                 65
+
+   Devil's Lake                                                   132
+
+      History of                                                  132
+
+      In glacial times                                            132
+
+      Location                                                   3, 9
+
+      Origin of                                                   132
+
+   Devil's Nose                                                5, 110
+
+   Divides, Shifting of                                            44
+
+   Dorward's Glen                                      10, 14, 29, 68
+
+   Drift                                                           73
+
+      Characteristics of                                           96
+
+      Constitution of                                              94
+
+      Deposits classified                                         127
+
+      Effect on topography                                     85, 88
+
+      Relation of stratified to unstratified                      125
+
+      Stratified                                                  111
+
+         Topography of                                       101, 103
+
+   Driftless area                                             79, 142
+
+   Drainage--
+
+      Adjustment of                                                62
+
+      Changes in, effected by the ice                        128, 142
+
+      Establishment of                                             61
+
+      Glacial                                                     113
+
+      Of drift-covered area                                       144
+
+      Of driftless area                                           144
+
+      Postglacial changes in                                      146
+
+
+   Endmoraene                                                      108
+
+   Erosion--
+
+      By rain, and rivers, general outline of                   36-58
+
+      Elements of                                                  36
+
+      Of folded strata                                             50
+
+      Of rocks of unequal hardness                                 47
+
+      Of the quartzite                                             25
+
+      Preglacial                                                   60
+
+      Topography                                                   12
+
+      Without valleys                                              37
+
+   Eskers                                                         124
+
+
+   Falls                                                           48
+
+   Fossils--
+
+      In limestone                                                 12
+
+      In sandstone                                              9, 11
+
+   Friendship mounds                                               71
+
+
+   Geographic features, general                                  3-20
+
+   Glacial drainage                                               113
+
+   Glaciated area                                         78, 91, 143
+
+   Glacier ice--
+
+      Deposition by                                                85
+
+      Direction of movement                                        88
+
+      Erosive work of                                           79-84
+
+      Formation of                                                 74
+
+      Movement of, affected by topography                          89
+
+   Glens                                                           68
+
+   Green Bay lobe                                                  91
+
+   Gibraltar rock                                                  63
+
+   Ground Moraine--
+
+      Constitution of                                              99
+
+      Location of                                                  97
+
+      Topography of                                               101
+
+   Groundwater level                                               41
+
+
+   Ice sheets--
+
+      Formation of                                                 74
+
+      History of                                                  114
+
+      Movement of                                              75, 88
+
+      North American ice sheet                                     78
+
+   Igneous rock                                                    18
+
+   Intermittent streams                                            42
+
+
+   Kames                                                          115
+
+
+   Lakes--
+
+      Wisconsin Lake                                              129
+
+      Baraboo Lake                                                130
+
+      Devil's Lake                                     3, 9, 132, 137
+
+   Limestone, see Lower Magnesian.
+
+   Lower Magnesian limestone--
+
+      Fossils of                                                   12
+
+      History of                                                31-32
+
+      Occurrence of                                                11
+
+      Origin of                                                    11
+
+      Position of                                                  12
+
+      Structure of                                                  8
+
+   Lower Narrows                                            5, 13, 67
+
+
+   Mantle rock                                                20, 144
+
+   Metamorphism                                                14, 24
+
+   Monadnocks                                                      51
+
+   Moraines (see terminal moraine and ground moraine).
+
+   Morainic aprons                                                119
+
+
+   Narrows                                                         49
+
+      In quartzite                                             66, 67
+
+   Natural bridge                                                  69
+
+   Navy Yard                                                       69
+
+   Niagara limestone                                               33
+
+   North American ice sheet                                        78
+
+   Nunatak                                                         89
+
+
+   Osars (see Eskers).
+
+   Outwash plains                                            118, 120
+
+   Overwash plains                                           118, 120
+
+
+   Parfrey's Glen                                      10, 14, 29, 68
+
+   Peneplain                                                   47, 50
+
+   Pewit's nest                                             9, 53, 69
+
+   Pine Hollow                                                     69
+
+   Postglacial changes                                            146
+
+   Potsdam sandstone--
+
+      Fossils of                                                9, 11
+
+      History of                                                27-31
+
+      Origin of                                                  9-11
+
+      Relation to quartzite                                        19
+
+      Structure of                                                  8
+
+
+   Quartzite (see also Baraboo quartzite ranges)--
+
+      Dynamic Metamorphism of                                      24
+
+      Erosion of                                                   25
+
+      Origin of                                                    23
+
+      Submergence of                                               27
+
+      Thickness of                                                 26
+
+      Uplift of                                                    24
+
+
+   Rapids                                                          48
+
+   Rejuvenation of streams                                         56
+
+   Ripple marks                                                 9, 15
+
+   Roches moutonnee                                                81
+
+
+   Sandstone (see Potsdam and St. Peters).
+
+   Sauk Prarie                                          117, 118, 119
+
+   Skillett Creek                                          8, 53, 138
+
+   Slope of upper surface of ice                                  111
+
+   Snow fields                                                     74
+
+   Soil                                                   7, 144, 146
+
+   Stand rock                                                      70
+
+   Steamboat rock                                                  70
+
+   St. Peter's sandstone                                           32
+
+   Stratified drift                                      111-112, 125
+
+   Streams, changes in                                            138
+
+   Subaqueous overwash plains                                     120
+
+   Subglacial till (ground moraines)                               99
+
+   Sugar Bowl                                                      70
+
+
+   Talus slopes                                                    65
+
+   Terminal moraines--
+
+      Across the United States                                     78
+
+      Development of                                              102
+
+      In Devil's Lake region                                      105
+
+      Boundaries of                                               106
+
+      Location of                                         92, 93, 108
+
+      On the main quartzite range                                 107
+
+      Width of                                                    106
+
+      Topography of                                               103
+
+   Till                                                            97
+
+   Topography--
+
+      Effect of, on ice movement                                   89
+
+      Erosion topography                                           12
+
+      Of drift-covered country                                 8, 143
+
+      Of driftless area                                 6, 7, 12, 143
+
+      Of plain surrounding quartzite ridge                          6
+
+      Of quartzite ridges                                           5
+
+   Transportation by streams                                       55
+
+   Tributary valleys                                               39
+
+   Turk's Head                                                     65
+
+
+   Unconformity                                                    19
+
+   Underground water                                               58
+
+   Unglaciated areas                                     79, 142, 143
+
+   Unstratified drift                                    99, 102, 125
+
+   Upper Narrows                                    5, 10, 17, 19, 67
+
+
+   Valley, the--
+
+      Beginning of                                                 37
+
+      Characteristics of, at various stages                     52-54
+
+      Course of                                                    39
+
+      How a valley gets a stream                                   40
+
+      Limits of                                                    43
+
+   Valley trains                                                  116
+
+
+   Waterfalls                                                      48
+
+   Weathering                                                      36
+
+   Webster's Prarie                                               119
+
+   Wisconsin Lake                                                 129
+
+   Wisconsin River                                                139
+
+   Witch's Gulch                                                   70
+
+
+
+
+
+End of the Project Gutenberg EBook of The Geography of the Region about
+Devils Lake and the Dalles of the Wisconsin, by Rollin D. Salisbury and Wallace W. Atwood
+
+*** END OF THIS PROJECT GUTENBERG EBOOK THE GEOGRAPHY OF THE REGION ***
+
+***** This file should be named 38148.txt or 38148.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/3/8/1/4/38148/
+
+Produced by David Edwards, Joanna Johnston and the Online
+Distributed Proofreading Team at http://www.pgdp.net (This
+file was produced from images generously made available
+by The Internet Archive)
+
+
+Updated editions will replace the previous one--the old editions
+will be renamed.
+
+Creating the works from public domain print editions means that no
+one owns a United States copyright in these works, so the Foundation
+(and you!) can copy and distribute it in the United States without
+permission and without paying copyright royalties.  Special rules,
+set forth in the General Terms of Use part of this license, apply to
+copying and distributing Project Gutenberg-tm electronic works to
+protect the PROJECT GUTENBERG-tm concept and trademark.  Project
+Gutenberg is a registered trademark, and may not be used if you
+charge for the eBooks, unless you receive specific permission.  If you
+do not charge anything for copies of this eBook, complying with the
+rules is very easy.  You may use this eBook for nearly any purpose
+such as creation of derivative works, reports, performances and
+research.  They may be modified and printed and given away--you may do
+practically ANYTHING with public domain eBooks.  Redistribution is
+subject to the trademark license, especially commercial
+redistribution.
+
+
+
+*** START: FULL LICENSE ***
+
+THE FULL PROJECT GUTENBERG LICENSE
+PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK
+
+To protect the Project Gutenberg-tm mission of promoting the free
+distribution of electronic works, by using or distributing this work
+(or any other work associated in any way with the phrase "Project
+Gutenberg"), you agree to comply with all the terms of the Full Project
+Gutenberg-tm License (available with this file or online at
+http://gutenberg.org/license).
+
+
+Section 1.  General Terms of Use and Redistributing Project Gutenberg-tm
+electronic works
+
+1.A.  By reading or using any part of this Project Gutenberg-tm
+electronic work, you indicate that you have read, understand, agree to
+and accept all the terms of this license and intellectual property
+(trademark/copyright) agreement.  If you do not agree to abide by all
+the terms of this agreement, you must cease using and return or destroy
+all copies of Project Gutenberg-tm electronic works in your possession.
+If you paid a fee for obtaining a copy of or access to a Project
+Gutenberg-tm electronic work and you do not agree to be bound by the
+terms of this agreement, you may obtain a refund from the person or
+entity to whom you paid the fee as set forth in paragraph 1.E.8.
+
+1.B.  "Project Gutenberg" is a registered trademark.  It may only be
+used on or associated in any way with an electronic work by people who
+agree to be bound by the terms of this agreement.  There are a few
+things that you can do with most Project Gutenberg-tm electronic works
+even without complying with the full terms of this agreement.  See
+paragraph 1.C below.  There are a lot of things you can do with Project
+Gutenberg-tm electronic works if you follow the terms of this agreement
+and help preserve free future access to Project Gutenberg-tm electronic
+works.  See paragraph 1.E below.
+
+1.C.  The Project Gutenberg Literary Archive Foundation ("the Foundation"
+or PGLAF), owns a compilation copyright in the collection of Project
+Gutenberg-tm electronic works.  Nearly all the individual works in the
+collection are in the public domain in the United States.  If an
+individual work is in the public domain in the United States and you are
+located in the United States, we do not claim a right to prevent you from
+copying, distributing, performing, displaying or creating derivative
+works based on the work as long as all references to Project Gutenberg
+are removed.  Of course, we hope that you will support the Project
+Gutenberg-tm mission of promoting free access to electronic works by
+freely sharing Project Gutenberg-tm works in compliance with the terms of
+this agreement for keeping the Project Gutenberg-tm name associated with
+the work.  You can easily comply with the terms of this agreement by
+keeping this work in the same format with its attached full Project
+Gutenberg-tm License when you share it without charge with others.
+
+1.D.  The copyright laws of the place where you are located also govern
+what you can do with this work.  Copyright laws in most countries are in
+a constant state of change.  If you are outside the United States, check
+the laws of your country in addition to the terms of this agreement
+before downloading, copying, displaying, performing, distributing or
+creating derivative works based on this work or any other Project
+Gutenberg-tm work.  The Foundation makes no representations concerning
+the copyright status of any work in any country outside the United
+States.
+
+1.E.  Unless you have removed all references to Project Gutenberg:
+
+1.E.1.  The following sentence, with active links to, or other immediate
+access to, the full Project Gutenberg-tm License must appear prominently
+whenever any copy of a Project Gutenberg-tm work (any work on which the
+phrase "Project Gutenberg" appears, or with which the phrase "Project
+Gutenberg" is associated) is accessed, displayed, performed, viewed,
+copied or distributed:
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+1.E.2.  If an individual Project Gutenberg-tm electronic work is derived
+from the public domain (does not contain a notice indicating that it is
+posted with permission of the copyright holder), the work can be copied
+and distributed to anyone in the United States without paying any fees
+or charges.  If you are redistributing or providing access to a work
+with the phrase "Project Gutenberg" associated with or appearing on the
+work, you must comply either with the requirements of paragraphs 1.E.1
+through 1.E.7 or obtain permission for the use of the work and the
+Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or
+1.E.9.
+
+1.E.3.  If an individual Project Gutenberg-tm electronic work is posted
+with the permission of the copyright holder, your use and distribution
+must comply with both paragraphs 1.E.1 through 1.E.7 and any additional
+terms imposed by the copyright holder.  Additional terms will be linked
+to the Project Gutenberg-tm License for all works posted with the
+permission of the copyright holder found at the beginning of this work.
+
+1.E.4.  Do not unlink or detach or remove the full Project Gutenberg-tm
+License terms from this work, or any files containing a part of this
+work or any other work associated with Project Gutenberg-tm.
+
+1.E.5.  Do not copy, display, perform, distribute or redistribute this
+electronic work, or any part of this electronic work, without
+prominently displaying the sentence set forth in paragraph 1.E.1 with
+active links or immediate access to the full terms of the Project
+Gutenberg-tm License.
+
+1.E.6.  You may convert to and distribute this work in any binary,
+compressed, marked up, nonproprietary or proprietary form, including any
+word processing or hypertext form.  However, if you provide access to or
+distribute copies of a Project Gutenberg-tm work in a format other than
+"Plain Vanilla ASCII" or other format used in the official version
+posted on the official Project Gutenberg-tm web site (www.gutenberg.org),
+you must, at no additional cost, fee or expense to the user, provide a
+copy, a means of exporting a copy, or a means of obtaining a copy upon
+request, of the work in its original "Plain Vanilla ASCII" or other
+form.  Any alternate format must include the full Project Gutenberg-tm
+License as specified in paragraph 1.E.1.
+
+1.E.7.  Do not charge a fee for access to, viewing, displaying,
+performing, copying or distributing any Project Gutenberg-tm works
+unless you comply with paragraph 1.E.8 or 1.E.9.
+
+1.E.8.  You may charge a reasonable fee for copies of or providing
+access to or distributing Project Gutenberg-tm electronic works provided
+that
+
+- You pay a royalty fee of 20% of the gross profits you derive from
+     the use of Project Gutenberg-tm works calculated using the method
+     you already use to calculate your applicable taxes.  The fee is
+     owed to the owner of the Project Gutenberg-tm trademark, but he
+     has agreed to donate royalties under this paragraph to the
+     Project Gutenberg Literary Archive Foundation.  Royalty payments
+     must be paid within 60 days following each date on which you
+     prepare (or are legally required to prepare) your periodic tax
+     returns.  Royalty payments should be clearly marked as such and
+     sent to the Project Gutenberg Literary Archive Foundation at the
+     address specified in Section 4, "Information about donations to
+     the Project Gutenberg Literary Archive Foundation."
+
+- You provide a full refund of any money paid by a user who notifies
+     you in writing (or by e-mail) within 30 days of receipt that s/he
+     does not agree to the terms of the full Project Gutenberg-tm
+     License.  You must require such a user to return or
+     destroy all copies of the works possessed in a physical medium
+     and discontinue all use of and all access to other copies of
+     Project Gutenberg-tm works.
+
+- You provide, in accordance with paragraph 1.F.3, a full refund of any
+     money paid for a work or a replacement copy, if a defect in the
+     electronic work is discovered and reported to you within 90 days
+     of receipt of the work.
+
+- You comply with all other terms of this agreement for free
+     distribution of Project Gutenberg-tm works.
+
+1.E.9.  If you wish to charge a fee or distribute a Project Gutenberg-tm
+electronic work or group of works on different terms than are set
+forth in this agreement, you must obtain permission in writing from
+both the Project Gutenberg Literary Archive Foundation and Michael
+Hart, the owner of the Project Gutenberg-tm trademark.  Contact the
+Foundation as set forth in Section 3 below.
+
+1.F.
+
+1.F.1.  Project Gutenberg volunteers and employees expend considerable
+effort to identify, do copyright research on, transcribe and proofread
+public domain works in creating the Project Gutenberg-tm
+collection.  Despite these efforts, Project Gutenberg-tm electronic
+works, and the medium on which they may be stored, may contain
+"Defects," such as, but not limited to, incomplete, inaccurate or
+corrupt data, transcription errors, a copyright or other intellectual
+property infringement, a defective or damaged disk or other medium, a
+computer virus, or computer codes that damage or cannot be read by
+your equipment.
+
+1.F.2.  LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right
+of Replacement or Refund" described in paragraph 1.F.3, the Project
+Gutenberg Literary Archive Foundation, the owner of the Project
+Gutenberg-tm trademark, and any other party distributing a Project
+Gutenberg-tm electronic work under this agreement, disclaim all
+liability to you for damages, costs and expenses, including legal
+fees.  YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT
+LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE
+PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE
+TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE
+LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR
+INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH
+DAMAGE.
+
+1.F.3.  LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a
+defect in this electronic work within 90 days of receiving it, you can
+receive a refund of the money (if any) you paid for it by sending a
+written explanation to the person you received the work from.  If you
+received the work on a physical medium, you must return the medium with
+your written explanation.  The person or entity that provided you with
+the defective work may elect to provide a replacement copy in lieu of a
+refund.  If you received the work electronically, the person or entity
+providing it to you may choose to give you a second opportunity to
+receive the work electronically in lieu of a refund.  If the second copy
+is also defective, you may demand a refund in writing without further
+opportunities to fix the problem.
+
+1.F.4.  Except for the limited right of replacement or refund set forth
+in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER
+WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
+WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE.
+
+1.F.5.  Some states do not allow disclaimers of certain implied
+warranties or the exclusion or limitation of certain types of damages.
+If any disclaimer or limitation set forth in this agreement violates the
+law of the state applicable to this agreement, the agreement shall be
+interpreted to make the maximum disclaimer or limitation permitted by
+the applicable state law.  The invalidity or unenforceability of any
+provision of this agreement shall not void the remaining provisions.
+
+1.F.6.  INDEMNITY - You agree to indemnify and hold the Foundation, the
+trademark owner, any agent or employee of the Foundation, anyone
+providing copies of Project Gutenberg-tm electronic works in accordance
+with this agreement, and any volunteers associated with the production,
+promotion and distribution of Project Gutenberg-tm electronic works,
+harmless from all liability, costs and expenses, including legal fees,
+that arise directly or indirectly from any of the following which you do
+or cause to occur: (a) distribution of this or any Project Gutenberg-tm
+work, (b) alteration, modification, or additions or deletions to any
+Project Gutenberg-tm work, and (c) any Defect you cause.
+
+
+Section  2.  Information about the Mission of Project Gutenberg-tm
+
+Project Gutenberg-tm is synonymous with the free distribution of
+electronic works in formats readable by the widest variety of computers
+including obsolete, old, middle-aged and new computers.  It exists
+because of the efforts of hundreds of volunteers and donations from
+people in all walks of life.
+
+Volunteers and financial support to provide volunteers with the
+assistance they need, are critical to reaching Project Gutenberg-tm's
+goals and ensuring that the Project Gutenberg-tm collection will
+remain freely available for generations to come.  In 2001, the Project
+Gutenberg Literary Archive Foundation was created to provide a secure
+and permanent future for Project Gutenberg-tm and future generations.
+To learn more about the Project Gutenberg Literary Archive Foundation
+and how your efforts and donations can help, see Sections 3 and 4
+and the Foundation web page at http://www.pglaf.org.
+
+
+Section 3.  Information about the Project Gutenberg Literary Archive
+Foundation
+
+The Project Gutenberg Literary Archive Foundation is a non profit
+501(c)(3) educational corporation organized under the laws of the
+state of Mississippi and granted tax exempt status by the Internal
+Revenue Service.  The Foundation's EIN or federal tax identification
+number is 64-6221541.  Its 501(c)(3) letter is posted at
+http://pglaf.org/fundraising.  Contributions to the Project Gutenberg
+Literary Archive Foundation are tax deductible to the full extent
+permitted by U.S. federal laws and your state's laws.
+
+The Foundation's principal office is located at 4557 Melan Dr. S.
+Fairbanks, AK, 99712., but its volunteers and employees are scattered
+throughout numerous locations.  Its business office is located at
+809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email
+business@pglaf.org.  Email contact links and up to date contact
+information can be found at the Foundation's web site and official
+page at http://pglaf.org
+
+For additional contact information:
+     Dr. Gregory B. Newby
+     Chief Executive and Director
+     gbnewby@pglaf.org
+
+
+Section 4.  Information about Donations to the Project Gutenberg
+Literary Archive Foundation
+
+Project Gutenberg-tm depends upon and cannot survive without wide
+spread public support and donations to carry out its mission of
+increasing the number of public domain and licensed works that can be
+freely distributed in machine readable form accessible by the widest
+array of equipment including outdated equipment.  Many small donations
+($1 to $5,000) are particularly important to maintaining tax exempt
+status with the IRS.
+
+The Foundation is committed to complying with the laws regulating
+charities and charitable donations in all 50 states of the United
+States.  Compliance requirements are not uniform and it takes a
+considerable effort, much paperwork and many fees to meet and keep up
+with these requirements.  We do not solicit donations in locations
+where we have not received written confirmation of compliance.  To
+SEND DONATIONS or determine the status of compliance for any
+particular state visit http://pglaf.org
+
+While we cannot and do not solicit contributions from states where we
+have not met the solicitation requirements, we know of no prohibition
+against accepting unsolicited donations from donors in such states who
+approach us with offers to donate.
+
+International donations are gratefully accepted, but we cannot make
+any statements concerning tax treatment of donations received from
+outside the United States.  U.S. laws alone swamp our small staff.
+
+Please check the Project Gutenberg Web pages for current donation
+methods and addresses.  Donations are accepted in a number of other
+ways including checks, online payments and credit card donations.
+To donate, please visit: http://pglaf.org/donate
+
+
+Section 5.  General Information About Project Gutenberg-tm electronic
+works.
+
+Professor Michael S. Hart is the originator of the Project Gutenberg-tm
+concept of a library of electronic works that could be freely shared
+with anyone.  For thirty years, he produced and distributed Project
+Gutenberg-tm eBooks with only a loose network of volunteer support.
+
+
+Project Gutenberg-tm eBooks are often created from several printed
+editions, all of which are confirmed as Public Domain in the U.S.
+unless a copyright notice is included.  Thus, we do not necessarily
+keep eBooks in compliance with any particular paper edition.
+
+
+Most people start at our Web site which has the main PG search facility:
+
+     http://www.gutenberg.org
+
+This Web site includes information about Project Gutenberg-tm,
+including how to make donations to the Project Gutenberg Literary
+Archive Foundation, how to help produce our new eBooks, and how to
+subscribe to our email newsletter to hear about new eBooks.
diff --git a/38148.zip b/38148.zip
new file mode 100644
index 0000000..9efb7dd
--- /dev/null
+++ b/38148.zip
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..6312041
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,11 @@
+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this eBook outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..97794d5
--- /dev/null
+++ b/README.md
@@ -0,0 +1,2 @@
+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #38148 (https://www.gutenberg.org/ebooks/38148)