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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf 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..94fe93a --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #50383 (https://www.gutenberg.org/ebooks/50383) diff --git a/old/50383-8.txt b/old/50383-8.txt deleted file mode 100644 index b6d698e..0000000 --- a/old/50383-8.txt +++ /dev/null @@ -1,4003 +0,0 @@ -The Project Gutenberg EBook of The National Geographic Magazine, Vol. I., -No. 3, July, 1889, by Various - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world 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. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The National Geographic Magazine, Vol. I., No. 3, July, 1889 - -Author: Various - -Release Date: November 4, 2015 [EBook #50383] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK NATIONAL GEOGRAPHIC MAG., JULY 1889 *** - - - - -Produced by Ron Swanson - - - - - -Vol. I. No. 3. - -THE NATIONAL GEOGRAPHIC MAGAZINE. - - - - -PUBLISHED BY THE - -NATIONAL GEOGRAPHIC SOCIETY. - -WASHINGTON, D. C. - - -Price 50 Cents. - - - - -CONTENTS. - - -The Rivers and Valleys of Pennsylvania: William Morris Davis - (Illustrated by one map and twenty-five cuts.) - -Topographic Models: Cosmos Mindeleff - (Illustrated by two plates.) - -National Geographic Society--Abstract of Minutes - -International Literary Contest to be held at Madrid, Spain - - July, 1889. - - - - -PRESS OF TUTTLE, MOREHOUSE & TAYLOR, NEW HAVEN, CONN. - - - - -THE NATIONAL GEOGRAPHIC MAGAZINE. - -Vol. I. 1889. No. 3. - - - - -THE RIVERS AND VALLEYS OF PENNSYLVANIA.[1] - -BY WILLIAM MORRIS DAVIS. - -"In Faltensystemen von sehr hohem Alter wurde die ursprüngliche -Anordnung der Langenthäler durch das Ueberhandnehmen der transversalen -Erosionsfurchen oft ganz und gar verwischt." - - LÖWL. Petermann's Mittheilungen, xxviii, 1882, 411. - -[Footnote 1: The substance of this essay was presented to the Society -in a lecture on February 8th, 1889, but since then it has been much -expanded.] - - -CONTENTS. - -PART FIRST. _Introductory_. - - 1. Plan of work here proposed. - 2. General description of the topography of Pennsylvania. - 3. The drainage of Pennsylvania. - 4. Previous studies of Appalachian drainage. - -PART SECOND. _Outline of the geological history of the region_. - - 5. Conditions of formation. - 6. Former extension of strata to the southeast. - 7. Cambro-Silurian and Permian deformations. - 8. Perm-Triassic denudation. - 9. Newark deposition. - 10. Jurassic tilting. - 11. Jura-Cretaceous denudation. - 12. Tertiary elevation and denudation. - 13. Later changes of level. - 14. Illustrations of Pennsylvanian topography. - -PART THIRD. _General conception of the history of a river_. - - 15. The complete cycle of river life: youth, adolescence, - maturity and old age. - 16. Mutual adjustment of river courses. - 17. Terminology of rivers changed by adjustment. - 18. Examples of adjustments. - 19. Revival of rivers by elevation and drowning by depression. - 20. Opportunity for new adjustments with revival. - 21. Antecedent and superimposed rivers. - 22. Simple, compound, composite and complex rivers. - -PART FOURTH. _The development of the rivers of Pennsylvania_. - - 23. Means of distinguishing between antecedent and adjusted - consequent rivers. - 24. Postulates of the argument. - 25. Constructional Permian topography and consequent drainage. - 26. The Jura mountains homologous with the Permian Alleghanies. - 27. Development and adjustment of the Permian drainage. - 28. Lateral water-gaps near the apex of synclinal ridges. - 29. Departure of the Juniata from the Juniata-Catawissa syncline. - 30. Avoidance of the Broad Top basin by the Juniata headwaters. - 31. Reversal of larger rivers to southeast courses. - 32. Capture of the Anthracite headwaters by the growing Susquehanna. - 33. Present outward drainage of the Anthracite basins. - 34. Homologies of the Susquehanna and Juniata. - 35. Superimposition of the Susquehanna on two synclinal ridges. - 36. Evidence of superimposition in the Susquehanna tributaries. - 37. Events of the Tertiary cycle. - 38. Tertiary adjustment of the Juniata on the Medina anticlines. - 39. Migration of the Atlantic-Ohio divide. - 40. Other examples of adjustments. - 41. Events of the Quaternary cycle. - 42. Doubtful cases. - 43. Complicated history of our actual rivers. - 44. Provisional conclusions. - - -PART FIRST. _Introductory_. - -1. _Plan of work here proposed_.--No one now regards a river and its -valley as ready-made features of the earth's surface. All are convinced -that rivers have come to be what they are by slow processes of natural -development, in which every peculiarity of river-course and valley-form -has its appropriate cause. Being fully persuaded of the gradual and -systematic evolution of topographic forms, it is now desired, in -studying the rivers and valleys of Pennsylvania, to seek the causes of -the location of the streams in their present courses; to go back if -possible to the early date when central Pennsylvania was first raised -above the sea and trace the development of the several river systems -then implanted upon it from their ancient beginning to the present -time. - -The existing topography and drainage system of the State will first be -briefly described. We must next inquire into the geological structure -of the region, follow at least in a general way the deformations and -changes of attitude and altitude that it has suffered, and consider the -amount of denudation that has been accomplished on its surface. We must -at the same time bear in mind the natural history of rivers, their -morphology and development; we must recognize the varying activities of -a river in its youth and old age, the adjustments of its adolescence -and maturity, and the revival of its decrepit powers when the land that -it drains is elevated and it enters a new cycle of life. Finally we -shall attempt to follow out the development of the rivers of -Pennsylvania by applying the general principles of river history to the -special case of Pennsylvania structure. - -2. _General description of the topography of Pennsylvania_.--The -strongly marked topographic districts of Pennsylvania can hardly be -better described than by quoting the account given over a century ago -by Lewis Evans, of Philadelphia, in his "Analysis of a map of the -middle British colonies in America" (1755), which is as valuable from -its appreciative perception as it is interesting from its early date. -The following paragraphs are selected from his early pages: - -"The land southwestward of Hudson's River is more regularly divided and -into a greater number of stages than the other. The first object worthy -of regard in this part is a rief or vein of rocks of the talky or -isinglassy kind, some two or three or half a dozen miles broad; rising -generally some small matter higher than the adjoining land; and -extending from New York city southwesterly by the lower falls of -Delaware, Schuylkill, Susquehanna, Gun-Powder, Patapsco, Potomack, -Rapahannock, James river and Ronoak. This was the antient maritime -boundary of America and forms a very regular curve. The land between -this rief and the sea and from the Navesink hills southwest ... may be -denominated the Lower Plains, and consists of soil washt down from -above and sand accumulated from the ocean. Where these plains are not -penetrated by rivers, they are a white sea-sand, about twenty feet deep -and perfectly barren, as no mixture of soil helps to enrich them. But -the borders of the rivers, which descend from the uplands, are rendered -fertile by the soil washt down with the floods and mixt with the sands -gathered from the sea. The substratum of sea-mud, shells and other -foreign subjects is a perfect confirmation of this supposition. And -hence it is that for 40 or 50 miles inland and all the way from the -Navesinks to Cape Florida, all is a perfect barren where the wash from -the uplands has not enriched the borders of the rivers; or some ponds -and defiles have not furnished proper support for the growth of white -cedars.... - -"From this rief of rocks, over which all the rivers fall, to that chain -of broken hills, called the South mountain, there is the distance of -50, 60 or 70 miles of very uneven ground, rising sensibly as you -advance further inland, and may be denominated the Upland. This -consists of veins of different kinds of soil and substrata some scores -of miles in length; and in some places overlaid with little ridges and -chains of hills. The declivity of the whole gives great rapidity to the -streams; and our violent gusts of rain have washt it all into gullies, -and carried down the soil to enrich the borders of the rivers in the -Lower Plains. These inequalities render half the country not easily -capable of culture, and impoverishes it, where torn up by the plow, by -daily washing away the richer mould that covers the surface. - -"The South mountain is not in ridges like the Endless mountains, but in -small, broken, steep, stoney hills; nor does it run with so much -regularity. In some places it gradually degenerates to nothing, not to -appear again for some miles, and in others it spreads several miles in -breadth. Between South mountain and the hither chain of the Endless -mountains (often for distinction called the North mountain, and in some -places the Kittatinni and Pequélin), there is a valley of pretty even -good land, some 8, 10 or 20 miles wide, and is the most considerable -quantity of valuable land that the English are possest of; and runs -through New Jersey, Pensilvania, Mariland and Virginia. It has yet -obtained no general name, but may properly enough be called Piemont, -from its situation. Besides conveniences always attending good land, -this valley is everywhere enriched with Limestone. - -"The Endless mountains, so called from a translation of the Indian name -bearing that signification, come next in order. They are not confusedly -scattered and in lofty peaks overtopping one another, but stretch in -long uniform ridges scarce half a mile perpendicular in any place above -the intermediate vallies. Their name is expressive of their extent, -though no doubt not in a literal sense.... The mountains are almost all -so many ridges with even tops and nearly of a height. To look from -these hills into the lower lands is but, as it were, into an ocean of -woods, swelled and deprest here and there by little inequalities, not -to be distinguished one part from another any more than the waves of -the real ocean. The uniformity of these mountains, though debarring us -of an advantage in this respect, makes some amends in another. They are -very regular in their courses, and confine the creeks and rivers that -run between; and if we know where the gaps are that let through these -streams, we are not at a loss to lay down their most considerable -inflections.... - -"To the northwestward of the Endless mountains is a country of vast -extent, and in a manner as high as the mountains themselves. To look at -the abrupt termination of it, near the sea level, as is the case on the -west side of Hudson's river below Albany, it looks as a vast high -mountain; for the Kaats Kills, though of more lofty stature than any -other mountains in these parts of America, are but the continuation of -the Plains on the top, and the cliffs of them in the front they present -towards Kinderhook. These Upper Plains are of extraordinary rich level -land, and extend from the Mohocks river through the country of the -Confederates.[2] Their termination northward is at a little distance -from Lake Ontario; but what it is westward is not known, for those most -extensive plains of Ohio are part of them." - -[Footnote 2: Referring to the league of Indian tribes, so-called.] - -These several districts recognized by Evans may be summarized as the -coastal plain, of nearly horizontal Cretaceous and later beds, just -entering the southeastern corner of Pennsylvania; the marginal upland -of contorted schists of disputed age; the South Mountain belt of -ancient and much disturbed crystalline rocks, commonly called Archean; -a space between these two traversed by the sandstone lowland of the -Newark formation;[3] the great Appalachian valley of crowded Cambrian -limestones and slates; the region of the even-crested, linear Paleozoic -ridges, bounded by Kittatinny or Blue mountain on the southeast and by -Alleghany mountain on the northwest, this being the area with which we -are here most concerned; and finally the Alleghany plateau, consisting -of nearly horizontal Devonian and Carboniferous beds and embracing all -the western part of the state. The whole region presents the most -emphatic expression not only of its structure but also of the more -recent cycles of development through which it has passed. Fig. 1 -represents the stronger ridges and larger streams of the greater part -of the central district: it is reproduced from the expressive -Topographic Map of Pennsylvania (1871) by Lesley. The Susquehanna flows -down the middle, receiving the West Branch from Lock Haven and -Williamsport, the East Branch from Wilkes-Barre in the Wyoming basin, -and the Juniata from the Broad Top region, south of Huntingdon. The -Anthracite basins lie on the right, enclosed by zigzag ridges of Pocono -and Pottsville sandstone; the Plateau, trenched by the West Branch of -the Susquehanna is in the northwest. Medina sandstone forms most of the -central ridges. - -[Footnote 3: Russell has lately recommended the revival of this term, -proposed many years ago by Redfield, as a non-committal name for the -"New red sandstones" of our Atlantic slope, commonly called Triassic.] - -[Illustration: FIG. 1. Part of Topographic Map of Pennsylvania, by J. -P. Lesley (1871).] - -3. _The drainage of Pennsylvania_.--The greater part of the Alleghany -plateau is drained westward into the Ohio, and with this we shall have -little to do. The remainder of the plateau drainage reaches the -Atlantic by two rivers, the Delaware and the Susquehanna, of which the -latter is the more special object of our study. The North and West -Branches of the Susquehanna rise in the plateau, which they traverse in -deep valleys; thence they enter the district of the central ranges, -where they unite and flow in broad lowlands among the even-crested -ridges. The Juniata brings the drainage of the Broad Top region to the -main stream just before their confluent current cuts across the -marginal Blue Mountain. The rock-rimmed basins of the anthracite region -are drained by small branches of the Susquehanna northward and -westward, and by the Schuylkill and Lehigh to the south and east. The -Delaware, which traverses the plateau between the Anthracite region and -the Catskill Mountain front, together with the Lehigh, the Schuylkill, -the little Swatara and the Susquehanna, cut the Blue Mountain by fine -water-gaps, and cross the great limestone valley. The Lehigh then turns -eastward and joins the Delaware, and the Swatara turns westward to the -Susquehanna; but the Delaware, Schuylkill and Susquehanna all continue -across South Mountain and the Newark belt, and into the low plateau of -schists beyond. The Schuylkill unites with the Delaware near -Philadelphia, just below the inner margin of the coastal plain; the -Delaware and the Susquehanna continue in their deflected estuaries to -the sea. All of these rivers and many of their side streams are at -present sunk in small valleys of moderate depth and width, below the -general surface of the lowlands, and are more or less complicated with -terrace gravels. - -4. _Previous studies of Appalachian drainage_.--There have been no -special studies of the history of the rivers of Pennsylvania in the -light of what is now known of river development. A few recent essays of -rather general character as far as our rivers are concerned, may be -mentioned. - -Peschel examined our rivers chiefly by means of general maps with -little regard to the structure and complicated history of the region. -He concluded that the several transverse rivers which break through the -mountains, namely, the Delaware, Susquehanna and Potomac, are guided by -fractures, anterior to the origin of the rivers.[4] There does not seem -to be sufficient evidence to support this obsolescent view, for most of -the water-gaps are located independently of fractures; nor can -Peschel's method of river study be trusted as leading to safe -conclusions. - -[Footnote 4: Physische Erdkunde, 1880, ii, 442.] - -Tietze regards our transverse valleys as antecedent;[5] but this was -made only as a general suggestion, for his examination of the structure -and development of the region is too brief to establish this and -exclude other views. - -[Footnote 5: Jahrbuch Geol. Reichsanstalt, xxviii, 1878, 600.] - -Löwl questions the conclusion reached by Tietze and ascribes the -transverse gaps to the backward or headwater erosion of external -streams, a process which he has done much to bring into its present -important position, and which for him replaces the persistence of -antecedent streams of other authors.[6] - -[Footnote 6: Pet. Mitth., 1882, 405; Ueber Thalbildung, Prag, 1884.] - -A brief article[7] that I wrote in comment on Löwl's first essay -several years ago now seems to me insufficient in its method. It -exaggerated the importance of antecedent streams; it took no sufficient -account of the several cycles of erosion through which the region has -certainly passed; and it neglected due consideration of the -readjustment of initial immature stream courses during more advanced -river-life. Since then, a few words in Löwl's essay have come to have -more and more significance to me; he says that in mountain systems of -very great age, the original arrangement of the longitudinal valleys -often becomes entirely confused by means of their conquest by -transverse erosion gaps. This suggestion has been so profitable to me -that I have placed the original sentence at the beginning of this -paper. Its thesis is the essential element of my present study. - -[Footnote 7: Origin of Cross-valleys. Science, i, 1883, 325.] - -Phillipson refers to the above-mentioned authors and gives a brief -account of the arrangement of drainage areas within our Appalachians, -but briefly dismisses the subject.[8] His essay contains a serviceable -bibliography. - -[Footnote 8: Studien über Wasserscheiden. Leipsig, 1886, 149.] - -If these several earlier essays have not reached any precise -conclusion, it may perhaps be because the details of the geological -structure and development of Pennsylvania have not been sufficiently -examined. Indeed, unless the reader has already become familiar with -the geological maps and reports of the Pennsylvania surveys and is -somewhat acquainted with its geography, I shall hardly hope to make my -case clear to him. The volumes that should be most carefully studied -are, first, the always inspiring classic, "Coal and its Topography" -(1856), by Lesley, in which the immediate relation of our topography to -the underlying structure is so finely described; the Geological Map of -Pennsylvania (1856), the result of the labors of the first survey of -the state; and the Geological Atlas of Counties, Volume X of the second -survey (1885). Besides these, the ponderous volumes of the final report -of the first survey and numerous reports on separate counties by the -second survey should be examined, as they contain many accounts of the -topography although saying very little about its development. If, in -addition to all this, the reader has seen the central district of the -state and marvelled at its even-crested, straight and zigzag ridges, -and walked through its narrow water-gaps into the enclosed coves that -they drain, he may then still better follow the considerations here -presented. - - -PART SECOND. _Outline of the geological history of the region_. - -5. _Conditions of formation_.--The region in which the Susquehanna and -the neighboring rivers are now located is built in chief part of marine -sediments derived in paleozoic time from a large land area to the -southeast, whose northwest coast-line probably crossed Pennsylvania -somewhere in the southeastern part of the state; doubtless varying its -position, however, by many miles as the sea advanced and receded in -accordance with the changes in the relative altitudes of the land and -water surfaces, such as have been discussed by Newberry and Claypole. -The sediments thus accumulated are of enormous thickness, measuring -twenty or thirty thousand feet from their crystalline foundation to the -uppermost layer now remaining. The whole mass is essentially -conformable in the central part of the state. Some of the formations -are resistent, and these have determined the position of our ridges; -others are weaker and are chosen as the sites of valleys and lowlands. -The first are the Oneida and Medina sandstones, which will be here -generally referred to under the latter name alone, the Pocono sandstone -and the Pottsville conglomerate; to these may be added the fundamental -crystalline mass on which the whole series of bedded formations was -deposited, and the basal sandstone that is generally associated with -it. Wherever we now see these harder rocks, they rise above the -surrounding lowland surface. On the other hand, the weaker beds are the -Cambrian limestones (Trenton) and slates (Hudson River), all the -Silurian except the Medina above named, the whole of the Devonian--in -which however there are two hard beds of subordinate value, the -Oriskany sandstone and a Chemung sandstone and conglomerate, that form -low and broken ridges over the softer ground on either side of -them--and the Carboniferous (Mauch Chunk) red shales and some of the -weaker sandstones (Coal measures). - -6. _Former extension of strata to the southeast_.--We are not much -concerned with the conditions under which this great series of beds was -formed; but, as will appear later, it is important for us to recognize -that the present southeastern margin of the beds is not by any means -their original margin in that direction. It is probable that the whole -mass of deposits, with greater or less variations of thickness, -extended at least twenty miles southeast of Blue Mountain, and that -many of the beds extended much farther. The reason for this conclusion -is a simple one. The several resistant beds above-mentioned consist of -quartz sand and pebbles that cannot be derived from the underlying beds -of limestones and shales; their only known source lay in the -crystalline rocks of the paleozoic land to the southeast. South -Mountain may possibly have made part of this paleozoic land; but it -seems more probable that it was land only during the earlier Archean -age, and that it was submerged and buried in Cambrian time and not -again brought to the light of day until it had been crushed into many -local anticlines[9] whose crests were uncovered by Permian and later -erosion. The occurrence of Cambrian limestone on either side of South -Mountain, taken with its compound anticlinal structure, makes it likely -that Medina time found this crystalline area entirely covered by the -Cambrian beds; Medina sands must therefore have come from farther still -to the southeast. A similar argument applies to the source of the -Pocono and Pottsville beds. The measure of twenty miles as the former -southeastern extension of the paleozoic formations therefore seems to -be a moderate one for the average of the whole series; perhaps forty -would be nearer the truth. - -[Footnote 9: Lesley, as below.] - -7. _Cambro-Silurian and Permian deformations_.--This great series of -once horizontal beds is now wonderfully distorted; but the distortions -follow a general rule of trending northeast and southwest, and of -diminishing in intensity from southeast to northwest. In the Hudson -Valley, it is well known that a considerable disturbance occurred -between Cambrian and Silurian time, for there the Medina lies -unconformably on the Hudson River shales. It seems likely, for reasons -that will be briefly given later on, that the same disturbance extended -into Pennsylvania and farther southwest, but that it affected only the -southeastern corner of the State; and that the unconformities in -evidence of it, which are preserved in the Hudson Valley, are here lost -by subsequent erosion. Waste of the ancient land and its -Cambro-Silurian annex still continued and furnished vast beds of -sandstone and sandy shales to the remaining marine area, until at last -the subsiding Paleozoic basin was filled up and the coal marshes -extended broadly across it. At this time we may picture the drainage of -the southeastern land area wandering rather slowly across the great -Carboniferous plains to the still submerged basin far to the west; a -condition of things that is not imperfectly represented, although in a -somewhat more advanced stage, by the existing drainage of the mountains -of the Carolinas across the more modern coastal plain to the Atlantic. - -This condition was interrupted by the great Permian deformation that -gave rise to the main ranges of the Appalachians in Pennsylvania, -Virginia and Tennessee. The Permian name seems appropriate here, for -while the deformation may have begun at an earlier date, and may have -continued into Triassic time, its culmination seems to have been within -Permian limits. It was characterized by a resistless force of -compression, exerted in a southeast-northwest line, in obedience to -which the whole series of Paleozoic beds, even twenty or more thousand -feet in thickness, was crowded gradually into great and small folds, -trending northeast and southwest. The subjacent Archean terrane -doubtless shared more or less in the disturbance: for example, South -Mountain is described by Lesley as "not one mountain, but a system of -mountains separated by valleys. It is, geologically considered, a -system of anticlinals with troughs between.... It appears that the -South Mountain range ends eastward [in Cumberland and York Counties] in -a hand with five [anticlinal] fingers."[10] - -[Footnote 10: Proc. Amer. Phil. Soc., xiii, 1873, 6.] - -It may be concluded with fair probability that the folds began to rise -in the southeast, where they are crowded closest together, some of them -having begun here while coal marshes were still forming farther west; -and that the last folds to be begun were the fainter ones on the -plateau, now seen in Negro mountain and Chestnut and Laurel ridges. In -consequence of the inequalities in the force of compression or in the -resistance of the yielding mass, the folds do not continue indefinitely -with horizontal axes, but vary in height, rising or falling away in -great variety. Several adjacent folds often follow some general control -in this respect, their axes rising and falling together. It is to an -unequal yielding of this kind that we owe the location of the -Anthracite synclinal basins in eastern Pennsylvania, the Coal Measures -being now worn away from the prolongation of the synclines, which rise -in either direction. - -8. _Perm-Triassic denudation_.--During and for a long time after this -period of mountain growth, the destructive processes of erosion wasted -the land and lowered its surface. An enormous amount of material was -thus swept away and laid down in some unknown ocean bed. We shall speak -of this as the Perm-Triassic period of erosion. A measure of its vast -accomplishment is seen when we find that the Newark formation, which is -generally correlated with Triassic or Jurassic time, lies unconformably -on the eroded surface of Cambrian and Archean rocks in the southeastern -part of the State, where we have concluded that the Paleozoic series -once existed; where the strata must have risen in a great mountain mass -as a result of the Appalachian deformations; and whence they must -therefore have been denuded before the deposition of the Newark beds. -Not only so; the moderate sinuosity of the southeastern or under -boundary of the Newark formation indicates clearly enough that the -surface on which that portion of the formation lies is one of no great -relief or inequality; and such a surface can be carved out of an -elevated land only after long continued denudation, by which -topographic development is carried beyond the time of its greatest -strength or maturity into the fainter expression of old age. This is a -matter of some importance in our study of the development of the rivers -of Pennsylvania; and it also constitutes a good part of the evidence -already referred to as indicating that there must have been some -earlier deformations of importance in the southeastern part of the -State; for it is hardly conceivable that the great Paleozoic mass could -have been so deeply worn off of the Newark belt between the making of -the last of the coal beds and the first of the Newark. It seems more in -accordance with the facts here recounted and with the teachings of -geological history in general to suppose, as we have here, that -something of the present deformation of the ancient rocks underlying -the Newark beds was given at an early date, such as that of the Green -Mountain growth; and that a certain amount of the erosion of the folded -beds was thus made possible in middle Paleozoic time; then again at -some later date, as Permian, a second period of mountain growth -arrived, and further folding was effected, and after this came deeper -erosion; thus dividing the destructive work that was done into several -parts, instead of crowding it all into the post-Carboniferous time -ordinarily assigned to it. It is indeed not impossible that an -important share of what we have called the Permian deformation was, as -above suggested, accomplished in the southeastern part of the State -while the coal beds were yet forming in the west; many grains of sand -in the sandstones of the Coal Measures may have had several temporary -halts in other sandstone beds between the time of their first erosion -from the Archean rocks and the much later time when they found the -resting place that they now occupy.[11] - -[Footnote 11: These considerations may have value in showing that the -time in which the lateral crushing of the Appalachians was accomplished -was not so brief as is stated by Reade in a recent article in the -American Geologist, iii, 1889, 106.] - -9. _Newark deposition_.--After the great Paleozoic and Perm-Triassic -erosions thus indicated, when the southeastern area of ancient -mountains had been well worn down and the Permian folds of the central -district had acquired a well developed drainage, there appeared an -opportunity for local deposition in the slow depression of a -northeast-southwest belt of the deeply wasted land, across the -southeastern part of the State; and into this trough-like depression, -the waste from the adjacent areas on either side was carried, building -the Newark formation. This may be referred to as the Newark or -Trias-Jurassic period of deposition. The volume of this formation is -unknown, as its thickness and original area are still undetermined; but -it is pretty surely of many thousand feet in vertical measure, and its -original area may have been easily a fifth or a quarter in excess of -its present area, if not larger yet. So great a local accumulation -seems to indicate that while the belt of deposition was sinking, the -adjacent areas were rising, in order to furnish a continual supply of -material; the occurrence of heavy conglomerates along the margins of -the Newark formation confirms this supposition, and the heavy breccias -near Reading indicate the occurrence of a strong topography and a -strong transporting agent to the northwest of this part of the Newark -belt. It will be necessary, when the development of the ancestors of -our present rivers is taken up, to consider the effects of the -depression that determined the locus of Newark deposition and of the -adjacent elevation that maintained a supply of material. - -10. _Jurassic tilting_.--Newark deposition was stopped by a gradual -reversal of the conditions that introduced it. The depression of the -Newark belt was after a time reversed into elevation, accompanied by a -peculiar tilting, and again the waste of the region was carried away to -some unknown resting place. This disturbance, which may be regarded as -a revival of the Permian activity, culminated in Jurassic, or at least -in post-Newark time, and resulted in the production of the singular -monoclinal attitude of the formation; and as far as I can correlate it -with the accompanying change in the underlying structures, it involved -there an over-pushing of the closed folds of the Archean and Paleozoic -rocks. This is illustrated in figs. 2 and 3, in which the original and -disturbed attitudes of the Newark and the underlying formations are -roughly shown, the over-pushing of the fundamental folds causing the -monoclinal and probably faulted structure in the overlying beds.[12] If -this be true, we might suspect that the unsymmetrical attitude of the -Appalachian folds, noted by Rogers as a characteristic of the range, is -a feature that was intensified if not originated in Jurassic and not in -Permian time. - -[Footnote 12: Amer. Journ. Science, xxxii, 1886, 342; and Seventh Ann. -Rept. U. S. Geol. Survey, 1888, 486.] - -[Illustration: FIG. 2.] - -[Illustration: FIG. 3.] - -It is not to be supposed that the Jurassic deformation was limited to -the area of the Newark beds; it may have extended some way on either -side; but it presumably faded out at no great distance, for it has not -been detected in the history of the Atlantic and Mississippi regions -remote from the Newark belt. In the district of the central folds of -Pennsylvania, with which we are particularly concerned, this -deformation was probably expressed in a further folding and -over-pushing of the already partly folded beds, with rapidly decreasing -effect to the northwest; and perhaps also by slip-faults, which at the -surface of the ground nearly followed the bedding planes: but this is -evidently hypothetical to a high degree. The essential point for our -subsequent consideration is that the Jurassic deformation was probably -accompanied by a moderate elevation, for it allowed the erosion of the -Newark beds and of laterally adjacent areas as well. - -11. _Jura-Cretaceous denudation_.--In consequence of this elevation, a -new cycle of erosion was entered upon, which I shall call the -Jura-Cretaceous cycle. It allowed the accomplishment of a vast work, -which ended in the production of a general lowland of denudation, a -wide area of faint relief, whose elevated remnants are now to be seen -in the even ridge-crests that so strongly characterize the central -district, as well as in certain other even uplands, now etched by the -erosion of a later cycle of destructive work. I shall not here take -space for the deliberate statement of the argument leading to this end, -but its elements are as follows: the extraordinarily persistent -accordance among the crest-line altitudes of many Medina and -Carboniferous ridges in the central district; the generally -corresponding elevation of the western plateau surface, itself a -surface of erosion, but now trenched by relatively deep and narrow -valleys; the generally uniform and consistent altitude of the uplands -in the crystalline highlands of northern New Jersey and in the South -Mountains of Pennsylvania; and the extension of the same general -surface, descending slowly eastward, over the even crest-lines of the -Newark trap ridges. Besides the evidence of less continental elevation -thus deduced from the topography, it may be noted that a lower stand of -the land in Cretaceous time than now is indicated by the erosion that -the Cretaceous beds have suffered in consequence of the elevation that -followed their deposition. The Cretaceous transgression in the western -states doubtless bears on the problem also. Finally it may be fairly -urged that it is more accordant with what is known about old mountains -in general to suppose that their mass has stood at different attitudes -with respect to base level during their long period of denudation than -to suppose that they have held one attitude through all the time since -their deformation. - -It is natural enough that the former maintenance of some lower altitude -than the present should have expression in the form of the country, if -not now extinguished by subsequent erosion. It is simply the reverse of -this statement that leads us to the above-stated conclusion. We may be -sure that the long maintained period of relative quiet was of great -importance in allowing time for the mature adjustment of the rivers of -the region, and hence due account must be taken of it in a later -section. I say relative quiet, for there were certainly subordinate -oscillations of greater or less value; McGee has detected records of -one of these about the beginning of Cretaceous time, but its effects -are not now known to be of geographic value; that is, they do not now -manifest themselves in the form of the present surface of the land, but -only in the manner of deposition and ancient erosion of certain -deposits.[13] Another subordinate oscillation in the sense of a -moderate depression seems to have extended through middle and later -Cretaceous time, resulting in an inland transgression of the sea and -the deposit of the Cretaceous formation unconformably on the previous -land surface for a considerable distance beyond the present margin of -the formation.[14] This is important as affecting our rivers. Although -these oscillations were of considerable geological value, I do not -think that for the present purposes they call for any primary division -of the Jura-Cretaceous cycle; for as the result of this long period of -denudation we find but a single record in the great lowland of erosion -above described, a record of prime importance in the geographic -development of our region, that will often be referred to. The surface -of faint relief then completed may be called the Cretaceous baselevel -lowland. It may be pictured as a low, undulating plain of wide extent, -with a portion of its Atlantic margin submerged and covered over with a -relatively thin marine deposit of sands, marls and clays. - -[Footnote 13: Amer. Jour. Science, xxxv, 1888, 367, 448.] - -[Footnote 14: This statement is based on a study of the geographic -evolution of northern New Jersey, in preparation for publication.] - -12. _Tertiary elevation and denudation_.--This broad lowland is a -lowland no longer. It has been raised over the greater part of its area -into a highland, with an elevation of from one to three thousand feet, -sloping gently eastward and descending under the Atlantic level near -the present margin of the Cretaceous formation. The elevation seems to -have taken place early in Tertiary time, and will be referred to as of -that date. Opportunity was then given for the revival of the previously -exhausted forces of denudation, and as a consequence we now see the -formerly even surface of the plain greatly roughened by the incision of -deep valleys and the opening of broad lowlands on its softer rocks. -Only the harder rocks retain indications of the even surface which once -stretched continuously across the whole area. The best indication of -the average altitude at which the mass stood through the greater part -of post-Cretaceous time is to be found on the weak shales of the Newark -formation in New Jersey and Pennsylvania, and on the weak Cambrian -limestones of the great Kittatinny valley; for both of these areas have -been actually almost baselevelled again in the Tertiary cycle. They -will be referred to as the Tertiary baselevel lowlands; and the valleys -corresponding to them, cut in the harder rocks, as well as the rolling -lowlands between the ridges of the central district of Pennsylvania -will be regarded as of the same date. Whatever variations of level -occurred in this cycle of development do not seem to have left marks of -importance on the inland surface, though they may have had greater -significance near the coast. - -13. _Later changes of level_.--Again at the close of Tertiary time, -there was an elevation of moderate amount, and to this may be referred -the trenches that are so distinctly cut across the Tertiary baselevel -lowland by the larger rivers, as well as the lateral shallower channels -of the smaller streams. This will be called the Quaternary cycle; and -for the present no further mention of the oscillations known to have -occurred in this division of time need be considered; the reader may -find careful discussion of them in the paper by McGee, above referred -to. It is proper that I should add that the suggestion of baselevelling -both of the crest-lines and of the lowlands, that I have found so -profitable in this and other work, is due largely to personal -conference with Messrs. Gilbert and McGee of the Geological Survey; but -it is not desired to make them in any way responsible for the -statements here given. - -[Illustration: FIG. 4.] - -[Illustration: FIG. 5.] - -14. _Illustrations of Pennsylvanian topography_.--A few sketches made -during a recent recess-trip with several students through Pennsylvania -may be introduced in this connection. The first, fig. 4, is a view from -Jenny Jump mountain, on the northwestern side of the New Jersey -highlands, looking northwest across the Kittatinny valley-lowland to -Blue or Kittatinny mountain, where it is cut at the Delaware Water-gap. -The extraordinarily level crest of the mountain preserves record of the -Cretaceous baselevel lowland; since the elevation of this ancient -lowland, its softer rocks have, as it were, been etched out, leaving -the harder ones in relief; thus the present valley-lowland is to be -explained. In consequence of the still later elevation of less amount, -the Delaware has cut a trench in the present lowland, which is partly -seen to the left in the sketch. Fig. 5 is a general view of the Lehigh -plateau and cañon, looking south from Bald Mountain just above Penn -Haven Junction. Blue mountain is the most distant crest, seen for a -little space. The ridges near and above Mauch Chunk form the other -outlines; all rising to an astonishingly even altitude, in spite of -their great diversity of structure. Before the existing valleys were -excavated, the upland surface must have been an even plain--the -Cretaceous baselevel lowland elevated into a plateau. The valleys cut -into the plateau during the Tertiary cycle are narrow here, because the -rocks are mostly hard. The steep slopes of the cañon-like valley of the -Lehigh and the even crests of the ridges manifestly belong to different -cycles of development. Figs. 6 and 7 are gaps cut in Black Log and -Shade mountain, by a small upper branch stream of the Juniata in -southeastern Huntingdon county. The stream traverses a breached -anticlinal of Medina sandstone, of which these mountains are the -lateral members. A long narrow valley is opened on the axial Trenton -limestone between the two. The gaps are not opposite to each other, and -therefore in looking through either gap from the outer country the even -crest of the further ridge is seen beyond the axial valley. The gap in -Black Log mountain, fig. 6, is located on a small fracture, but in this -respect it is unlike most of its fellows.[15] The striking similarity -of the two views illustrates the uniformity that so strongly -characterizes the Medina ridges of the central district. Fig. 8 is in -good part an ideal view, based on sketches on the upper Susquehanna, -and designed to present a typical illustration of the more significant -features of the region. It shows the even crest-lines of a high Medina -or Pocono ridge in the background, retaining the form given to it in -the Cretaceous cycle; the even lowlands in the foreground, opened on -the weaker Siluro-Devonian rocks in the Tertiary cycle; and the uneven -ridges in the middle distance marking the Oriskany and Chemung beds of -intermediate hardness that have lost the Cretaceous level and yet have -not been reduced to the Tertiary lowland. The Susquehanna flows -distinctly below the lowland plain, and the small side streams run in -narrow trenches of late Tertiary and Quaternary date. - -[Footnote 15: Second Geol. Surv. Pa., Report T_{3}, 19.] - -[Illustration: FIG. 6.] - -[Illustration: FIG. 7.] - -[Illustration: FIG. 8.] - -If this interpretation is accepted, and the Permian mountains are seen -to have been once greatly reduced and at a later time worn out, while -the ridges of to-day are merely the relief left by the etching of -Tertiary valleys in a Cretaceous baselevelled lowland, then we may well -conclude with Powell that "mountains cannot remain long as mountains; -they are ephemeral topographic forms."[16] - -[Footnote 16: Geol. Uinta Mountains, 1876, 196.] - - -PART THIRD. _General conception of the history of a river_. - -15. _The complete cycle of river life: youth, adolescence, maturity and -old age_.--The general outline of an ideal river's history may be now -considered, preparatory to examining the special history of the rivers -of Pennsylvania, as controlled by the geological events just narrated. - -Rivers are so long lived and survive with more or less modification so -many changes in the attitude and even in the structure of the land, -that the best way of entering on their discussion seems to be to -examine the development of an ideal river of simple history, and from -the general features thus discovered, it may then be possible to -unravel the complex sequence of events that leads to the present -condition of actual rivers of complicated history. - -A river that is established on a new land may be called an original -river. It must at first be of the kind known as a consequent river, for -it has no ancestor from which to be derived. Examples of simple -original rivers may be seen in young plains, of which southern New -Jersey furnishes a fair illustration. Examples of essentially original -rivers may be seen also in regions of recent and rapid displacement, -such as the Jura or the broken country of southern Idaho, where the -directly consequent character of the drainage leads us to conclude -that, if any rivers occupied these regions before their recent -deformation, they were so completely extinguished by the newly made -slopes that we see nothing of them now. - -Once established, an original river advances through its long life, -manifesting certain peculiarities of youth, maturity and old age, by -which its successive stages of growth may be recognized without much -difficulty. For the sake of simplicity, let us suppose the land mass, -on which an original river has begun its work, stands perfectly still -after its first elevation or deformation, and so remains until the -river has completed its task of carrying away all the mass of rocks -that rise above its baselevel. This lapse of time will be called a -cycle in the life of a river. A complete cycle is a long measure of -time in regions of great elevation or of hard rocks; but whether or not -any river ever passed through a single cycle of life without -interruption we need not now inquire. Our purpose is only to learn what -changes it would experience if it did thus develop steadily from -infancy to old age without disturbance. - -In its infancy, the river drains its basin imperfectly; for it is then -embarrassed by the original inequalities of the surface, and lakes -collect in all the depressions. At such time, the ratio of evaporation -to rainfall is relatively large, and the ratio of transported land -waste to rainfall is small. The channels followed by the streams that -compose the river as a whole are narrow and shallow, and their number -is small compared to that which will be developed at a later stage. The -divides by which the side-streams are separated are poorly marked, and -in level countries are surfaces of considerable area and not lines at -all. It is only in the later maturity of a system that the divides are -reduced to lines by the consumption of the softer rocks on either side. -The difference between constructional forms and those forms that are -due to the action of denuding forces is in a general way so easily -recognized, that immaturity and maturity of a drainage area can be -readily discriminated. In the truly infantile drainage system of the -Red River of the North, the inter-stream areas are so absolutely flat -that water collects on them in wet weather, not having either original -structural slope or subsequently developed denuded slope to lead it to -the streams. On the almost equally young lava blocks of southern -Oregon, the well-marked slopes are as yet hardly channeled by the flow -of rain down them, and the depressions among the tilted blocks are -still undrained, unfilled basins. - -As the river becomes adolescent, its channels are deepened and all the -larger ones descend close to baselevel. If local contrasts of hardness -allow a quick deepening of the down-stream part of the channel, while -the part next up-stream resists erosion, a cascade or waterfall -results; but like the lakes of earlier youth, it is evanescent, and -endures but a small part of the whole cycle of growth; but the falls on -the small headwater streams of a large river may last into its -maturity, just as there are young twigs on the branches of a large -tree. With the deepening of the channels, there comes an increase in -the number of gulleys on the slopes of the channel; the gulleys grow -into ravines and these into side valleys, joining their master streams -at right angles (La Noë and Margerie). With their continued -development, the maturity of the system is reached; it is marked by an -almost complete acquisition of every part of the original -constructional surface by erosion under the guidance of the streams, so -that every drop of rain that falls finds a way prepared to lead it to a -stream and then to the ocean, its goal. The lakes of initial -imperfection have long since disappeared; the waterfalls of adolescence -have been worn back, unless on the still young headwaters. With the -increase of the number of side-streams, ramifying into all parts of the -drainage basin, there is a proportionate increase in the surface of the -valley slopes, and with this comes an increase in the rate of waste -under atmospheric forces; hence it is at maturity that the river -receives and carries the greatest load; indeed, the increase may be -carried so far that the lower trunk-stream, of gentle slope in its -early maturity, is unable to carry the load brought to it by the upper -branches, and therefore resorts to the temporary expedient of laying it -aside in a flood-plain. The level of the flood-plain is sometimes built -up faster than the small side-streams of the lower course can fill -their valleys, and hence they are converted for a little distance above -their mouths into shallow lakes. The growth of the flood-plain also -results in carrying the point of junction of tributaries farther and -farther down stream, and at last in turning lateral streams aside from -the main stream, sometimes forcing them to follow independent courses -to the sea (Lombardini). But although thus separated from the main -trunk, it would be no more rational to regard such streams as -independent rivers than it would be to regard the branch of an old -tree, now fallen to the ground in the decay of advancing age, as an -independent plant; both are detached portions of a single individual, -from which they have been separated in the normal processes of growth -and decay. - -In the later and quieter old age of a river system, the waste of the -land is yielded slower by reason of the diminishing slopes of the -valley sides; then the headwater streams deliver less detritus to the -main channel, which, thus relieved, turns to its postponed task of -carrying its former excess of load to the sea, and cuts terraces in its -flood-plain, preparatory to sweeping it away. It does not always find -the buried channel again, and perhaps settling down on a low spur a -little to one side of its old line, produces a rapid or a low fall on -the lower slope of such an obstruction (Penck). Such courses may be -called locally superimposed. - -It is only during maturity and for a time before and afterwards that -the three divisions of a river, commonly recognized, appear most -distinctly; the torrent portion being the still young headwater -branches, growing by gnawing backwards at their sources; the valley -portion proper, where longer time of work has enabled the valley to -obtain a greater depth and width; and the lower flood-plain portion, -where the temporary deposition of the excess of load is made until the -activity of middle life is past. - -Maturity seems to be a proper term to apply to this long enduring -stage; for as in organic forms, where the term first came into use, it -here also signifies the highest development of all functions between a -youth of endeavor towards better work and an old age of relinquishment -of fullest powers. It is the mature river in which the rainfall is best -lead away to the sea, and which carries with it the greatest load of -land waste; it is at maturity that the regular descent and steady flow -of the river is best developed, being the least delayed in lakes and -least overhurried in impetuous falls. - -Maturity past, and the power of the river is on the decay. The relief -of the land diminishes, for the streams no longer deepen their valleys -although the hill tops are degraded; and with the general loss of -elevation, there is a failure of rainfall to a certain extent; for it -is well known that up to certain considerable altitudes rainfall -increases with height. A hyetographic and a hypsometric map of a -country for this reason show a marked correspondence. The slopes of the -headwaters decrease and the valley sides widen so far that the land -waste descends from them slower than before. Later, what with failure -of rainfall and decrease of slope, there is perhaps a return to the -early imperfection of drainage, and the number of side streams -diminishes as branches fall from a dying tree. The flood-plains of -maturity are carried down to the sea, and at last the river settles -down to an old age of well-earned rest with gentle flow and light load, -little work remaining to be done. The great task that the river entered -upon is completed. - -16. _Mutual adjustment of river courses_.--In certain structures, -chiefly those of mountainous disorder on which the streams are at first -high above baselevel, there is a process of adjustment extremely -characteristic of quiet river development, by which the down-hill -courses that were chosen in early life, and as we may say unadvisedly -and with the heedlessness and little foresight of youth, are given up -for others better fitted for the work of the mature river system. A -change of this kind happens when the young stream taking the lowest -line for its guide happens to flow on a hard bed at a considerable -height above baselevel, while its branches on one side or the other -have opened channels on softer beds: a part of the main channel may -then be deserted by the withdrawal of its upper waters to a lower -course by way of a side stream. The change to better adjustment also -happens when the initial course of the main stream is much longer than -a course that may be offered to its upper portion by the backward -gnawing of an adjacent stream (Löwl, Penck). Sometimes the lateral -cutting or planation that characterizes the main trunk of a mature -river gives it possession of an adjacent smaller stream whose bed is at -a higher level (Gilbert). A general account of these processes may be -found in Phillippson's serviceable "Studien über Wasserscheiden" -(Leipzig, 1886). This whole matter is of much importance and deserves -deliberate examination. It should be remembered that changes in river -courses of the kind now referred to are unconnected with any external -disturbance of the river basin, and are purely normal spontaneous acts -during advancing development. Two examples, pertinent to our special -study, will be considered. - -[Illustration: FIG. 9.] - -[Illustration: FIG. 10.] - -Let AB, fig. 9, be a stream whose initial consequent course led it down -the gently sloping axial trough of a syncline. The constructional -surface of the syncline is shown by contours. Let the succession of -beds to be discovered by erosion be indicated in a section, laid in -proper position on the several diagrams, but revolved into the -horizontal plane, the harder beds being dotted and the baselevel -standing at OO. Small side streams will soon be developed on the slopes -of the syncline, in positions determined by cross-fractures or more -often by what we call accident; the action of streams in similar -synclines on the outside of the enclosing anticlines will be omitted -for the sake of simplicity. In time, the side streams will cut through -the harder upper bed M and enter the softer bed N, on which -longitudinal channels, indicated by hachures, will be extended along -the strike, fig. 10 (La Noë and Margerie). Let these be called -"subsequent" streams. Consider two side streams of this kind, C and D, -heading against each other at E, one joining the main stream lower down -the axis of the syncline than the other. The headwaters of C will rob -the headwaters of D, because the deepening of the channel of D is -retarded by its having to join the main stream at a point where the -hard bed in the axis of the fold holds the main channel well above -baselevel. The notch cut by D will then be changed from a water-gap to -a wind-gap and the upper portion of D will find exit through the notch -cut by C, as in fig. 11. As other subsequent headwaters make capture of -C, the greater depth to which the lateral valley is cut on the soft -rock causes a slow migration of the divides in the abandoned gaps -towards the main stream, and before long the upper part of the main -stream itself will be led out of the synclinal axis to follow the -monoclinal valley at one side for a distance, fig. 12, until the axis -can be rejoined through the gap where the axial portion of the -controlling hard bed is near or at baselevel. The upper part of the -synclinal trough will then be attacked by undercutting on the slope of -the quickly deepened channels of the lateral streams, and the hard bed -will be worn away in the higher part of the axis before it is consumed -in the lower part. The location of the successful lateral stream on one -or the other side of the syncline may be determined by the dip of the -beds, gaps being cut quicker on steep than on gentle dips. If another -hard bed is encountered below the soft one, the process will be -repeated; and the mature arrangement of the streams will be as in fig. -13 (on a smaller scale than the preceding), running obliquely off the -axis of the fold where a hard bed of the syncline rises above -baselevel, and returning to the axis where the hard bed is below or at -baselevel; a monoclinal stream wandering gradually from the axis along -the strike of the soft bed, AE, by which the side-valley is located and -returning abruptly to the axis by a cataclinal[17] stream in a -transverse gap, EB, in the next higher hard bed, and there rejoining -the diminished representative or survivor of the original axial or -synclinal stream, GB. - -[Footnote 17: See the terminology suggested by Powell. Expl. Col. R. of -the West, 1875, 160. This terminology is applicable only to the most -detailed study of our rivers, by reason of their crossing so many -folds, and changing so often from longitudinal to transverse courses.] - -[Illustration: FIG. 11.] - -[Illustration: FIG. 12.] - -[Illustration: FIG. 13.] - -17. _Terminology of rivers changed by adjustment_.--A special -terminology is needed for easy reference to the several parts of the -streams concerned in such an adjustment. Let AB and CD, fig. 14, be -streams of unequal size cutting gaps, H and G, in a ridge that lies -transverse to their course. CD being larger than AB will deepen its gap -faster. Of two subsequent streams, JE and JF, growing on the up-stream -side of the ridge, JE will have the steeper slope, because it joins the -deeper master-stream. The divide, J, will therefore be driven towards -AB, and if all the conditions concerned conspire favorably, JE will at -last tap AB at F, and lead the upper part, AF, out by the line FEGD, -fig. 15, through the deeper gap, G. We may then say that JE becomes the -_divertor_ of AF, which is _diverted_; and when the process is -completed, by the transfer of the divide from J, on the soft rocks, to -a stable location, H, on the hard rocks, there will be a short -_inverted_ stream, HF; while HB is the remaining _beheaded_ portion of -the original stream, AB, and the water-gap of AB becomes a wind-gap, H. -It is very desirable that geographic exploration should discover -examples of the process of adjustment in its several stages. The -preparatory stage is easily recognized by the difference in the size of -the two main streams, the difference in the depth of their gaps, and -the unsymmetrical position of the divide, J. The very brief stage of -transition gives us the rare examples of bifurcating streams. For a -short time after capture of the diverted stream by the divertor, the -new divide will lie between F and H, in an unstable position, the -duration of this time depending on the energy of the process of -capture. - -[Illustration: FIG. 14.] - -[Illustration: FIG. 15.] - -The consequences resulting from readjustments of this kind by which -their recent occurrence can be detected are: a relatively sudden -increase of volume of the divertor and hence a rapid deepening of the -course of the diverting stream, FE, and of the diverted, AF, near the -point of capture; small side-streams of these two being unable to keep -pace with this change will join their masters in local rapids, which -work up stream gradually and fade away (Löwl, Penck, McGee). The -expanded portion, ED, of the larger stream, CD, already of faint slope, -may be locally overcome for a time with the increase of detritus that -will be thus delivered to it at the entrance, E, of the divertor; while -the beheaded stream, HB, will find itself embarrassed to live up to the -habits of its large valley [Heim]. Geographic exploration with these -matters in mind offers opportunity for the most attractive discoveries. - -[Illustration: FIG. 16.] - -[Illustration: FIG. 17.] - -[Illustration: FIG. 18.] - -18. _Examples of adjustment_.--Another case is roughly figured in the -next three diagrams, figs. 16, 17, 18. Two adjacent synclinal streams, -EA and HB, join a transverse master stream, C, but the synclines are of -different forms; the surface axis of one, EA, stands at some altitude -above baselevel until it nearly reaches the place of the transverse -stream; while the axis of the other, HB, descends near baselevel at a -considerable distance from the transverse stream. As lateral valleys, E -and D, are opened on the anticline between the synclines by a process -similar to that already described, the divide separating them will -shift towards the stream of fainter slope, that is, towards the -syncline, EA, whose axis holds its hard beds above baselevel; and in -time the upper part of the main stream will be withdrawn from this -syncline to follow an easier course by crossing to the other, as in -fig. 17. If the elevation of the synclinal axis, AES, take the shape of -a long flat arch, descending at the further end into a synclinal lake -basin, S, whose outlet is along the arching axis, SA, then the mature -arrangement of stream courses will lead the lake outlet away from the -axis by some gap in the nearer ascending part of the arch where the -controlling hard bed falls near to baselevel, as at F, fig. 18,[18] and -will take it by some subsequent course, FD, across the lowland that is -opened on the soft beds between the synclines, and carry it into the -lower syncline, HB, at D where the hard beds descend below baselevel. - -[Footnote 18: This figure would be improved if a greater amount of -wasting around the margin of the hard bed were indicated in comparison -with the preceding figure.] - -The variety of adjustments following the general principle here -indicated is infinite. Changes of greater or less value are thus -introduced in the initial drainage areas, until, after attaining an -attitude of equilibrium, further change is arrested, or if occurring, -is relatively insignificant. It should be noticed that the new stream -courses thus chosen are not named by any of the terms now current to -express the relation of stream and land history; they are neither -consequent, antecedent nor superimposed. The stream is truly still an -original stream, although no longer young; but its channel is not in -all parts strictly consequent on the initial constructional form of the -land that it drains. Streams thus re-arranged may therefore be named -original streams of mature adjustment. - -It should be clearly recognized that the process of adjustment is a -very slow one, unless measured in the extremely long units of a river's -life. It progresses no faster than the weathering away of the slopes of -a divide, and here as a rule weathering is deliberate to say the least, -unless accelerated by a fortunate combination of favoring conditions. -Among these conditions, great altitude of the mass exposed to erosion -stands first, and deep channeling of streams below the surface--that -is, the adolescent stage of drainage development--stands second. The -opportunity for the lateral migration of a divide will depend on the -inequality of the slopes on its two sides, and here the most important -factors are length of the two opposite stream courses from the water -parting to the common baselevel of the two, and inequality of structure -by which one stream may have an easy course and the other a hard one. -It is manifest that all these conditions for active shifting of divides -are best united in young and high mountain ranges, and hence it is that -river adjustments have been found and studied more in the Alps than -elsewhere. - -19. _Revival of rivers by elevation and drowning by depression_.--I -make no contention that any river in the world ever passed through a -simple uninterrupted cycle of the orderly kind here described. But by -examining many rivers, some young and some old, I do not doubt that -this portrayal of the ideal would be found to be fairly correct if -opportunity were offered for its development. The intention of the -sketch is simply to prepare the way for the better understanding of our -actual rivers of more complicated history. - -At the close or at any time during the passage of an initial cycle such -as the one just considered, the drainage area of a river system may be -bodily elevated. The river is then turned back to a new youth and -enters a new cycle of development. This is an extremely common -occurrence with rivers, whose life is so long that they commonly -outlive the duration of a quiescent stage in the history of the land. -Such rivers may be called revived. Examples may be given in which -streams are now in their second or third period of revival, the -elevations that separate their cycles following so soon that but little -work was accomplished in the quiescent intervals. - -The antithesis of this is the effect of depression, by which the lower -course may be drowned, flooded or fjorded. This change is, if slow, -favorable to the development of flood-plains in the lower course; but -it is not essential to their production. If the change is more rapid, -open estuaries are formed, to be transformed to delta-lowlands later -on. - -20. _Opportunity for new adjustments with revival_.--One of the most -common effects of the revival of a river by general elevation is a new -adjustment of its course to a greater or less extent, as a result of -the new relation of baselevel to the hard and soft beds on which the -streams had adjusted themselves in the previous cycle. Synclinal -mountains are most easily explained as results of drainage changes of -this kind [Science, Dec. 21st, 1888]. Streams thus rearranged may be -said to be adjusted through elevation or revival. It is to be hoped -that, as our study advances, single names of brief and appropriate form -may replace these paraphrases; but at present it seems advisable to -keep the desired idea before the mind by a descriptive phrase, even at -the sacrifice of brevity. A significant example may be described. - -[Illustration: FIG. 19.] - -[Illustration: FIG. 20.] - -Let it be supposed that an originally consequent river system has lived -into advanced maturity on a surface whose structure is, like that of -Pennsylvania, composed of closely adjacent anticlinal and synclinal -folds with rising and falling axes, and that a series of particularly -resistant beds composes the upper members of the folded mass. The -master stream, A, fig. 19, at maturity still resides where the original -folds were lowest, but the side streams have departed more less from -the axes of the synclinals that they first followed, in accordance with -the principles of adjustment presented above. The relief of the surface -is moderate, except around the synclinal troughs, where the rising -margins of the hard beds still appear as ridges of more or less -prominence. The minute hachures in figure 19 are drawn on the outcrop -side of these ridges. Now suppose a general elevation of the region, -lifting the synclinal troughs of the hard beds up to baselevel or even -somewhat above it. The deepening of the revived master-stream will be -greatly retarded by reason of its having to cross so many outcrops of -the hard beds, and thus excellent opportunity will be given for -readjustment by the growth of some diverting stream, B, whose beginning -on adjacent softer rocks was already made in the previous cycle. This -will capture the main river at some up-stream point, and draw it nearly -all away from its hard path across the synclinal troughs to an easier -path across the lowlands that had been opened on the underlying softer -beds, leaving only a small beheaded remnant in the lower course. The -final re-arrangement may be indicated in fig. 20. It should be noted -that every capture of branches of the initial main stream made by the -diverting stream adds to its ability for further encroachments, for -with increase of volume the channel is deepened and a flatter slope is -assumed, and the whole process of pushing away the divides is thereby -accelerated. In general it may be said that the larger the stream and -the less its elevation above baselevel, the less likely is it to be -diverted, for with large volume and small elevation it will early cut -down its channel so close to baselevel that no other stream can offer -it a better course to the sea; it may also be said that, as a rule, of -two equal streams, the headwaters of the one having a longer or a -harder course will be diverted by a branch of the stream on the shorter -or easier course. Every case must therefore be examined for itself -before the kind of re-arrangement that may be expected or that may have -already taken place can be discovered. - -21. _Antecedent and superimposed rivers_.--It not infrequently -happens that the surface, on which a drainage system is more or -less fully developed, suffers deformation by tilting, folding or -faulting. Then, in accordance with the rate of disturbance, and -dependent on the size and slope of the streams and the resistance of -the rocks, the streams will be more or less re-arranged, some of the -larger ones persisting in their courses and cutting their channels down -almost as fast as the mass below them is raised and offered to their -action. It is manifest that streams of large volume and considerable -slope are the ones most likely to persevere in this way, while small -streams and large ones of moderate slope may be turned from their -former courses to new courses consequent on the new constructional form -of the land. Hence, after a disturbance, we may expect to find the -smaller streams of the former cycle pretty completely destroyed, while -some of the larger ones may still persist; these would then be called -antecedent streams in accordance with the nomenclature introduced by -Powell.[19] A fuller acquaintance with the development of our rivers -will probably give us examples of river systems of all degrees of -extinction or persistence at times of disturbance. - -[Footnote 19: Exploration of the Colorada River of the West, 1875, 153, -163-166.] - -Since Powell introduced the idea of antecedent valleys and Tietze, -Medlicott and others showed the validity of the explanation in other -regions than the one for which it was first proposed, it has found much -acceptance. Löwl's objection to it does not seem to me to be nearly so -well founded as his suggestion of an additional method of river -development by means of backward headwater erosion and subsequent -capture of other streams, as already described. And yet I cannot help -thinking that the explanation of transverse valleys as antecedent -courses savors of the Gordian method of explaining a difficult matter. -The case of the Green river, to which Powell first gave this -explanation, seems well supported; the examples given by Medlicott in -the Himalayas are as good: but still it does not seem advisable to -explain all transverse streams in this way, merely because they are -transverse. Perhaps one reason why the explanation has become so -popular is that it furnishes an escape from the old catastrophic idea -that fractures control the location of valleys, and is at the same time -fully accordant with the ideas of the uniformitarian school that have -become current in this half of our century. But when it is remembered -that most of the streams of a region are extinguished at the time of -mountain growth, that only a few of the larger ones can survive, and -that there are other ways in which transverse streams may -originate,[20] it is evident that the possibility of any given -transverse stream being antecedent must be regarded only as a -suggestion, until some independent evidence is introduced in its favor. -This may be difficult to find, but it certainly must be searched for; -if not then forthcoming, the best conclusion may be to leave the case -open until the evidence appears. Certainly, if we find a river course -that is accordant in its location with the complicated results of other -methods of origin, then the burden of proof may be said to lie with -those who would maintain that an antecedent origin would locate the -river in so specialized a manner. Even if a river persist for a time in -an antecedent course, this may not prevent its being afterwards -affected by the various adjustments and revivals that have been -explained above: rivers so distinctly antecedent as the Green and the -Sutlej may hereafter be more or less affected by processes of -adjustment, which they are not yet old enough to experience. Hence in -mountains as old as the Appalachians the courses of the present rivers -need not coincide with the location of the pre-Permian rivers, even if -the latter persisted in their courses through the growth of the Permian -folding; subsequent elevations and adjustments to hard beds, at first -buried and unseen, may have greatly displaced them, in accordance with -Löwl's principle. - -[Footnote 20: Hilber, Pet. Mitth., xxxv, 1889, 13.] - -When the deeper channelling of a stream discovers an unconformable -subjacent terrane, the streams persist at least for a time in the -courses that were determined in the overlying mass; they are then -called superimposed (Powell), inherited (Shaler), or epigenetic -(Richthofen). Such streams are particularly liable to readjustment by -transfer of channels from courses that lead them over hard beds to -others on which the hard beds are avoided; for the first choice of -channels, when the unconformable cover was still present, was made -without any knowledge of the buried rock structure or of the -difficulties in which the streams would be involved when they -encountered it. The examples of falls produced when streams terrace -their flood-plains and run on buried spurs has already been referred to -as superimposed; and the rivers of Minnesota now disclosing half-buried -ledges here and there may be instanced as illustrating the transition -stage between simple consequent courses, determined by the form of the -drift sheet on which their flow began, and the fully inconsequent -courses that will be developed there in the future. - -22. _Simple, compound, composite and complex rivers_.--We have thus far -considered an ideal river. It now seems advisable to introduce a few -terms with which to indicate concisely certain well marked -peculiarities in the history of actual rivers. - -An original river has already been defined as one which first takes -possession of a land area, or which replaces a completely extinguished -river on a surface of rapid deformation. - -A river may be simple, if its drainage area is of practically one kind -of structure and of one age; like the rivers of southern New Jersey. -Such rivers are generally small. It may be composite, when drainage -areas of different structure are included in the basin of a single -stream. This is the usual case. - -A compound river is one which is of different ages in its different -parts; as certain rivers of North Carolina, which have old headwaters -rising in the mountains, and young lower courses traversing the coastal -plain. - -A river is complex when it has entered a second or later cycle of -development; the headwaters of a compound river are therefore complex, -while the lower course may be simple, in its first cycle. The degree of -complexity measures the number of cycles that the river has entered. - -When the study of rivers is thus attempted, its necessary complications -may at first seem so great as to render it of no value; but in answer -to this I believe that it may be fairly urged that, although -complicated, the results are true to nature, and if so, we can have no -ground of complaint against them. Moreover, while it is desirable to -reduce the study of the development of rivers to its simplest form, in -order to make it available for instruction and investigation, it must -be remembered that this cannot be done by neglecting to investigate the -whole truth in the hope of avoiding too great complexity, but that -simplicity can be reached safely only through fullness of knowledge, if -at all. - -It is with these points in mind that I have attempted to decipher the -history of the rivers of Pennsylvania. We find in the Susquehanna, -which drains a great area in the central part of the state, an example -of a river which is at once composite, compound and highly complex. It -drains districts of divers structure; it traverses districts of -different ages; and it is at present in its fourth or fifth degree of -complexity, its fourth or fifth cycle of development at least. In -unravelling its history and searching out the earlier courses of -streams which may have long since been abandoned in the processes of -mature adjustment, it will be seen that the size of the present streams -is not always a measure of their previous importance, and to this we -may ascribe the difficulty that attends the attempt to decipher a -river's history from general maps of its stream lines. Nothing but a -detailed examination of geological structure and history suffices to -detect facts and conditions that are essential to the understanding of -the result. - -If the postulates that I shall use seem unsound and the arguments seem -overdrawn, error may at least be avoided by not holding fast to the -conclusions that are presented, for they are presented only -tentatively. I do not feel by any means absolutely persuaded of the -correctness of the results, but at the same time deem them worth giving -out for discussion. The whole investigation was undertaken as an -experiment to see where it might lead, and with the hope that it might -lead at least to a serious study of our river problems. - - -PART FOURTH. _The development of the rivers of Pennsylvania_. - -23. _Means of distinguishing between antecedent and adjusted consequent -rivers_.--The outline of the geological history of Pennsylvania given -above affords means of dividing the long progress of the development of -our rivers into the several cycles which make up their complete life. -We must go far back into the past and imagine ancient streams flowing -down from the Archean land towards the paleozoic sea; gaining length by -addition to their lower portions as the land grew with the building on -of successive mountain ranges; for example, if there were a -Cambro-Silurian deformation, a continuation of the Green Mountains into -Pennsylvania, we suppose that the pre-existent streams must in some -manner have found their way westward to the new coastline; and from the -date of this mountain growth, it is apparent that any streams then born -must have advanced far in their history before the greater Appalachian -disturbance began. At the beginning of the latter, as of the former, -there must have been streams running from the land into the sea, and at -times of temporary elevation of the broad sand-flats of the coal -measures, such streams must have had considerable additions to their -lower length; rising in long-growing Archean highlands or mountains, -snow-capped and drained by glaciers for all we can say to the contrary, -descending across the Green Mountain belt, by that time worn to -moderate relief in the far advanced stage of its topographic -development, and finally flowing across the coal-measure lowlands of -recent appearance. It was across the lower courses of such rivers that -the Appalachian folds were formed, and the first step in our problem -consists in deciding if possible whether the streams held their courses -after the antecedent fashion, or whether they were thrown into new -courses by the growing folds, so that a new drainage system would be -formed. Possibly both conditions prevailed; the larger streams holding -their courses little disturbed, and the smaller ones disappearing, to -be replaced by others as the slopes of the growing surface should -demand. It is not easy to make choice in this matter. To decide that -the larger streams persisted and are still to be seen in the greater -rivers of to-day, only reversed in direction of flow, is certainly a -simple method of treating the problem, but unless some independent -reasons are found for this choice, it savors of assumption. Moreover, -it is difficult to believe that any streams, even if antecedent and -more or less persistent for a time during the mountain growth, could -preserve till now their pre-Appalachian courses through all the varying -conditions presented by the alternations of hard and soft rocks through -which they have had to cut, and at all the different altitudes above -baselevel in which they have stood. A better means of deciding the -question will be to admit provisionally the occurrence of a completely -original system of consequent drainage, located in perfect accord with -the slopes of the growing mountains; to study out the changes of -stream-courses that would result from later disturbances and from the -mutual adjustments of the several members of such a system in the -different cycles of its history; and finally to compare the courses -thus deduced with those now seen. If there be no accord, either the -method is wrong or the streams are not consequent but of some other -origin, such as antecedent; if the accord between deduction and fact be -well marked, varying only where no definite location can be given to -the deduced streams, but agreeing where they can be located more -precisely, then it seems to me that the best conclusion is distinctly -in favor of the correctness of the deductions. For it is not likely, -even if it be possible, that antecedent streams should have -accidentally taken, before the mountains were formed, just such -locations as would have resulted from the subsequent growth of the -mountains and from the complex changes in the initial river courses due -to later adjustments. I shall therefore follow the deductive method -thus indicated and attempt to trace out the history of a completely -original, consequent system of drainage accordant with the growth of -the central mountain district. - -In doing this, it is first necessary to restore the constructional -topography of the region; that is, the form that the surface would have -had if no erosion had accompanied its deformation. This involves -certain postulates which must be clearly conceived if any measure of -confidence is to be gained in the results based upon them. - -24. _Postulates of the argument_.--In the first place, I assume an -essential constancy in the thickness of the paleozoic sediments over -the entire area in question. This is warranted here because the known -variations of thickness are relatively of a second order, and will not -affect the distribution of high and low ground as produced by the -intense Permian folding. The reasons for maintaining that the whole -series had a considerable extension southeast of the present margin of -the Medina sandstone have already been presented. - -In the second place, I shall assume that the dips and folds of the beds -now exposed at the surface of the ground may be projected upwards into -the air in order to restore the form of the eroded beds. This is -certainly inadmissible in detail, for it cannot be assumed that the -folded slates and limestones of the Nittany valley, for instance, give -any close indication of the form that the coal measures would have -taken, had they extended over this district, unworn. But in a general -way, the Nittany massif was a complex arch in the coal measures as well -as in the Cambrian beds; for our purpose and in view of the moderate -relief of the existing topography, it suffices to say that wherever the -lower rocks are now revealed in anticlinal structure, there was a great -upfolding and elevation of the original surface; and wherever the -higher rocks are still preserved, there was a relatively small -elevation. - -In the third place, I assume that by reconstructing from the completed -folds the form which the country would have had if unworn, we gain a -sufficiently definite picture of the form through which it actually -passed at the time of initial and progressive folding. The difference -between the form of the folds completely restored and the form that the -surface actually reached is rather one of degree than of kind; the two -must correspond in the general distribution of high and low ground and -this is the chief consideration in our problem. When we remember how -accurately water finds its level, it will be clearer that what is -needed in the discussion is the location of the regions that were -relatively raised and lowered, as we shall then have marked out the -general course of the consequent water ways and the trend of the -intervening constructional ridges. - -Accepting these postulates, it may be said in brief that the outlines -of the formations as at present exposed are in effect so many contour -lines of the old constructional surface, on which the Permian rivers -took their consequent courses. Where the Trenton limestone is now seen, -the greatest amount of overlying strata must have been removed; hence -the outline of the Trenton formation is our highest contour line. Where -the Helderberg limestone appears, there has been a less amount of -material removed; hence the Helderberg outcrop is a contour of less -elevation. Where the coal beds still are preserved, there has been -least wasting, and these beds therefore mark the lowest contour of the -early surface. It is manifest that this method assumes that the present -outcrops are on a level surface; this is not true, for the ridges -through the State rise a thousand feet more or less over the -intervening valley lowlands, and yet the existing relief does not count -for much in discussing the enormous relief of the Permian surface that -must have been measured in tens of thousands of feet at the time of its -greatest strength. - -[Illustration: FIG. 21. Constructional Permian topography of -Pennsylvania.] - -25. _Constructional Permian topography and consequent drainage_.--A -rough restoration of the early constructional topography is given in -fig. 21 for the central part of the State, the closest shading being -the area of the Trenton limestone, indicating the highest ground, or -better, the places of greatest elevation, while the Carboniferous area -is unshaded, indicating the early lowlands. The prevalence of northeast -and southwest trends was then even more pronounced than now. Several of -the stronger elements of form deserve names, for convenient reference. -Thus we have the great Kittatinny or Cumberland highland, C, C, on the -southeast, backed by the older mountains of Cambrian and Archean rocks, -falling by the Kittatinny slope to the synclinal lowland troughs of the -central district. In this lower ground lay the synclinal troughs of the -eastern coal regions, and the more local Broad Top basin, BT, on the -southwest, then better than now deserving the name of basins. Beyond -the corrugated area that connected the coal basins rose the great -Nittany highland, N, and its southwest extension in the Bedford range, -with the less conspicuous Kishicoquilas highland, K, in the foreground. -Beyond all stretched the great Alleghany lowland plains. The names thus -suggested are compounded of the local names of to-day and the -morphological names of Permian time. - -What would be the drainage of such a country? Deductively we are led to -believe that it consisted of numerous streams as marked in full lines -on the figure, following synclinal axes until some master streams led -them across the intervening anticlinal ridges at the lowest points of -their crests and away into the open country to the northwest. All the -enclosed basins would hold lakes, overflowing at the lowest part of the -rim. The general discharge of the whole system would be to the -northwest. Here again we must resort to special names for the easy -indication of these well-marked features of the ancient and now -apparently lost drainage system. The master stream of the region is the -great Anthracite river, carrying the overflow of the Anthracite lakes -off to the northwest and there perhaps turning along one of the faintly -marked synclines of the plateau and joining the original Ohio, which -was thus confirmed in its previous location across the Carboniferous -marshes. The synclinal streams that entered the Anthracite lakes from -the southwest may be named, beginning on the south, the Swatara, S, -fig. 21, the Wiconisco, Wo, the Tuscarora-Mahanoy, M, the -Juniata-Catawissa, C, and the Wyoming, Wy. One of these, probably the -fourth, led the overflow from the Broad Top lake into the Catawissa -lake on the middle Anthracite river. The Nittany highland formed a -strong divide between the central and northwestern rivers, and on its -outer slope there must have been streams descending to the Alleghany -lowlands; and some of these may be regarded as the lower courses of -Carboniferous rivers, that once rose in the Archean mountains, now -beheaded by the growth of mountain ranges across their middle. - -26. _The Jura mountains homologous with the Permian -Alleghanies_.--However willing one may be to grant the former existence -of such a drainage system as the above, an example of a similar one -still in existence would be acceptable as a witness to the -possibilities of the past. Therefore we turn for a moment to the Jura -mountains, always compared to the Appalachians on account of the -regular series of folds by which the two are characterized. But while -the initial topography is long lost in our old mountains, it is still -clearly perceptible in the young Jura, where the anticlines are still -ridges and the longitudinal streams still follow the synclinal troughs; -while the transverse streams cross from one synclinal valley to another -at points where the intervening anticlinal arches are lowest.[21] We -could hardly ask for better illustration of the deductive drainage -system of our early Appalachians than is here presented. - -[Footnote 21: This is beautifully illustrated in the recent monograph -by La Noë and Margerie on "Les Formes du Terrain."] - -27. _Development and adjustment of the Permian drainage_.--The problem -is now before us. Can the normal sequence of changes in the regular -course of river development, aided by the post-Permian deformations and -elevations, evolve the existing rivers out of the ancient ones? - -In order to note the degree of comparison that exists between the two, -several of the larger rivers of to-day are dotted on the figure. The -points of agreement are indeed few and small. Perhaps the most -important ones are that the Broad Top region is drained by a stream, -the Juniata, which for a short distance follows near the course -predicted for it; and that the Nittany district, then a highland, is -still a well-marked divide although now a lowland. But there is no -Anthracite river, and the region of the ancient coal-basin lakes is now -avoided by large streams; conversely, a great river--the -Susquehanna--appears where no consequent river ran in Permian time, and -the early synclinal streams frequently turn from the structural troughs -to valleys located on the structural arches. - -28. _Lateral water-gaps near the apex of synclinal ridges_.--One of the -most frequent discrepancies between the hypothetical and actual streams -is that the latter never follow the axis of a descending syncline along -its whole length, as the original streams must have done, but depart -for a time from the axis and then return to it, notching the ridge -formed on any hard bed at the side instead of at the apex of its curve -across the axis of the syncline. There is not a single case in the -state of a stream cutting a gap at the apex of such a synclinal curve, -but there are perhaps hundreds of cases where the streams notch the -curve to one side of the apex. This, however, is precisely the -arrangement attained by spontaneous adjustment from an initial axial -course, as indicated in figure 13. The gaps may be located on small -transverse faults, but as a rule they seem to have no such guidance. It -is true that most of our streams now run out of and not into the -synclinal basins, but a reason for this will be found later; for the -present we look only at the location of the streams, not at their -direction of flow. As far as this illustration goes, it gives evidence -that the smaller streams at least possess certain peculiarities that -could not be derived from persistence in a previous accidental -location, but which would be necessarily derived from a process of -adjustment following the original establishment of strictly consequent -streams. Hence the hypothesis that these smaller streams were long ago -consequent on the Permian folding receives confirmation; but this says -nothing as to the origin of the larger rivers, which might at the same -time be antecedent. - -29. _Departure of the Juniata from the Juniata-Catawissa syncline_.--It -may be next noted that the drainage of the Broad Top region does not -follow a single syncline to the Anthracite region, as it should have in -the initial stage of the consequent Permian drainage, but soon turns -aside from the syncline in which it starts and runs across country to -the Susquehanna. It is true that in its upper course the Juniata -departs from the Broad Top region by one of the two synclines that were -indicated as the probable line of discharge of the ancient Broad Top -lake in our restoration of the constructional topography of the State; -there does not appear to be any significant difference between the -summit altitudes of the Tuscarora-Mahanoy and the Juniata-Catawissa -synclinal axes and hence the choice must have been made for reasons -that cannot be detected; or it may be that the syncline lying more to -the northwest was raised last, and for this reason was taken as the -line of overflow. The beginning of the river is therefore not -discordant with the hypothesis of consequent drainage, but the -southward departure from the Catawissa syncline at Lewistown remains to -be explained. It seems to me that some reason for the departure may be -found by likening it to the case already given in figs. 16-18. The -several synclines with which the Juniata is concerned have precisely -the relative attitudes that are there discussed. The Juniata-Catawissa -syncline has parallel sides for many miles about its middle, and hence -must have long maintained the initial Juniata well above baselevel over -all this distance; the progress of cutting down a channel through all -the hard Carboniferous sandstones for so great a distance along the -axis must have been exceedingly slow. But the synclines next south, the -Tuscarora-Mahanoy and the Wiconisco, plunge to the northeast more -rapidly, as the rapid divergence of their margins demonstrates, and -must for this reason have carried the hard sandstones below baselevel -in a shorter distance and on a steeper slope than in the Catawissa -syncline. The further southwestward extension of the Pocono sandstone -ridges in the southern than in the northern syncline gives further -illustration of this peculiarity of form. Lateral capture of the -Juniata by a branch of the initial Tuscarora, and of the latter by a -branch of the Wiconisco therefore seems possible, and the accordance of -the facts with so highly specialized an arrangement is certainly again -indicative of the correctness of the hypothesis of consequent drainage, -and this time in a larger stream than before. At first sight, it -appears that an easier lateral capture might have been made by some of -the streams flowing from the outer slope of the Nittany highland; but -this becomes improbable when it is perceived that the heavy Medina -sandstone would here have to be worn through as well as the repeated -arches of the Carboniferous beds in the many high folds of the Seven -Mountains. Again, as far as present appearances go, we can give no -sufficient reason to explain why possession of the headwaters of the -Juniata was not gained by some subsequent stream of its own, such as G, -fig. 18, instead of by a side-stream of the river in the neighboring -syncline; but it may be admitted, on the other hand, that as far as we -can estimate the chances for conquest, there was nothing distinctly in -favor of one or the other of the side-streams concerned; and as long as -the problem is solved indifferently in favor of one or the other, we -may accept the lead of the facts and say that some control not now -apparent determined that the diversion should be, as drawn, through D -and not through G. The detailed location of the Juniata in its middle -course below Lewistown will be considered in a later section. - -[Illustration: FIG. 22.] - -[Illustration: FIG. 23.] - -[Illustration: FIG. 24.] - -30. _Avoidance of the Broad Top basin by the Juniata -headwaters_.--Another highly characteristic change that the Juniata has -suffered is revealed by examining the adjustments that would have taken -place in the general topography of the Broad Top district during the -Perm-Triassic cycle of erosion. When the basin, BT, fig. 22, was first -outlined, centripetal streams descended its slopes from all sides and -their waters accumulated as a lake in the center, overflowing to the -east into the subordinate basin, A, in the Juniata syncline along side -of the larger basin, and thence escaping northeast. In due time, the -breaching of the slopes opened the softer Devonian rocks beneath and -peripheral lowlands were opened on them. The process by which the -Juniata departed from its original axial location, J, fig. 22, to a -parallel course on the southeastern side of the syncline, J, fig. 23, -has been described (fig. 18). The subsequent changes are manifest. Some -lateral branch of the Juniata, like N, fig. 23, would work its way -around the northern end of the Broad Top canoe on the soft underlying -rocks and capture the axial stream, C, that came from the depression -between Nittany and Kishicoquillas highlands; thus reënforced, capture -would be made of a radial stream from the west, Tn, the existing Tyrone -branch of the Juniata; in a later stage the other streams of the -western side of the basin would be acquired, their divertor -constituting the Little Juniata of to-day; and the end would be when -the original Juniata, A, fig. 22, that once issued from the subordinate -synclinal as a large stream, had lost all its western tributaries, and -was but a shrunken beheaded remnant of a river, now seen in Aughwick -creek, A, fig. 24. In the meantime, the former lake basin was fast -becoming a synclinal mountain of diminishing perimeter. The only really -mysterious courses of the present streams are where the Little Juniata -runs in and out of the western border of the Broad Top synclinal, and -where the Frankstown (FT) branch of the Juniata maintains its -independent gap across Tussey's mountain (Medina), although diverted to -the Tyrone or main Juniata (Tn) by Warrior's ridge (Oriskany) just -below. At the time of the early predatory growth of the initial -divertor, N, its course lay by the very conditions of its growth on -only the weakest rocks; but after this little stream had grown to a -good-sized river, further rising of the land, probably in the time of -the Jurassic elevation, allowed the river to sink its channel to a -greater depth, and in doing so, it encountered the hard Medina -anticline of Jack's mountain; here it has since persisted, because, as -we may suppose, there has been no stream able to divert the course of -so large a river from its crossing of a single hard anticlinal. - -The doubt that one must feel as to the possibility of the processes -just outlined arises, if I may gauge it by my own feeling, rather from -incredulity than from direct objections. It seems incredible that the -waste of the valley slopes should allow the backward growth of N at -such a rate as to enable it to capture the heads of C, Tn, F, and so -on, before they had cut their beds down close enough to the baselevel -of the time to be safe from capture. But it is difficult to urge -explicit objections against the process or to show its quantitative -insufficiency. It must be remembered that when these adjustments were -going on, the region was one of great altitude, its rocks then had the -same strong contrasts of strength and weakness that are so apparent in -the present relief of the surface and the streams concerned were of -moderate size; less than now, for at the time, the Tyrone, Frankstown -and Bedford head branches of the Juniata had not acquired drainage west -of the great Nittany-Bedford anticlinal axis, but were supplied only by -the rainfall on its eastern slope (see section 39)--and all these -conditions conspired to favor the adjustment. Finally, while apparently -extraordinary and difficult of demonstration, the explanation if -applicable at all certainly gives rational correlation to a number of -peculiar and special stream courses in the upper Juniata district that -are meaningless under any other theory that has come to my notice. It -is chiefly for this reason that I am inclined to accept the -explanation. - -31. _Reversal of larger rivers to southeast courses_.--Our large rivers -at present flow to the southeast, not to the northwest. It is difficult -to find any precise date for this reversal of flow from the initial -hypothetical direction, but it may be suggested that it occurred about -the time of the Triassic depression of the Newark belt. We have been -persuaded that much time elapsed between the Permian folding and the -Newark deposition, even under the most liberal allowance for -pre-Permian erosion in the Newark belt; hence when the depression -began, the rivers must have had but moderate northwestward declivity. -The depression and submergence of the broad Newark belt may at this -time have broken the continuity of the streams that once flowed across -it. The headwater streams from the ancient Archean country maintained -their courses to the depression; the lower portions of the rivers may -also have gone on as before; but the middle courses were perhaps turned -from the central part of the state back of the Newark belt. No change -of attitude gives so fitting a cause of the southeastward flow of our -rivers as this. The only test that I have been able to devise for the -suggestion is one that is derived from the relation that exists between -the location of the Newark belt along the Atlantic slope and the course -of the neighboring transverse rivers. In Pennsylvania, where the belt -reaches somewhat beyond the northwestern margin of the crystalline -rocks in South mountain, the streams are reversed, as above stated; but -in the Carolinas where the Newark belt lies far to the east of the -boundary between the Cambrian and crystalline rocks, the Tennessee -streams persevere in what we suppose to have been their original -direction of flow. This may be interpreted as meaning that in the -latter region, the Newark depression was not felt distinctly enough, if -at all, within the Alleghany belt to reverse the flow of the streams; -while in the former region, it was nearer to these streams and -determined a change in their courses. The original Anthracite river ran -to the northwest, but its middle course was afterwards turned to the -southeast. - -I am free to allow that this has the appearance of heaping hypothesis -on hypothesis; but in no other way does the analysis of the history of -our streams seem possible, and the success of the experiment can be -judged only after making it. At the same time, I am constrained to -admit that this is to my own view the least satisfactory of the -suggestions here presented. It may be correct, but there seems to be no -sufficient exclusion of other possibilities. For example, it must not -be overlooked that, if the Anthracite river ran southeast during Newark -deposition, the formation of the Newark northwestward monocline by the -Jurassic tilting would have had a tendency to turn the river back again -to its northwest flow. But as the drainage of the region is still -southeastward, I am tempted to think that the Jurassic tilting was not -here strong enough to reverse the flow of so strong and mature a river -as the Anthracite had by that time come to be; and that the elevation -that accompanied the tilting was not so powerful in reversing the river -to a northwest course as the previous depression of the Newark basin -had been in turning it to the southeast. If the Anthracite did continue -to flow to the southeast, it may be added that the down-cutting of its -upper branches was greatly retarded by the decrease of slope in its -lower course when the monocline was formed. - -The only other method of reversing the original northwestward flow of -the streams that I have imagined is by capture of their headwaters by -Atlantic rivers. This seems to me less effective than the method just -considered; but they are not mutually exclusive and the actual result -may be the sum of the two processes. The outline of the idea is as -follows. The long continued supply of sedimentary material from the -Archean land on the southeast implies that it was as continually -elevated. But there came a time when there is no record of further -supply of material, and when we may therefore suppose the elevation was -no longer maintained. From that time onward, the Archean range must -have dwindled away, what with the encroachment of the Atlantic on its -eastern shore and the general action of denuding forces on its surface. -The Newark depression was an effective aid to the same end, as has been -stated above, and for a moderate distance westward of the depressed -belt, the former direction of the streams must certainly have been -reversed; but the question remains whether this reversal extended as -far as the Wyoming basin, and whether the subsequent formation of the -Newark monocline did not undo the effect of the Newark depression. It -is manifest that as far as our limited knowledge goes, it is impossible -to estimate these matters quantitatively, and hence the importance of -looking for additional processes that may supplement the effect of the -Newark depression and counteract the effect of the Newark uplift in -changing the course of the rivers. Let it be supposed for the moment -that at the end of the Jurassic uplift by which the Newark monocline -was formed, the divide between the Ohio and the Atlantic drainage lay -about the middle of the Newark belt. There was a long gentle descent -westward from this watershed and a shorter and hence steeper descent -eastward. Under such conditions, the divide must have been pushed -westward, and as long as the rocks were so exposed as to open areas of -weak sediments on which capture by the Atlantic streams could go on -with relative rapidity, the westward migration of the divide would be -important. For this reason, it might be carried from the Newark belt as -far as the present Alleghany front, beyond which further pushing would -be slow, on account of the broad stretch of country there covered by -hard horizontal beds. - -The end of this is that, under any of the circumstances here detailed, -there would be early in the Jurassic-Cretaceous cycle a distinct -tendency to a westward migration of the Atlantic-Ohio divide; it is the -consequences of this that have now to be examined. - -32. _Capture of the Anthracite headwaters by the growing -Susquehanna_.--Throughout the Perm-Triassic period of denudation, a -great work was done in wearing down the original Alleghanies. -Anticlines of hard sandstone were breached, and broad lowlands were -opened on the softer rocks beneath. Little semblance of the early -constructional topography remained when the period of Newark depression -was brought to a close; and all the while the headwater streams of the -region were gnawing at the divides, seeking to develop the most perfect -arrangement of waterways. Several adjustments have taken place, and the -larger streams have been reversed in the direction of their flow; but a -more serious problem is found in the disappearance of the original -master stream, the great Anthracite river, which must have at first led -away the water from all the lateral synclinal streams. Being a large -river, it could not have been easily diverted from its course, unless -it was greatly retarded in cutting down its channel by the presence of -many beds of hard rocks on its way. The following considerations may -perhaps throw some light on this obscure point. - -[Illustration: FIG. 25. General distribution of high and low land and -drainage in early Jurassic time.] - -It may be assumed that the whole group of mountains formed by the -Permian deformation had been reduced to a moderate relief when the -Newark deposition was stopped by the Jurassic elevation. The harder -ribs of rock doubtless remained as ridges projecting above the -intervening lowlands, but the strength of relief that had been given by -the constructional forces had been lost. The general distribution of -residual elevations then remaining unsubdued is indicated in fig. 25, -in which the Crystalline, the Medina, and the two Carboniferous -sandstone ridges are denoted by appropriate symbols. In restoring this -phase of the surface form, when the country stood lower than now, I -have reduced the anticlines from their present outlines and increased -the synclines, the change of area being made greatest where the dips -are least, and hence most apparent at the ends of the plunging -anticlines and synclines. Some of the Medina anticlines of Perry and -Juniata counties are not indicated because they were not then -uncovered. The country between the residual ridges of Jurassic time was -chiefly Cambrian limestone and Siluro-Devonian shales and soft -sandstones. The moderate ridges developed on the Oriskany and Chemung -sandstones are not represented. The drainage of this stage retained the -original courses of the streams, except for the adjustments that have -been described, but the great Anthracite river is drawn as if it had -been controlled by the Newark depression and reversed in the direction -of its flow, so that its former upper course on the Cambrian rocks was -replaced by a superimposed Newark lower course. Fig. 25 therefore -represents the streams for the most part still following near their -synclinal axes, although departing from them where they have to enter a -synclinal cove-mountain ridge; the headwaters of the Juniata avoid the -mass of hard sandstones discovered in the bottom of old Broad Top lake, -and flow around them to the north, and then by a cross-country course -to the Wiconisco synclinal, as already described in detail. Several -streams come from the northeast, entering the Anthracite district after -the fashion generalized in fig. 13. Three of the many streams that were -developed on the great Kittatinny slope are located, with their -direction of flow reversed; these are marked Sq, L and D, and are -intended to represent the ancestors of the existing Susquehanna, Lehigh -and Delaware. We have now to examine the opportunities offered to these -small streams to increase their drainage areas. - -The Jurassic elevation, by which the Newark deposition was stopped, -restored to activity all the streams that had in the previous cycle -sought and found a course close to baselevel. They now all set to work -again deepening their channels. But in this restoration of lost -activity with reference to a new baselevel, there came the best -possible chance for numerous re-arrangements of drainage areas by -mutual adjustment into which we must inquire. - -I have already illustrated what seems to me to be the type of the -conditions involved at this time in figs. 19 and 20. The master stream, -A, traversing the synclines, corresponds to the reversed Anthracite -river; the lowlands at the top are those that have been opened out on -the Siluro-Devonian beds of the present Susquehanna middle course -between the Pocono and the Medina ridges. The small stream, B, that is -gaining drainage area in these lowlands, corresponds to the embryo of -the present Susquehanna, Sq, fig. 25, this having been itself once a -branch on the south side of the Swatara synclinal stream, fig. 21, from -which it was first turned by the change of slope accompanying the -Newark depression; but it is located a little farther west than the -actual Susquehanna, so as to avoid the two synclinal cove mountains of -Pocono sandstone that the Susquehanna now traverses, for reasons to be -stated below (section 35). This stream had to cross only one bed of -hard rock, the outer wall of Medina sandstone, between the broad inner -lowlands of the relatively weak Siluro-Devonian rocks and the great -valley lowlands on the still weaker Cambrian limestones. Step by step -it must have pushed its headwater divide northward, and from time to -time it would have thus captured a subsequent stream, that crossed the -lowlands eastward, and entered a Carboniferous syncline by one of the -lateral gaps already described. With every such capture, the power of -the growing stream to capture others was increased. Fig. 19 represents -a stage after the streams in the Swatara and Wiconisco synclines (the -latter then having gained the Juniata) had been turned aside on their -way to the Carboniferous basins. On the other hand, the Anthracite -river, rising somewhere on the plains north of the Wyoming syncline and -pursuing an irregular course from one coal basin to another, found an -extremely difficult task in cutting down its channel across the -numerous hard beds of the Carboniferous sandstones, so often repeated -in the rolling folds of the coal fields. It is also important to -remember that an aid to other conditions concerned in the diversion of -the upper Anthracite is found in the decrease of slope that its lower -course suffered in crossing the coal fields, if that area took any part -in the deformation that produced the Newark monocline--whichever theory -prove true in regard to the origin of the southeastward flow of the -rivers--for loss of slope in the middle course, where the river had to -cross many reefs of hard sandstone, would have been very effective in -lengthening the time allowed for the diversion of the headwaters. - -The question is, therefore, whether the retardation of down-cutting -here experienced by the Anthracite was sufficient to allow the capture -of its headwaters by the Susquehanna. There can be little doubt as to -the correct quality of the process, but whether it was quantitatively -sufficient is another matter. In the absence of any means of testing -its sufficiency, may the result not be taken as the test? Is not the -correspondence between deduction and fact close enough to prove the -correctness of the deduction? - -33. _Present outward drainage of the Anthracite basins_.--The Lehigh, -like the Susquehanna, made an attempt to capture the headwaters of -adjacent streams, but failed to acquire much territory from the -Anthracite because the Carboniferous sandstones spread out between the -two in a broad plateau of hard rocks, across which the divide made -little movement. The plateau area that its upper branches drain is, I -think, the conquest of a later cycle of growth. The Delaware had little -success, except as against certain eastern synclinal branches of the -Anthracite, for the same reason. The ancestor of the Swatara of to-day -made little progress in extending its headwaters because its point of -attack was against the repeated Carboniferous sandstones in the Swatara -synclinal. One early stream alone found a favorable opportunity for -conquest, and thus grew to be the master river--the Susquehanna of -to-day. The head of the Anthracite was carried away by this captor, and -its beheaded lower portion remains in our Schuylkill. The Anthracite -coal basins, formerly drained by the single master stream, have since -been apportioned to the surrounding rivers. As the Siluro-Devonian -lowlands were opened around the coal-basins, especially on the north -and west, the streams that formerly flowed into the basins were -gradually inverted and flowed out of them, as they still do. The extent -of the inversion seems to be in a general way proportionate to its -opportunity. The most considerable conquests were made in the upper -basins, where the Catawissa and Nescopec streams of to-day drain many -square miles of wide valleys opened on the Mauch Chunk red shale -between the Pocono and Pottsville sandstone ridges; the ancient middle -waters of the Anthracite here being inverted to the Susquehanna -tributaries, because the northern coal basins were degraded very slowly -after the upper Anthracite had been diverted. The Schuylkill as the -modern representative of the Anthracite retains only certain streams -south of a medial divide between Nescopec and Blue mountains. The only -considerable part of the old Anthracite river that still retains a -course along the axis of a synclinal trough seems to be that part which -follows the Wyoming basin; none of the many other coal basins are now -occupied by the large stream that originally followed them. The reason -for this is manifestly to be found in the great depth of the Wyoming -basin, whereby the axial portion of its hard sandstones are even now -below baselevel, and hence have never yet acted to throw the river from -its axial course. Indeed, during the early cycles of denudation, this -basin must have been changed from a deep lake to a lacustrine plain by -the accumulation in it of waste from the surrounding highlands, and for -a time the streams that entered it may have flowed in meandering -courses across the ancient alluvial surface; the lacustrine and -alluvial condition may have been temporarily revived at the time of the -Jurassic elevation. It is perhaps as an inheritance from a course thus -locally superimposed that we may come to regard the deflection of the -river at Nanticoke from the axis of the syncline to a narrow shale -valley on its northern side, before turning south again and leaving the -basin altogether. But like certain other suggestions, this can only be -regarded as an open hypothesis, to be tested by some better method of -river analysis than we now possess; like several of the other -explanations here offered, it is presented more as a possibility to be -discussed than as a conclusion to be accepted. - -I believe that it was during the earlier part of the great -Jura-Cretaceous cycle of denudation that the Susquehanna thus became -the master stream of the central district of the state. For the rest of -the cycle, it was occupied in carrying off the waste and reducing the -surface to a well finished baselevel lowland that characterized the end -of Cretaceous time. From an active youth of conquest, the Susquehanna -advanced into an old age of established boundaries; and in later times, -its area of drainage does not seem to have been greatly altered from -that so long ago defined; except perhaps in the districts drained by -the West and North Branch headwaters. - -34. _Homologies of the Susquehanna and Juniata_.--Looking at the change -from the Anthracite to the Susquehanna in a broad way, one may perceive -that it is an effect of the same order as the peripheral diversion of -the Broad Top drainage, illustrated in figures 22, 23 and 24; another -example of a similar change is seen in the lateral diversion of the -Juniata above Lewistown and its rectilinear continuation in Aughwick -creek, from their original axial location when they formed the initial -Broad Top outlet. They have departed from the axis of their syncline to -the softer beds on its southern side; FE of fig. 17 has been diverted -to FD of fig. 18. - -All of these examples are truly only special cases of the one already -described in which the Juniata left its original syncline for others to -the south. The general case may be stated in a few words. A stream -flowing along a syncline of hard beds (Carboniferous sandstones) -develops side streams which breach the adjacent anticlines and open -lowlands in the underlying softer beds (Devonian and Silurian). On -these lowlands, the headwaters of side streams from other synclines are -encountered and a contest ensues as to possession of the drainage -territory. The divides are pushed away from those headwaters whose -lower course leads them over the fewest hard barriers; this conquest -goes on until the upper course of the initial main stream is diverted -to a new and easier path than the one it chose in its youth in -obedience to the first deformation of the region. Thus the Juniata now -avoids the center and once deepest part of the old Broad Top lake, -because in the general progress of erosion, lowlands on soft Devonian -beds were opened all around the edge of the great mass of sandstones -that held the lake; the original drainage across the lake, from its -western slopes to its outlet just south of the Jack's mountain -anticline, has now taken an easier path along the Devonian beds to the -west of the old lake basin, and is seen in the Little Juniata, flowing -along the outer side of Terrace mountain and rounding the northern -synclinal point where Terrace mountain joins Sideling hill. It then -crosses Jack's mountain at a point where the hard Medina sandstones of -the mountain were still buried at the time of the choice of this -channel. In the same way, the drainage of the subordinate basin, -through which the main lake discharged eastward, is now not along the -axis of the Juniata-Catawissa syncline, but on the softer beds along -one side of it; and along the southern side because the easier escape -that was provided for it lay on that side, namely, via the Tuscarora -and Wiconisco synclines, as already described. The much broader change -from the Anthracite to the Susquehanna was only another form of the -same process. Taking a transverse view of the whole system of central -folds, it is perceived that their axes descend into the Anthracite -district from the east and rise westward therefrom; it is as if the -whole region had received a slight transverse folding, and the -transverse axis of depression thus formed defined the initial course of -the first master stream. But this master stream deserted its original -course on the transverse axis of depression because a lateral course -across lowlands on softer beds was opened by its side streams; and in -the contest on these lowlands with an external stream, the Susquehanna, -the upper portion of the Anthracite was diverted from the hard rocks -that had appeared on the transverse axis. The distance of diversion -from the axial to the lateral course in this case was great because of -the gentle quality of the transverse folding; or, better said, because -of the gentle dips of the axes of the longitudinal folds. This -appearance of systematic re-arrangement in the several river courses -where none was expected is to my mind a strong argument in favor of the -originally consequent location of the rivers and their later mutual -adjustment. It may perhaps be conceived that antecedent streams might -imitate one another roughly in the attitude that they prophetically -chose with regard to folds subsequently formed, but no reason has been -suggested for the imitation being carried to so remarkable and definite -a degree as that here outlined. - -35. _Superimposition of the Susquehanna on two synclinal -ridges_.--There is however one apparently venturesome postulate that -may have been already noted as such by the reader; unless it can be -reasonably accounted for and shown to be a natural result of the long -sequence of changes here considered, it will seriously militate against -the validity of the whole argument. The present course of the middle -Susquehanna leads it through the apical curves of two Pocono synclinal -ridges, which were disregarded in the statement given above. It was -then assumed that the embryonic Susquehanna gained possession of the -Siluro-Devonian lowland drainage by gnawing out a course to the west of -these synclinal points; for it is not to be thought of that any -conquest of the headwaters of the Anthracite river could have been made -by the Susquehanna if it had had to gnaw out the existing four -traverses of the Pocono sandstones before securing the drainage of the -lowlands above them. The backward progress of the Susquehanna could not -in that case have been nearly fast enough to reach the Anthracite -before the latter had sunk its channel to a safe depth. It is therefore -important to justify the assumption as to the more westerly location of -the embryonic Susquehanna; and afterwards, to explain how it should -have since then been transferred to its present course. A short cut -through all this round-about method is open to those who adopt in the -beginning the theory that the Susquehanna was an antecedent river; but -as I have said at the outset of this inquiry, it seems to me that such -a method is not freer from assumption, even though shorter than the one -here adopted; and it has the demerit of not considering all the curious -details that follow the examination of consequent and adjusted courses. - -The sufficient reason for the assumption that the embryonic Susquehanna -lay farther west than the present one in the neighborhood of the Pocono -synclinals is simply that--in the absence of any antecedent stream--it -must have lain there. The whole explanation of the development of the -Siluro-Devonian lowlands between the Pocono and Medina ridges depends -simply on their being weathered out where the rocks are weak enough to -waste faster than the enclosing harder ridges through which the streams -escape. In this process, the streams exercise no control whatever over -the direction in which their headwaters shall grow; they leave this -entirely to the structure of the district that they drain. It thus -appears that, under the postulate as to the initial location of the -Susquehanna as one of the many streams descending the great slope of -the Kittatinny (Cumberland) highland into the Swatara syncline, its -course being reversed from northward to southward by the Newark -depression, we are required to suppose that its headwater (northward) -growth at the time of the Jurassic elevation must have been on the -Siluro-Devonian beds, so as to avoid the harder rocks on either side. -Many streams competed for the distinction of becoming the master, and -that one gained its ambition whose initial location gave it the best -subsequent opportunity. It remains then to consider the means by which -the course of the conquering Susquehanna may have been subsequently -changed from the lowlands on to the two Pocono synclines that it now -traverses. Some departure from its early location may have been due to -eastward planation in its advanced age, when it had large volume and -gentle slope and was therefore swinging and cutting laterally in its -lower course. This may have had a share in the result, but there is -another process that seems to me more effective. - -In the latter part of the Jura-Cretaceous cycle, the whole country -hereabout suffered a moderate depression, by which the Atlantic -transgressed many miles inland from its former shoreline, across the -lowlands of erosion that had been developed on the litoral belt. Such a -depression must have had a distinct effect on the lower courses of the -larger rivers, which having already cut their channels down close to -baselevel and opened their valleys wide on the softer rocks, were then -"estuaried," or at least so far checked as to build wide flood-plains -over their lower stretches. Indeed, the flood-plains may have been -begun at an earlier date, and have been confirmed and extended in the -later time of depression. Is it possible that in the latest stage of -this process, the almost baselevelled remnants of Blue mountain and the -Pocono ridges could have been buried under the flood-plain in the -neighborhood of the river? - -If this be admitted, it is then natural for the river to depart from -the line of its buried channel and cross the buried ridges on which it -might settle down as a superimposed river in the next cycle of -elevation. It is difficult to decide such general questions as these; -and it may be difficult for the reader to gain much confidence in the -efficacy of the processes suggested; but there are certain features in -the side streams of the Susquehanna that lend some color of probability -to the explanation as offered. - -Admit, for the moment, that the aged Susquehanna, in the later part of -the Jura-Cretaceous cycle, did change its channel somewhat by cutting -to one side, or by planation, as it is called. Admit, also, that in the -natural progress of its growth it had built a broad flood plain over -the Siluro-Devonian lowlands, and that the depth of this deposit was -increased by the formation of an estuarine delta upon it when the -country sank at the time of the mid-Cretaceous transgression of the -sea. It is manifest that one of the consequences of all this might be -the peculiar course of the river that is to be explained, namely, its -superimposition on the two Pocono synclinal ridges in the next cycle of -its history, after the Tertiary elevation had given it opportunity to -re-discover them. It remains to inquire what other consequences should -follow from the same conditions, and from these to devise tests of the -hypothesis. - -36. _Evidence of superimposition in the Susquehanna tributaries_.--One -of the peculiarities of flood-plained rivers is that the lateral -streams shift their points of union with the main stream farther and -farther down the valley, as Lombardini has shown in the case of the Po. -If the Susquehanna were heavily flood-plained at the close of the -Jura-Cretaceous cycle, some of its tributaries should manifest signs of -this kind of deflection from their structural courses along the strike -of the rocks. Side streams that once joined the main stream on the line -of some of the softer northeast-southwest beds, leaving the stronger -beds as faint hills on either side, must have forgotten such control -after it was baselevelled and buried; as the flood plain grew, they -properly took more and more distinctly downward deflected courses, and -these deflections should be maintained in subsequent cycles as -superimposed courses independent of structural guidance. Such I believe -to be the fact. The downstream deflection is so distinctly a -peculiarity of a number of tributaries that join the Susquehanna on the -west side (see figure 1) that it cannot be ascribed to accident, but -must be referred to some systematic cause. Examples of deflection are -found in Penn's creek, Middle creek and North Mahantango creek in -Snyder county; West Mahantango between the latter and Juniata county; -and in the Juniata and Little Juniata rivers of Perry county. On the -other side of the Susquehanna, the examples are not so distinct, but -the following may be mentioned: Delaware and Warrior runs, -Chillisquaque creek and Little Shamokin creek, all in Northumberland -county. It may be remarked that it does not seem impossible that the -reason for the more distinct deflection of the western streams may be -that the Susquehanna is at present east of its old course, and hence -towards the eastern margin of its flood plain, as, indeed its position -on the Pocono synclinals implies. A reason for the final location of -the superimposed river on the eastern side of the old flood plain may -perhaps be found in the eastward tilting that is known to have -accompanied the elevation of the Cretaceous lowland. - -It follows from the foregoing that the present lower course of the -Susquehanna must also be of superimposed origin; for the flood plain of -the middle course must have extended down stream to its delta, and -there have become confluent with the sheet of Cretaceous sediments that -covered all the southeastern lowland, over which the sea had -transgressed. McGee has already pointed out indications of superimposed -stream courses in the southeastern part of the State;[22] but I am not -sure that he would regard them as of the date here referred to. - -[Footnote 22: Amer. Journ. Science, xxxv, 1888, 121, 134.] - -The theory of the location of the Susquehanna on the Pocono synclinal -ridges therefore stands as follows. The general position of the river -indicates that it has been located by some process of slow -self-adjusting development and that it is not a persistent antecedent -river; and yet there is no reason to think that it could have been -brought into its present special position by any process of shifting -divides. The processes that have been suggested to account for its -special location, as departing slightly from a location due to slow -adjustments following an ancient consequent origin, call for the -occurrence of certain additional peculiarities in the courses of its -tributary streams, entirely unforeseen and unnoticed until this point -in the inquiry is reached; and on looking at the map to see if they -occur, they are found with perfect distinctness. The hypothesis of -superimposition may therefore be regarded as having advanced beyond the -stage of mere suggestion and as having gained some degree of -confirmation from the correlations that it detects and explains. It -only remains to ask if these correlations might have originated in any -other way, and if the answer to this is in the negative, the case may -be looked upon as having a fair measure of evidence in its favor. The -remaining consideration may be taken up at once as the first point to -be examined in the Tertiary cycle of development. - -37. _Events of the Tertiary cycle_.--The elevation given to the region -by which Cretaceous baselevelling was terminated, and which I have -called the early Tertiary elevation, offered opportunity for the -streams to deepen their channels once more. In doing so, certain -adjustments of moderate amount occurred, which will be soon examined. -As time went on, much denudation was effected, but no wide-spread -baselevelling was reached, for the Cretaceous crest lines of the hard -sandstone ridges still exist. The Tertiary cycle was an incomplete one. -At its close, lowlands had been opened only on the weaker rocks between -the hard beds. Is it not possible that the flood-plaining of the -Susquehanna and the down-stream deflection of its branches took place -in the closing stages of this cycle, instead of at the end of the -previous cycle? If so, the deflection might appear on the branches, but -the main river would not be transferred to the Pocono ridges. This -question may be safely answered in the negative; for the Tertiary -lowland is by no means well enough baselevelled to permit such an -event. The beds of intermediate resistance, the Oriskany and certain -Chemung sandstones, had not been worn down to baselevel at the close of -the Tertiary cycle; they had indeed lost much of the height that they -possessed at the close of the previous cycle, but they had not been -reduced as low as the softer beds on either side. They were only -reduced to ridges of moderate and unequal height over the general plain -of the Siluro-Devonian low country, without great strength of relief -but quite strong enough to call for obedience from the streams along -side of them. And yet near Selin's Grove, for example, in Snyder -county, Penn's and Middle creeks depart most distinctly from the strike -of the local rocks as they near the Susquehanna, and traverse certain -well-marked ridges on their way to the main river. Such aberrant -streams cannot be regarded as superimposed at the close of the -incomplete Tertiary cycle; they cannot be explained by any process of -spontaneous adjustment yet described, nor can they be regarded as -vastly ancient streams of antecedent courses; I am therefore much -tempted to consider them as of superimposed origin, inheriting their -present courses from the flood-plain cover of the Susquehanna in the -latest stage of the Jura-Cretaceous cycle. With this tentative -conclusion in mind as to the final events of Jura-Cretaceous time, we -may take up the more deliberate consideration of the work of the -Tertiary cycle. - -The chief work of the Tertiary cycle was merely the opening of the -valley lowlands; little opportunity for river adjustment occurred -except on a small scale. The most evident cases of adjustment have -resulted in the change of water-gaps into wind-gaps, of which several -examples can be given, the one best known being the Delaware wind-gap -between the Lehigh and Delaware water-gaps in Blue mountain. The -wind-gap marks the unfinished notch of some stream that once crossed -the ridge here and whose headwaters have since then been diverted, -probably to the Lehigh. The difficulty in the case is not at all how -the stream that once flowed here was diverted, but how a stream that -could be diverted in the Tertiary cycle could have escaped diversion at -some earlier date. The relative rarity of wind-gaps indicates that -nearly all of the initial lateral streams, which may have crossed the -ridges at an early epoch in the history of the rivers, have been -beheaded in some cycle earlier than the Tertiary and their gaps -thereafter obliterated. Why the Delaware wind-gap stream should have -endured into a later cycle does not at present appear. Other wind-gaps -of apparently similar origin may be found in Blue mountain west of the -Schuylkill and east of the Susquehanna. It is noteworthy that if any -small streams still persevere in their gaps across a hard ridge, they -are not very close to any large river-gap; hence it is only at the very -headwaters of Conedogwinet creek, in the northern part of Franklin -county, that any water is still drawn from the back of Blue mountain. -Again, these small stream gaps do not lie between large river-gaps and -wind-gaps, but wind-gaps lie between the gaps of large rivers and those -of small streams that are not yet diverted. Excellent illustration of -this is found on the "Piedmont sheet" of the contoured maps issued by -the United States Geological Survey. The sheet covers part of Maryland -and West Virginia, near where the North Branch of the Potomac comes out -of the plateau and crosses New Creek mountain. Eleven miles south of -the Potomac gap there is a deep wind-gap; but further on, at twenty, -twenty-five and twenty-nine miles from the river-gap are three fine -water-gaps occupied by small streams. This example merely shows how -many important points in the history of our rivers will be made clear -when the country is properly portrayed on contoured maps. - -A few lines may be given to the general absence of gaps in Blue -Mountain in Pennsylvania. When the initial consequent drainage was -established, many streams must have been located on the northward slope -of the great Cumberland highland, C, C, fig. 21; they must have gullied -the slope to great depths and carried away great volumes of the weak -Cambrian beds that lay deep within the hard outer casings of the mass. -Minor adjustments served to diminish the number of these streams, but -the more effective cause of their present rarity lay in the natural -selection of certain of them to become large streams; the smaller ones -were generally beheaded by these. The only examples of streams that -still cross this ridge with their initial Permian direction of flow to -the northwest are found in two southern branches of Tuscarora creek at -the southern point of Juniata county; and these survive because of -their obscure location among the many Medina ridges of that district, -where they were not easily accessible to capture by other streams. - -38. _Tertiary adjustment of the Juniata on the Medina anticlines_.--The -lower course of the Juniata presents several examples of adjustment -referable to the last part of the Jura-Cretaceous cycle and to the -Tertiary cycle. The explanation offered for the escape of this river -from its initial syncline did not show any reason for its peculiar -position with respect to the several Medina anticlines that it now -borders, because at the time when it was led across country to the -Wiconisco syncline, the hard Medina beds of these anticlines were not -discovered. It is therefore hardly to be thought that the location of -the Juniata in the Narrows below Lewistown between Blue Ridge and Shade -mountain and its avoidance of Tuscarora mountain could have been -defined at that early date. But all these Medina anticlines rise more -or less above the Cretaceous baselevel, and must have had some effect -on the position taken by the river about the middle of that cycle when -its channel sank upon them. Blue Ridge and Black Log anticlines rise -highest. The first location of the cross-country stream that led the -early Juniata away from its initial syncline probably traversed the -Blue Ridge and Black Log anticlines while they were yet buried; but its -channel-cutting was much retarded on encountering them, and some branch -stream working around from the lower side of the obstructions may have -diverted the river to an easier path. The only path of the kind is the -narrow one between the overlapping anticlines of Blue Ridge and Shade -mountains, and there the Juniata now flows. If another elevation should -occur in the future, it might happen that the slow deepening of the -channel in the hard Medina beds which now floor the Narrows would allow -Middle creek of Snyder county to tap the Juniata at Lewistown and lead -it by direct course past Middleburgh to the Susquehanna; thus it would -return to the path of its youth. - -The location of the Juniata at the end of Tuscarora mountain is again -so definite that it can hardly be referred to a time when the mountain -had not been revealed. The most likely position of the original -cross-country stream which brought the Juniata into the Wiconisco -syncline was somewhere on the line of the existing mountain, and -assuming it to have been there, we must question how it has been -displaced. The process seems to have been of the same kind as that just -given; the retardation of channel-cutting in the late Cretaceous cycle, -when the Medina beds of Tuscarora anticline were discovered, allowed a -branch from the lower part of the river to work around the end of the -mountain and lead the river out that way. The occurrence of a shallow -depression across the summit of the otherwise remarkably even crest of -Tuscarora mountain suggests that this diversion was not finally -accomplished until shortly after the Tertiary elevation of the country; -but at whatever date the adjustment occurred, it is natural that it -should pass around the eastern end of the mountain and not around the -western end, where the course would have been much longer, and -therefore not successfully to be taken by a diverting stream. - -While the quality of these processes appears satisfactory, I am not -satisfied as to the sufficiency of their quantity. If diversion was -successfully practiced at the crossing of the Tuscarora anticline, why -not also at the crossing of Jack's mountain anticline, on which the -river still perseveres. It is difficult here to decide how much -confidence may be placed in the explanation, because of its giving -reason for the location of certain streams, and how much doubt must be -cast upon it, because it seems impossible and is not of universal -application. - -39. _Migration of the Atlantic-Ohio divide_.--There are certain shifted -courses which cannot be definitely referred to any particular cycle, -and which may therefore be mentioned now. Among the greatest are those -by which the divide between the Atlantic and the Ohio streams has been -changed from its initial position on the great constructional Nittany -highland and Bedford range. There was probably no significant change -until after Newark depression, for the branches of the Anthracite river -could not have begun to push the divide westward till after the -eastward flow of the river was determined; until then, there does not -seem to have been any marked advantage possessed by the eastward -streams over the westward. But with the eastward escape of the -Anthracite, it probably found a shorter course to the sea and one that -led it over alternately soft and hard rocks, instead of the longer -course followed by the Ohio streams over continuous sandstones. The -advantage given by the greater extent of soft beds is indicated by the -great breadth of the existing valleys in the central district compared -with the less breadth of those in the plateau to the west. Consider the -effect of this advantage at the time of the Jurassic elevation. As the -streams on the eastern slope of the Nittany divide had the shortest and -steepest courses to the sea, they deepened their valleys faster than -those on the west and acquired drainage area from them; hence we find -reason for the drainage of the entire Nittany and Bedford district by -the Atlantic streams at present. Various branches of what are now the -Alleghany and Monongahela originally rose on the western slope of the -dividing range. These probably reached much farther east in pre-Permian -time, but had their headwaters turned another way by the growth of the -great anticlinal divide; but the smaller anticlines of Laurel ridge and -Negro mountain farther west do not seem to have been strong enough to -form a divide, for the rivers still traverse them. Now as the -headwaters of the Juniata breached the eastern slope of the -Nittany-Bedford range and pushed the divide westward, they at last -gained possession of the Siluro-Devonian monocline on its western -slope; but beyond this it has not been possible for them yet to go. As -the streams cut down deeper and encountered the Medina anticline near -the core of the ridge, they sawed a passage through it; the Cambrian -beds were discovered below and a valley was opened on them as the -Medina cover wore away. The most important point about this is that we -find in it an adequate explanation of the opposite location of -water-gaps in pairs, such as characterize the branches of the Juniata -below Tyrone and again below Bedford. This opposite location has been -held to indicate an antecedent origin of the river that passes through -the gaps, while gaps formed by self-developed streams are not thought -to present such correspondence (Hilber). Yet this special case of -paired gaps in the opposite walls of a breached anticline is manifestly -a direct sequence of the development of the Juniata headwaters. The -settling down of the main Juniata on Jack's mountain anticline below -Huntingdon is another case of the same kind, in which the relatively -low anticlinal crest is as yet not widely breached; the gaps below -Bedford stand apart, as the crest is there higher, and hence wider -opened; and the gaps below Tyrone are separated by some ten or twelve -miles. - -When the headwater streams captured the drainage of the Siluro-Devonian -monocline on the western side of the ancient dividing anticline, they -developed subsequent rectangular branches growing like a well-trained -grape vine. Most of this valley has been acquired by the west branch of -the Susquehanna, probably because it traversed the Medina beds less -often than the Juniata. For the same reason, it may be, the West Branch -has captured a considerable area of plateau drainage that must have -once belonged to the Ohio, while the Juniata has none of it; but if so, -the capture must have been before the Tertiary cycle, for since that -time the ability of the West Branch and of the Juniata as regards such -capture appears about alike. On the other hand, Castleman's river, a -branch of the Monongahela, still retains the drainage of a small bit of -the Siluro-Devonian monocline, at the southern border of the State, -where the Juniata headwaters had the least opportunity to capture it; -but the change here is probably only retarded, not prevented entirely; -the Juniata will some day push the divide even here back to the -Alleghany Front, the frontal bluff of the plateau. - -[Illustration: FIG. 26.] - -40. _Other examples of adjustments_.--Other examples of small -adjustments are found around the Wyoming basin, fig. 26. Originally all -these streams ran centripetally down the enclosing slopes, and in such -locations they must have cut gullies and breaches in the hard -Carboniferous beds and opened low back country on the weaker Devonians. -Some of the existing streams still do so, and these are precisely the -ones that are not easily reached by divertors. The Susquehanna in its -course outside of the basin has sent out branches that have beheaded -all the centripetal streams within reach; where the same river enters -the basin, the centripetal streams have been shortened if not -completely beheaded. A branch of the Delaware has captured the heads of -some of the streams near the eastern end of the basin. Elsewhere, the -centripetal streams still exist of good length. The contrast between -the persistence of some of the centripetal streams here and their -peripheral diversion around Broad Top is a consequence of the -difference of altitude of the old lake bottoms in the two cases. It is -not to be doubted that we shall become acquainted with many examples of -this kind as our intimacy with rivers increases. - -41. _Events of the Quaternary cycle_.--The brief quaternary cycle does -not offer many examples of the kind that we have considered, and all -that are found are of small dimensions. The only capturing stream that -need be mentioned has lately been described as a "river pirate;"[23] -but its conquest is only a Schleswig-Holstein affair compared to the -Goth- and Hun-like depredations of the greater streams in earlier -cycles. - -[Footnote 23: Science, xiii, 1889, 108.] - -The character of the streams and their valleys as they now exist is -strikingly dependent in many ways on the relation of the incipient -quaternary cycle to the longer cycles of the past. No lakes occur, -exception being made only of the relatively small ponds due to drift -obstruction within the glaciated area. Waterfalls are found only at the -headwaters of small streams in the plateau district, exception again -being made only for certain cases of larger streams that have been -thrown from their pre-glacial courses by drift barriers, and which are -now in a very immature state on their new lines of flow. The small -valleys of this cycle are shallow and narrow, always of a size strictly -proportional to the volume of the stream and the hardness of the -enclosing rocks, exception being made only in the case of post-glacial -gorges whose streams have been displaced from their pre-glacial -channels. The terraces that are seen, especially on the streams that -flow in or from the glaciated district, are merely a temporary and -subordinate complication of the general development of the valleys. In -the region that has been here considered, the streams have been seldom -much displaced from their pre-glacial channels; but in the northwestern -part of the State, where the drift in the valleys seems to be heavier, -more serious disturbance of pre-glacial courses is reported. The facts -here referred to in regard to lakes, falls, gorges, terraces and -displaced streams are to be found in the various volumes of the Second -Geological Survey of the State;[24] in regard to the terraces and the -estuarine deflections of the Delaware and Susquehanna, reference should -be made also to McGee's studies.[25] - -[Footnote 24: Especially Carll, Reports I_{3}, I_{4}; White, Reports -G_{5}, G_{6}; Lewis, Report Z.] - -[Footnote 25: Amer. Journ. Science, xxxv, 1888, 367, 448; Seventh -Annual Rep. U. S. G. S., 1888, 545.] - -42. _Doubtful cases_.--It is hardly necessary to state that there are -many facts for which no satisfactory explanation is found under the -theory of adjustments that we have been considering. Some will -certainly include the location of the Susquehanna on the points of the -Pocono synclines under this category; all must feel that such a -location savors of an antecedent origin. The same is true of the -examples of the alignment of water-gaps found on certain streams; for -example, the four gaps cut in the two pairs of Pocono and Pottsville -outcrops at the west end of the Wyoming syncline, and the three gaps -where the Little Schuylkill crosses the coal basin at Tamaqua; the -opposite gaps in pairs at Tyrone and Bedford have already been -sufficiently explained. The location of the upper North Branch of the -Susquehanna is also unrelated to processes of adjustment as far as I -can see them, and the great area of plateau drainage that is now -possessed by the West Branch is certainly difficult to understand as -the result of conquest. The two independent gaps in Tussey's mountain, -maintained by the Juniata and its Frankstown branch below Tyrone are -curious, especially in view of the apparent diversion of the branch to -the main stream on the upper side of Warrior's ridge (Oriskany), just -east of Tussey's mountain. - -43. _Complicated history of our actual rivers_.--If this theory of the -history of our rivers is correct, it follows that any one river as it -now exists is of so complicated an origin that its development cannot -become a matter of general study and must unhappily remain only a -subject for special investigation for some time to come. It was my hope -on beginning this essay to find some teachable sequence of facts that -would serve to relieve the usual routine of statistical and descriptive -geography, but this is not the result that has been attained. The -history of the Susquehanna, the Juniata, or the Schuylkill, is too -involved with complex changes, if not enshrouded in mystery, to become -intelligible to any but advanced students; only the simplest cases of -river development can be introduced into the narrow limits of ordinary -instruction. The single course of an ancient stream is now broken into -several independent parts; witness the disjointing and diversion of the -original Juniata, which, as I have supposed, once extended from Broad -Top lake to the Catawissa basin. Now the upper part of the stream, -representing the early Broad Top outlet, is reduced to small volume in -Aughwick creek; the continuation of the stream to Lewistown is first -set to one side of its original axial location and is then diverted to -another syncline; the beheaded portion now represented by Middle creek -is diverted from its course to the Catawissa basin by the Susquehanna; -perhaps the Catawissa of the present day represents the reversed course -of the lower Juniata where it joined the Anthracite. This unserviceably -complicated statement is not much simplified if instead of beginning -with an original stream and searching out its present disjointed parts, -we trace the composition of a single existing stream from its once -independent parts. The Juniata of to-day consists of headwaters -acquired from Ohio streams; the lake in which the river once gathered -its upper branches is now drained and the lake bottom has become a -mountain top; the streams flow around the margin of the lake, not -across its basin; a short course towards Lewistown nearly coincides -with the original location of the stream, but to confound this with a -precise agreement is to lose the true significance of river history; -the lower course is the product of diversion at least at two epochs and -certainly in several places; and where the river now joins the -Susquehanna, it is suspected of having a superimposed course unlike any -of the rest of the stream. This is too complicated, even if it should -ever be demonstrated to be wholly true, to serve as material for -ordinary study; but as long as it has a savor of truth, and as long as -we are ignorant of the whole history of our rivers, through which alone -their present features can be rightfully understood, we must continue -to search after the natural processes of their development as carefully -and thoroughly as the biologist searches for the links missing from his -scheme of classification. - -44. _Provisional Conclusions_.--It is in view of these doubts and -complications that I feel that the history of our rivers is not yet -settled; but yet the numerous accordances of actual and deductive -locations appear so definite and in some cases so remarkable that they -cannot be neglected, as they must be if we should adhere to the -antecedent origin of the river courses. - -The method adopted on an early page therefore seems to be justified. -The provisional system of ancient consequent drainage, illustrated on -fig. 21, does appear to be sufficiently related to the streams of -to-day to warrant the belief that most of our rivers took their first -courses between the primitive folds of our mountains, and that from -that distant time to the present the changes they have suffered are due -to their own interaction--to their own mutual adjustment more than to -any other cause. The Susquehanna, Schuylkill, Lehigh and Delaware are -compound, composite and highly complex rivers, of repeated mature -adjustment. The middle Susquehanna and its branches and the upper -portions of the Schuylkill and Lehigh are descendants of original -Permian rivers consequent on the constructional topography of that -time; Newark depression reversed the flow of some of the transverse -streams, and the spontaneous changes or adjustments from immature to -mature courses in the several cycles of development are so numerous and -extensive that, as Löwl truly says, the initial drainage has almost -disappeared. The larger westward-flowing streams of the plateau are of -earlier, Carboniferous birth, and have suffered little subsequent -change beyond a loss of headwaters. The lower courses of the Atlantic -rivers are younger, having been much shifted from their Permian or -pre-Permian courses by Newark and Cretaceous superimposition, as well -as by recent downward deformation of the surface in their existing -estuaries. No recognizable remnant of rivers antecedent to the Permian -deformation are found in the central part of the State; and with the -exception of parts of the upper Schuylkill and of the Susquehanna near -Wilkes-Barre, there are no large survivors of Permian consequent -streams in the ordinary meaning of the term "consequent." The shifting -of courses in the progress of mature adjustment has had more to do with -determining the actual location of our rivers and streams than any -other process. - - Harvard College, June, 1889. - - - - -TOPOGRAPHIC MODELS. - -BY COSMOS MINDELEFF. - - -Of the many methods by which it has been sought to represent the relief -of a country or district, only two have been at all widely used. These -methods are, in the order of their development, by hachured and by -contoured maps. Both have advantages and both have serious -disadvantages. Without entering into the controversy that is even yet -raging over the relative merits of the two systems, some slight notice -of what each claims to accomplish is necessary. - -The representation of relief by hachures is a graphic system, and in -the best examples we have is an attempt to show, upon a plane surface, -the actual appearance of a given area under given conditions of -lighting,--as in the Dufour map of the Alps. Of course certain details -that would really disappear if the assumed conditions were actual ones, -must be shown upon the map,--so that it is, after all, but a -conventional representation. The very best examples are, for this and -other reasons, unsatisfactory, and far more so is this the case in the -vastly larger class of medium grade and poor work. - -The contour system represents relief by a series of lines, each of -which is, at every point throughout its length, at a certain stated -elevation above sea-level, or some other datum-plane; in other words, -each contour line represents what would be the water's edge, if the sea -were to rise to that elevation. It possesses the advantage of great -clearness, but fails to a large degree in the representation of surface -detail; moreover, one must have considerable knowledge of topography, -in order to read the map correctly.[1] - -[Footnote 1: For specimens of representation of the same subject on -different scales, in both the hachure and contour systems, see plate -from "Enthoffer's Topographical Atlas."] - -To those who must give first place to the quantity of relief rather -than the quality, as, for example, the geologist or the engineer, a -contoured map is now considered essential. On the other hand, where -quality of relief is the prime consideration and the quantity a -secondary one, as, for example, for the use of the army, a hachured map -is considered the best. The method of hachures may be roughly -characterized as a graphic system with a conventional element, and the -contour method as a conventional system with a graphic element,--for if -the contour interval is small enough a sort of shading is produced -which helps considerably the idea of relief. - -In addition to these two great systems, with which everyone is more or -less familiar, there is another method of representing a country or -district,--a method that succeeds where others fail, and which although -by no means new, has not received the attention it deserves: this is -the representation of a country by a model in relief. Certain striking -advantages of models over maps of all kinds are, indeed, so apparent -that one almost loses sight of such slight disadvantages as can, of -course, be urged against them. In the graphic representation of the -surface they are far superior to the hachured map, and they have the -further advantage of expressing the relative relief, which the hachured -map fails to do, except in a very general way. They have also the -advantage of showing actual shadows, exactly as they would be seen in a -bird's-eye view of the district, instead of more or less conventional -ones, and are, consequently, more easily comprehended by the layman, -without becoming any less valuable to the skilled topographer. In -short, they combine all the graphic features of a hachured map with all -the advantages of the best class of contoured maps, and in addition -they show more of the surface detail, upon which so much of the -character of the country depends and which is very inadequately -expressed by hachures and almost completely ignored in a contoured map -of large interval. The contours themselves can be made to appear upon -the model very easily and without interfering with other features. - -The uses of models are many and various. Within the past few years -their usefulness has been much extended, and, now that they are -becoming better known, will probably receive a still further extension. -To the geologist they are often of great value in working out the -structure of complicated districts, for the reason that so many -important structural relations can be presented to the eye at a single -glance. Similarly, for the graphic presentation of results there is no -better method, as the topography, the surface geology, and any number -of sections can be shown together and seen in their proper -relationship. To the engineer an accurate model is often of the -greatest assistance in working out his problems, and it is simply -invaluable to explain the details of a plan to anyone who has little or -no technical training; for, as has been stated, a model is easily -comprehended by anyone, while more or less technical knowledge is -required for the proper understanding of even the best maps. - -I might go on cataloguing in detail the many uses to which models may -be put, but shall now mention only one more--perhaps the most important -of all--their use in the education of the young. No method has yet been -devised that is capable of giving so clear and accurate a conception of -the principles of physical geography as a series of well selected -models; models have, indeed, already been used for this purpose, but -unfortunately their great cost has prevented their general use in -schools. Since, however, the study of geography has been placed upon a -new basis and a new life has been infused into it, many men have given -their attention to the subject of models, and have experimented with a -view to cheapen the cost of reproduction, which has hitherto prevented -their wide distribution; and probably this objection will soon be -remedied. The ability to read a map correctly,--to obtain from a study -of the map a clear conception of the country represented,--is more -uncommon than is usually supposed. Some of the recent methods of -teaching geography are intended to cultivate this very faculty, but it -is doubtful whether there is any better method than that which consists -in the study of a series of good models in conjunction with a series of -maps, all on the same scale and of the same areas. The value of a -series of good models in teaching geology is so apparent that it need -only be mentioned. It is often, for reasons stated above, far more -valuable even, than field instruction. - -For the construction of a good relief map the first requisite is a good -contoured map. To this should be added, when possible, a good hachured -map, upon which the elevations of the principal points are stated,--if -the interval in the contoured map is a large one,--and as much material -in the way of photographs and sketches as it is possible to procure. -The modeler should, moreover, have some personal acquaintance with the -region to be represented, or, failing that, a general knowledge of -topographic forms, and at least a clear conception of the general -character of the country which he seeks to represent. This is very -important, for it is here that many modelers fail: the mechanical -portion of the work any ordinarily intelligent person can do. A model -may be as accurate as the map from which it is made, every contour may -be placed exactly where it belongs, and yet the resulting model may -be,--indeed, often is--"flat," expressionless, and unsatisfactory. -Every topographer in drawing his map is compelled to generalize more or -less, and it is fortunate for the map if this be done in the field -instead of in the draughtsman's office. But topographers differ among -themselves: there may be, and often is, considerable difference in two -maps of the same region made by different men; in other words, the -"personal equation" is a larger element in a map than is usually -supposed. This being the case, there is something more required in a -modeler than the mere transferring of the matter in the map,--giving it -three dimensions instead of two: he must supply through his special -knowledge of the region (or, failing that through his general -knowledge) certain characteristics that do not appear upon the map, and -undo, so far as it is necessary, certain generalizations of the -topographer and draughtsman. This artistic or technical skill required -correctly to represent the _individuality_ of a given district is -especially important in the modeler; it is more important, perhaps, in -small-scale maps of large districts than in large-scale maps of small -ones,--for in the latter the generalizing process has not been carried -so far, and the smaller interval of the contour lines preserves much of -the detail. - -The methods by which relief maps are made have always received more -attention than would, at first sight, appear to be their proper -proportion. It may be due, however, to the difficulty of applying any -test to determine the accuracy of the finished model, and perhaps also -to the general impression that any one can make a relief map,--and so -he can, though of course there will be a wide difference in the value -of the results. Some, indeed, have devoted their attention to methods -exclusively, letting the result take care of itself,--and the models -show it. There is no more reason why a modeler should tie himself down -to one method of work, than that a water-colorist, or a chemist, or -anyone engaged in technical work, should do so; though in some cases he -might be required, as the chemist is, to show his methods as well as -his results. - -One of the earliest methods, with any pretension to what we may term -mechanical control, is that described by the Messrs. Harden in a paper -on "The construction of maps in relief," read before the American -Institute of Mining Engineers in 1887. The method was published in -1838. Upon a contoured map as a basis cross-section lines are drawn at -small and regular intervals, and, if the topography be intricate, -corresponding lines at right angles. The sections thus secured are -transferred to thin strips of some suitable material, such as -card-board or metal, and cut down to the surface line,--the strips -themselves thus forming the cross-sections. These cross-sections are -mounted upon a suitable base-board, and the cavities or boxes are then -filled up with some easily carved material, such as plaster or wax. The -top is then carved down to the form of the country or district,--the -necessary guidance being obtained by the upper edges of the strips that -form the cross-sections. It will be readily seen that this method is a -very crude and laborious one. It necessitates in the first place a good -contoured map upon which to draw the sections, but sacrifices much of -the advantage thus gained because only a number of points on each -contour line are used, instead of the entire line. It is no better, -although actually more laborious, than the later method of driving -contour pins (whose height above a base-board may be accurately -measured,) along the contour lines, and then filling in. A slight -modification of the latter method can be used to advantage when no -contoured map is available, and when the points whose elevation is -known are not numerous enough to permit the construction of one. In -this case the only control that can be secured is by means of a number -of pins driven into the base-board at those points whose elevation is -known. The remainder of the map is then sketched in. This method is -perhaps as satisfactory as any, when the material upon the map is -scanty. Another method, however, growing out of the same scantiness of -material, is in some cases to be preferred, especially for large -models. The map is enlarged to the required size, and a tracing of it -is mounted upon a frame. Another deep frame, just large enough to -contain the mounted tracing, is made, and laid upon a suitable -base-board upon which a copy of the map has been mounted. Upon this -base-board the model is then commenced, in clay or wax. The low areas -are modeled first,--horizontal control being obtained by pricking -through the mounted tracing of the map with a needle point, and -vertical control by measuring down from a straight edge sliding on the -top of the deep frame. This system is rather crude, and only useful -where the material upon the map is very scanty, but it gives excellent -control. - -A method used by Mr. F. H. King in the preparation of his large map of -the United States is described by him in a letter to Messrs. Harden, -and published by them in the place mentioned. A solid block of plaster -is used,--the contoured map being transferred to it--and the plaster is -carved down to produce a series of steps like those made by building up -the contours. The shoulders are then carved down to produce a -continuous surface. This method is one of the best of those that -require carving instead of modeling. - -Many other methods of producing relief maps might be mentioned, but, as -most of them have been used only to make special models, they need not -be described. The method that has been more used than any other still -remains to be described. It is that which the writer has used almost -exclusively, and consists in building up the model and modeling the -detail, instead of carving it. It is a maxim of the modeler that the -subject should be built up as far as possible, should be produced by -adding bits of clay or wax, or other material, and not by carving away -what is already on,--by addition and not by subtraction. This may be -illustrated by a reference to the methods of the sculptor. The bust, or -figure, or whatever the subject may be, is first modeled in clay or -wax; from this model a plaster mould is made, and from this mould a -plaster cast is taken. This cast is called the original, and the -finished production, whether in marble, bronze, or any other hard -substance, is simply a copy of this original. No one ever attempts to -produce the finished bust or figure directly from the object itself. -Even where the artist has for a guide a death mask, the procedure does -not change. The bust is first made in clay, and this clay model, as a -rule, contains all the detail which subsequently appears in the -finished bust. It seems strange, therefore, that the relief map maker -should use a method which the sculptor, with infinitely more skill and -judgment, is afraid to use; and this on subjects that do not differ as -much as might be imagined. - -The contour interval to be used depends on the use to which the model -is to be put. It is not always necessary to carry into the model all -the contour lines upon the map: I may go further and say that it is not -always desirable to do so. The number to be used depends to some extent -on the skill of the modeler. As already stated, the contours are only a -means of control, and one modeler requires more than another. To build -into a model every contour in a contoured map of ten foot interval is a -very laborious proceeding, and not worth the time it takes, as in nine -out of ten maps of such interval only the fifty-foot or the one -hundred-foot curves are definitely fixed, the intermediate lines being -merely filled in. This filling in can be done as well, or better, by -the modeler. - -The question as to the proper amount of exaggeration to be given the -vertical scale, as compared with the horizontal, is the question about -which has raged most of the controversy connected with relief map -making. This controversy has been rather bitter; some of the opponents -of vertical exaggeration going to the length of saying that no -exaggeration is necessary, and that "he that will distort or exaggerate -the scale of anything will lie." On the other hand the great majority -of those who have made relief maps insist upon the necessity of more or -less exaggeration of the vertical scale--generally more than seems to -me necessary, however. - -An increase of angle of slope accompanies all vertical exaggeration, -and this is apparent even in models in which the vertical element is -only very slightly exaggerated. It produces a false effect by -diminishing the proportionate width of the valleys, and by making the -country seem much more rugged and mountainous than it really is. A -secondary effect is to make the region represented look very small--all -idea of the extent of the country being lost. This can be illustrated -better than described. The King model of the United States is an -example of one extreme; it is worthy of note that no examples of the -other extreme--too little exaggeration--are known. - -In small-scale models of large districts some exaggeration of the -vertical scale is necessary in order to make the relief apparent, but -the amount of this exaggeration is often increased much beyond what is -essential. The proportion of scales must depend to a large extent on -the character of the country represented, and on the purposes for which -the model is made. It has been suggested by a writer, quoted by the -Messrs. Harden, that the following exaggeration would afford a pleasing -relief: "For a map, scale 6 inches to 1 mile: if mountainous, 1:3; if -only hilly, 1:2; if gently undulating, 2:3. For smaller scales, except -for very rugged tracts, the exaggeration should be correspondingly -increased. For a tract consisting wholly of mountains no exaggeration -is necessary." I know of no country of such a character that its -relief, in all its detail, cannot be shown upon a scale of 6 inches to -1 mile without any exaggeration at all. - -It seems to me that the absolute and not the relative amount of relief -is the desideratum, and I have always used this as my guiding -principle. For small scale models I have found half an inch of relief -ample. It may be worth while to state that in a model of the United -States made for the Messrs. Butler, of Philadelphia, the horizontal -scale was 77 miles to 1 inch, the vertical scale 40,000 feet to 1 inch, -and the proportion of scales as 1 to 10. This proportion could have -been brought down as low as 1:6 with advantage. One-fortieth of an inch -to a thousand feet seems a very small vertical scale, but it sufficed -to show all the important features of the relief. It should be stated, -moreover, that the model in question was very hurriedly made--in fact, -was hardly more than a sketch-model--and that more care and more minute -work would have brought out many details that do not now appear. This -amount of care was not considered necessary in this instance, as the -model was made to be photographed and published as a photo-engraving, -and was to suffer an enormous reduction--coming down to five by seven -inches.[2] - -[Footnote 2: See plate from "Butler's Complete Geography."] - -It has been frequently urged by the advocates of large exaggeration -that the details of a country cannot be shown unless the vertical scale -is exaggerated; that hills 200, 300, or even 500 feet high--depending -of course upon the scale--flatten out or disappear entirely. This seems -plausible, but the advantages of great exaggeration are more apparent -than real. Its effect upon the model has already been mentioned; it -should be added that, with the proper amount of care in finishing the -model, exceedingly small relief can be so brought out as to be readily -seen. With ordinary care, one-fortieth of an inch can be easily shown, -and with great care and skill certainly one-eightieth and probably -one-hundredth of an inch. Another plausible argument that has been -advanced in favor of vertical exaggeration as a principle, is well -stated by Mr. A. E. Lehman, of the Pennsylvania Geological Survey, in a -paper on "Topographical Models," read before the American Institute of -Mining Engineers in 1885. "A perfectly natural expression is of course -desired; and to cause this the features of the topography should be -distorted and exaggerated in vertical scale just enough to produce the -same effect on the beholder or student of the district of country -exhibited as his idea of it would be if he were on the real ground -itself. Care should be taken, however, not to make the scales so -disproportionate as to do violence to mental impressions. Often, -indeed, prominent or important features, when they will bear it, may be -still more effectively shown by additional exaggeration in the vertical -scale." The fallacy of this argument is obvious. It assumes that the -object of a model is to show the country as it appears to one passing -through it, and not as it really is--and there is often a very wide -difference between the two. The impression derived from passing through -a country is, if I may use the term, a very large-scale impression, as -any one who has tried it can certify; it is certainly a mistake to -attempt to reproduce this impression in a small-scale model, with the -help of vertical exaggeration. Even if the principle were a good one, -its application would be very limited. It could only be used in -large-scale models; to apply it to a model of a large area--the United -States, for example--is obviously absurd. - -The method referred to as being now generally in use may be briefly -described as follows: requisites, a good contoured map; a hachured map -in addition, if possible; a clear conception on the part of the modeler -of the country to be represented; and a fair amount of skill. -Materials: a base-board of wood or other suitable material; card-board -or wood of the thickness required by the contour interval and the -scale; and modeling wax or clay. Procedure: reproduce the contours in -the wood or other material; mount these upon the base-board in their -proper relationship; then fill in the intervening spaces, and the space -above the topmost contour, with the modeling material. - -In a series of models of the Grand Divisions of the earth, made about a -year and a half ago, the contours of card-board were made as follows: -the map was photographed up to the required scale, and as many prints -were made as there were contour intervals to be represented--in a model -of the United States of 1,000 feet contour interval there were fourteen -prints. Thirteen of these were mounted upon card-board of the exact -thickness required by the vertical scale, and one upon the base-board. -All large paper companies use a micrometer gauge, and card-board can -easily be obtained of the exact thickness required--even to less than -the thousandth part of an inch. The lowest contour was then sawed out -upon a scroll saw, and placed upon the corresponding line of the map -mounted upon the base-board. This process was repeated with each of the -succeeding contours until all were placed and glued into their proper -positions. At this stage the model presents the relief in a series of -steps, each step representing a rise corresponding to the contour -interval. The disadvantages of the method lie in the fact that unless -the greatest care is exercised in making the photographic prints there -will be considerable distortion, owing to the stretching of the paper -in different directions, and consequently much trouble in fitting the -contours. If care be exercised in having the grain of the paper run in -the same direction in all the prints, trouble in fitting the contours -will be much reduced, but the distortion in one direction will remain. -In our experience this distortion amounts to about two per cent.; in -other words, a model that should be fifty inches long will in reality -be fifty-one inches; but, as this error is distributed over the whole -fifty inches, it is not too great for an ordinary model. If greater -accuracy be required, it can be secured by transferring the contours to -the card-board by means of tracing or transfer paper. The great -advantage of the photographic method lies in the fact that when the -model has been built up, with all the contours in position, it presents -a copy of the map itself, with all the details, drainage, etc., in -position, instead of blank intervals between the contours. Such details -and drainage are a great help in the subsequent modeling. - -The next step in the process is to fill in with clay or wax the -intervals between the contours. I have always found wax more convenient -than clay for this purpose as, unless the surface coating is a thick -one, the clay is difficult to keep moist. To obviate this difficulty, -some modelers have used clay mixed with glycerine instead of water; -this, of course, does not become dry, but the material is, at its best, -unsatisfactory. The filling-in process is the most important one in -relief map making, for it is here that the modeler must show his -knowledge of, and feeling for, topographic forms. Some models seem to -have been constructed with the idea that when the contours have been -accurately placed the work of the modeler is practically done. This is -a great mistake. The card-board contours are only a means of control, -occupying somewhat the same relation to the relief map that a core or -base of bricks, or a frame of wood, does to other constructions as, for -example, an architectural ornament or a bust. It is sometimes necessary -to cut away the contour card; for, as has been already explained, a map -is more or less generalized, and a contour is frequently carried across -a ravine, instead of following it up, as it would do if the map were on -a larger scale. Such generalizing is of course perfectly proper in a -map, but, with the same scale, we expect more detail in a model. The -modeler must have judgment enough and skill enough to read between the -lines, and to undo the generalizing of the topographer and draughtsman, -thus supplying the material omitted from the map. This can be done -without materially affecting the accuracy of the model, considered even -as a copy of the contoured map. - -The contours of card-board or other material are, let me repeat, only a -means of control. The perfect modeler--a variety, by the way, yet to be -evolved--would be able to make an accurate relief map without them, in -the same way that other subjects are made; as, for example, a flower -panel, an architectural ornament, or any other subject in low relief, -where the object sought is artistic effect and great accuracy is not a -desideratum. It is the converse of this idea that has produced the -numerous models that one sees; accurate enough, perhaps, but wholly -expressionless and absolutely without feeling. This is the great fault -of nearly all models made by building up the contours in wood and then -carving down the shoulders. It is then necessary to sand-paper them, -and what little character they might otherwise have had is completely -obliterated by the sand-paper. Such models almost invariably _look_ -wooden. Let the modeler, then, have a clear conception of his subject -and not depend wholly on the contours, and let him work out that -conception in his model, "controlled" and helped by the contours, but -not bound by them; the resulting model will thus be far more -satisfactory and a far better representation of his subject, in other -words, it will be more life-like--more nearly true to nature. - -The model, provided it be not of clay, is sometimes used in the state -in which it is left when finished. It is much more common, however, to -make a plaster mould, and from this a plaster cast. For this purpose a -moulder is usually called in; but moulders as a rule are ignorant men, -accustomed to one line of work only, and the result is not always -satisfactory. It is much better for the modeler himself to do this -work, though to obtain good results from plaster it is necessary to -know the material thoroughly, and this knowledge comes only from -experience. The mould is generally made quite heavy, in order to stand -the subsequent hard treatment that it may receive, and should be -retouched and thoroughly dried before being prepared for the cast. The -method used by some modelers of placing a frame about the model and -pouring in the plaster, filling the frame to the top, is a crude and -very wasteful one and not at all to be recommended. In a model of large -size--say seven or eight feet square--it would require a derrick to -move the mould. It is wholly unnecessary, as, with a small amount of -care, a good mould can be made not more than an inch thick, or, at -most, an inch and a half. The drying of the mould before use can -sometimes be dispensed with, but is always desirable. - -Nearly all American moulders (as distinguished from French and Italian -ones) varnish the mould, and thus lose some of the finest detail and -sharpness. This is unnecessary. The mould can be easily prepared with a -solution of soap so as to leave nothing on the surface but a very thin -coating of oil, which is taken up and replaced by the plaster of the -cast. Of course, if the model has been sand-papered, no fine work in -moulding or casting is necessary, as there is nothing to save. If the -subject is a very intricate one, with "undercuts" (as they are called), -it is customary to make a waste mould; as this is very seldom necessary -in relief map work, however, the process need not be described. - -To make the cast it is only necessary to repeat the processes used in -making the mould. With great care and some skill a cast can be produced -but little inferior in point of sharpness and detail to the original -model. It is customary to make the cast very thick, and, consequently, -very heavy; this is unnecessary. In our work we seldom make a cast -thicker than one inch, and yet are never troubled with changes in the -model after it is finished. Even in a very large cast (now in the -National Museum), weighing nearly 1,500 pounds and presenting a surface -of over 160 square feet, the average thickness is less than one inch, -although it required over five barrels of plaster to make it. The cast, -after being thoroughly dried, should be finished--all its imperfections -being carefully repaired. The surface, however, should be touched as -little as possible, as the slight roughness of surface that comes from -the original model, through the mould, is removed by any tooling. This -roughness adds much to the effect of the model; in fact, where the -scale is large enough, it is sometimes desirable to emphasize it. - -The proper way to paint a model is a matter that must rest principally -upon the judgment of the modeler, depending to some extent, also, on -the use to which the model is to be put. The plain cast is sometimes -used, drainage, lettering, etc., being put directly upon it. This has -the advantage of preserving all the detail that comes from the mould, -but it has also the disadvantage of a surface easily soiled and -impossible to clean. If the model is to be photographed, the surface -should be nearly white--in our practice we use a small amount of yellow -with the white. This yellow is hardly appreciable by the eye, but its -effect upon the photographic negative is quite marked. Yellow becomes -grey in a photograph, and, in a photograph of a model colored as -described, a grey tint is given to the whole surface. The high lights -are not pure white, and there is no harsh contrast between light and -shade. There is another point of great importance in photographing -models: the surface should have a dead finish--that is, should have no -gloss, or, at most, should have only what is known among painters as an -egg-shell gloss. It is almost impossible satisfactorily to photograph a -model that has a shiny surface. Any portion of a model that it is -desired to separate from the rest should be painted a different -color--the water, for example, should be painted a light blue; not a -blue composed of indigo, however, or any of the grey blues, as these -produce in the photograph a dead grey, and are not pleasant to the eye. -The most satisfactory color that we have used is a mixture of -cobalt--the purest of the blues--with Antwerp blue--which is quite -green--and white. This gives a color that is pleasant to the eye, has -the retreating quality to perfection, and photographs well. - -Models intended for exhibition as such should be painted realistically. -There is room here for an immense improvement in the usual practice, -which is to paint the model either in some conventional scheme of light -and shade, or else to put a single flat tint upon it. If the model is -to be colored conventionally it is, in my opinion, much better to use a -flat tint, light in tone, and with a dead surface. The use of a variety -of colors upon the face of a model interferes materially with the -relief, especially if the relief is finely modeled. For this reason -models colored to indicate geologic formations should always be -accompanied by duplicates representing topography only, colored -realistically, if possible, and without lettering. Well-defined lines -other than those pertaining to the model itself, such, for example, as -those used to define the boundaries of geologic formations, should not -be allowed upon a model when it is desired to bring out all the relief. -The lettering on such models should be kept down as small as possible, -or wholly dispensed with. The latter is much the better method. - -The cheap reproduction of models is the most important problem -connected with the art, and the one that is attracting most attention -among those engaged in it; as, until models can be reproduced cheaply, -they will never have any wide distribution and there will be far less -incentive to the modeler. Various materials have been suggested and -experimented on, but nine-tenths of the models that are made to-day are -made of plaster of Paris. Although this material was the first to be -used for this purpose, it has not yet been superseded. A plaster cast -is heavy, expensive and easily injured; but plaster gives an accurate -copy of the original, retains permanently the form given it, and is -easily finished and repaired. The weight is an obstacle that can be -easily overcome. By the incorporation in the plaster of fine tow, or of -bagging or netting of various kinds, the cast can be made very light -and at the same time strong, but the expense is increased rather than -diminished by this method. Models made in this way, however, have the -advantage that when broken the pieces do not fall out, they are, -however, fully as liable to surface injury as the other kind. The large -cast in the National Museum, before referred to, was made in this way. -It weighed nearly 2,000 pounds when boxed--not an easy thing to -handle--but it stood shipment to New Orleans and back without suffering -any material injury. This would hardly have been possible had the cast -been made from plaster alone. - -Paper seems, at first sight, to be the material best adapted for the -reproduction of models; but no one has succeeded well enough with it to -bring it into use. Like nearly all those who have given this subject -attention, I have experimented with paper, but the only positive result -has been a loss of a large part of the confidence that I once had in -the suitability of the material. Paper has been used extensively for -large scale models of pueblos, ruins, etc., but I have never obtained a -satisfactory result with subjects in low relief and fine detail. A -paper cast may look well when first made, but it absorbs moisture from -the atmosphere, and contracts and expands with the weather. The -contraction is apt to flatten out the model and the expansion to make -it buckle up. - -Casts of models have been made in iron; but this, while suitable -perhaps for models of mounds and subjects of like character, would -hardly be applicable to small scale models with fine detail; such casts -require too much surface finishing. The material known as -Lincrusta-Walton seems to me to be the ideal material for this purpose. -It is tougher than rubber, will take the finest detail, and its surface -can be treated in any way desired. Unfortunately the manufacture of -models in this material would require expensive machinery, and is -outside the scope of a modeling room. Should it ever become -commercially advantageous, however, casts of a model of ordinary size, -in every way equal to the original, can be turned out in this material -at a very small cost. - -It remains to speak of the reproduction of models by -process-engravings--a method that will probably receive much more -attention in the future than it has in the past. It is perhaps along -this line that the cheap reproduction of models will develop; but the -subject is too large a one to be adequately treated here, and must be -postponed until some future occasion. - -[Illustration: HACHURED AND CONTOURED MAPS. - -REPRESENTATION OF A HILL ACCORDING TO THE TWO SYSTEMS AND ON DIFFERENT -SCALES. - -From Supplement to Enthoffer's Topographical Atlas by permission of Mr. -Enthoffer.] - -[Illustration: FROM BUTLER'S COMPLETE GEOGRAPHY. - -COPYRIGHT, 1888, BY E. H. BUTLER & CO. - -Printed by permission.] - - - - -NATIONAL GEOGRAPHIC SOCIETY. - -ABSTRACT OF MINUTES. - - -_October 5, 1888, Ninth Meeting_. - -A paper was read entitled, "Topographic Models," by Mr. Cosmos -Mindeleff. Published in the "National Geographic Magazine," Vol. I, No. -3. - - -_October 19, 1888, Tenth Meeting_. - -The attendance being very small, no paper was read. - - -_November 2, 1888, Eleventh Meeting_. - -The paper of the evening was entitled, "Surveys, their Kinds and -Purposes," by Mr. Marcus Baker. The paper was discussed by Messrs. -Ogden, Goodfellow, Gannett and Baker. Published in "Science," Vol. XII, -No. 304. - - -_November 16, 1888, Twelfth Meeting_. - -A paper was read by Mr. Henry Gannett, giving certain "Physical -Statistics Relating to Massachusetts," derived from the map of that -State recently prepared by the United States Geological Survey. A -discussion followed which was participated in by Messrs. Baker, -Kenaston, Fernow, Weed, and the author. A second paper entitled, -"Something about Tornadoes," was read by Lieut. J. P. Finley, U. S. -Signal Corps. - - -_November 30, 1888, Thirteenth Meeting_. - -The annual reports of vice-Presidents Herbert G. Ogden and Gen. A. W. -Greely were delivered. Published in the "National Geographic Magazine," -Vol. I, No. 2. - - -_December 20, 1888, Fourteenth Meeting_. - -Held in the Law Lecture Room of the Columbian University. The President -delivered his Annual Address, entitled, "Africa." Published in the -"National Geographic Magazine," Vol. I, No. 2. - - -_December 28, 1888, Fifteenth Meeting_. - -The Society met in the Society Hall of the Cosmos Club, President -Hubbard in the chair. Owing to the absence from the city of the -Secretaries, Mr. O. H. Tittmann was requested to act as Secretary of -the meeting. The minutes of the first and fourteenth meetings were read -and approved. The report of the Secretaries was read, in their absence, -by the temporary Secretary, and was approved. The Treasurer's report, -showing a balance on hand of $626.70, was read and approved, as was -also that of the auditing committee. - -The President announced that vacancies caused by the resignation of two -of the managers, Messrs. W. D. Johnson and Henry Mitchell, had been -filled by the Board on the 15th of November, by the election of Messrs. -O. H. Tittmann and C. A. Kenaston; and that a vacancy caused by the -resignation of Vice-President John R. Bartlett, had been filled by the -election of Lieut. George L. Dyer, on November 30th. - -The Society then proceeded to the election of officers, with following -result: - - _President_--GARDINER G. HUBBARD. - _Vice-Presidents_--HERBERT G. OGDEN, [land]; GEORGE L. DYER, [sea]; - A. W. GREELY, [air]; C. HART MERRIAM, [life]; A. H. THOMPSON, - [art]. - _Treasurer_--CHARLES J. BELL. - _Recording Secretary_--HENRY GANNETT. - _Corresponding Secretary_--GEORGE KENNAN. - _Managers_--CLEVELAND ABBE, MARCUS BAKER, ROGERS BIRNIE, JR., - G. BROWNE GOODE, W. B. POWELL, J. C. WELLING, C. A. KENASTON, - O. H. TITTMANN. - - -_January 11, 1889, Sixteenth Meeting_. - -The paper of the evening was entitled, "The Great Plains of Canada," -and was presented by Professor C. A. Kenaston, of Howard University. - - -_January 25, 1889, Seventeenth Meeting_. - -The paper of the evening was entitled, "Irrigation in California," by -Mr. William Hammond Hall, State Engineer of California. To be published -in the "National Geographic Magazine," Vol. I, No. 4. - - -_February 8, 1889, Eighteenth Meeting_. - -The following papers were read by Prof. W. M. Davis, of Harvard -University: "Topographic Models," and "Certain Peculiarities of the -Rivers of Pennsylvania." Published in the "National Geographic -Magazine," Vol. I, No. 3. - - -_February 22, 1889, Nineteenth Meeting_. - -The paper of the evening was entitled, "Round about Asheville, N. C.," -by Mr. Bailey Willis. The paper was illustrated by charcoal sketches -and lantern slides. Discussion followed, which was participated in by -Messrs. Baker, Merriam and McGee. To be published in the "National -Geographic Magazine," Vol. I, No. 4. - - -_March 8, 1889, Twentieth Meeting_. - -The following amendments to the By-Laws were adopted. - -[For Article VI substitute the following]: - -ARTICLE VI. - -MEETINGS. - -"Regular meetings of the Society shall be held on alternate Fridays, -from November until May, and excepting the annual meeting, they shall -be devoted to communications. The Board of Managers shall, however, -have power to postpone or omit meetings, when deemed desirable. Special -meetings may be called by the President. - -"The annual meeting for the election of officers shall be the last -regular meeting in December. - -"The meeting preceding the annual meeting shall be devoted to the -President's annual address. - -"The reports of the retiring Vice-Presidents shall be presented at the -meetings in January. - -"A quorum for the transaction of business shall consist of twenty-five -active members." - -In Article V, the following paragraph was introduced immediately after -the first paragraph of the article: - -"The dues of members elected in November and December shall be credited -to the succeeding year." - -The following papers were then presented: "A Trip to Panama and -Darien," by Mr. R. U. Goode, and "Survey of Mason and Dixon's Line," by -Mr. Mark B. Kerr. - -A Trip to Panama and Darien, to be published in the "National -Geographic Magazine," Vol. I, No. 4. - - -_March 22, 1889, Twenty-first Meeting_. - -The paper of the evening was entitled, "Recent Events in the U. S. of -Columbia," by Mr. W. E. Curtis. The discussion which followed was -participated in by Messrs. Baker, Gannett, and others. - - -_April 5, 1889, Twenty-second Meeting_. - -The paper of the evening was entitled, "House Life in Mexico," by Mr. -A. B. Johnson. - - -_April 19, 1889, Twenty-third Meeting_. - -This meeting was devoted to papers upon the Samoan Islands. The -following programme was presented: - -"Samoa; the General Geography and Hydrography of the Islands and -Adjacent Seas," by Mr. Everett Hayden. - -"Climate," by Prof. Cleveland Abbe. - -"Narrative of a Cruise Among the Islands," by Capt. R. W. Meade, U. S. -N. - -"The Home Life of the Samoans and the Botany of the Islands," by Mr. W. -E. Safford, U. S. N. - - -_May 3, 1889, Twenty-fourth Meeting_. - -The paper of the evening was entitled, "Across Nicaragua with Transit -and Machéte," by Mr. R. E. Peary, U. S. N. To be published in the -"National Geographic Magazine," Vol. I, No. 4. - - -_May 17, 1889, Twenty-fifth Meeting_. - -The paper of the evening was entitled, "The Krakatoa Eruption," by Dr. -A. Graham Bell. The paper was discussed by Captain C. E. Dutton. - - - - -(Translated by Mr. R. L. Lerch.) - -INTERNATIONAL LITERARY CONTEST - -To be held at Madrid, Spain, under the auspices of the Commission in -charge of the celebration of the Fourth Centennial Anniversary of the -Discovery of America. - - -PROGRAM. - -The work for which a prize is offered is to be a prose essay, a true -historic picture giving a just estimate of the grandeur of the occasion -to be celebrated. - -So much has been written on this subject since the opening of the XVIth -century that it would seem difficult to say anything new and good. -Perhaps the details, perhaps the circumstances in the life and acts of -Columbus are worthy of no little research; but already the Royal -Academy of History is engaged in the erudite and diligent task of -bringing together and publishing the un-edited or little known papers -bearing on this question. - -The book required by this contest must be of a different nature: it -must be comprehensive and synoptic, and must be sufficiently concise -without being either obscure or dry. - -Although there is an abundance of histories of America, of voyages and -discoveries, of geographic science, and of the establishment of -Europeans in remote regions of the earth, there is no book that sets -forth as it can be done the combined efforts of the nations of the -Iberian peninsula, who, since the commencement of the XVth century, -have, with a fixity of purpose and marvelous tenacity, in almost a -single century of silent efforts brought about the exploration of vast -continents and islands, traversed seas never before cut by Christian -prows, and in emulous strife obtained almost a complete knowledge of -the planet on which we live. - -There is a growing interest and manifest unity in all those more -important events; not to mention the circumstantial evidence borne by -the charts of 1375 and the semi-fabulous voyages, such as that of Doria -y Vivaldi and others less apocryphal though isolated and barren of -results, like that of Ferrer, begun in 1434, when Gil Eannes doubled -Cape Bojador, discovered Guinea, and dispelled the terror inspired by -the unknown ocean, and ended in 1522 with Elcano's arrival at Sanlucar -after circumnavigating the globe. - -In all this activity very little occurs by chance. The progressive -series of geographic discoveries, due to persistent premeditation and -not to accident, was inaugurated at Sagres by the Infante D. Enrique -and his illustrious pilot Jaime de Mallorca. - -Well might Pedro Nuñes exclaim that from that time forth until the form -and size of the terraqueous globe were thoroughly known, the most to be -obtained would not be firmly established, "unless our mariners sailed -away better instructed and provided with better instruments and rules -of Astronomy and Geography than the things with which cosmographers -supplied them." - -The culmination in the progress of that beautiful history falls on the -12th of October, 1492, when Columbus was the first European to set foot -upon the intertropical shores of the New World. But this act, -considered apart from its intrinsic value, as purely the individual -inspiration of a mariner and the generous enthusiasm of a patron Queen, -derives a higher value when regarded as part of a summation of efforts, -a grand development of an idea, a purpose to explore and know the whole -globe, to spread the name and the law of Christ together with the -civilization of Europe, and to reap a harvest of gold, spices, and all -the riches of which costly samples and exaggerated reports were -furnished by the traffic of the Venetians, Genoese and Catalonians, who -in turn got them from Mussulmans. - -Doubtless the moving cause, whose gorgeous banner so many men of our -peninsula followed, was clothed in great sentiments, good or bad; their -hearts were filled with religious fervor, thirst for glory, ambition, -Christian love, cupidity, curiosity, and violent dissatisfaction (even -during the Renaissance), to seek and undergo real adventures that -should surpass the vain, fruitless, and fanciful adventures of -chivalry; and to make voyages and conquests eclipsing those of the -Greeks and Romans, many of which, recorded in classic histories and -fables, were now disinterred by the learned. - -What must be described is the complete picture in all its sumptuousness -so that its magnificent meaning may stand out distinctly, without which -the conviction would be lacking that the studies, voyages, and happy -audacity of Bartolomé Diaz, Gama, Alburquerque, Cabral, Balboa, -Magallanes, Cortes, Pizarro, Orellana, and a host of others, do not dim -the glory of the hero whose centennary is to be celebrated, even though -it heighten and add greater luster to the work of civilization begun by -Portugal.... - -The book here vaguely outlined must also contain a compendious -introduction, notices of voyages, ideas, and geographic progress up to -the date of D. Enrique's establishment at Sagres, and an epilogue or -conclusion of greater extent, in which are examined and weighed the -changes and progress that our subject has made, collectively, in the -civilization of the world--in the commerce, economics and politics of -the peoples, in regard to the broad field opened to the intelligent -activity of Europe, over which it could spread and dominate; the -abundance of data, sunken hopes, and more secure basis lent to the -studious and wise for the extension of our knowledge of Nature, the -unraveling of her laws, and penetration of her mysteries. - -The vast, elevated argument of the book requires it be a finished work -of art, not in fullness and richness of diction, but in plan and order, -in sobriety and unity of style, whose nobility and beauty must lie in -simplicity of phrase, correctness of judgment and richness of thought. - -There may enter into this contest any unpublished work written to this -end in Spanish, Portuguese, English, German, French or Italian. - -The tribunal that is to award the prize will be composed of two members -of the R. Acad. of History, and one member from each of the Spanish R. -Academies of Moral Sciences and Politics, and Exact and Natural -Sciences--all to be chosen by the Academies themselves. - -Furthermore, there will be included in the tribunal the diplomatic -representative of every power whose subject or subjects wish to enter -the contest, which is to be done through said representative or some -person duly appointed to act in his place. - -The tribunal will elect its presiding officer and will decide on the -best works by an absolute majority of all the jurors who take part in -the vote. - -Each work submitted in this contest must be neatly copied, in legible -writing, on good paper, without the author's name but with a quotation -to identify him afterwards. - -Each author will inclose a separate folded sheet on whose exterior is -written the quotation he has chosen and the opening sentence of his -work; within, he will write his name and residence. - -The folded sheets corresponding to the works that did not get a prize -will be burnt publicly without being opened. - -Though it is difficult to set a limit as to size, the works should not -have more reading matter than is contained in two volumes of the shape -and size of the complete works of Cervantes issued by Rivadeneyra in -1863-4. - -If the plan or purpose of any of the works require it, there may be -added another volume of documents, maps, or other illustrations. - -As it will take time to examine and judge the works, they should be -sent to the Secretary of the R. Acad. of Hist. prior to January 1, -1892. - -There will be first prize of 30,000 pesetas ($5,790) and a second of -15,000 pesetas ($2,895). - -Besides this, each of the two successful authors will receive 500 -copies of the printed edition of his work. - -It rests with the Centennial Commission to determine the number of -copies in the edition of each of the two prize works, and what -disposition is to be made of the copies that are not given to the -authors. - -These (the authors) keep the right to re-print and to sell their works, -and to translate them into other tongues. - -The Commission, however, will have the right, if either or both prize -works are in a foreign tongue, to have them translated and published in -Castilian. - -The Commission affix their seal to the preceding directions for the -information of the public and government of those persons who desire to -participate in the contest. - -Madrid, June 19, 1889. - -The Vice President, DUKE OF VERAGUA. - -Secretaries, JUAN VALERA, JUAN F. RIAÑO. - - - - - - -End of the Project Gutenberg EBook of The National Geographic Magazine, Vol. -I., No. 3, July, 1889, by Various - -*** END OF THIS PROJECT GUTENBERG EBOOK NATIONAL GEOGRAPHIC MAG., JULY 1889 *** - -***** This file should be named 50383-8.txt or 50383-8.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/0/3/8/50383/ - -Produced by Ron Swanson -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law 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. 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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: 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/old/50383-8.zip b/old/50383-8.zip Binary files differdeleted file mode 100644 index d596c5d..0000000 --- a/old/50383-8.zip +++ /dev/null diff --git a/old/50383-h.zip b/old/50383-h.zip Binary files differdeleted file mode 100644 index 501b5cc..0000000 --- a/old/50383-h.zip +++ /dev/null diff --git a/old/50383-h/50383-h.htm b/old/50383-h/50383-h.htm deleted file mode 100644 index 1f41bcc..0000000 --- a/old/50383-h/50383-h.htm +++ /dev/null @@ -1,4238 +0,0 @@ - -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> - -<html> -<head> - <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> - <title>The Project Gutenberg e-Book of The National Geographic Magazine, Vol. 1, No. 3, by Various</title> - <link rel="coverpage" href="images/img-cover.jpg"> - <style type="text/css"> - <!-- - body {margin:10%; text-align:justify} - h1 {text-align:center} - h2 {text-align:center} - h3 {text-align:center} - h4 {text-align:center} --> - </style> -</head> - -<body> - - -<pre> - -The Project Gutenberg EBook of The National Geographic Magazine, Vol. I., -No. 3, July, 1889, by Various - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world 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. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The National Geographic Magazine, Vol. I., No. 3, July, 1889 - -Author: Various - -Release Date: November 4, 2015 [EBook #50383] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK NATIONAL GEOGRAPHIC MAG., JULY 1889 *** - - - - -Produced by Ron Swanson - - - - - -</pre> - -<center><img src="images/img-cover.jpg" alt="cover"></center> -<br> -<br> -<br> -<br> -<h3>CONTENTS.</h3> -<hr align="center" width="25%"> -<br> - -<p><a href="#chap1">The Rivers and Valleys of Pennsylvania</a>: William Morris Davis<br> - (Illustrated by one map and twenty-five cuts.)</p> - -<p><a href="#chap2">Topographic Models</a>: Cosmos Mindeleff<br> - (Illustrated by two plates.)</p> - -<p><a href="#chap3">National Geographic Society—Abstract of Minutes</a></p> - -<p><a href="#chap4">International Literary Contest to be held at Madrid, Spain</a></p> - -<blockquote>July, 1889.</blockquote> -<br> -<br> -<br> -<br> -<center><small><small>PRESS OF TUTTLE, MOREHOUSE & TAYLOR, NEW HAVEN, CONN.</small></small></center> -<br> -<br> -<br> -<br> -<h4>THE</h4> -<h2>NATIONAL GEOGRAPHIC MAGAZINE.</h2> -<hr align="center" width="100%"> -<center>Vol. I. -1889. No. 3.</center> -<hr align="center" width="100%"> -<br> -<br><a name="chap1"></a> -<br> -<br> -<h3>THE RIVERS AND VALLEYS OF PENNSYLVANIA.<small><sup>1</sup></small></h3> - -<center>B<small>Y</small> W<small>ILLIAM</small> M<small>ORRIS</small> D<small>AVIS</small>.</center> - -<blockquote>"In Faltensystemen von sehr hohem Alter wurde die ursprüngliche -Anordnung der Langenthäler durch das Ueberhandnehmen der transversalen -Erosionsfurchen oft ganz und gar verwischt."</blockquote> - -<center>L<small>ÖWL</small>. Petermann's Mittheilungen, xxviii, 1882, 411. </center> - -<blockquote><small><small><sup>1</sup></small> The substance of this essay was presented to the Society -in a lecture on February 8th, 1889, but since then it has been much -expanded.</small></blockquote> -<br> - -<center>CONTENTS.</center> - -<p>P<small>ART FIRST</small>. <a href="#part1"><i>Introductory</i></a>.<br> - 1. <a href="#sect1">Plan of work here proposed</a>.<br> - 2. <a href="#sect2">General description of the topography of Pennsylvania</a>.<br> - 3. <a href="#sect3">The drainage of Pennsylvania</a>.<br> - 4. <a href="#sect4">Previous studies of Appalachian drainage</a>.</p> - -<p>P<small>ART SECOND</small>. <a href="#part2"><i>Outline of the geological history of the region</i></a>.<br> - 5. <a href="#sect5">Conditions of formation</a>.<br> - 6. <a href="#sect6">Former extension of strata to the southeast</a>.<br> - 7. <a href="#sect7">Cambro-Silurian and Permian deformations</a>.<br> - 8. <a href="#sect8">Perm-Triassic denudation</a>.<br> - 9. <a href="#sect9">Newark deposition</a>.<br> - 10. <a href="#sect10">Jurassic tilting</a>.<br> - 11. <a href="#sect11">Jura-Cretaceous denudation</a>.<br> - 12. <a href="#sect12">Tertiary elevation and denudation</a>.<br> - 13. <a href="#sect13">Later changes of level</a>.<br> - 14. <a href="#sect14">Illustrations of Pennsylvanian topography</a>.</p> - -<p>P<small>ART THIRD</small>. <a href="#part3"><i>General conception of the history of a river</i></a>.<br> - 15. <a href="#sect15">The complete cycle of river life: youth, adolescence, maturity and old age</a>.<br> - 16. <a href="#sect16">Mutual adjustment of river courses</a>.<br> - 17. <a href="#sect17">Terminology of rivers changed by adjustment</a>.<br> - 18. <a href="#sect18">Examples of adjustments</a>.<br> - 19. <a href="#sect19">Revival of rivers by elevation and drowning by depression</a>.<br> - 20. <a href="#sect20">Opportunity for new adjustments with revival</a>.<br> - 21. <a href="#sect21">Antecedent and superimposed rivers</a>.<br> - 22. <a href="#sect22">Simple, compound, composite and complex rivers</a>.</p> - -<p>P<small>ART FOURTH</small>. <a href="#part4"><i>The development of the rivers of Pennsylvania</i></a>.<br> - 23. <a href="#sect23">Means of distinguishing between antecedent and adjusted consequent rivers</a>.<br> - 24. <a href="#sect24">Postulates of the argument</a>.<br> - 25. <a href="#sect25">Constructional Permian topography and consequent drainage</a>.<br> - 26. <a href="#sect26">The Jura mountains homologous with the Permian Alleghanies</a>.<br> - 27. <a href="#sect27">Development and adjustment of the Permian drainage</a>.<br> - 28. <a href="#sect28">Lateral water-gaps near the apex of synclinal ridges</a>.<br> - 29. <a href="#sect29">Departure of the Juniata from the Juniata-Catawissa syncline</a>.<br> - 30. <a href="#sect30">Avoidance of the Broad Top basin by the Juniata headwaters</a>.<br> - 31. <a href="#sect31">Reversal of larger rivers to southeast courses</a>.<br> - 32. <a href="#sect32">Capture of the Anthracite headwaters by the growing Susquehanna</a>.<br> - 33. <a href="#sect33">Present outward drainage of the Anthracite basins</a>.<br> - 34. <a href="#sect34">Homologies of the Susquehanna and Juniata</a>.<br> - 35. <a href="#sect35">Superimposition of the Susquehanna on two synclinal ridges</a>.<br> - 36. <a href="#sect36">Evidence of superimposition in the Susquehanna tributaries</a>.<br> - 37. <a href="#sect37">Events of the Tertiary cycle</a>.<br> - 38. <a href="#sect38">Tertiary adjustment of the Juniata on the Medina anticlines</a>.<br> - 39. <a href="#sect39">Migration of the Atlantic-Ohio divide</a>.<br> - 40. <a href="#sect40">Other examples of adjustments</a>.<br> - 41. <a href="#sect41">Events of the Quaternary cycle</a>.<br> - 42. <a href="#sect42">Doubtful cases</a>.<br> - 43. <a href="#sect43">Complicated history of our actual rivers</a>.<br> - 44. <a href="#sect44">Provisional conclusions</a>.</p> -<a name="part1"></a><a name="sect1"></a> -<br> -<center>P<small>ART FIRST</small>. <i>Introductory</i>.</center> - -<p>1. <i>Plan of work here proposed</i>.—No one now regards a river and its -valley as ready-made features of the earth's surface. All are convinced -that rivers have come to be what they are by slow processes of natural -development, in which every peculiarity of river-course and valley-form -has its appropriate cause. Being fully persuaded of the gradual and -systematic evolution of topographic forms, it is now desired, in -studying the rivers and valleys of Pennsylvania, to seek the causes of -the location of the streams in their present courses; to go back if -possible to the early date when central Pennsylvania was first raised -above the sea and trace the development of the several river systems -then implanted upon it from their ancient beginning to the present -time.</p> - -<p>The existing topography and drainage system of the State will first be -briefly described. We must next inquire into the geological structure -of the region, follow at least in a general way the deformations and -changes of attitude and altitude that it has suffered, and consider the -amount of denudation that has been accomplished on its surface. We must -at the same time bear in mind the natural history of rivers, their -morphology and development; we must recognize the varying activities of -a river in its youth and old age, the adjustments of its adolescence -and maturity, and the revival of its decrepit powers when the land that -it drains is elevated and it enters a new cycle of life. Finally we -shall attempt to follow out the development of the rivers of -Pennsylvania by applying the general principles of river history to the -special case of Pennsylvania structure.</p> -<a name="sect2"></a> -<p>2. <i>General description of the topography of Pennsylvania</i>.—The -strongly marked topographic districts of Pennsylvania can hardly be -better described than by quoting the account given over a century ago -by Lewis Evans, of Philadelphia, in his "Analysis of a map of the -middle British colonies in America" (1755), which is as valuable from -its appreciative perception as it is interesting from its early date. -The following paragraphs are selected from his early pages:</p> - -<blockquote>"The land southwestward of Hudson's River is more regularly divided and -into a greater number of stages than the other. The first object worthy -of regard in this part is a rief or vein of rocks of the talky or -isinglassy kind, some two or three or half a dozen miles broad; rising -generally some small matter higher than the adjoining land; and -extending from New York city southwesterly by the lower falls of -Delaware, Schuylkill, Susquehanna, Gun-Powder, Patapsco, Potomack, -Rapahannock, James river and Ronoak. This was the antient maritime -boundary of America and forms a very regular curve. The land between -this rief and the sea and from the Navesink hills southwest ... may be -denominated the Lower Plains, and consists of soil washt down from -above and sand accumulated from the ocean. Where these plains are not -penetrated by rivers, they are a white sea-sand, about twenty feet deep -and perfectly barren, as no mixture of soil helps to enrich them. But -the borders of the rivers, which descend from the uplands, are rendered -fertile by the soil washt down with the floods and mixt with the sands -gathered from the sea. The substratum of sea-mud, shells and other -foreign subjects is a perfect confirmation of this supposition. And -hence it is that for 40 or 50 miles inland and all the way from the -Navesinks to Cape Florida, all is a perfect barren where the wash from -the uplands has not enriched the borders of the rivers; or some ponds -and defiles have not furnished proper support for the growth of white -cedars....</blockquote> - -<blockquote>"From this rief of rocks, over which all the rivers fall, to that chain -of broken hills, called the South mountain, there is the distance of -50, 60 or 70 miles of very uneven ground, rising sensibly as you -advance further inland, and may be denominated the Upland. This -consists of veins of different kinds of soil and substrata some scores -of miles in length; and in some places overlaid with little ridges and -chains of hills. The declivity of the whole gives great rapidity to the -streams; and our violent gusts of rain have washt it all into gullies, -and carried down the soil to enrich the borders of the rivers in the -Lower Plains. These inequalities render half the country not easily -capable of culture, and impoverishes it, where torn up by the plow, by -daily washing away the richer mould that covers the surface.</blockquote> - -<blockquote>"The South mountain is not in ridges like the Endless mountains, but in -small, broken, steep, stoney hills; nor does it run with so much -regularity. In some places it gradually degenerates to nothing, not to -appear again for some miles, and in others it spreads several miles in -breadth. Between South mountain and the hither chain of the Endless -mountains (often for distinction called the North mountain, and in some -places the Kittatinni and Pequélin), there is a valley of pretty even -good land, some 8, 10 or 20 miles wide, and is the most considerable -quantity of valuable land that the English are possest of; and runs -through New Jersey, Pensilvania, Mariland and Virginia. It has yet -obtained no general name, but may properly enough be called Piemont, -from its situation. Besides conveniences always attending good land, -this valley is everywhere enriched with Limestone.</blockquote> - -<blockquote>"The Endless mountains, so called from a translation of the Indian name -bearing that signification, come next in order. They are not confusedly -scattered and in lofty peaks overtopping one another, but stretch in -long uniform ridges scarce half a mile perpendicular in any place above -the intermediate vallies. Their name is expressive of their extent, -though no doubt not in a literal sense.... The mountains are almost all -so many ridges with even tops and nearly of a height. To look from -these hills into the lower lands is but, as it were, into an ocean of -woods, swelled and deprest here and there by little inequalities, not -to be distinguished one part from another any more than the waves of -the real ocean. The uniformity of these mountains, though debarring us -of an advantage in this respect, makes some amends in another. They are -very regular in their courses, and confine the creeks and rivers that -run between; and if we know where the gaps are that let through these -streams, we are not at a loss to lay down their most considerable -inflections....</blockquote> - -<blockquote>"To the northwestward of the Endless mountains is a country of vast -extent, and in a manner as high as the mountains themselves. To look at -the abrupt termination of it, near the sea level, as is the case on the -west side of Hudson's river below Albany, it looks as a vast high -mountain; for the Kaats Kills, though of more lofty stature than any -other mountains in these parts of America, are but the continuation of -the Plains on the top, and the cliffs of them in the front they present -towards Kinderhook. These Upper Plains are of extraordinary rich level -land, and extend from the Mohocks river through the country of the -Confederates.<small><small><sup>2</sup></small></small> Their termination northward is at a little distance -from Lake Ontario; but what it is westward is not known, for those most -extensive plains of Ohio are part of them."</blockquote> - -<blockquote><small><small><sup>2</sup></small> Referring to the league of Indian tribes, so-called.</small></blockquote> - -<p>These several districts recognized by Evans may be summarized as the -coastal plain, of nearly horizontal Cretaceous and later beds, just -entering the southeastern corner of Pennsylvania; the marginal upland -of contorted schists of disputed age; the South Mountain belt of -ancient and much disturbed crystalline rocks, commonly called Archean; -a space between these two traversed by the sandstone lowland of the -Newark formation;<small><small><sup>3</sup></small></small> the great Appalachian valley of crowded Cambrian -limestones and slates; the region of the even-crested, linear Paleozoic -ridges, bounded by Kittatinny or Blue mountain on the southeast and by -Alleghany mountain on the northwest, this being the area with which we -are here most concerned; and finally the Alleghany plateau, consisting -of nearly horizontal Devonian and Carboniferous beds and embracing all -the western part of the state. The whole region presents the most -emphatic expression not only of its structure but also of the more -recent cycles of development through which it has passed. Fig. 1 -represents the stronger ridges and larger streams of the greater part -of the central district: it is reproduced from the expressive -Topographic Map of Pennsylvania (1871) by Lesley. The Susquehanna flows -down the middle, receiving the West Branch from Lock Haven and -Williamsport, the East Branch from Wilkes-Barre in the Wyoming basin, -and the Juniata from the Broad Top region, south of Huntingdon. The -Anthracite basins lie on the right, enclosed by zigzag ridges of Pocono -and Pottsville sandstone; the Plateau, trenched by the West Branch of -the Susquehanna is in the northwest. Medina sandstone forms most of the -central ridges.</p> - -<blockquote><small><small><sup>3</sup></small> Russell has lately recommended the revival of this term, -proposed many years ago by Redfield, as a non-committal name for the -"New red sandstones" of our Atlantic slope, commonly called Triassic.</small></blockquote> -<a name="figure1"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 1"> - <tr> - <td width="708"> - <img src="images/01.jpg" alt="Part of Topographic Map of Pennsylvania"> - </td> - </tr> - <tr> - <td width="708" align="center"> - <small>F<small>IG</small>. 1. Part of Topographic Map of Pennsylvania, by J. - P. Lesley (1871).</small> - </td> - </tr> -</table> -<a name="sect3"></a> -<p>3. <i>The drainage of Pennsylvania</i>.—The greater part of the Alleghany -plateau is drained westward into the Ohio, and with this we shall have -little to do. The remainder of the plateau drainage reaches the -Atlantic by two rivers, the Delaware and the Susquehanna, of which the -latter is the more special object of our study. The North and West -Branches of the Susquehanna rise in the plateau, which they traverse in -deep valleys; thence they enter the district of the central ranges, -where they unite and flow in broad lowlands among the even-crested -ridges. The Juniata brings the drainage of the Broad Top region to the -main stream just before their confluent current cuts across the -marginal Blue Mountain. The rock-rimmed basins of the anthracite region -are drained by small branches of the Susquehanna northward and -westward, and by the Schuylkill and Lehigh to the south and east. The -Delaware, which traverses the plateau between the Anthracite region and -the Catskill Mountain front, together with the Lehigh, the Schuylkill, -the little Swatara and the Susquehanna, cut the Blue Mountain by fine -water-gaps, and cross the great limestone valley. The Lehigh then turns -eastward and joins the Delaware, and the Swatara turns westward to the -Susquehanna; but the Delaware, Schuylkill and Susquehanna all continue -across South Mountain and the Newark belt, and into the low plateau of -schists beyond. The Schuylkill unites with the Delaware near -Philadelphia, just below the inner margin of the coastal plain; the -Delaware and the Susquehanna continue in their deflected estuaries to -the sea. All of these rivers and many of their side streams are at -present sunk in small valleys of moderate depth and width, below the -general surface of the lowlands, and are more or less complicated with -terrace gravels.</p> -<a name="sect4"></a> -<p>4. <i>Previous studies of Appalachian drainage</i>.—There have been no -special studies of the history of the rivers of Pennsylvania in the -light of what is now known of river development. A few recent essays of -rather general character as far as our rivers are concerned, may be -mentioned.</p> - -<p>Peschel examined our rivers chiefly by means of general maps with -little regard to the structure and complicated history of the region. -He concluded that the several transverse rivers which break through the -mountains, namely, the Delaware, Susquehanna and Potomac, are guided by -fractures, anterior to the origin of the rivers.<small><small><sup>4</sup></small></small> There does not seem -to be sufficient evidence to support this obsolescent view, for most of -the water-gaps are located independently of fractures; nor can -Peschel's method of river study be trusted as leading to safe -conclusions.</p> - -<blockquote><small><small><sup>4</sup></small> Physische Erdkunde, 1880, ii, 442.</small></blockquote> - -<p>Tietze regards our transverse valleys as antecedent;<small><small><sup>5</sup></small></small> but this was -made only as a general suggestion, for his examination of the structure -and development of the region is too brief to establish this and -exclude other views.</p> - -<blockquote><small><small><sup>5</sup></small> Jahrbuch Geol. Reichsanstalt, -xxviii, 1878, 600.</small></blockquote> - -<p>Löwl questions the conclusion reached by Tietze and ascribes the -transverse gaps to the backward or headwater erosion of external -streams, a process which he has done much to bring into its present -important position, and which for him replaces the persistence of -antecedent streams of other authors.<small><small><sup>6</sup></small></small></p> - -<blockquote><small><small><sup>6</sup></small> Pet. Mitth., 1882, 405; -Ueber Thalbildung, Prag, 1884.</small></blockquote> - -<p>A brief article<small><small><sup>7</sup></small></small> that I wrote in comment on Löwl's first essay -several years ago now seems to me insufficient in its method. It -exaggerated the importance of antecedent streams; it took no sufficient -account of the several cycles of erosion through which the region has -certainly passed; and it neglected due consideration of the -readjustment of initial immature stream courses during more advanced -river-life. Since then, a few words in Löwl's essay have come to have -more and more significance to me; he says that in mountain systems of -very great age, the original arrangement of the longitudinal valleys -often becomes entirely confused by means of their conquest by -transverse erosion gaps. This suggestion has been so profitable to me -that I have placed the original sentence at the beginning of this -paper. Its thesis is the essential element of my present study.</p> - -<blockquote><small><small><sup>7</sup></small> Origin of Cross-valleys. -Science, i, 1883, 325.</small></blockquote> - -<p>Phillipson refers to the above-mentioned authors and gives a brief -account of the arrangement of drainage areas within our Appalachians, -but briefly dismisses the subject.<small><small><sup>8</sup></small></small> His essay contains a serviceable -bibliography.</p> - -<blockquote><small><small><sup>8</sup></small> Studien über Wasserscheiden. -Leipsig, 1886, 149.</small></blockquote> - -<p>If these several earlier essays have not reached any precise -conclusion, it may perhaps be because the details of the geological -structure and development of Pennsylvania have not been sufficiently -examined. Indeed, unless the reader has already become familiar with -the geological maps and reports of the Pennsylvania surveys and is -somewhat acquainted with its geography, I shall hardly hope to make my -case clear to him. The volumes that should be most carefully studied -are, first, the always inspiring classic, "Coal and its Topography" -(1856), by Lesley, in which the immediate relation of our topography to -the underlying structure is so finely described; the Geological Map of -Pennsylvania (1856), the result of the labors of the first survey of -the state; and the Geological Atlas of Counties, Volume X of the second -survey (1885). Besides these, the ponderous volumes of the final report -of the first survey and numerous reports on separate counties by the -second survey should be examined, as they contain many accounts of the -topography although saying very little about its development. If, in -addition to all this, the reader has seen the central district of the -state and marvelled at its even-crested, straight and zigzag ridges, -and walked through its narrow water-gaps into the enclosed coves that -they drain, he may then still better follow the considerations here presented.</p> -<a name="part2"></a><a name="sect5"></a> -<br> -<center>P<small>ART SECOND</small>. <i>Outline of the geological history of the region</i>.</center> - -<p>5. <i>Conditions of formation</i>.—The region in which the Susquehanna and -the neighboring rivers are now located is built in chief part of marine -sediments derived in paleozoic time from a large land area to the -southeast, whose northwest coast-line probably crossed Pennsylvania -somewhere in the southeastern part of the state; doubtless varying its -position, however, by many miles as the sea advanced and receded in -accordance with the changes in the relative altitudes of the land and -water surfaces, such as have been discussed by Newberry and Claypole. -The sediments thus accumulated are of enormous thickness, measuring -twenty or thirty thousand feet from their crystalline foundation to the -uppermost layer now remaining. The whole mass is essentially -conformable in the central part of the state. Some of the formations -are resistent, and these have determined the position of our ridges; -others are weaker and are chosen as the sites of valleys and lowlands. -The first are the Oneida and Medina sandstones, which will be here -generally referred to under the latter name alone, the Pocono sandstone -and the Pottsville conglomerate; to these may be added the fundamental -crystalline mass on which the whole series of bedded formations was -deposited, and the basal sandstone that is generally associated with -it. Wherever we now see these harder rocks, they rise above the -surrounding lowland surface. On the other hand, the weaker beds are the -Cambrian limestones (Trenton) and slates (Hudson River), all the -Silurian except the Medina above named, the whole of the Devonian—in -which however there are two hard beds of subordinate value, the -Oriskany sandstone and a Chemung sandstone and conglomerate, that form -low and broken ridges over the softer ground on either side of -them—and the Carboniferous (Mauch Chunk) red shales and some of the -weaker sandstones (Coal measures).</p> -<a name="sect6"></a> -<p>6. <i>Former extension of strata to the southeast</i>.—We are not much -concerned with the conditions under which this great series of beds was -formed; but, as will appear later, it is important for us to recognize -that the present southeastern margin of the beds is not by any means -their original margin in that direction. It is probable that the whole -mass of deposits, with greater or less variations of thickness, -extended at least twenty miles southeast of Blue Mountain, and that -many of the beds extended much farther. The reason for this conclusion -is a simple one. The several resistant beds above-mentioned consist of -quartz sand and pebbles that cannot be derived from the underlying beds -of limestones and shales; their only known source lay in the -crystalline rocks of the paleozoic land to the southeast. South -Mountain may possibly have made part of this paleozoic land; but it -seems more probable that it was land only during the earlier Archean -age, and that it was submerged and buried in Cambrian time and not -again brought to the light of day until it had been crushed into many -local anticlines<small><small><sup>9</sup></small></small> whose crests were uncovered by Permian and later -erosion. The occurrence of Cambrian limestone on either side of South -Mountain, taken with its compound anticlinal structure, makes it likely -that Medina time found this crystalline area entirely covered by the -Cambrian beds; Medina sands must therefore have come from farther still -to the southeast. A similar argument applies to the source of the -Pocono and Pottsville beds. The measure of twenty miles as the former -southeastern extension of the paleozoic formations therefore seems to -be a moderate one for the average of the whole series; perhaps forty -would be nearer the truth.</p> - -<blockquote><small><small><sup>9</sup></small> Lesley, as below.</small></blockquote> -<a name="sect7"></a> -<p>7. <i>Cambro-Silurian and Permian deformations</i>.—This great series of -once horizontal beds is now wonderfully distorted; but the distortions -follow a general rule of trending northeast and southwest, and of -diminishing in intensity from southeast to northwest. In the Hudson -Valley, it is well known that a considerable disturbance occurred -between Cambrian and Silurian time, for there the Medina lies -unconformably on the Hudson River shales. It seems likely, for reasons -that will be briefly given later on, that the same disturbance extended -into Pennsylvania and farther southwest, but that it affected only the -southeastern corner of the State; and that the unconformities in -evidence of it, which are preserved in the Hudson Valley, are here lost -by subsequent erosion. Waste of the ancient land and its -Cambro-Silurian annex still continued and furnished vast beds of -sandstone and sandy shales to the remaining marine area, until at last -the subsiding Paleozoic basin was filled up and the coal marshes -extended broadly across it. At this time we may picture the drainage of -the southeastern land area wandering rather slowly across the great -Carboniferous plains to the still submerged basin far to the west; a -condition of things that is not imperfectly represented, although in a -somewhat more advanced stage, by the existing drainage of the mountains -of the Carolinas across the more modern coastal plain to the Atlantic.</p> - -<p>This condition was interrupted by the great Permian deformation that -gave rise to the main ranges of the Appalachians in Pennsylvania, -Virginia and Tennessee. The Permian name seems appropriate here, for -while the deformation may have begun at an earlier date, and may have -continued into Triassic time, its culmination seems to have been within -Permian limits. It was characterized by a resistless force of -compression, exerted in a southeast-northwest line, in obedience to -which the whole series of Paleozoic beds, even twenty or more thousand -feet in thickness, was crowded gradually into great and small folds, -trending northeast and southwest. The subjacent Archean terrane -doubtless shared more or less in the disturbance: for example, South -Mountain is described by Lesley as "not one mountain, but a system of -mountains separated by valleys. It is, geologically considered, a -system of anticlinals with troughs between.... It appears that the -South Mountain range ends eastward [in Cumberland and York Counties] in -a hand with five [anticlinal] fingers."<small><small><sup>10</sup></small></small></p> - -<blockquote><small><small><sup>10</sup></small> Proc. Amer. Phil. Soc., xiii, 1873, 6.</small></blockquote> - -<p>It may be concluded with fair probability that the folds began to rise -in the southeast, where they are crowded closest together, some of them -having begun here while coal marshes were still forming farther west; -and that the last folds to be begun were the fainter ones on the -plateau, now seen in Negro mountain and Chestnut and Laurel ridges. In -consequence of the inequalities in the force of compression or in the -resistance of the yielding mass, the folds do not continue indefinitely -with horizontal axes, but vary in height, rising or falling away in -great variety. Several adjacent folds often follow some general control -in this respect, their axes rising and falling together. It is to an -unequal yielding of this kind that we owe the location of the -Anthracite synclinal basins in eastern Pennsylvania, the Coal Measures -being now worn away from the prolongation of the synclines, which rise -in either direction.</p> -<a name="sect8"></a> -<p>8. <i>Perm-Triassic denudation</i>.—During and for a long time after this -period of mountain growth, the destructive processes of erosion wasted -the land and lowered its surface. An enormous amount of material was -thus swept away and laid down in some unknown ocean bed. We shall speak -of this as the Perm-Triassic period of erosion. A measure of its vast -accomplishment is seen when we find that the Newark formation, which is -generally correlated with Triassic or Jurassic time, lies unconformably -on the eroded surface of Cambrian and Archean rocks in the southeastern -part of the State, where we have concluded that the Paleozoic series -once existed; where the strata must have risen in a great mountain mass -as a result of the Appalachian deformations; and whence they must -therefore have been denuded before the deposition of the Newark beds. -Not only so; the moderate sinuosity of the southeastern or under -boundary of the Newark formation indicates clearly enough that the -surface on which that portion of the formation lies is one of no great -relief or inequality; and such a surface can be carved out of an -elevated land only after long continued denudation, by which -topographic development is carried beyond the time of its greatest -strength or maturity into the fainter expression of old age. This is a -matter of some importance in our study of the development of the rivers -of Pennsylvania; and it also constitutes a good part of the evidence -already referred to as indicating that there must have been some -earlier deformations of importance in the southeastern part of the -State; for it is hardly conceivable that the great Paleozoic mass could -have been so deeply worn off of the Newark belt between the making of -the last of the coal beds and the first of the Newark. It seems more in -accordance with the facts here recounted and with the teachings of -geological history in general to suppose, as we have here, that -something of the present deformation of the ancient rocks underlying -the Newark beds was given at an early date, such as that of the Green -Mountain growth; and that a certain amount of the erosion of the folded -beds was thus made possible in middle Paleozoic time; then again at -some later date, as Permian, a second period of mountain growth -arrived, and further folding was effected, and after this came deeper -erosion; thus dividing the destructive work that was done into several -parts, instead of crowding it all into the post-Carboniferous time -ordinarily assigned to it. It is indeed not impossible that an -important share of what we have called the Permian deformation was, as -above suggested, accomplished in the southeastern part of the State -while the coal beds were yet forming in the west; many grains of sand -in the sandstones of the Coal Measures may have had several temporary -halts in other sandstone beds between the time of their first erosion -from the Archean rocks and the much later time when they found the -resting place that they now occupy.<small><small><sup>11</sup></small></small></p> - -<blockquote><small><small><sup>11</sup></small> These considerations may have value in showing that the -time in which the lateral crushing of the Appalachians was accomplished -was not so brief as is stated by Reade in a recent article in the -American Geologist, iii, 1889, 106.</small></blockquote> -<a name="sect9"></a> -<p>9. <i>Newark deposition</i>.—After the great Paleozoic and Perm-Triassic -erosions thus indicated, when the southeastern area of ancient -mountains had been well worn down and the Permian folds of the central -district had acquired a well developed drainage, there appeared an -opportunity for local deposition in the slow depression of a -northeast-southwest belt of the deeply wasted land, across the -southeastern part of the State; and into this trough-like depression, -the waste from the adjacent areas on either side was carried, building -the Newark formation. This may be referred to as the Newark or -Trias-Jurassic period of deposition. The volume of this formation is -unknown, as its thickness and original area are still undetermined; but -it is pretty surely of many thousand feet in vertical measure, and its -original area may have been easily a fifth or a quarter in excess of -its present area, if not larger yet. So great a local accumulation -seems to indicate that while the belt of deposition was sinking, the -adjacent areas were rising, in order to furnish a continual supply of -material; the occurrence of heavy conglomerates along the margins of -the Newark formation confirms this supposition, and the heavy breccias -near Reading indicate the occurrence of a strong topography and a -strong transporting agent to the northwest of this part of the Newark -belt. It will be necessary, when the development of the ancestors of -our present rivers is taken up, to consider the effects of the -depression that determined the locus of Newark deposition and of the -adjacent elevation that maintained a supply of material.</p> -<a name="sect10"></a> -<p>10. <i>Jurassic tilting</i>.—Newark deposition was stopped by a gradual -reversal of the conditions that introduced it. The depression of the -Newark belt was after a time reversed into elevation, accompanied by a -peculiar tilting, and again the waste of the region was carried away to -some unknown resting place. This disturbance, which may be regarded as -a revival of the Permian activity, culminated in Jurassic, or at least -in post-Newark time, and resulted in the production of the singular -monoclinal attitude of the formation; and as far as I can correlate it -with the accompanying change in the underlying structures, it involved -there an over-pushing of the closed folds of the Archean and Paleozoic -rocks. This is illustrated in figs. 2 and 3, in which the original and -disturbed attitudes of the Newark and the underlying formations are -roughly shown, the over-pushing of the fundamental folds causing the -monoclinal and probably faulted structure in the overlying beds.<small><small><sup>12</sup></small></small> If -this be true, we might suspect that the unsymmetrical attitude of the -Appalachian folds, noted by Rogers as a characteristic of the range, is -a feature that was intensified if not originated in Jurassic and not in -Permian time.</p> - -<blockquote><small><small><sup>12</sup></small> Amer. Journ. Science, xxxii, 1886, 342; and Seventh Ann. -Rept. U. S. Geol. Survey, 1888, 486.</small></blockquote> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 2 and 3"> - <tr> - <td width="327"> - <img src="images/02.jpg" alt="Fig 2"> - </td> - <td width="314"> - <img src="images/03.jpg" alt="Fig 3"> - </td> - </tr> - <tr> - <td width="327" align="center"> - <small>F<small>IG</small>. 2.</small> - </td> - <td width="314" align="center"> - <small>F<small>IG</small>. 3.</small> - </td> - </tr> -</table> - -<p>It is not to be supposed that the Jurassic deformation was limited to -the area of the Newark beds; it may have extended some way on either -side; but it presumably faded out at no great distance, for it has not -been detected in the history of the Atlantic and Mississippi regions -remote from the Newark belt. In the district of the central folds of -Pennsylvania, with which we are particularly concerned, this -deformation was probably expressed in a further folding and -over-pushing of the already partly folded beds, with rapidly decreasing -effect to the northwest; and perhaps also by slip-faults, which at the -surface of the ground nearly followed the bedding planes: but this is -evidently hypothetical to a high degree. The essential point for our -subsequent consideration is that the Jurassic deformation was probably -accompanied by a moderate elevation, for it allowed the erosion of the -Newark beds and of laterally adjacent areas as well.</p> -<a name="sect11"></a> -<p>11. <i>Jura-Cretaceous denudation</i>.—In consequence of this elevation, a -new cycle of erosion was entered upon, which I shall call the -Jura-Cretaceous cycle. It allowed the accomplishment of a vast work, -which ended in the production of a general lowland of denudation, a -wide area of faint relief, whose elevated remnants are now to be seen -in the even ridge-crests that so strongly characterize the central -district, as well as in certain other even uplands, now etched by the -erosion of a later cycle of destructive work. I shall not here take -space for the deliberate statement of the argument leading to this end, -but its elements are as follows: the extraordinarily persistent -accordance among the crest-line altitudes of many Medina and -Carboniferous ridges in the central district; the generally -corresponding elevation of the western plateau surface, itself a -surface of erosion, but now trenched by relatively deep and narrow -valleys; the generally uniform and consistent altitude of the uplands -in the crystalline highlands of northern New Jersey and in the South -Mountains of Pennsylvania; and the extension of the same general -surface, descending slowly eastward, over the even crest-lines of the -Newark trap ridges. Besides the evidence of less continental elevation -thus deduced from the topography, it may be noted that a lower stand of -the land in Cretaceous time than now is indicated by the erosion that -the Cretaceous beds have suffered in consequence of the elevation that -followed their deposition. The Cretaceous transgression in the western -states doubtless bears on the problem also. Finally it may be fairly -urged that it is more accordant with what is known about old mountains -in general to suppose that their mass has stood at different attitudes -with respect to base level during their long period of denudation than -to suppose that they have held one attitude through all the time since -their deformation.</p> - -<p>It is natural enough that the former maintenance of some lower altitude -than the present should have expression in the form of the country, if -not now extinguished by subsequent erosion. It is simply the reverse of -this statement that leads us to the above-stated conclusion. We may be -sure that the long maintained period of relative quiet was of great -importance in allowing time for the mature adjustment of the rivers of -the region, and hence due account must be taken of it in a later -section. I say relative quiet, for there were certainly subordinate -oscillations of greater or less value; McGee has detected records of -one of these about the beginning of Cretaceous time, but its effects -are not now known to be of geographic value; that is, they do not now -manifest themselves in the form of the present surface of the land, but -only in the manner of deposition and ancient erosion of certain -deposits.<small><small><sup>13</sup></small></small> Another subordinate oscillation in the sense of a -moderate depression seems to have extended through middle and later -Cretaceous time, resulting in an inland transgression of the sea and -the deposit of the Cretaceous formation unconformably on the previous -land surface for a considerable distance beyond the present margin of -the formation.<small><small><sup>14</sup></small></small> This is important as affecting our rivers. Although -these oscillations were of considerable geological value, I do not -think that for the present purposes they call for any primary division -of the Jura-Cretaceous cycle; for as the result of this long period of -denudation we find but a single record in the great lowland of erosion -above described, a record of prime importance in the geographic -development of our region, that will often be referred to. The surface -of faint relief then completed may be called the Cretaceous baselevel -lowland. It may be pictured as a low, undulating plain of wide extent, -with a portion of its Atlantic margin submerged and covered over with a -relatively thin marine deposit of sands, marls and clays.</p> - -<blockquote><small><small><sup>13</sup></small> Amer. Jour. Science, xxxv, 1888, 367, 448.</small></blockquote> - -<blockquote><small><small><sup>14</sup></small> This statement is based on a study of the geographic -evolution of northern New Jersey, in preparation for publication.</small></blockquote> -<a name="sect12"></a> -<p>12. <i>Tertiary elevation and denudation</i>.—This broad lowland is a -lowland no longer. It has been raised over the greater part of its area -into a highland, with an elevation of from one to three thousand feet, -sloping gently eastward and descending under the Atlantic level near -the present margin of the Cretaceous formation. The elevation seems to -have taken place early in Tertiary time, and will be referred to as of -that date. Opportunity was then given for the revival of the previously -exhausted forces of denudation, and as a consequence we now see the -formerly even surface of the plain greatly roughened by the incision of -deep valleys and the opening of broad lowlands on its softer rocks. -Only the harder rocks retain indications of the even surface which once -stretched continuously across the whole area. The best indication of -the average altitude at which the mass stood through the greater part -of post-Cretaceous time is to be found on the weak shales of the Newark -formation in New Jersey and Pennsylvania, and on the weak Cambrian -limestones of the great Kittatinny valley; for both of these areas have -been actually almost baselevelled again in the Tertiary cycle. They -will be referred to as the Tertiary baselevel lowlands; and the valleys -corresponding to them, cut in the harder rocks, as well as the rolling -lowlands between the ridges of the central district of Pennsylvania -will be regarded as of the same date. Whatever variations of level -occurred in this cycle of development do not seem to have left marks of -importance on the inland surface, though they may have had greater -significance near the coast.</p> -<a name="sect13"></a> -<p>13. <i>Later changes of level</i>.—Again at the close of Tertiary time, -there was an elevation of moderate amount, and to this may be referred -the trenches that are so distinctly cut across the Tertiary baselevel -lowland by the larger rivers, as well as the lateral shallower channels -of the smaller streams. This will be called the Quaternary cycle; and -for the present no further mention of the oscillations known to have -occurred in this division of time need be considered; the reader may -find careful discussion of them in the paper by McGee, above referred -to. It is proper that I should add that the suggestion of baselevelling -both of the crest-lines and of the lowlands, that I have found so -profitable in this and other work, is due largely to personal -conference with Messrs. Gilbert and McGee of the Geological Survey; but -it is not desired to make them in any way responsible for the -statements here given.</p> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 4"> - <tr> - <td width="638"> - <img src="images/04.jpg" alt="Fig 4"> - </td> - </tr> - <tr> - <td width="638" align="center"> - <small>F<small>IG</small>. 4.</small> - </td> - </tr> -</table> -<br> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 5"> - <tr> - <td width="708"> - <img src="images/05.jpg" alt="Fig 5"> - </td> - </tr> - <tr> - <td width="708" align="center"> - <small>F<small>IG</small>. 5.</small> - </td> - </tr> -</table> -<a name="sect14"></a> -<p>14. <i>Illustrations of Pennsylvanian topography</i>.—A few sketches made -during a recent recess-trip with several students through Pennsylvania -may be introduced in this connection. The first, fig. 4, is a view from -Jenny Jump mountain, on the northwestern side of the New Jersey -highlands, looking northwest across the Kittatinny valley-lowland to -Blue or Kittatinny mountain, where it is cut at the Delaware Water-gap. -The extraordinarily level crest of the mountain preserves record of the -Cretaceous baselevel lowland; since the elevation of this ancient -lowland, its softer rocks have, as it were, been etched out, leaving -the harder ones in relief; thus the present valley-lowland is to be -explained. In consequence of the still later elevation of less amount, -the Delaware has cut a trench in the present lowland, which is partly -seen to the left in the sketch. Fig. 5 is a general view of the Lehigh -plateau and cañon, looking south from Bald Mountain just above Penn -Haven Junction. Blue mountain is the most distant crest, seen for a -little space. The ridges near and above Mauch Chunk form the other -outlines; all rising to an astonishingly even altitude, in spite of -their great diversity of structure. Before the existing valleys were -excavated, the upland surface must have been an even plain—the -Cretaceous baselevel lowland elevated into a plateau. The valleys cut -into the plateau during the Tertiary cycle are narrow here, because the -rocks are mostly hard. The steep slopes of the cañon-like valley of the -Lehigh and the even crests of the ridges manifestly belong to different -cycles of development. Figs. 6 and 7 are gaps cut in Black Log and -Shade mountain, by a small upper branch stream of the Juniata in -southeastern Huntingdon county. The stream traverses a breached -anticlinal of Medina sandstone, of which these mountains are the -lateral members. A long narrow valley is opened on the axial Trenton -limestone between the two. The gaps are not opposite to each other, and -therefore in looking through either gap from the outer country the even -crest of the further ridge is seen beyond the axial valley. The gap in -Black Log mountain, fig. 6, is located on a small fracture, but in this -respect it is unlike most of its fellows.<small><small><sup>15</sup></small></small> The striking similarity -of the two views illustrates the uniformity that so strongly -characterizes the Medina ridges of the central district. Fig. 8 is in -good part an ideal view, based on sketches on the upper Susquehanna, -and designed to present a typical illustration of the more significant -features of the region. It shows the even crest-lines of a high Medina -or Pocono ridge in the background, retaining the form given to it in -the Cretaceous cycle; the even lowlands in the foreground, opened on -the weaker Siluro-Devonian rocks in the Tertiary cycle; and the uneven -ridges in the middle distance marking the Oriskany and Chemung beds of -intermediate hardness that have lost the Cretaceous level and yet have -not been reduced to the Tertiary lowland. The Susquehanna flows -distinctly below the lowland plain, and the small side streams run in -narrow trenches of late Tertiary and Quaternary date.</p> - -<blockquote><small><small><sup>15</sup></small> Second Geol. Surv. Pa., Report T<small><sub>3</sub></small>, 19.</small></blockquote> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 6"> - <tr> - <td width="703"> - <img src="images/06.jpg" alt="Fig 6"> - </td> - </tr> - <tr> - <td width="703" align="center"> - <small>F<small>IG</small>. 6.</small> - </td> - </tr> -</table> -<br> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 7"> - <tr> - <td width="701"> - <img src="images/07.jpg" alt="Fig 7"> - </td> - </tr> - <tr> - <td width="701" align="center"> - <small>F<small>IG</small>. 7.</small> - </td> - </tr> -</table> -<br> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 8"> - <tr> - <td width="640"> - <img src="images/08.jpg" alt="Fig 8"> - </td> - </tr> - <tr> - <td width="640" align="center"> - <small>F<small>IG</small>. 8.</small> - </td> - </tr> -</table> - -<p>If this interpretation is accepted, and the Permian mountains are seen -to have been once greatly reduced and at a later time worn out, while -the ridges of to-day are merely the relief left by the etching of -Tertiary valleys in a Cretaceous baselevelled lowland, then we may well -conclude with Powell that "mountains cannot remain long as mountains; -they are ephemeral topographic forms."<small><small><sup>16</sup></small></small></p> - -<blockquote><small><small><sup>16</sup></small> Geol. Uinta Mountains, 1876, 196.</small></blockquote> -<a name="part3"></a><a name="sect15"></a> -<br> -<center>P<small>ART THIRD</small>. <i>General conception of the history of a river</i>.</center> - -<p>15. <i>The complete cycle of river life: youth, adolescence, maturity and -old age</i>.—The general outline of an ideal river's history may be now -considered, preparatory to examining the special history of the rivers -of Pennsylvania, as controlled by the geological events just narrated.</p> - -<p>Rivers are so long lived and survive with more or less modification so -many changes in the attitude and even in the structure of the land, -that the best way of entering on their discussion seems to be to -examine the development of an ideal river of simple history, and from -the general features thus discovered, it may then be possible to -unravel the complex sequence of events that leads to the present -condition of actual rivers of complicated history.</p> - -<p>A river that is established on a new land may be called an original -river. It must at first be of the kind known as a consequent river, for -it has no ancestor from which to be derived. Examples of simple -original rivers may be seen in young plains, of which southern New -Jersey furnishes a fair illustration. Examples of essentially original -rivers may be seen also in regions of recent and rapid displacement, -such as the Jura or the broken country of southern Idaho, where the -directly consequent character of the drainage leads us to conclude -that, if any rivers occupied these regions before their recent -deformation, they were so completely extinguished by the newly made -slopes that we see nothing of them now.</p> - -<p>Once established, an original river advances through its long life, -manifesting certain peculiarities of youth, maturity and old age, by -which its successive stages of growth may be recognized without much -difficulty. For the sake of simplicity, let us suppose the land mass, -on which an original river has begun its work, stands perfectly still -after its first elevation or deformation, and so remains until the -river has completed its task of carrying away all the mass of rocks -that rise above its baselevel. This lapse of time will be called a -cycle in the life of a river. A complete cycle is a long measure of -time in regions of great elevation or of hard rocks; but whether or not -any river ever passed through a single cycle of life without -interruption we need not now inquire. Our purpose is only to learn what -changes it would experience if it did thus develop steadily from -infancy to old age without disturbance.</p> - -<p>In its infancy, the river drains its basin imperfectly; for it is then -embarrassed by the original inequalities of the surface, and lakes -collect in all the depressions. At such time, the ratio of evaporation -to rainfall is relatively large, and the ratio of transported land -waste to rainfall is small. The channels followed by the streams that -compose the river as a whole are narrow and shallow, and their number -is small compared to that which will be developed at a later stage. The -divides by which the side-streams are separated are poorly marked, and -in level countries are surfaces of considerable area and not lines at -all. It is only in the later maturity of a system that the divides are -reduced to lines by the consumption of the softer rocks on either side. -The difference between constructional forms and those forms that are -due to the action of denuding forces is in a general way so easily -recognized, that immaturity and maturity of a drainage area can be -readily discriminated. In the truly infantile drainage system of the -Red River of the North, the inter-stream areas are so absolutely flat -that water collects on them in wet weather, not having either original -structural slope or subsequently developed denuded slope to lead it to -the streams. On the almost equally young lava blocks of southern -Oregon, the well-marked slopes are as yet hardly channeled by the flow -of rain down them, and the depressions among the tilted blocks are -still undrained, unfilled basins.</p> - -<p>As the river becomes adolescent, its channels are deepened and all the -larger ones descend close to baselevel. If local contrasts of hardness -allow a quick deepening of the down-stream part of the channel, while -the part next up-stream resists erosion, a cascade or waterfall -results; but like the lakes of earlier youth, it is evanescent, and -endures but a small part of the whole cycle of growth; but the falls on -the small headwater streams of a large river may last into its -maturity, just as there are young twigs on the branches of a large -tree. With the deepening of the channels, there comes an increase in -the number of gulleys on the slopes of the channel; the gulleys grow -into ravines and these into side valleys, joining their master streams -at right angles (La Noë and Margerie). With their continued -development, the maturity of the system is reached; it is marked by an -almost complete acquisition of every part of the original -constructional surface by erosion under the guidance of the streams, so -that every drop of rain that falls finds a way prepared to lead it to a -stream and then to the ocean, its goal. The lakes of initial -imperfection have long since disappeared; the waterfalls of adolescence -have been worn back, unless on the still young headwaters. With the -increase of the number of side-streams, ramifying into all parts of the -drainage basin, there is a proportionate increase in the surface of the -valley slopes, and with this comes an increase in the rate of waste -under atmospheric forces; hence it is at maturity that the river -receives and carries the greatest load; indeed, the increase may be -carried so far that the lower trunk-stream, of gentle slope in its -early maturity, is unable to carry the load brought to it by the upper -branches, and therefore resorts to the temporary expedient of laying it -aside in a flood-plain. The level of the flood-plain is sometimes built -up faster than the small side-streams of the lower course can fill -their valleys, and hence they are converted for a little distance above -their mouths into shallow lakes. The growth of the flood-plain also -results in carrying the point of junction of tributaries farther and -farther down stream, and at last in turning lateral streams aside from -the main stream, sometimes forcing them to follow independent courses -to the sea (Lombardini). But although thus separated from the main -trunk, it would be no more rational to regard such streams as -independent rivers than it would be to regard the branch of an old -tree, now fallen to the ground in the decay of advancing age, as an -independent plant; both are detached portions of a single individual, -from which they have been separated in the normal processes of growth -and decay.</p> - -<p>In the later and quieter old age of a river system, the waste of the -land is yielded slower by reason of the diminishing slopes of the -valley sides; then the headwater streams deliver less detritus to the -main channel, which, thus relieved, turns to its postponed task of -carrying its former excess of load to the sea, and cuts terraces in its -flood-plain, preparatory to sweeping it away. It does not always find -the buried channel again, and perhaps settling down on a low spur a -little to one side of its old line, produces a rapid or a low fall on -the lower slope of such an obstruction (Penck). Such courses may be -called locally superimposed.</p> - -<p>It is only during maturity and for a time before and afterwards that -the three divisions of a river, commonly recognized, appear most -distinctly; the torrent portion being the still young headwater -branches, growing by gnawing backwards at their sources; the valley -portion proper, where longer time of work has enabled the valley to -obtain a greater depth and width; and the lower flood-plain portion, -where the temporary deposition of the excess of load is made until the -activity of middle life is past.</p> - -<p>Maturity seems to be a proper term to apply to this long enduring -stage; for as in organic forms, where the term first came into use, it -here also signifies the highest development of all functions between a -youth of endeavor towards better work and an old age of relinquishment -of fullest powers. It is the mature river in which the rainfall is best -lead away to the sea, and which carries with it the greatest load of -land waste; it is at maturity that the regular descent and steady flow -of the river is best developed, being the least delayed in lakes and -least overhurried in impetuous falls.</p> - -<p>Maturity past, and the power of the river is on the decay. The relief -of the land diminishes, for the streams no longer deepen their valleys -although the hill tops are degraded; and with the general loss of -elevation, there is a failure of rainfall to a certain extent; for it -is well known that up to certain considerable altitudes rainfall -increases with height. A hyetographic and a hypsometric map of a -country for this reason show a marked correspondence. The slopes of the -headwaters decrease and the valley sides widen so far that the land -waste descends from them slower than before. Later, what with failure -of rainfall and decrease of slope, there is perhaps a return to the -early imperfection of drainage, and the number of side streams -diminishes as branches fall from a dying tree. The flood-plains of -maturity are carried down to the sea, and at last the river settles -down to an old age of well-earned rest with gentle flow and light load, -little work remaining to be done. The great task that the river entered -upon is completed.</p> -<a name="sect16"></a> -<p>16. <i>Mutual adjustment of river courses</i>.—In certain structures, -chiefly those of mountainous disorder on which the streams are at first -high above baselevel, there is a process of adjustment extremely -characteristic of quiet river development, by which the down-hill -courses that were chosen in early life, and as we may say unadvisedly -and with the heedlessness and little foresight of youth, are given up -for others better fitted for the work of the mature river system. A -change of this kind happens when the young stream taking the lowest -line for its guide happens to flow on a hard bed at a considerable -height above baselevel, while its branches on one side or the other -have opened channels on softer beds: a part of the main channel may -then be deserted by the withdrawal of its upper waters to a lower -course by way of a side stream. The change to better adjustment also -happens when the initial course of the main stream is much longer than -a course that may be offered to its upper portion by the backward -gnawing of an adjacent stream (Löwl, Penck). Sometimes the lateral -cutting or planation that characterizes the main trunk of a mature -river gives it possession of an adjacent smaller stream whose bed is at -a higher level (Gilbert). A general account of these processes may be -found in Phillippson's serviceable "Studien über Wasserscheiden" -(Leipzig, 1886). This whole matter is of much importance and deserves -deliberate examination. It should be remembered that changes in river -courses of the kind now referred to are unconnected with any external -disturbance of the river basin, and are purely normal spontaneous acts -during advancing development. Two examples, pertinent to our special -study, will be considered.</p> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 9 and 10"> - <tr> - <td width="229"> - <img src="images/09.jpg" alt="Fig 9"> - </td> - <td width="212"> - <img src="images/10.jpg" alt="Fig 10"> - </td> - </tr> - <tr> - <td width="229" align="center"> - <small>F<small>IG</small>. 9.</small> - </td> - <td width="212" align="center"> - <small>F<small>IG</small>. 10.</small> - </td> - </tr> -</table> - -<p>Let AB, fig. 9, be a stream whose initial consequent course led it down -the gently sloping axial trough of a syncline. The constructional -surface of the syncline is shown by contours. Let the succession of -beds to be discovered by erosion be indicated in a section, laid in -proper position on the several diagrams, but revolved into the -horizontal plane, the harder beds being dotted and the baselevel -standing at OO. Small side streams will soon be developed on the slopes -of the syncline, in positions determined by cross-fractures or more -often by what we call accident; the action of streams in similar -synclines on the outside of the enclosing anticlines will be omitted -for the sake of simplicity. In time, the side streams will cut through -the harder upper bed M and enter the softer bed N, on which -longitudinal channels, indicated by hachures, will be extended along -the strike, fig. 10 (La Noë and Margerie). Let these be called -"subsequent" streams. Consider two side streams of this kind, C and D, -heading against each other at E, one joining the main stream lower down -the axis of the syncline than the other. The headwaters of C will rob -the headwaters of D, because the deepening of the channel of D is -retarded by its having to join the main stream at a point where the -hard bed in the axis of the fold holds the main channel well above -baselevel. The notch cut by D will then be changed from a water-gap to -a wind-gap and the upper portion of D will find exit through the notch -cut by C, as in fig. 11. As other subsequent headwaters make capture of -C, the greater depth to which the lateral valley is cut on the soft -rock causes a slow migration of the divides in the abandoned gaps -towards the main stream, and before long the upper part of the main -stream itself will be led out of the synclinal axis to follow the -monoclinal valley at one side for a distance, fig. 12, until the axis -can be rejoined through the gap where the axial portion of the -controlling hard bed is near or at baselevel. The upper part of the -synclinal trough will then be attacked by undercutting on the slope of -the quickly deepened channels of the lateral streams, and the hard bed -will be worn away in the higher part of the axis before it is consumed -in the lower part. The location of the successful lateral stream on one -or the other side of the syncline may be determined by the dip of the -beds, gaps being cut quicker on steep than on gentle dips. If another -hard bed is encountered below the soft one, the process will be -repeated; and the mature arrangement of the streams will be as in fig. -13 (on a smaller scale than the preceding), running obliquely off the -axis of the fold where a hard bed of the syncline rises above -baselevel, and returning to the axis where the hard bed is below or at -baselevel; a monoclinal stream wandering gradually from the axis along -the strike of the soft bed, AE, by which the side-valley is located and -returning abruptly to the axis by a cataclinal<small><small><sup>17</sup></small></small> stream in a -transverse gap, EB, in the next higher hard bed, and there rejoining -the diminished representative or survivor of the original axial or -synclinal stream, GB.</p> - -<blockquote><small><small><sup>17</sup></small> See the terminology suggested by Powell. Expl. Col. R. of -the West, 1875, 160. This terminology is applicable only to the most -detailed study of our rivers, by reason of their crossing so many -folds, and changing so often from longitudinal to transverse courses.</small></blockquote> -<a name="figure13"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 11, 12 and 13"> - <tr> - <td width="219"> - <img src="images/11.jpg" alt="Fig 11"> - </td> - <td width="223"> - <img src="images/12.jpg" alt="Fig 12"> - </td> - <td width="175"> - <img src="images/13.jpg" alt="Fig 13"> - </td> - </tr> - <tr> - <td width="219" align="center"> - <small>F<small>IG</small>. 11.</small> - </td> - <td width="223" align="center"> - <small>F<small>IG</small>. 12.</small> - </td> - <td width="175" align="center"> - <small>F<small>IG</small>. 13.</small> - </td> - </tr> -</table> -<a name="sect17"></a> -<p>17. <i>Terminology of rivers changed by adjustment</i>.—A special -terminology is needed for easy reference to the several parts of the -streams concerned in such an adjustment. Let AB and CD, fig. 14, be -streams of unequal size cutting gaps, H and G, in a ridge that lies -transverse to their course. CD being larger than AB will deepen its gap -faster. Of two subsequent streams, JE and JF, growing on the up-stream -side of the ridge, JE will have the steeper slope, because it joins the -deeper master-stream. The divide, J, will therefore be driven towards -AB, and if all the conditions concerned conspire favorably, JE will at -last tap AB at F, and lead the upper part, AF, out by the line FEGD, -fig. 15, through the deeper gap, G. We may then say that JE becomes the -<i>divertor</i> of AF, which is <i>diverted;</i> and when the process is -completed, by the transfer of the divide from J, on the soft rocks, to -a stable location, H, on the hard rocks, there will be a short -<i>inverted</i> stream, HF; while HB is the remaining <i>beheaded</i> portion of -the original stream, AB, and the water-gap of AB becomes a wind-gap, H. -It is very desirable that geographic exploration should discover -examples of the process of adjustment in its several stages. The -preparatory stage is easily recognized by the difference in the size of -the two main streams, the difference in the depth of their gaps, and -the unsymmetrical position of the divide, J. The very brief stage of -transition gives us the rare examples of bifurcating streams. For a -short time after capture of the diverted stream by the divertor, the -new divide will lie between F and H, in an unstable position, the -duration of this time depending on the energy of the process of capture.</p> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 14 and 15"> - <tr> - <td width="245"> - <img src="images/14.jpg" alt="Fig 14"> - </td> - <td width="214"> - <img src="images/15.jpg" alt="Fig 15"> - </td> - </tr> - <tr> - <td width="245" align="center"> - <small>F<small>IG</small>. 14.</small> - </td> - <td width="214" align="center"> - <small>F<small>IG</small>. 15.</small> - </td> - </tr> -</table> - -<p>The consequences resulting from readjustments of this kind by which -their recent occurrence can be detected are: a relatively sudden -increase of volume of the divertor and hence a rapid deepening of the -course of the diverting stream, FE, and of the diverted, AF, near the -point of capture; small side-streams of these two being unable to keep -pace with this change will join their masters in local rapids, which -work up stream gradually and fade away (Löwl, Penck, McGee). The -expanded portion, ED, of the larger stream, CD, already of faint slope, -may be locally overcome for a time with the increase of detritus that -will be thus delivered to it at the entrance, E, of the divertor; while -the beheaded stream, HB, will find itself embarrassed to live up to the -habits of its large valley [Heim]. Geographic exploration with these -matters in mind offers opportunity for the most attractive discoveries.</p> -<a name="figure16"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 16, 17 and 18"> - <tr> - <td width="220"> - <img src="images/16.jpg" alt="Fig 16"> - </td> - <td width="214"> - <img src="images/17.jpg" alt="Fig 17"> - </td> - <td width="205"> - <img src="images/18.jpg" alt="Fig 18"> - </td> - </tr> - <tr> - <td width="220" align="center"> - <small>F<small>IG</small>. 16.</small> - </td> - <td width="214" align="center"> - <small>F<small>IG</small>. 17.</small> - </td> - <td width="205" align="center"> - <small>F<small>IG</small>. 18.</small> - </td> - </tr> -</table> -<a name="sect18"></a> -<p>18. <i>Examples of adjustment</i>.—Another case is roughly figured in the -next three diagrams, figs. 16, 17, 18. Two adjacent synclinal streams, -EA and HB, join a transverse master stream, C, but the synclines are of -different forms; the surface axis of one, EA, stands at some altitude -above baselevel until it nearly reaches the place of the transverse -stream; while the axis of the other, HB, descends near baselevel at a -considerable distance from the transverse stream. As lateral valleys, E -and D, are opened on the anticline between the synclines by a process -similar to that already described, the divide separating them will -shift towards the stream of fainter slope, that is, towards the -syncline, EA, whose axis holds its hard beds above baselevel; and in -time the upper part of the main stream will be withdrawn from this -syncline to follow an easier course by crossing to the other, as in -fig. 17. If the elevation of the synclinal axis, AES, take the shape of -a long flat arch, descending at the further end into a synclinal lake -basin, S, whose outlet is along the arching axis, SA, then the mature -arrangement of stream courses will lead the lake outlet away from the -axis by some gap in the nearer ascending part of the arch where the -controlling hard bed falls near to baselevel, as at F, fig. 18,<small><small><sup>18</sup></small></small> and -will take it by some subsequent course, FD, across the lowland that is -opened on the soft beds between the synclines, and carry it into the -lower syncline, HB, at D where the hard beds descend below baselevel.</p> - -<blockquote><small><small><sup>18</sup></small> This figure would be improved if a greater amount of -wasting around the margin of the hard bed were indicated in comparison -with the preceding figure.</small></blockquote> - -<p>The variety of adjustments following the general principle here -indicated is infinite. Changes of greater or less value are thus -introduced in the initial drainage areas, until, after attaining an -attitude of equilibrium, further change is arrested, or if occurring, -is relatively insignificant. It should be noticed that the new stream -courses thus chosen are not named by any of the terms now current to -express the relation of stream and land history; they are neither -consequent, antecedent nor superimposed. The stream is truly still an -original stream, although no longer young; but its channel is not in -all parts strictly consequent on the initial constructional form of the -land that it drains. Streams thus re-arranged may therefore be named -original streams of mature adjustment.</p> - -<p>It should be clearly recognized that the process of adjustment is a -very slow one, unless measured in the extremely long units of a river's -life. It progresses no faster than the weathering away of the slopes of -a divide, and here as a rule weathering is deliberate to say the least, -unless accelerated by a fortunate combination of favoring conditions. -Among these conditions, great altitude of the mass exposed to erosion -stands first, and deep channeling of streams below the surface—that -is, the adolescent stage of drainage development—stands second. The -opportunity for the lateral migration of a divide will depend on the -inequality of the slopes on its two sides, and here the most important -factors are length of the two opposite stream courses from the water -parting to the common baselevel of the two, and inequality of structure -by which one stream may have an easy course and the other a hard one. -It is manifest that all these conditions for active shifting of divides -are best united in young and high mountain ranges, and hence it is that -river adjustments have been found and studied more in the Alps than elsewhere.</p> -<a name="sect19"></a> -<p>19. <i>Revival of rivers by elevation and drowning by depression</i>.—I -make no contention that any river in the world ever passed through a -simple uninterrupted cycle of the orderly kind here described. But by -examining many rivers, some young and some old, I do not doubt that -this portrayal of the ideal would be found to be fairly correct if -opportunity were offered for its development. The intention of the -sketch is simply to prepare the way for the better understanding of our -actual rivers of more complicated history.</p> - -<p>At the close or at any time during the passage of an initial cycle such -as the one just considered, the drainage area of a river system may be -bodily elevated. The river is then turned back to a new youth and -enters a new cycle of development. This is an extremely common -occurrence with rivers, whose life is so long that they commonly -outlive the duration of a quiescent stage in the history of the land. -Such rivers may be called revived. Examples may be given in which -streams are now in their second or third period of revival, the -elevations that separate their cycles following so soon that but little -work was accomplished in the quiescent intervals.</p> - -<p>The antithesis of this is the effect of depression, by which the lower -course may be drowned, flooded or fjorded. This change is, if slow, -favorable to the development of flood-plains in the lower course; but -it is not essential to their production. If the change is more rapid, -open estuaries are formed, to be transformed to delta-lowlands later on.</p> -<a name="sect20"></a> -<p>20. <i>Opportunity for new adjustments with revival</i>.—One of the most -common effects of the revival of a river by general elevation is a new -adjustment of its course to a greater or less extent, as a result of -the new relation of baselevel to the hard and soft beds on which the -streams had adjusted themselves in the previous cycle. Synclinal -mountains are most easily explained as results of drainage changes of -this kind [Science, Dec. 21st, 1888]. Streams thus rearranged may be -said to be adjusted through elevation or revival. It is to be hoped -that, as our study advances, single names of brief and appropriate form -may replace these paraphrases; but at present it seems advisable to -keep the desired idea before the mind by a descriptive phrase, even at -the sacrifice of brevity. A significant example may be described.</p> -<a name="figure19"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 19 and 20"> - <tr> - <td width="294"> - <img src="images/19.jpg" alt="Fig 19"> - </td> - <td width="289"> - <img src="images/20.jpg" alt="Fig 20"> - </td> - </tr> - <tr> - <td width="294" align="center"> - <small>F<small>IG</small>. 19.</small> - </td> - <td width="289" align="center"> - <small>F<small>IG</small>. 20.</small> - </td> - </tr> -</table> - -<p>Let it be supposed that an originally consequent river system has lived -into advanced maturity on a surface whose structure is, like that of -Pennsylvania, composed of closely adjacent anticlinal and synclinal -folds with rising and falling axes, and that a series of particularly -resistant beds composes the upper members of the folded mass. The -master stream, A, fig. 19, at maturity still resides where the original -folds were lowest, but the side streams have departed more less from -the axes of the synclinals that they first followed, in accordance with -the principles of adjustment presented above. The relief of the surface -is moderate, except around the synclinal troughs, where the rising -margins of the hard beds still appear as ridges of more or less -prominence. The minute hachures in figure 19 are drawn on the outcrop -side of these ridges. Now suppose a general elevation of the region, -lifting the synclinal troughs of the hard beds up to baselevel or even -somewhat above it. The deepening of the revived master-stream will be -greatly retarded by reason of its having to cross so many outcrops of -the hard beds, and thus excellent opportunity will be given for -readjustment by the growth of some diverting stream, B, whose beginning -on adjacent softer rocks was already made in the previous cycle. This -will capture the main river at some up-stream point, and draw it nearly -all away from its hard path across the synclinal troughs to an easier -path across the lowlands that had been opened on the underlying softer -beds, leaving only a small beheaded remnant in the lower course. The -final re-arrangement may be indicated in fig. 20. It should be noted -that every capture of branches of the initial main stream made by the -diverting stream adds to its ability for further encroachments, for -with increase of volume the channel is deepened and a flatter slope is -assumed, and the whole process of pushing away the divides is thereby -accelerated. In general it may be said that the larger the stream and -the less its elevation above baselevel, the less likely is it to be -diverted, for with large volume and small elevation it will early cut -down its channel so close to baselevel that no other stream can offer -it a better course to the sea; it may also be said that, as a rule, of -two equal streams, the headwaters of the one having a longer or a -harder course will be diverted by a branch of the stream on the shorter -or easier course. Every case must therefore be examined for itself -before the kind of re-arrangement that may be expected or that may have -already taken place can be discovered.</p> -<a name="sect21"></a> -<p>21. <i>Antecedent and superimposed rivers</i>.—It not infrequently -happens that the surface, on which a drainage system is more or -less fully developed, suffers deformation by tilting, folding or -faulting. Then, in accordance with the rate of disturbance, and -dependent on the size and slope of the streams and the resistance of -the rocks, the streams will be more or less re-arranged, some of the -larger ones persisting in their courses and cutting their channels down -almost as fast as the mass below them is raised and offered to their -action. It is manifest that streams of large volume and considerable -slope are the ones most likely to persevere in this way, while small -streams and large ones of moderate slope may be turned from their -former courses to new courses consequent on the new constructional form -of the land. Hence, after a disturbance, we may expect to find the -smaller streams of the former cycle pretty completely destroyed, while -some of the larger ones may still persist; these would then be called -antecedent streams in accordance with the nomenclature introduced by -Powell.<small><small><sup>19</sup></small></small> A fuller acquaintance with the development of our rivers -will probably give us examples of river systems of all degrees of -extinction or persistence at times of disturbance.</p> - -<blockquote><small><small><sup>19</sup></small> Exploration of the Colorada River of the West, 1875, 153, -163-166.</small></blockquote> - -<p>Since Powell introduced the idea of antecedent valleys and Tietze, -Medlicott and others showed the validity of the explanation in other -regions than the one for which it was first proposed, it has found much -acceptance. Löwl's objection to it does not seem to me to be nearly so -well founded as his suggestion of an additional method of river -development by means of backward headwater erosion and subsequent -capture of other streams, as already described. And yet I cannot help -thinking that the explanation of transverse valleys as antecedent -courses savors of the Gordian method of explaining a difficult matter. -The case of the Green river, to which Powell first gave this -explanation, seems well supported; the examples given by Medlicott in -the Himalayas are as good: but still it does not seem advisable to -explain all transverse streams in this way, merely because they are -transverse. Perhaps one reason why the explanation has become so -popular is that it furnishes an escape from the old catastrophic idea -that fractures control the location of valleys, and is at the same time -fully accordant with the ideas of the uniformitarian school that have -become current in this half of our century. But when it is remembered -that most of the streams of a region are extinguished at the time of -mountain growth, that only a few of the larger ones can survive, and -that there are other ways in which transverse streams may -originate,<small><small><sup>20</sup></small></small> it is evident that the possibility of any given -transverse stream being antecedent must be regarded only as a -suggestion, until some independent evidence is introduced in its favor. -This may be difficult to find, but it certainly must be searched for; -if not then forthcoming, the best conclusion may be to leave the case -open until the evidence appears. Certainly, if we find a river course -that is accordant in its location with the complicated results of other -methods of origin, then the burden of proof may be said to lie with -those who would maintain that an antecedent origin would locate the -river in so specialized a manner. Even if a river persist for a time in -an antecedent course, this may not prevent its being afterwards -affected by the various adjustments and revivals that have been -explained above: rivers so distinctly antecedent as the Green and the -Sutlej may hereafter be more or less affected by processes of -adjustment, which they are not yet old enough to experience. Hence in -mountains as old as the Appalachians the courses of the present rivers -need not coincide with the location of the pre-Permian rivers, even if -the latter persisted in their courses through the growth of the Permian -folding; subsequent elevations and adjustments to hard beds, at first -buried and unseen, may have greatly displaced them, in accordance with -Löwl's principle.</p> - -<blockquote><small><small><sup>20</sup></small> Hilber, Pet. -Mitth., xxxv, 1889, 13.</small></blockquote> - -<p>When the deeper channelling of a stream discovers an unconformable -subjacent terrane, the streams persist at least for a time in the -courses that were determined in the overlying mass; they are then -called superimposed (Powell), inherited (Shaler), or epigenetic -(Richthofen). Such streams are particularly liable to readjustment by -transfer of channels from courses that lead them over hard beds to -others on which the hard beds are avoided; for the first choice of -channels, when the unconformable cover was still present, was made -without any knowledge of the buried rock structure or of the -difficulties in which the streams would be involved when they -encountered it. The examples of falls produced when streams terrace -their flood-plains and run on buried spurs has already been referred to -as superimposed; and the rivers of Minnesota now disclosing half-buried -ledges here and there may be instanced as illustrating the transition -stage between simple consequent courses, determined by the form of the -drift sheet on which their flow began, and the fully inconsequent -courses that will be developed there in the future.</p> -<a name="sect22"></a> -<p>22. <i>Simple, compound, composite and complex rivers</i>.—We have thus far -considered an ideal river. It now seems advisable to introduce a few -terms with which to indicate concisely certain well marked -peculiarities in the history of actual rivers.</p> - -<p>An original river has already been defined as one which first takes -possession of a land area, or which replaces a completely extinguished -river on a surface of rapid deformation.</p> - -<p>A river may be simple, if its drainage area is of practically one kind -of structure and of one age; like the rivers of southern New Jersey. -Such rivers are generally small. It may be composite, when drainage -areas of different structure are included in the basin of a single -stream. This is the usual case.</p> - -<p>A compound river is one which is of different ages in its different -parts; as certain rivers of North Carolina, which have old headwaters -rising in the mountains, and young lower courses traversing the coastal -plain.</p> - -<p>A river is complex when it has entered a second or later cycle of -development; the headwaters of a compound river are therefore complex, -while the lower course may be simple, in its first cycle. The degree of -complexity measures the number of cycles that the river has entered.</p> - -<p>When the study of rivers is thus attempted, its necessary complications -may at first seem so great as to render it of no value; but in answer -to this I believe that it may be fairly urged that, although -complicated, the results are true to nature, and if so, we can have no -ground of complaint against them. Moreover, while it is desirable to -reduce the study of the development of rivers to its simplest form, in -order to make it available for instruction and investigation, it must -be remembered that this cannot be done by neglecting to investigate the -whole truth in the hope of avoiding too great complexity, but that -simplicity can be reached safely only through fullness of knowledge, if -at all.</p> - -<p>It is with these points in mind that I have attempted to decipher the -history of the rivers of Pennsylvania. We find in the Susquehanna, -which drains a great area in the central part of the state, an example -of a river which is at once composite, compound and highly complex. It -drains districts of divers structure; it traverses districts of -different ages; and it is at present in its fourth or fifth degree of -complexity, its fourth or fifth cycle of development at least. In -unravelling its history and searching out the earlier courses of -streams which may have long since been abandoned in the processes of -mature adjustment, it will be seen that the size of the present streams -is not always a measure of their previous importance, and to this we -may ascribe the difficulty that attends the attempt to decipher a -river's history from general maps of its stream lines. Nothing but a -detailed examination of geological structure and history suffices to -detect facts and conditions that are essential to the understanding of -the result.</p> - -<p>If the postulates that I shall use seem unsound and the arguments seem -overdrawn, error may at least be avoided by not holding fast to the -conclusions that are presented, for they are presented only -tentatively. I do not feel by any means absolutely persuaded of the -correctness of the results, but at the same time deem them worth giving -out for discussion. The whole investigation was undertaken as an -experiment to see where it might lead, and with the hope that it might -lead at least to a serious study of our river problems.</p> -<a name="part4"></a><a name="sect23"></a> -<br> -<center>P<small>ART FOURTH</small>. <i>The development of the rivers of Pennsylvania</i>.</center> - -<p>23. <i>Means of distinguishing between antecedent and adjusted consequent -rivers</i>.—The outline of the geological history of Pennsylvania given -above affords means of dividing the long progress of the development of -our rivers into the several cycles which make up their complete life. -We must go far back into the past and imagine ancient streams flowing -down from the Archean land towards the paleozoic sea; gaining length by -addition to their lower portions as the land grew with the building on -of successive mountain ranges; for example, if there were a -Cambro-Silurian deformation, a continuation of the Green Mountains into -Pennsylvania, we suppose that the pre-existent streams must in some -manner have found their way westward to the new coastline; and from the -date of this mountain growth, it is apparent that any streams then born -must have advanced far in their history before the greater Appalachian -disturbance began. At the beginning of the latter, as of the former, -there must have been streams running from the land into the sea, and at -times of temporary elevation of the broad sand-flats of the coal -measures, such streams must have had considerable additions to their -lower length; rising in long-growing Archean highlands or mountains, -snow-capped and drained by glaciers for all we can say to the contrary, -descending across the Green Mountain belt, by that time worn to -moderate relief in the far advanced stage of its topographic -development, and finally flowing across the coal-measure lowlands of -recent appearance. It was across the lower courses of such rivers that -the Appalachian folds were formed, and the first step in our problem -consists in deciding if possible whether the streams held their courses -after the antecedent fashion, or whether they were thrown into new -courses by the growing folds, so that a new drainage system would be -formed. Possibly both conditions prevailed; the larger streams holding -their courses little disturbed, and the smaller ones disappearing, to -be replaced by others as the slopes of the growing surface should -demand. It is not easy to make choice in this matter. To decide that -the larger streams persisted and are still to be seen in the greater -rivers of to-day, only reversed in direction of flow, is certainly a -simple method of treating the problem, but unless some independent -reasons are found for this choice, it savors of assumption. Moreover, -it is difficult to believe that any streams, even if antecedent and -more or less persistent for a time during the mountain growth, could -preserve till now their pre-Appalachian courses through all the varying -conditions presented by the alternations of hard and soft rocks through -which they have had to cut, and at all the different altitudes above -baselevel in which they have stood. A better means of deciding the -question will be to admit provisionally the occurrence of a completely -original system of consequent drainage, located in perfect accord with -the slopes of the growing mountains; to study out the changes of -stream-courses that would result from later disturbances and from the -mutual adjustments of the several members of such a system in the -different cycles of its history; and finally to compare the courses -thus deduced with those now seen. If there be no accord, either the -method is wrong or the streams are not consequent but of some other -origin, such as antecedent; if the accord between deduction and fact be -well marked, varying only where no definite location can be given to -the deduced streams, but agreeing where they can be located more -precisely, then it seems to me that the best conclusion is distinctly -in favor of the correctness of the deductions. For it is not likely, -even if it be possible, that antecedent streams should have -accidentally taken, before the mountains were formed, just such -locations as would have resulted from the subsequent growth of the -mountains and from the complex changes in the initial river courses due -to later adjustments. I shall therefore follow the deductive method -thus indicated and attempt to trace out the history of a completely -original, consequent system of drainage accordant with the growth of -the central mountain district.</p> - -<p>In doing this, it is first necessary to restore the constructional -topography of the region; that is, the form that the surface would have -had if no erosion had accompanied its deformation. This involves -certain postulates which must be clearly conceived if any measure of -confidence is to be gained in the results based upon them.</p> -<a name="sect24"></a> -<p>24. <i>Postulates of the argument</i>.—In the first place, I assume an -essential constancy in the thickness of the paleozoic sediments over -the entire area in question. This is warranted here because the known -variations of thickness are relatively of a second order, and will not -affect the distribution of high and low ground as produced by the -intense Permian folding. The reasons for maintaining that the whole -series had a considerable extension southeast of the present margin of -the Medina sandstone have already been presented.</p> - -<p>In the second place, I shall assume that the dips and folds of the beds -now exposed at the surface of the ground may be projected upwards into -the air in order to restore the form of the eroded beds. This is -certainly inadmissible in detail, for it cannot be assumed that the -folded slates and limestones of the Nittany valley, for instance, give -any close indication of the form that the coal measures would have -taken, had they extended over this district, unworn. But in a general -way, the Nittany massif was a complex arch in the coal measures as well -as in the Cambrian beds; for our purpose and in view of the moderate -relief of the existing topography, it suffices to say that wherever the -lower rocks are now revealed in anticlinal structure, there was a great -upfolding and elevation of the original surface; and wherever the -higher rocks are still preserved, there was a relatively small elevation.</p> - -<p>In the third place, I assume that by reconstructing from the completed -folds the form which the country would have had if unworn, we gain a -sufficiently definite picture of the form through which it actually -passed at the time of initial and progressive folding. The difference -between the form of the folds completely restored and the form that the -surface actually reached is rather one of degree than of kind; the two -must correspond in the general distribution of high and low ground and -this is the chief consideration in our problem. When we remember how -accurately water finds its level, it will be clearer that what is -needed in the discussion is the location of the regions that were -relatively raised and lowered, as we shall then have marked out the -general course of the consequent water ways and the trend of the -intervening constructional ridges.</p> - -<p>Accepting these postulates, it may be said in brief that the outlines -of the formations as at present exposed are in effect so many contour -lines of the old constructional surface, on which the Permian rivers -took their consequent courses. Where the Trenton limestone is now seen, -the greatest amount of overlying strata must have been removed; hence -the outline of the Trenton formation is our highest contour line. Where -the Helderberg limestone appears, there has been a less amount of -material removed; hence the Helderberg outcrop is a contour of less -elevation. Where the coal beds still are preserved, there has been -least wasting, and these beds therefore mark the lowest contour of the -early surface. It is manifest that this method assumes that the present -outcrops are on a level surface; this is not true, for the ridges -through the State rise a thousand feet more or less over the -intervening valley lowlands, and yet the existing relief does not count -for much in discussing the enormous relief of the Permian surface that -must have been measured in tens of thousands of feet at the time of its -greatest strength.</p> -<a name="figure21"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 21"> - <tr> - <td width="709"> - <img src="images/21.jpg" alt="Fig 21"> - </td> - </tr> - <tr> - <td width="709" align="center"> - <small>F<small>IG</small>. 21. Constructional Permian topography of - Pennsylvania</small> - </td> - </tr> -</table> -<a name="sect25"></a> -<p>25. <i>Constructional Permian topography and consequent drainage</i>.—A -rough restoration of the early constructional topography is given in -fig. 21 for the central part of the State, the closest shading being -the area of the Trenton limestone, indicating the highest ground, or -better, the places of greatest elevation, while the Carboniferous area -is unshaded, indicating the early lowlands. The prevalence of northeast -and southwest trends was then even more pronounced than now. Several of -the stronger elements of form deserve names, for convenient reference. -Thus we have the great Kittatinny or Cumberland highland, C, C, on the -southeast, backed by the older mountains of Cambrian and Archean rocks, -falling by the Kittatinny slope to the synclinal lowland troughs of the -central district. In this lower ground lay the synclinal troughs of the -eastern coal regions, and the more local Broad Top basin, BT, on the -southwest, then better than now deserving the name of basins. Beyond -the corrugated area that connected the coal basins rose the great -Nittany highland, N, and its southwest extension in the Bedford range, -with the less conspicuous Kishicoquilas highland, K, in the foreground. -Beyond all stretched the great Alleghany lowland plains. The names thus -suggested are compounded of the local names of to-day and the -morphological names of Permian time.</p> - -<p>What would be the drainage of such a country? Deductively we are led to -believe that it consisted of numerous streams as marked in full lines -on the figure, following synclinal axes until some master streams led -them across the intervening anticlinal ridges at the lowest points of -their crests and away into the open country to the northwest. All the -enclosed basins would hold lakes, overflowing at the lowest part of the -rim. The general discharge of the whole system would be to the -northwest. Here again we must resort to special names for the easy -indication of these well-marked features of the ancient and now -apparently lost drainage system. The master stream of the region is the -great Anthracite river, carrying the overflow of the Anthracite lakes -off to the northwest and there perhaps turning along one of the faintly -marked synclines of the plateau and joining the original Ohio, which -was thus confirmed in its previous location across the Carboniferous -marshes. The synclinal streams that entered the Anthracite lakes from -the southwest may be named, beginning on the south, the Swatara, S, -fig. 21, the Wiconisco, Wo, the Tuscarora-Mahanoy, M, the -Juniata-Catawissa, C, and the Wyoming, Wy. One of these, probably the -fourth, led the overflow from the Broad Top lake into the Catawissa -lake on the middle Anthracite river. The Nittany highland formed a -strong divide between the central and northwestern rivers, and on its -outer slope there must have been streams descending to the Alleghany -lowlands; and some of these may be regarded as the lower courses of -Carboniferous rivers, that once rose in the Archean mountains, now -beheaded by the growth of mountain ranges across their middle.</p> -<a name="sect26"></a> -<p>26. <i>The Jura mountains homologous with the Permian -Alleghanies</i>.—However willing one may be to grant the former existence -of such a drainage system as the above, an example of a similar one -still in existence would be acceptable as a witness to the -possibilities of the past. Therefore we turn for a moment to the Jura -mountains, always compared to the Appalachians on account of the -regular series of folds by which the two are characterized. But while -the initial topography is long lost in our old mountains, it is still -clearly perceptible in the young Jura, where the anticlines are still -ridges and the longitudinal streams still follow the synclinal troughs; -while the transverse streams cross from one synclinal valley to another -at points where the intervening anticlinal arches are lowest.<small><small><sup>21</sup></small></small> We -could hardly ask for better illustration of the deductive drainage -system of our early Appalachians than is here presented.</p> - -<blockquote><small><small><sup>21</sup></small> This is beautifully illustrated in the recent monograph -by La Noë and Margerie on "Les Formes du Terrain."</small></blockquote> -<a name="sect27"></a> -<p>27. <i>Development and adjustment of the Permian drainage</i>.—The -problem is now before us. Can the normal sequence of changes in the -regular course of river development, aided by the post-Permian -deformations and elevations, evolve the existing rivers out of the -ancient ones?</p> - -<p>In order to note the degree of comparison that exists between the two, -several of the larger rivers of to-day are dotted on the figure. The -points of agreement are indeed few and small. Perhaps the most -important ones are that the Broad Top region is drained by a stream, -the Juniata, which for a short distance follows near the course -predicted for it; and that the Nittany district, then a highland, is -still a well-marked divide although now a lowland. But there is no -Anthracite river, and the region of the ancient coal-basin lakes is now -avoided by large streams; conversely, a great river—the -Susquehanna—appears where no consequent river ran in Permian time, and -the early synclinal streams frequently turn from the structural troughs -to valleys located on the structural arches.</p> -<a name="sect28"></a> -<p>28. <i>Lateral water-gaps near the apex of synclinal ridges</i>.—One of the -most frequent discrepancies between the hypothetical and actual streams -is that the latter never follow the axis of a descending syncline along -its whole length, as the original streams must have done, but depart -for a time from the axis and then return to it, notching the ridge -formed on any hard bed at the side instead of at the apex of its curve -across the axis of the syncline. There is not a single case in the -state of a stream cutting a gap at the apex of such a synclinal curve, -but there are perhaps hundreds of cases where the streams notch the -curve to one side of the apex. This, however, is precisely the -arrangement attained by spontaneous adjustment from an initial axial -course, as indicated in <a href="#figure13">figure 13</a>. The gaps may be located on small -transverse faults, but as a rule they seem to have no such guidance. It -is true that most of our streams now run out of and not into the -synclinal basins, but a reason for this will be found later; for the -present we look only at the location of the streams, not at their -direction of flow. As far as this illustration goes, it gives evidence -that the smaller streams at least possess certain peculiarities that -could not be derived from persistence in a previous accidental -location, but which would be necessarily derived from a process of -adjustment following the original establishment of strictly consequent -streams. Hence the hypothesis that these smaller streams were long ago -consequent on the Permian folding receives confirmation; but this says -nothing as to the origin of the larger rivers, which might at the same -time be antecedent.</p> -<a name="sect29"></a> -<p>29. <i>Departure of the Juniata from the Juniata-Catawissa syncline</i>.—It -may be next noted that the drainage of the Broad Top region does not -follow a single syncline to the Anthracite region, as it should have in -the initial stage of the consequent Permian drainage, but soon turns -aside from the syncline in which it starts and runs across country to -the Susquehanna. It is true that in its upper course the Juniata -departs from the Broad Top region by one of the two synclines that were -indicated as the probable line of discharge of the ancient Broad Top -lake in our restoration of the constructional topography of the State; -there does not appear to be any significant difference between the -summit altitudes of the Tuscarora-Mahanoy and the Juniata-Catawissa -synclinal axes and hence the choice must have been made for reasons -that cannot be detected; or it may be that the syncline lying more to -the northwest was raised last, and for this reason was taken as the -line of overflow. The beginning of the river is therefore not -discordant with the hypothesis of consequent drainage, but the -southward departure from the Catawissa syncline at Lewistown remains to -be explained. It seems to me that some reason for the departure may be -found by likening it to the case already given in <a href="#figure16">figs. 16-18</a>. The -several synclines with which the Juniata is concerned have precisely -the relative attitudes that are there discussed. The Juniata-Catawissa -syncline has parallel sides for many miles about its middle, and hence -must have long maintained the initial Juniata well above baselevel over -all this distance; the progress of cutting down a channel through all -the hard Carboniferous sandstones for so great a distance along the -axis must have been exceedingly slow. But the synclines next south, the -Tuscarora-Mahanoy and the Wiconisco, plunge to the northeast more -rapidly, as the rapid divergence of their margins demonstrates, and -must for this reason have carried the hard sandstones below baselevel -in a shorter distance and on a steeper slope than in the Catawissa -syncline. The further southwestward extension of the Pocono sandstone -ridges in the southern than in the northern syncline gives further -illustration of this peculiarity of form. Lateral capture of the -Juniata by a branch of the initial Tuscarora, and of the latter by a -branch of the Wiconisco therefore seems possible, and the accordance of -the facts with so highly specialized an arrangement is certainly again -indicative of the correctness of the hypothesis of consequent drainage, -and this time in a larger stream than before. At first sight, it -appears that an easier lateral capture might have been made by some of -the streams flowing from the outer slope of the Nittany highland; but -this becomes improbable when it is perceived that the heavy Medina -sandstone would here have to be worn through as well as the repeated -arches of the Carboniferous beds in the many high folds of the Seven -Mountains. Again, as far as present appearances go, we can give no -sufficient reason to explain why possession of the headwaters of the -Juniata was not gained by some subsequent stream of its own, such as G, -<a href="#figure16">fig. 18</a>, instead of by a side-stream of the river in the neighboring -syncline; but it may be admitted, on the other hand, that as far as we -can estimate the chances for conquest, there was nothing distinctly in -favor of one or the other of the side-streams concerned; and as long as -the problem is solved indifferently in favor of one or the other, we -may accept the lead of the facts and say that some control not now -apparent determined that the diversion should be, as drawn, through D -and not through G. The detailed location of the Juniata in its middle -course below Lewistown will be considered in a later section.</p> -<a name="figure22"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figures 22, 23 and 24"> - <tr> - <td width="198"> - <img src="images/22.jpg" alt="Fig 22"> - </td> - <td width="176"> - <img src="images/23.jpg" alt="Fig 23"> - </td> - <td width="192"> - <img src="images/24.jpg" alt="Fig 24"> - </td> - </tr> - <tr> - <td width="198" align="center"> - <small>F<small>IG</small>. 22.</small> - </td> - <td width="176" align="center"> - <small>F<small>IG</small>. 23.</small> - </td> - <td width="192" align="center"> - <small>F<small>IG</small>. 24.</small> - </td> - </tr> -</table> -<a name="sect30"></a> -<p>30. <i>Avoidance of the Broad Top basin by the Juniata -headwaters</i>.—Another highly characteristic change that the Juniata has -suffered is revealed by examining the adjustments that would have taken -place in the general topography of the Broad Top district during the -Perm-Triassic cycle of erosion. When the basin, BT, fig. 22, was first -outlined, centripetal streams descended its slopes from all sides and -their waters accumulated as a lake in the center, overflowing to the -east into the subordinate basin, A, in the Juniata syncline along side -of the larger basin, and thence escaping northeast. In due time, the -breaching of the slopes opened the softer Devonian rocks beneath and -peripheral lowlands were opened on them. The process by which the -Juniata departed from its original axial location, J, fig. 22, to a -parallel course on the southeastern side of the syncline, J, fig. 23, -has been described (<a href="#figure16">fig. 18</a>). The subsequent changes are manifest. Some -lateral branch of the Juniata, like N, fig. 23, would work its way -around the northern end of the Broad Top canoe on the soft underlying -rocks and capture the axial stream, C, that came from the depression -between Nittany and Kishicoquillas highlands; thus reënforced, capture -would be made of a radial stream from the west, Tn, the existing Tyrone -branch of the Juniata; in a later stage the other streams of the -western side of the basin would be acquired, their divertor -constituting the Little Juniata of to-day; and the end would be when -the original Juniata, A, fig. 22, that once issued from the subordinate -synclinal as a large stream, had lost all its western tributaries, and -was but a shrunken beheaded remnant of a river, now seen in Aughwick -creek, A, fig. 24. In the meantime, the former lake basin was fast -becoming a synclinal mountain of diminishing perimeter. The only really -mysterious courses of the present streams are where the Little Juniata -runs in and out of the western border of the Broad Top synclinal, and -where the Frankstown (FT) branch of the Juniata maintains its -independent gap across Tussey's mountain (Medina), although diverted to -the Tyrone or main Juniata (Tn) by Warrior's ridge (Oriskany) just -below. At the time of the early predatory growth of the initial -divertor, N, its course lay by the very conditions of its growth on -only the weakest rocks; but after this little stream had grown to a -good-sized river, further rising of the land, probably in the time of -the Jurassic elevation, allowed the river to sink its channel to a -greater depth, and in doing so, it encountered the hard Medina -anticline of Jack's mountain; here it has since persisted, because, as -we may suppose, there has been no stream able to divert the course of -so large a river from its crossing of a single hard anticlinal.</p> - -<p>The doubt that one must feel as to the possibility of the processes -just outlined arises, if I may gauge it by my own feeling, rather from -incredulity than from direct objections. It seems incredible that the -waste of the valley slopes should allow the backward growth of N at -such a rate as to enable it to capture the heads of C, Tn, F, and so -on, before they had cut their beds down close enough to the baselevel -of the time to be safe from capture. But it is difficult to urge -explicit objections against the process or to show its quantitative -insufficiency. It must be remembered that when these adjustments were -going on, the region was one of great altitude, its rocks then had the -same strong contrasts of strength and weakness that are so apparent in -the present relief of the surface and the streams concerned were of -moderate size; less than now, for at the time, the Tyrone, Frankstown -and Bedford head branches of the Juniata had not acquired drainage west -of the great Nittany-Bedford anticlinal axis, but were supplied only by -the rainfall on its eastern slope (see <a href="#sect39">section 39</a>)—and all these -conditions conspired to favor the adjustment. Finally, while apparently -extraordinary and difficult of demonstration, the explanation if -applicable at all certainly gives rational correlation to a number of -peculiar and special stream courses in the upper Juniata district that -are meaningless under any other theory that has come to my notice. It -is chiefly for this reason that I am inclined to accept the explanation.</p> -<a name="sect31"></a> -<p>31. <i>Reversal of larger rivers to southeast courses</i>.—Our large rivers -at present flow to the southeast, not to the northwest. It is difficult -to find any precise date for this reversal of flow from the initial -hypothetical direction, but it may be suggested that it occurred about -the time of the Triassic depression of the Newark belt. We have been -persuaded that much time elapsed between the Permian folding and the -Newark deposition, even under the most liberal allowance for -pre-Permian erosion in the Newark belt; hence when the depression -began, the rivers must have had but moderate northwestward declivity. -The depression and submergence of the broad Newark belt may at this -time have broken the continuity of the streams that once flowed across -it. The headwater streams from the ancient Archean country maintained -their courses to the depression; the lower portions of the rivers may -also have gone on as before; but the middle courses were perhaps turned -from the central part of the state back of the Newark belt. No change -of attitude gives so fitting a cause of the southeastward flow of our -rivers as this. The only test that I have been able to devise for the -suggestion is one that is derived from the relation that exists between -the location of the Newark belt along the Atlantic slope and the course -of the neighboring transverse rivers. In Pennsylvania, where the belt -reaches somewhat beyond the northwestern margin of the crystalline -rocks in South mountain, the streams are reversed, as above stated; but -in the Carolinas where the Newark belt lies far to the east of the -boundary between the Cambrian and crystalline rocks, the Tennessee -streams persevere in what we suppose to have been their original -direction of flow. This may be interpreted as meaning that in the -latter region, the Newark depression was not felt distinctly enough, if -at all, within the Alleghany belt to reverse the flow of the streams; -while in the former region, it was nearer to these streams and -determined a change in their courses. The original Anthracite river ran -to the northwest, but its middle course was afterwards turned to the southeast.</p> - -<p>I am free to allow that this has the appearance of heaping hypothesis -on hypothesis; but in no other way does the analysis of the history of -our streams seem possible, and the success of the experiment can be -judged only after making it. At the same time, I am constrained to -admit that this is to my own view the least satisfactory of the -suggestions here presented. It may be correct, but there seems to be no -sufficient exclusion of other possibilities. For example, it must not -be overlooked that, if the Anthracite river ran southeast during Newark -deposition, the formation of the Newark northwestward monocline by the -Jurassic tilting would have had a tendency to turn the river back again -to its northwest flow. But as the drainage of the region is still -southeastward, I am tempted to think that the Jurassic tilting was not -here strong enough to reverse the flow of so strong and mature a river -as the Anthracite had by that time come to be; and that the elevation -that accompanied the tilting was not so powerful in reversing the river -to a northwest course as the previous depression of the Newark basin -had been in turning it to the southeast. If the Anthracite did continue -to flow to the southeast, it may be added that the down-cutting of its -upper branches was greatly retarded by the decrease of slope in its -lower course when the monocline was formed.</p> - -<p>The only other method of reversing the original northwestward flow of -the streams that I have imagined is by capture of their headwaters by -Atlantic rivers. This seems to me less effective than the method just -considered; but they are not mutually exclusive and the actual result -may be the sum of the two processes. The outline of the idea is as -follows. The long continued supply of sedimentary material from the -Archean land on the southeast implies that it was as continually -elevated. But there came a time when there is no record of further -supply of material, and when we may therefore suppose the elevation was -no longer maintained. From that time onward, the Archean range must -have dwindled away, what with the encroachment of the Atlantic on its -eastern shore and the general action of denuding forces on its surface. -The Newark depression was an effective aid to the same end, as has been -stated above, and for a moderate distance westward of the depressed -belt, the former direction of the streams must certainly have been -reversed; but the question remains whether this reversal extended as -far as the Wyoming basin, and whether the subsequent formation of the -Newark monocline did not undo the effect of the Newark depression. It -is manifest that as far as our limited knowledge goes, it is impossible -to estimate these matters quantitatively, and hence the importance of -looking for additional processes that may supplement the effect of the -Newark depression and counteract the effect of the Newark uplift in -changing the course of the rivers. Let it be supposed for the moment -that at the end of the Jurassic uplift by which the Newark monocline -was formed, the divide between the Ohio and the Atlantic drainage lay -about the middle of the Newark belt. There was a long gentle descent -westward from this watershed and a shorter and hence steeper descent -eastward. Under such conditions, the divide must have been pushed -westward, and as long as the rocks were so exposed as to open areas of -weak sediments on which capture by the Atlantic streams could go on -with relative rapidity, the westward migration of the divide would be -important. For this reason, it might be carried from the Newark belt as -far as the present Alleghany front, beyond which further pushing would -be slow, on account of the broad stretch of country there covered by -hard horizontal beds.</p> - -<p>The end of this is that, under any of the circumstances here detailed, -there would be early in the Jurassic-Cretaceous cycle a distinct -tendency to a westward migration of the Atlantic-Ohio divide; it is the -consequences of this that have now to be examined.</p> -<a name="sect32"></a> -<p>32. <i>Capture of the Anthracite headwaters by the growing -Susquehanna</i>.—Throughout the Perm-Triassic period of denudation, a -great work was done in wearing down the original Alleghanies. -Anticlines of hard sandstone were breached, and broad lowlands were -opened on the softer rocks beneath. Little semblance of the early -constructional topography remained when the period of Newark depression -was brought to a close; and all the while the headwater streams of the -region were gnawing at the divides, seeking to develop the most perfect -arrangement of waterways. Several adjustments have taken place, and the -larger streams have been reversed in the direction of their flow; but a -more serious problem is found in the disappearance of the original -master stream, the great Anthracite river, which must have at first led -away the water from all the lateral synclinal streams. Being a large -river, it could not have been easily diverted from its course, unless -it was greatly retarded in cutting down its channel by the presence of -many beds of hard rocks on its way. The following considerations may -perhaps throw some light on this obscure point.</p> -<a name="figure25"></a> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 25"> - <tr> - <td width="701"> - <img src="images/25.jpg" alt="Fig 25"> - </td> - </tr> - <tr> - <td width="701" align="center"> - <small>F<small>IG</small>. 25. General distribution of high and low land and - drainage in early Jurassic time.</small> - </td> - </tr> -</table> - -<p>It may be assumed that the whole group of mountains formed by the -Permian deformation had been reduced to a moderate relief when the -Newark deposition was stopped by the Jurassic elevation. The harder -ribs of rock doubtless remained as ridges projecting above the -intervening lowlands, but the strength of relief that had been given by -the constructional forces had been lost. The general distribution of -residual elevations then remaining unsubdued is indicated in fig. 25, -in which the Crystalline, the Medina, and the two Carboniferous -sandstone ridges are denoted by appropriate symbols. In restoring this -phase of the surface form, when the country stood lower than now, I -have reduced the anticlines from their present outlines and increased -the synclines, the change of area being made greatest where the dips -are least, and hence most apparent at the ends of the plunging -anticlines and synclines. Some of the Medina anticlines of Perry and -Juniata counties are not indicated because they were not then -uncovered. The country between the residual ridges of Jurassic time was -chiefly Cambrian limestone and Siluro-Devonian shales and soft -sandstones. The moderate ridges developed on the Oriskany and Chemung -sandstones are not represented. The drainage of this stage retained the -original courses of the streams, except for the adjustments that have -been described, but the great Anthracite river is drawn as if it had -been controlled by the Newark depression and reversed in the direction -of its flow, so that its former upper course on the Cambrian rocks was -replaced by a superimposed Newark lower course. Fig. 25 therefore -represents the streams for the most part still following near their -synclinal axes, although departing from them where they have to enter a -synclinal cove-mountain ridge; the headwaters of the Juniata avoid the -mass of hard sandstones discovered in the bottom of old Broad Top lake, -and flow around them to the north, and then by a cross-country course -to the Wiconisco synclinal, as already described in detail. Several -streams come from the northeast, entering the Anthracite district after -the fashion generalized in <a href="#figure13">fig. 13</a>. Three of the many streams that were -developed on the great Kittatinny slope are located, with their -direction of flow reversed; these are marked Sq, L and D, and are -intended to represent the ancestors of the existing Susquehanna, Lehigh -and Delaware. We have now to examine the opportunities offered to these -small streams to increase their drainage areas.</p> - -<p>The Jurassic elevation, by which the Newark deposition was stopped, -restored to activity all the streams that had in the previous cycle -sought and found a course close to baselevel. They now all set to work -again deepening their channels. But in this restoration of lost -activity with reference to a new baselevel, there came the best -possible chance for numerous re-arrangements of drainage areas by -mutual adjustment into which we must inquire.</p> - -<p>I have already illustrated what seems to me to be the type of the -conditions involved at this time in <a href="#figure19">figs. 19 and 20</a>. The master stream, -A, traversing the synclines, corresponds to the reversed Anthracite -river; the lowlands at the top are those that have been opened out on -the Siluro-Devonian beds of the present Susquehanna middle course -between the Pocono and the Medina ridges. The small stream, B, that is -gaining drainage area in these lowlands, corresponds to the embryo of -the present Susquehanna, Sq, <a href="#figure25">fig. 25</a>, this having been itself once a -branch on the south side of the Swatara synclinal stream, <a href="#figure21">fig. 21</a>, from -which it was first turned by the change of slope accompanying the -Newark depression; but it is located a little farther west than the -actual Susquehanna, so as to avoid the two synclinal cove mountains of -Pocono sandstone that the Susquehanna now traverses, for reasons to be -stated below (<a href="#sect35">section 35</a>). This stream had to cross only one bed of -hard rock, the outer wall of Medina sandstone, between the broad inner -lowlands of the relatively weak Siluro-Devonian rocks and the great -valley lowlands on the still weaker Cambrian limestones. Step by step -it must have pushed its headwater divide northward, and from time to -time it would have thus captured a subsequent stream, that crossed the -lowlands eastward, and entered a Carboniferous syncline by one of the -lateral gaps already described. With every such capture, the power of -the growing stream to capture others was increased. <a href="#figure19">Fig. 19</a> represents -a stage after the streams in the Swatara and Wiconisco synclines (the -latter then having gained the Juniata) had been turned aside on their -way to the Carboniferous basins. On the other hand, the Anthracite -river, rising somewhere on the plains north of the Wyoming syncline and -pursuing an irregular course from one coal basin to another, found an -extremely difficult task in cutting down its channel across the -numerous hard beds of the Carboniferous sandstones, so often repeated -in the rolling folds of the coal fields. It is also important to -remember that an aid to other conditions concerned in the diversion of -the upper Anthracite is found in the decrease of slope that its lower -course suffered in crossing the coal fields, if that area took any part -in the deformation that produced the Newark monocline—whichever theory -prove true in regard to the origin of the southeastward flow of the -rivers—for loss of slope in the middle course, where the river had to -cross many reefs of hard sandstone, would have been very effective in -lengthening the time allowed for the diversion of the headwaters.</p> - -<p>The question is, therefore, whether the retardation of down-cutting -here experienced by the Anthracite was sufficient to allow the capture -of its headwaters by the Susquehanna. There can be little doubt as to -the correct quality of the process, but whether it was quantitatively -sufficient is another matter. In the absence of any means of testing -its sufficiency, may the result not be taken as the test? Is not the -correspondence between deduction and fact close enough to prove the -correctness of the deduction?</p> -<a name="sect33"></a> -<p>33. <i>Present outward drainage of the Anthracite basins</i>.—The Lehigh, -like the Susquehanna, made an attempt to capture the headwaters of -adjacent streams, but failed to acquire much territory from the -Anthracite because the Carboniferous sandstones spread out between the -two in a broad plateau of hard rocks, across which the divide made -little movement. The plateau area that its upper branches drain is, I -think, the conquest of a later cycle of growth. The Delaware had little -success, except as against certain eastern synclinal branches of the -Anthracite, for the same reason. The ancestor of the Swatara of to-day -made little progress in extending its headwaters because its point of -attack was against the repeated Carboniferous sandstones in the Swatara -synclinal. One early stream alone found a favorable opportunity for -conquest, and thus grew to be the master river—the Susquehanna of -to-day. The head of the Anthracite was carried away by this captor, and -its beheaded lower portion remains in our Schuylkill. The Anthracite -coal basins, formerly drained by the single master stream, have since -been apportioned to the surrounding rivers. As the Siluro-Devonian -lowlands were opened around the coal-basins, especially on the north -and west, the streams that formerly flowed into the basins were -gradually inverted and flowed out of them, as they still do. The extent -of the inversion seems to be in a general way proportionate to its -opportunity. The most considerable conquests were made in the upper -basins, where the Catawissa and Nescopec streams of to-day drain many -square miles of wide valleys opened on the Mauch Chunk red shale -between the Pocono and Pottsville sandstone ridges; the ancient middle -waters of the Anthracite here being inverted to the Susquehanna -tributaries, because the northern coal basins were degraded very slowly -after the upper Anthracite had been diverted. The Schuylkill as the -modern representative of the Anthracite retains only certain streams -south of a medial divide between Nescopec and Blue mountains. The only -considerable part of the old Anthracite river that still retains a -course along the axis of a synclinal trough seems to be that part which -follows the Wyoming basin; none of the many other coal basins are now -occupied by the large stream that originally followed them. The reason -for this is manifestly to be found in the great depth of the Wyoming -basin, whereby the axial portion of its hard sandstones are even now -below baselevel, and hence have never yet acted to throw the river from -its axial course. Indeed, during the early cycles of denudation, this -basin must have been changed from a deep lake to a lacustrine plain by -the accumulation in it of waste from the surrounding highlands, and for -a time the streams that entered it may have flowed in meandering -courses across the ancient alluvial surface; the lacustrine and -alluvial condition may have been temporarily revived at the time of the -Jurassic elevation. It is perhaps as an inheritance from a course thus -locally superimposed that we may come to regard the deflection of the -river at Nanticoke from the axis of the syncline to a narrow shale -valley on its northern side, before turning south again and leaving the -basin altogether. But like certain other suggestions, this can only be -regarded as an open hypothesis, to be tested by some better method of -river analysis than we now possess; like several of the other -explanations here offered, it is presented more as a possibility to be -discussed than as a conclusion to be accepted.</p> - -<p>I believe that it was during the earlier part of the great -Jura-Cretaceous cycle of denudation that the Susquehanna thus became -the master stream of the central district of the state. For the rest of -the cycle, it was occupied in carrying off the waste and reducing the -surface to a well finished baselevel lowland that characterized the end -of Cretaceous time. From an active youth of conquest, the Susquehanna -advanced into an old age of established boundaries; and in later times, -its area of drainage does not seem to have been greatly altered from -that so long ago defined; except perhaps in the districts drained by -the West and North Branch headwaters.</p> -<a name="sect34"></a> -<p>34. <i>Homologies of the Susquehanna and Juniata</i>.—Looking at the change -from the Anthracite to the Susquehanna in a broad way, one may perceive -that it is an effect of the same order as the peripheral diversion of -the Broad Top drainage, illustrated in <a href="#figure22">figures 22, 23 and 24</a>; another -example of a similar change is seen in the lateral diversion of the -Juniata above Lewistown and its rectilinear continuation in Aughwick -creek, from their original axial location when they formed the initial -Broad Top outlet. They have departed from the axis of their syncline to -the softer beds on its southern side; FE of <a href="#figure16">fig. 17</a> has been diverted -to FD of <a href="#figure16">fig. 18</a>.</p> - -<p>All of these examples are truly only special cases of the one already -described in which the Juniata left its original syncline for others to -the south. The general case may be stated in a few words. A stream -flowing along a syncline of hard beds (Carboniferous sandstones) -develops side streams which breach the adjacent anticlines and open -lowlands in the underlying softer beds (Devonian and Silurian). On -these lowlands, the headwaters of side streams from other synclines are -encountered and a contest ensues as to possession of the drainage -territory. The divides are pushed away from those headwaters whose -lower course leads them over the fewest hard barriers; this conquest -goes on until the upper course of the initial main stream is diverted -to a new and easier path than the one it chose in its youth in -obedience to the first deformation of the region. Thus the Juniata now -avoids the center and once deepest part of the old Broad Top lake, -because in the general progress of erosion, lowlands on soft Devonian -beds were opened all around the edge of the great mass of sandstones -that held the lake; the original drainage across the lake, from its -western slopes to its outlet just south of the Jack's mountain -anticline, has now taken an easier path along the Devonian beds to the -west of the old lake basin, and is seen in the Little Juniata, flowing -along the outer side of Terrace mountain and rounding the northern -synclinal point where Terrace mountain joins Sideling hill. It then -crosses Jack's mountain at a point where the hard Medina sandstones of -the mountain were still buried at the time of the choice of this -channel. In the same way, the drainage of the subordinate basin, -through which the main lake discharged eastward, is now not along the -axis of the Juniata-Catawissa syncline, but on the softer beds along -one side of it; and along the southern side because the easier escape -that was provided for it lay on that side, namely, via the Tuscarora -and Wiconisco synclines, as already described. The much broader change -from the Anthracite to the Susquehanna was only another form of the -same process. Taking a transverse view of the whole system of central -folds, it is perceived that their axes descend into the Anthracite -district from the east and rise westward therefrom; it is as if the -whole region had received a slight transverse folding, and the -transverse axis of depression thus formed defined the initial course of -the first master stream. But this master stream deserted its original -course on the transverse axis of depression because a lateral course -across lowlands on softer beds was opened by its side streams; and in -the contest on these lowlands with an external stream, the Susquehanna, -the upper portion of the Anthracite was diverted from the hard rocks -that had appeared on the transverse axis. The distance of diversion -from the axial to the lateral course in this case was great because of -the gentle quality of the transverse folding; or, better said, because -of the gentle dips of the axes of the longitudinal folds. This -appearance of systematic re-arrangement in the several river courses -where none was expected is to my mind a strong argument in favor of the -originally consequent location of the rivers and their later mutual -adjustment. It may perhaps be conceived that antecedent streams might -imitate one another roughly in the attitude that they prophetically -chose with regard to folds subsequently formed, but no reason has been -suggested for the imitation being carried to so remarkable and definite -a degree as that here outlined.</p> -<a name="sect35"></a> -<p>35. <i>Superimposition of the Susquehanna on two synclinal -ridges</i>.—There is however one apparently venturesome postulate that -may have been already noted as such by the reader; unless it can be -reasonably accounted for and shown to be a natural result of the long -sequence of changes here considered, it will seriously militate against -the validity of the whole argument. The present course of the middle -Susquehanna leads it through the apical curves of two Pocono synclinal -ridges, which were disregarded in the statement given above. It was -then assumed that the embryonic Susquehanna gained possession of the -Siluro-Devonian lowland drainage by gnawing out a course to the west of -these synclinal points; for it is not to be thought of that any -conquest of the headwaters of the Anthracite river could have been made -by the Susquehanna if it had had to gnaw out the existing four -traverses of the Pocono sandstones before securing the drainage of the -lowlands above them. The backward progress of the Susquehanna could not -in that case have been nearly fast enough to reach the Anthracite -before the latter had sunk its channel to a safe depth. It is therefore -important to justify the assumption as to the more westerly location of -the embryonic Susquehanna; and afterwards, to explain how it should -have since then been transferred to its present course. A short cut -through all this round-about method is open to those who adopt in the -beginning the theory that the Susquehanna was an antecedent river; but -as I have said at the outset of this inquiry, it seems to me that such -a method is not freer from assumption, even though shorter than the one -here adopted; and it has the demerit of not considering all the curious -details that follow the examination of consequent and adjusted courses.</p> - -<p>The sufficient reason for the assumption that the embryonic Susquehanna -lay farther west than the present one in the neighborhood of the Pocono -synclinals is simply that—in the absence of any antecedent stream—it -must have lain there. The whole explanation of the development of the -Siluro-Devonian lowlands between the Pocono and Medina ridges depends -simply on their being weathered out where the rocks are weak enough to -waste faster than the enclosing harder ridges through which the streams -escape. In this process, the streams exercise no control whatever over -the direction in which their headwaters shall grow; they leave this -entirely to the structure of the district that they drain. It thus -appears that, under the postulate as to the initial location of the -Susquehanna as one of the many streams descending the great slope of -the Kittatinny (Cumberland) highland into the Swatara syncline, its -course being reversed from northward to southward by the Newark -depression, we are required to suppose that its headwater (northward) -growth at the time of the Jurassic elevation must have been on the -Siluro-Devonian beds, so as to avoid the harder rocks on either side. -Many streams competed for the distinction of becoming the master, and -that one gained its ambition whose initial location gave it the best -subsequent opportunity. It remains then to consider the means by which -the course of the conquering Susquehanna may have been subsequently -changed from the lowlands on to the two Pocono synclines that it now -traverses. Some departure from its early location may have been due to -eastward planation in its advanced age, when it had large volume and -gentle slope and was therefore swinging and cutting laterally in its -lower course. This may have had a share in the result, but there is -another process that seems to me more effective.</p> - -<p>In the latter part of the Jura-Cretaceous cycle, the whole country -hereabout suffered a moderate depression, by which the Atlantic -transgressed many miles inland from its former shoreline, across the -lowlands of erosion that had been developed on the litoral belt. Such a -depression must have had a distinct effect on the lower courses of the -larger rivers, which having already cut their channels down close to -baselevel and opened their valleys wide on the softer rocks, were then -"estuaried," or at least so far checked as to build wide flood-plains -over their lower stretches. Indeed, the flood-plains may have been -begun at an earlier date, and have been confirmed and extended in the -later time of depression. Is it possible that in the latest stage of -this process, the almost baselevelled remnants of Blue mountain and the -Pocono ridges could have been buried under the flood-plain in the -neighborhood of the river?</p> - -<p>If this be admitted, it is then natural for the river to depart from -the line of its buried channel and cross the buried ridges on which it -might settle down as a superimposed river in the next cycle of -elevation. It is difficult to decide such general questions as these; -and it may be difficult for the reader to gain much confidence in the -efficacy of the processes suggested; but there are certain features in -the side streams of the Susquehanna that lend some color of probability -to the explanation as offered.</p> - -<p>Admit, for the moment, that the aged Susquehanna, in the later part of -the Jura-Cretaceous cycle, did change its channel somewhat by cutting -to one side, or by planation, as it is called. Admit, also, that in the -natural progress of its growth it had built a broad flood plain over -the Siluro-Devonian lowlands, and that the depth of this deposit was -increased by the formation of an estuarine delta upon it when the -country sank at the time of the mid-Cretaceous transgression of the -sea. It is manifest that one of the consequences of all this might be -the peculiar course of the river that is to be explained, namely, its -superimposition on the two Pocono synclinal ridges in the next cycle of -its history, after the Tertiary elevation had given it opportunity to -re-discover them. It remains to inquire what other consequences should -follow from the same conditions, and from these to devise tests of the hypothesis.</p> -<a name="sect36"></a> -<p>36. <i>Evidence of superimposition in the Susquehanna tributaries</i>.—One -of the peculiarities of flood-plained rivers is that the lateral -streams shift their points of union with the main stream farther and -farther down the valley, as Lombardini has shown in the case of the Po. -If the Susquehanna were heavily flood-plained at the close of the -Jura-Cretaceous cycle, some of its tributaries should manifest signs of -this kind of deflection from their structural courses along the strike -of the rocks. Side streams that once joined the main stream on the line -of some of the softer northeast-southwest beds, leaving the stronger -beds as faint hills on either side, must have forgotten such control -after it was baselevelled and buried; as the flood plain grew, they -properly took more and more distinctly downward deflected courses, and -these deflections should be maintained in subsequent cycles as -superimposed courses independent of structural guidance. Such I believe -to be the fact. The downstream deflection is so distinctly a -peculiarity of a number of tributaries that join the Susquehanna on the -west side (see <a href="#figure1">figure 1</a>) that it cannot be ascribed to accident, but -must be referred to some systematic cause. Examples of deflection are -found in Penn's creek, Middle creek and North Mahantango creek in -Snyder county; West Mahantango between the latter and Juniata county; -and in the Juniata and Little Juniata rivers of Perry county. On the -other side of the Susquehanna, the examples are not so distinct, but -the following may be mentioned: Delaware and Warrior runs, -Chillisquaque creek and Little Shamokin creek, all in Northumberland -county. It may be remarked that it does not seem impossible that the -reason for the more distinct deflection of the western streams may be -that the Susquehanna is at present east of its old course, and hence -towards the eastern margin of its flood plain, as, indeed its position -on the Pocono synclinals implies. A reason for the final location of -the superimposed river on the eastern side of the old flood plain may -perhaps be found in the eastward tilting that is known to have -accompanied the elevation of the Cretaceous lowland.</p> - -<p>It follows from the foregoing that the present lower course of the -Susquehanna must also be of superimposed origin; for the flood plain of -the middle course must have extended down stream to its delta, and -there have become confluent with the sheet of Cretaceous sediments that -covered all the southeastern lowland, over which the sea had -transgressed. McGee has already pointed out indications of superimposed -stream courses in the southeastern part of the State;<small><small><sup>22</sup></small></small> but I am not -sure that he would regard them as of the date here referred to.</p> - -<blockquote><small><small><sup>22</sup></small> Amer. Journ. Science, xxxv, -1888, 121, 134.</small></blockquote> - -<p>The theory of the location of the Susquehanna on the Pocono synclinal -ridges therefore stands as follows. The general position of the river -indicates that it has been located by some process of slow -self-adjusting development and that it is not a persistent antecedent -river; and yet there is no reason to think that it could have been -brought into its present special position by any process of shifting -divides. The processes that have been suggested to account for its -special location, as departing slightly from a location due to slow -adjustments following an ancient consequent origin, call for the -occurrence of certain additional peculiarities in the courses of its -tributary streams, entirely unforeseen and unnoticed until this point -in the inquiry is reached; and on looking at the map to see if they -occur, they are found with perfect distinctness. The hypothesis of -superimposition may therefore be regarded as having advanced beyond the -stage of mere suggestion and as having gained some degree of -confirmation from the correlations that it detects and explains. It -only remains to ask if these correlations might have originated in any -other way, and if the answer to this is in the negative, the case may -be looked upon as having a fair measure of evidence in its favor. The -remaining consideration may be taken up at once as the first point to -be examined in the Tertiary cycle of development.</p> -<a name="sect37"></a> -<p>37. <i>Events of the Tertiary cycle</i>.—The elevation given to the region -by which Cretaceous baselevelling was terminated, and which I have -called the early Tertiary elevation, offered opportunity for the -streams to deepen their channels once more. In doing so, certain -adjustments of moderate amount occurred, which will be soon examined. -As time went on, much denudation was effected, but no wide-spread -baselevelling was reached, for the Cretaceous crest lines of the hard -sandstone ridges still exist. The Tertiary cycle was an incomplete one. -At its close, lowlands had been opened only on the weaker rocks between -the hard beds. Is it not possible that the flood-plaining of the -Susquehanna and the down-stream deflection of its branches took place -in the closing stages of this cycle, instead of at the end of the -previous cycle? If so, the deflection might appear on the branches, but -the main river would not be transferred to the Pocono ridges. This -question may be safely answered in the negative; for the Tertiary -lowland is by no means well enough baselevelled to permit such an -event. The beds of intermediate resistance, the Oriskany and certain -Chemung sandstones, had not been worn down to baselevel at the close of -the Tertiary cycle; they had indeed lost much of the height that they -possessed at the close of the previous cycle, but they had not been -reduced as low as the softer beds on either side. They were only -reduced to ridges of moderate and unequal height over the general plain -of the Siluro-Devonian low country, without great strength of relief -but quite strong enough to call for obedience from the streams along -side of them. And yet near Selin's Grove, for example, in Snyder -county, Penn's and Middle creeks depart most distinctly from the strike -of the local rocks as they near the Susquehanna, and traverse certain -well-marked ridges on their way to the main river. Such aberrant -streams cannot be regarded as superimposed at the close of the -incomplete Tertiary cycle; they cannot be explained by any process of -spontaneous adjustment yet described, nor can they be regarded as -vastly ancient streams of antecedent courses; I am therefore much -tempted to consider them as of superimposed origin, inheriting their -present courses from the flood-plain cover of the Susquehanna in the -latest stage of the Jura-Cretaceous cycle. With this tentative -conclusion in mind as to the final events of Jura-Cretaceous time, we -may take up the more deliberate consideration of the work of the -Tertiary cycle.</p> - -<p>The chief work of the Tertiary cycle was merely the opening of the -valley lowlands; little opportunity for river adjustment occurred -except on a small scale. The most evident cases of adjustment have -resulted in the change of water-gaps into wind-gaps, of which several -examples can be given, the one best known being the Delaware wind-gap -between the Lehigh and Delaware water-gaps in Blue mountain. The -wind-gap marks the unfinished notch of some stream that once crossed -the ridge here and whose headwaters have since then been diverted, -probably to the Lehigh. The difficulty in the case is not at all how -the stream that once flowed here was diverted, but how a stream that -could be diverted in the Tertiary cycle could have escaped diversion at -some earlier date. The relative rarity of wind-gaps indicates that -nearly all of the initial lateral streams, which may have crossed the -ridges at an early epoch in the history of the rivers, have been -beheaded in some cycle earlier than the Tertiary and their gaps -thereafter obliterated. Why the Delaware wind-gap stream should have -endured into a later cycle does not at present appear. Other wind-gaps -of apparently similar origin may be found in Blue mountain west of the -Schuylkill and east of the Susquehanna. It is noteworthy that if any -small streams still persevere in their gaps across a hard ridge, they -are not very close to any large river-gap; hence it is only at the very -headwaters of Conedogwinet creek, in the northern part of Franklin -county, that any water is still drawn from the back of Blue mountain. -Again, these small stream gaps do not lie between large river-gaps and -wind-gaps, but wind-gaps lie between the gaps of large rivers and those -of small streams that are not yet diverted. Excellent illustration of -this is found on the "Piedmont sheet" of the contoured maps issued by -the United States Geological Survey. The sheet covers part of Maryland -and West Virginia, near where the North Branch of the Potomac comes out -of the plateau and crosses New Creek mountain. Eleven miles south of -the Potomac gap there is a deep wind-gap; but further on, at twenty, -twenty-five and twenty-nine miles from the river-gap are three fine -water-gaps occupied by small streams. This example merely shows how -many important points in the history of our rivers will be made clear -when the country is properly portrayed on contoured maps.</p> - -<p>A few lines may be given to the general absence of gaps in Blue -Mountain in Pennsylvania. When the initial consequent drainage was -established, many streams must have been located on the northward slope -of the great Cumberland highland, C, C, <a href="#figure21">fig. 21</a>; they must have gullied -the slope to great depths and carried away great volumes of the weak -Cambrian beds that lay deep within the hard outer casings of the mass. -Minor adjustments served to diminish the number of these streams, but -the more effective cause of their present rarity lay in the natural -selection of certain of them to become large streams; the smaller ones -were generally beheaded by these. The only examples of streams that -still cross this ridge with their initial Permian direction of flow to -the northwest are found in two southern branches of Tuscarora creek at -the southern point of Juniata county; and these survive because of -their obscure location among the many Medina ridges of that district, -where they were not easily accessible to capture by other streams.</p> -<a name="sect38"></a> -<p>38. <i>Tertiary adjustment of the Juniata on the Medina anticlines</i>.—The -lower course of the Juniata presents several examples of adjustment -referable to the last part of the Jura-Cretaceous cycle and to the -Tertiary cycle. The explanation offered for the escape of this river -from its initial syncline did not show any reason for its peculiar -position with respect to the several Medina anticlines that it now -borders, because at the time when it was led across country to the -Wiconisco syncline, the hard Medina beds of these anticlines were not -discovered. It is therefore hardly to be thought that the location of -the Juniata in the Narrows below Lewistown between Blue Ridge and Shade -mountain and its avoidance of Tuscarora mountain could have been -defined at that early date. But all these Medina anticlines rise more -or less above the Cretaceous baselevel, and must have had some effect -on the position taken by the river about the middle of that cycle when -its channel sank upon them. Blue Ridge and Black Log anticlines rise -highest. The first location of the cross-country stream that led the -early Juniata away from its initial syncline probably traversed the -Blue Ridge and Black Log anticlines while they were yet buried; but its -channel-cutting was much retarded on encountering them, and some branch -stream working around from the lower side of the obstructions may have -diverted the river to an easier path. The only path of the kind is the -narrow one between the overlapping anticlines of Blue Ridge and Shade -mountains, and there the Juniata now flows. If another elevation should -occur in the future, it might happen that the slow deepening of the -channel in the hard Medina beds which now floor the Narrows would allow -Middle creek of Snyder county to tap the Juniata at Lewistown and lead -it by direct course past Middleburgh to the Susquehanna; thus it would -return to the path of its youth.</p> - -<p>The location of the Juniata at the end of Tuscarora mountain is again -so definite that it can hardly be referred to a time when the mountain -had not been revealed. The most likely position of the original -cross-country stream which brought the Juniata into the Wiconisco -syncline was somewhere on the line of the existing mountain, and -assuming it to have been there, we must question how it has been -displaced. The process seems to have been of the same kind as that just -given; the retardation of channel-cutting in the late Cretaceous cycle, -when the Medina beds of Tuscarora anticline were discovered, allowed a -branch from the lower part of the river to work around the end of the -mountain and lead the river out that way. The occurrence of a shallow -depression across the summit of the otherwise remarkably even crest of -Tuscarora mountain suggests that this diversion was not finally -accomplished until shortly after the Tertiary elevation of the country; -but at whatever date the adjustment occurred, it is natural that it -should pass around the eastern end of the mountain and not around the -western end, where the course would have been much longer, and -therefore not successfully to be taken by a diverting stream.</p> - -<p>While the quality of these processes appears satisfactory, I am not -satisfied as to the sufficiency of their quantity. If diversion was -successfully practiced at the crossing of the Tuscarora anticline, why -not also at the crossing of Jack's mountain anticline, on which the -river still perseveres. It is difficult here to decide how much -confidence may be placed in the explanation, because of its giving -reason for the location of certain streams, and how much doubt must be -cast upon it, because it seems impossible and is not of universal application.</p> -<a name="sect39"></a> -<p>39. <i>Migration of the Atlantic-Ohio divide</i>.—There are certain shifted -courses which cannot be definitely referred to any particular cycle, -and which may therefore be mentioned now. Among the greatest are those -by which the divide between the Atlantic and the Ohio streams has been -changed from its initial position on the great constructional Nittany -highland and Bedford range. There was probably no significant change -until after Newark depression, for the branches of the Anthracite river -could not have begun to push the divide westward till after the -eastward flow of the river was determined; until then, there does not -seem to have been any marked advantage possessed by the eastward -streams over the westward. But with the eastward escape of the -Anthracite, it probably found a shorter course to the sea and one that -led it over alternately soft and hard rocks, instead of the longer -course followed by the Ohio streams over continuous sandstones. The -advantage given by the greater extent of soft beds is indicated by the -great breadth of the existing valleys in the central district compared -with the less breadth of those in the plateau to the west. Consider the -effect of this advantage at the time of the Jurassic elevation. As the -streams on the eastern slope of the Nittany divide had the shortest and -steepest courses to the sea, they deepened their valleys faster than -those on the west and acquired drainage area from them; hence we find -reason for the drainage of the entire Nittany and Bedford district by -the Atlantic streams at present. Various branches of what are now the -Alleghany and Monongahela originally rose on the western slope of the -dividing range. These probably reached much farther east in pre-Permian -time, but had their headwaters turned another way by the growth of the -great anticlinal divide; but the smaller anticlines of Laurel ridge and -Negro mountain farther west do not seem to have been strong enough to -form a divide, for the rivers still traverse them. Now as the -headwaters of the Juniata breached the eastern slope of the -Nittany-Bedford range and pushed the divide westward, they at last -gained possession of the Siluro-Devonian monocline on its western -slope; but beyond this it has not been possible for them yet to go. As -the streams cut down deeper and encountered the Medina anticline near -the core of the ridge, they sawed a passage through it; the Cambrian -beds were discovered below and a valley was opened on them as the -Medina cover wore away. The most important point about this is that we -find in it an adequate explanation of the opposite location of -water-gaps in pairs, such as characterize the branches of the Juniata -below Tyrone and again below Bedford. This opposite location has been -held to indicate an antecedent origin of the river that passes through -the gaps, while gaps formed by self-developed streams are not thought -to present such correspondence (Hilber). Yet this special case of -paired gaps in the opposite walls of a breached anticline is manifestly -a direct sequence of the development of the Juniata headwaters. The -settling down of the main Juniata on Jack's mountain anticline below -Huntingdon is another case of the same kind, in which the relatively -low anticlinal crest is as yet not widely breached; the gaps below -Bedford stand apart, as the crest is there higher, and hence wider -opened; and the gaps below Tyrone are separated by some ten or twelve miles.</p> - -<p>When the headwater streams captured the drainage of the Siluro-Devonian -monocline on the western side of the ancient dividing anticline, they -developed subsequent rectangular branches growing like a well-trained -grape vine. Most of this valley has been acquired by the west branch of -the Susquehanna, probably because it traversed the Medina beds less -often than the Juniata. For the same reason, it may be, the West Branch -has captured a considerable area of plateau drainage that must have -once belonged to the Ohio, while the Juniata has none of it; but if so, -the capture must have been before the Tertiary cycle, for since that -time the ability of the West Branch and of the Juniata as regards such -capture appears about alike. On the other hand, Castleman's river, a -branch of the Monongahela, still retains the drainage of a small bit of -the Siluro-Devonian monocline, at the southern border of the State, -where the Juniata headwaters had the least opportunity to capture it; -but the change here is probably only retarded, not prevented entirely; -the Juniata will some day push the divide even here back to the -Alleghany Front, the frontal bluff of the plateau.</p> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 26"> - <tr> - <td width="454"> - <img src="images/26.jpg" alt="Fig 26"> - </td> - </tr> - <tr> - <td width="454" align="center"> - <small>F<small>IG</small>. 26.</small> - </td> - </tr> -</table> -<a name="sect40"></a> -<p>40. <i>Other examples of adjustments</i>.—Other examples of small -adjustments are found around the Wyoming basin, fig. 26. Originally all -these streams ran centripetally down the enclosing slopes, and in such -locations they must have cut gullies and breaches in the hard -Carboniferous beds and opened low back country on the weaker Devonians. -Some of the existing streams still do so, and these are precisely the -ones that are not easily reached by divertors. The Susquehanna in its -course outside of the basin has sent out branches that have beheaded -all the centripetal streams within reach; where the same river enters -the basin, the centripetal streams have been shortened if not -completely beheaded. A branch of the Delaware has captured the heads of -some of the streams near the eastern end of the basin. Elsewhere, the -centripetal streams still exist of good length. The contrast between -the persistence of some of the centripetal streams here and their -peripheral diversion around Broad Top is a consequence of the -difference of altitude of the old lake bottoms in the two cases. It is -not to be doubted that we shall become acquainted with many examples of -this kind as our intimacy with rivers increases.</p> -<a name="sect41"></a> -<p>41. <i>Events of the Quaternary cycle</i>.—The brief quaternary cycle does -not offer many examples of the kind that we have considered, and all -that are found are of small dimensions. The only capturing stream that -need be mentioned has lately been described as a "river pirate;"<small><small><sup>23</sup></small></small> -but its conquest is only a Schleswig-Holstein affair compared to the -Goth- and Hun-like depredations of the greater streams in earlier cycles.</p> - -<blockquote><small><small><sup>23</sup></small> Science, xiii, 1889, 108.</small></blockquote> - -<p>The character of the streams and their valleys as they now exist is -strikingly dependent in many ways on the relation of the incipient -quaternary cycle to the longer cycles of the past. No lakes occur, -exception being made only of the relatively small ponds due to drift -obstruction within the glaciated area. Waterfalls are found only at the -headwaters of small streams in the plateau district, exception again -being made only for certain cases of larger streams that have been -thrown from their pre-glacial courses by drift barriers, and which are -now in a very immature state on their new lines of flow. The small -valleys of this cycle are shallow and narrow, always of a size strictly -proportional to the volume of the stream and the hardness of the -enclosing rocks, exception being made only in the case of post-glacial -gorges whose streams have been displaced from their pre-glacial -channels. The terraces that are seen, especially on the streams that -flow in or from the glaciated district, are merely a temporary and -subordinate complication of the general development of the valleys. In -the region that has been here considered, the streams have been seldom -much displaced from their pre-glacial channels; but in the northwestern -part of the State, where the drift in the valleys seems to be heavier, -more serious disturbance of pre-glacial courses is reported. The facts -here referred to in regard to lakes, falls, gorges, terraces and -displaced streams are to be found in the various volumes of the Second -Geological Survey of the State;<small><small><sup>24</sup></small></small> in regard to the terraces and the -estuarine deflections of the Delaware and Susquehanna, reference should -be made also to McGee's studies.<small><small><sup>25</sup></small></small></p> - -<blockquote><small><small><sup>24</sup></small> Especially Carll, Reports I<small><sub>3</sub></small>, -I<small><sub>4</sub></small>; White, Reports -G<small><sub>5</sub></small>, G<small><sub>6</sub></small>; Lewis, Report Z.</small></blockquote> - -<blockquote><small><small><sup>25</sup></small> Amer. Journ. Science, xxxv, 1888, 367, 448; Seventh -Annual Rep. U. S. G. S., 1888, 545.</small></blockquote> -<a name="sect42"></a> -<p>42. <i>Doubtful cases</i>.—It is hardly necessary to state that there are -many facts for which no satisfactory explanation is found under the -theory of adjustments that we have been considering. Some will -certainly include the location of the Susquehanna on the points of the -Pocono synclines under this category; all must feel that such a -location savors of an antecedent origin. The same is true of the -examples of the alignment of water-gaps found on certain streams; for -example, the four gaps cut in the two pairs of Pocono and Pottsville -outcrops at the west end of the Wyoming syncline, and the three gaps -where the Little Schuylkill crosses the coal basin at Tamaqua; the -opposite gaps in pairs at Tyrone and Bedford have already been -sufficiently explained. The location of the upper North Branch of the -Susquehanna is also unrelated to processes of adjustment as far as I -can see them, and the great area of plateau drainage that is now -possessed by the West Branch is certainly difficult to understand as -the result of conquest. The two independent gaps in Tussey's mountain, -maintained by the Juniata and its Frankstown branch below Tyrone are -curious, especially in view of the apparent diversion of the branch to -the main stream on the upper side of Warrior's ridge (Oriskany), just -east of Tussey's mountain.</p> -<a name="sect43"></a> -<p>43. <i>Complicated history of our actual rivers</i>.—If this theory of the -history of our rivers is correct, it follows that any one river as it -now exists is of so complicated an origin that its development cannot -become a matter of general study and must unhappily remain only a -subject for special investigation for some time to come. It was my hope -on beginning this essay to find some teachable sequence of facts that -would serve to relieve the usual routine of statistical and descriptive -geography, but this is not the result that has been attained. The -history of the Susquehanna, the Juniata, or the Schuylkill, is too -involved with complex changes, if not enshrouded in mystery, to become -intelligible to any but advanced students; only the simplest cases of -river development can be introduced into the narrow limits of ordinary -instruction. The single course of an ancient stream is now broken into -several independent parts; witness the disjointing and diversion of the -original Juniata, which, as I have supposed, once extended from Broad -Top lake to the Catawissa basin. Now the upper part of the stream, -representing the early Broad Top outlet, is reduced to small volume in -Aughwick creek; the continuation of the stream to Lewistown is first -set to one side of its original axial location and is then diverted to -another syncline; the beheaded portion now represented by Middle creek -is diverted from its course to the Catawissa basin by the Susquehanna; -perhaps the Catawissa of the present day represents the reversed course -of the lower Juniata where it joined the Anthracite. This unserviceably -complicated statement is not much simplified if instead of beginning -with an original stream and searching out its present disjointed parts, -we trace the composition of a single existing stream from its once -independent parts. The Juniata of to-day consists of headwaters -acquired from Ohio streams; the lake in which the river once gathered -its upper branches is now drained and the lake bottom has become a -mountain top; the streams flow around the margin of the lake, not -across its basin; a short course towards Lewistown nearly coincides -with the original location of the stream, but to confound this with a -precise agreement is to lose the true significance of river history; -the lower course is the product of diversion at least at two epochs and -certainly in several places; and where the river now joins the -Susquehanna, it is suspected of having a superimposed course unlike any -of the rest of the stream. This is too complicated, even if it should -ever be demonstrated to be wholly true, to serve as material for -ordinary study; but as long as it has a savor of truth, and as long as -we are ignorant of the whole history of our rivers, through which alone -their present features can be rightfully understood, we must continue -to search after the natural processes of their development as carefully -and thoroughly as the biologist searches for the links missing from his -scheme of classification.</p> -<a name="sect44"></a> -<p>44. <i>Provisional Conclusions</i>.—It is in view of these doubts and -complications that I feel that the history of our rivers is not yet -settled; but yet the numerous accordances of actual and deductive -locations appear so definite and in some cases so remarkable that they -cannot be neglected, as they must be if we should adhere to the -antecedent origin of the river courses.</p> - -<p>The method adopted on an early page therefore seems to be justified. -The provisional system of ancient consequent drainage, illustrated on -<a href="#figure21">fig. 21</a>, does appear to be sufficiently related to the streams of -to-day to warrant the belief that most of our rivers took their first -courses between the primitive folds of our mountains, and that from -that distant time to the present the changes they have suffered are due -to their own interaction—to their own mutual adjustment more than to -any other cause. The Susquehanna, Schuylkill, Lehigh and Delaware are -compound, composite and highly complex rivers, of repeated mature -adjustment. The middle Susquehanna and its branches and the upper -portions of the Schuylkill and Lehigh are descendants of original -Permian rivers consequent on the constructional topography of that -time; Newark depression reversed the flow of some of the transverse -streams, and the spontaneous changes or adjustments from immature to -mature courses in the several cycles of development are so numerous and -extensive that, as Löwl truly says, the initial drainage has almost -disappeared. The larger westward-flowing streams of the plateau are of -earlier, Carboniferous birth, and have suffered little subsequent -change beyond a loss of headwaters. The lower courses of the Atlantic -rivers are younger, having been much shifted from their Permian or -pre-Permian courses by Newark and Cretaceous superimposition, as well -as by recent downward deformation of the surface in their existing -estuaries. No recognizable remnant of rivers antecedent to the Permian -deformation are found in the central part of the State; and with the -exception of parts of the upper Schuylkill and of the Susquehanna near -Wilkes-Barre, there are no large survivors of Permian consequent -streams in the ordinary meaning of the term "consequent." The shifting -of courses in the progress of mature adjustment has had more to do with -determining the actual location of our rivers and streams than any -other process.</p> - -<blockquote>Harvard College, June, 1889.</blockquote> -<br> -<br><a name="chap2"></a> -<br> -<br> -<h3>TOPOGRAPHIC MODELS.</h3> - -<center>B<small>Y</small> C<small>OSMOS</small> M<small>INDELEFF</small>.</center> -<br> - -<p>Of the many methods by which it has been sought to represent the relief -of a country or district, only two have been at all widely used. These -methods are, in the order of their development, by hachured and by -contoured maps. Both have advantages and both have serious -disadvantages. Without entering into the controversy that is even yet -raging over the relative merits of the two systems, some slight notice -of what each claims to accomplish is necessary.</p> - -<p>The representation of relief by hachures is a graphic system, and in -the best examples we have is an attempt to show, upon a plane surface, -the actual appearance of a given area under given conditions of -lighting,—as in the Dufour map of the Alps. Of course certain details -that would really disappear if the assumed conditions were actual ones, -must be shown upon the map,—so that it is, after all, but a -conventional representation. The very best examples are, for this and -other reasons, unsatisfactory, and far more so is this the case in the -vastly larger class of medium grade and poor work.</p> - -<p>The contour system represents relief by a series of lines, each of -which is, at every point throughout its length, at a certain stated -elevation above sea-level, or some other datum-plane; in other words, -each contour line represents what would be the water's edge, if the sea -were to rise to that elevation. It possesses the advantage of great -clearness, but fails to a large degree in the representation of surface -detail; moreover, one must have considerable knowledge of topography, -in order to read the map correctly.<small><small><sup>1</sup></small></small></p> - -<blockquote><small><small><sup>1</sup></small> For specimens of representation of the same subject on -different scales, in both the hachure and contour systems, see plate -from "Enthoffer's Topographical Atlas."</small></blockquote> - -<p>To those who must give first place to the quantity of relief rather -than the quality, as, for example, the geologist or the engineer, a -contoured map is now considered essential. On the other hand, where -quality of relief is the prime consideration and the quantity a -secondary one, as, for example, for the use of the army, a hachured map -is considered the best. The method of hachures may be roughly -characterized as a graphic system with a conventional element, and the -contour method as a conventional system with a graphic element,—for if -the contour interval is small enough a sort of shading is produced -which helps considerably the idea of relief.</p> - -<p>In addition to these two great systems, with which everyone is more or -less familiar, there is another method of representing a country or -district,—a method that succeeds where others fail, and which although -by no means new, has not received the attention it deserves: this is -the representation of a country by a model in relief. Certain striking -advantages of models over maps of all kinds are, indeed, so apparent -that one almost loses sight of such slight disadvantages as can, of -course, be urged against them. In the graphic representation of the -surface they are far superior to the hachured map, and they have the -further advantage of expressing the relative relief, which the hachured -map fails to do, except in a very general way. They have also the -advantage of showing actual shadows, exactly as they would be seen in a -bird's-eye view of the district, instead of more or less conventional -ones, and are, consequently, more easily comprehended by the layman, -without becoming any less valuable to the skilled topographer. In -short, they combine all the graphic features of a hachured map with all -the advantages of the best class of contoured maps, and in addition -they show more of the surface detail, upon which so much of the -character of the country depends and which is very inadequately -expressed by hachures and almost completely ignored in a contoured map -of large interval. The contours themselves can be made to appear upon -the model very easily and without interfering with other features.</p> - -<p>The uses of models are many and various. Within the past few years -their usefulness has been much extended, and, now that they are -becoming better known, will probably receive a still further extension. -To the geologist they are often of great value in working out the -structure of complicated districts, for the reason that so many -important structural relations can be presented to the eye at a single -glance. Similarly, for the graphic presentation of results there is no -better method, as the topography, the surface geology, and any number -of sections can be shown together and seen in their proper -relationship. To the engineer an accurate model is often of the -greatest assistance in working out his problems, and it is simply -invaluable to explain the details of a plan to anyone who has little or -no technical training; for, as has been stated, a model is easily -comprehended by anyone, while more or less technical knowledge is -required for the proper understanding of even the best maps.</p> - -<p>I might go on cataloguing in detail the many uses to which models may -be put, but shall now mention only one more—perhaps the most important -of all—their use in the education of the young. No method has yet been -devised that is capable of giving so clear and accurate a conception of -the principles of physical geography as a series of well selected -models; models have, indeed, already been used for this purpose, but -unfortunately their great cost has prevented their general use in -schools. Since, however, the study of geography has been placed upon a -new basis and a new life has been infused into it, many men have given -their attention to the subject of models, and have experimented with a -view to cheapen the cost of reproduction, which has hitherto prevented -their wide distribution; and probably this objection will soon be -remedied. The ability to read a map correctly,—to obtain from a study -of the map a clear conception of the country represented,—is more -uncommon than is usually supposed. Some of the recent methods of -teaching geography are intended to cultivate this very faculty, but it -is doubtful whether there is any better method than that which consists -in the study of a series of good models in conjunction with a series of -maps, all on the same scale and of the same areas. The value of a -series of good models in teaching geology is so apparent that it need -only be mentioned. It is often, for reasons stated above, far more -valuable even, than field instruction.</p> - -<p>For the construction of a good relief map the first requisite is a good -contoured map. To this should be added, when possible, a good hachured -map, upon which the elevations of the principal points are stated,—if -the interval in the contoured map is a large one,—and as much material -in the way of photographs and sketches as it is possible to procure. -The modeler should, moreover, have some personal acquaintance with the -region to be represented, or, failing that, a general knowledge of -topographic forms, and at least a clear conception of the general -character of the country which he seeks to represent. This is very -important, for it is here that many modelers fail: the mechanical -portion of the work any ordinarily intelligent person can do. A model -may be as accurate as the map from which it is made, every contour may -be placed exactly where it belongs, and yet the resulting model may -be,—indeed, often is—"flat," expressionless, and unsatisfactory. -Every topographer in drawing his map is compelled to generalize more or -less, and it is fortunate for the map if this be done in the field -instead of in the draughtsman's office. But topographers differ among -themselves: there may be, and often is, considerable difference in two -maps of the same region made by different men; in other words, the -"personal equation" is a larger element in a map than is usually -supposed. This being the case, there is something more required in a -modeler than the mere transferring of the matter in the map,—giving it -three dimensions instead of two: he must supply through his special -knowledge of the region (or, failing that through his general -knowledge) certain characteristics that do not appear upon the map, and -undo, so far as it is necessary, certain generalizations of the -topographer and draughtsman. This artistic or technical skill required -correctly to represent the <i>individuality</i> of a given district is -especially important in the modeler; it is more important, perhaps, in -small-scale maps of large districts than in large-scale maps of small -ones,—for in the latter the generalizing process has not been carried -so far, and the smaller interval of the contour lines preserves much of -the detail.</p> - -<p>The methods by which relief maps are made have always received more -attention than would, at first sight, appear to be their proper -proportion. It may be due, however, to the difficulty of applying any -test to determine the accuracy of the finished model, and perhaps also -to the general impression that any one can make a relief map,—and so -he can, though of course there will be a wide difference in the value -of the results. Some, indeed, have devoted their attention to methods -exclusively, letting the result take care of itself,—and the models -show it. There is no more reason why a modeler should tie himself down -to one method of work, than that a water-colorist, or a chemist, or -anyone engaged in technical work, should do so; though in some cases he -might be required, as the chemist is, to show his methods as well as -his results.</p> - -<p>One of the earliest methods, with any pretension to what we may term -mechanical control, is that described by the Messrs. Harden in a paper -on "The construction of maps in relief," read before the American -Institute of Mining Engineers in 1887. The method was published in -1838. Upon a contoured map as a basis cross-section lines are drawn at -small and regular intervals, and, if the topography be intricate, -corresponding lines at right angles. The sections thus secured are -transferred to thin strips of some suitable material, such as card-board -or metal, and cut down to the surface line,—the strips themselves thus -forming the cross-sections. These cross-sections are mounted upon a -suitable base-board, and the cavities or boxes are then filled up with -some easily carved material, such as plaster or wax. The top is then -carved down to the form of the country or district,—the necessary -guidance being obtained by the upper edges of the strips that form the -cross-sections. It will be readily seen that this method is a very -crude and laborious one. It necessitates in the first place a good -contoured map upon which to draw the sections, but sacrifices much of -the advantage thus gained because only a number of points on each -contour line are used, instead of the entire line. It is no better, -although actually more laborious, than the later method of driving -contour pins (whose height above a base-board may be accurately -measured,) along the contour lines, and then filling in. A slight -modification of the latter method can be used to advantage when no -contoured map is available, and when the points whose elevation is -known are not numerous enough to permit the construction of one. In -this case the only control that can be secured is by means of a number -of pins driven into the base-board at those points whose elevation is -known. The remainder of the map is then sketched in. This method is -perhaps as satisfactory as any, when the material upon the map is -scanty. Another method, however, growing out of the same scantiness of -material, is in some cases to be preferred, especially for large -models. The map is enlarged to the required size, and a tracing of it -is mounted upon a frame. Another deep frame, just large enough to -contain the mounted tracing, is made, and laid upon a suitable -base-board upon which a copy of the map has been mounted. Upon this -base-board the model is then commenced, in clay or wax. The low areas -are modeled first,—horizontal control being obtained by pricking -through the mounted tracing of the map with a needle point, and -vertical control by measuring down from a straight edge sliding on the -top of the deep frame. This system is rather crude, and only useful -where the material upon the map is very scanty, but it gives excellent control.</p> - -<p>A method used by Mr. F. H. King in the preparation of his large map of -the United States is described by him in a letter to Messrs. Harden, -and published by them in the place mentioned. A solid block of plaster -is used,—the contoured map being transferred to it—and the plaster is -carved down to produce a series of steps like those made by building up -the contours. The shoulders are then carved down to produce a -continuous surface. This method is one of the best of those that -require carving instead of modeling.</p> - -<p>Many other methods of producing relief maps might be mentioned, but, as -most of them have been used only to make special models, they need not -be described. The method that has been more used than any other still -remains to be described. It is that which the writer has used almost -exclusively, and consists in building up the model and modeling the -detail, instead of carving it. It is a maxim of the modeler that the -subject should be built up as far as possible, should be produced by -adding bits of clay or wax, or other material, and not by carving away -what is already on,—by addition and not by subtraction. This may be -illustrated by a reference to the methods of the sculptor. The bust, or -figure, or whatever the subject may be, is first modeled in clay or -wax; from this model a plaster mould is made, and from this mould a -plaster cast is taken. This cast is called the original, and the -finished production, whether in marble, bronze, or any other hard -substance, is simply a copy of this original. No one ever attempts to -produce the finished bust or figure directly from the object itself. -Even where the artist has for a guide a death mask, the procedure does -not change. The bust is first made in clay, and this clay model, as a -rule, contains all the detail which subsequently appears in the -finished bust. It seems strange, therefore, that the relief map maker -should use a method which the sculptor, with infinitely more skill and -judgment, is afraid to use; and this on subjects that do not differ as -much as might be imagined.</p> - -<p>The contour interval to be used depends on the use to which the model -is to be put. It is not always necessary to carry into the model all -the contour lines upon the map: I may go further and say that it is not -always desirable to do so. The number to be used depends to some extent -on the skill of the modeler. As already stated, the contours are only a -means of control, and one modeler requires more than another. To build -into a model every contour in a contoured map of ten foot interval is a -very laborious proceeding, and not worth the time it takes, as in nine -out of ten maps of such interval only the fifty-foot or the one -hundred-foot curves are definitely fixed, the intermediate lines being -merely filled in. This filling in can be done as well, or better, by -the modeler.</p> - -<p>The question as to the proper amount of exaggeration to be given the -vertical scale, as compared with the horizontal, is the question about -which has raged most of the controversy connected with relief map -making. This controversy has been rather bitter; some of the opponents -of vertical exaggeration going to the length of saying that no -exaggeration is necessary, and that "he that will distort or exaggerate -the scale of anything will lie." On the other hand the great majority -of those who have made relief maps insist upon the necessity of more or -less exaggeration of the vertical scale—generally more than seems to -me necessary, however.</p> - -<p>An increase of angle of slope accompanies all vertical exaggeration, -and this is apparent even in models in which the vertical element is -only very slightly exaggerated. It produces a false effect by -diminishing the proportionate width of the valleys, and by making the -country seem much more rugged and mountainous than it really is. A -secondary effect is to make the region represented look very small—all -idea of the extent of the country being lost. This can be illustrated -better than described. The King model of the United States is an -example of one extreme; it is worthy of note that no examples of the -other extreme—too little exaggeration—are known.</p> - -<p>In small-scale models of large districts some exaggeration of the -vertical scale is necessary in order to make the relief apparent, but -the amount of this exaggeration is often increased much beyond what is -essential. The proportion of scales must depend to a large extent on -the character of the country represented, and on the purposes for which -the model is made. It has been suggested by a writer, quoted by the -Messrs. Harden, that the following exaggeration would afford a pleasing -relief: "For a map, scale 6 inches to 1 mile: if mountainous, 1:3; if -only hilly, 1:2; if gently undulating, 2:3. For smaller scales, except -for very rugged tracts, the exaggeration should be correspondingly -increased. For a tract consisting wholly of mountains no exaggeration -is necessary." I know of no country of such a character that its -relief, in all its detail, cannot be shown upon a scale of 6 inches to -1 mile without any exaggeration at all.</p> - -<p>It seems to me that the absolute and not the relative amount of relief -is the desideratum, and I have always used this as my guiding -principle. For small scale models I have found half an inch of relief -ample. It may be worth while to state that in a model of the United -States made for the Messrs. Butler, of Philadelphia, the horizontal -scale was 77 miles to 1 inch, the vertical scale 40,000 feet to 1 inch, -and the proportion of scales as 1 to 10. This proportion could have -been brought down as low as 1:6 with advantage. One-fortieth of an inch -to a thousand feet seems a very small vertical scale, but it sufficed -to show all the important features of the relief. It should be stated, -moreover, that the model in question was very hurriedly made—in fact, -was hardly more than a sketch-model—and that more care and more minute -work would have brought out many details that do not now appear. This -amount of care was not considered necessary in this instance, as the -model was made to be photographed and published as a photo-engraving, -and was to suffer an enormous reduction—coming down to five by seven -inches.<small><small><sup>2</sup></small></small></p> - -<blockquote><small><small><sup>2</sup></small> See <a href="#figure28">plate</a> from -"Butler's Complete Geography."</small></blockquote> - -<p>It has been frequently urged by the advocates of large exaggeration -that the details of a country cannot be shown unless the vertical scale -is exaggerated; that hills 200, 300, or even 500 feet high—depending -of course upon the scale—flatten out or disappear entirely. This seems -plausible, but the advantages of great exaggeration are more apparent -than real. Its effect upon the model has already been mentioned; it -should be added that, with the proper amount of care in finishing the -model, exceedingly small relief can be so brought out as to be readily -seen. With ordinary care, one-fortieth of an inch can be easily shown, -and with great care and skill certainly one-eightieth and probably -one-hundredth of an inch. Another plausible argument that has been -advanced in favor of vertical exaggeration as a principle, is well -stated by Mr. A. E. Lehman, of the Pennsylvania Geological Survey, in a -paper on "Topographical Models," read before the American Institute of -Mining Engineers in 1885. "A perfectly natural expression is of course -desired; and to cause this the features of the topography should be -distorted and exaggerated in vertical scale just enough to produce the -same effect on the beholder or student of the district of country -exhibited as his idea of it would be if he were on the real ground -itself. Care should be taken, however, not to make the scales so -disproportionate as to do violence to mental impressions. Often, -indeed, prominent or important features, when they will bear it, may be -still more effectively shown by additional exaggeration in the vertical -scale." The fallacy of this argument is obvious. It assumes that the -object of a model is to show the country as it appears to one passing -through it, and not as it really is—and there is often a very wide -difference between the two. The impression derived from passing through -a country is, if I may use the term, a very large-scale impression, as -any one who has tried it can certify; it is certainly a mistake to -attempt to reproduce this impression in a small-scale model, with the -help of vertical exaggeration. Even if the principle were a good one, -its application would be very limited. It could only be used in -large-scale models; to apply it to a model of a large area—the United -States, for example—is obviously absurd.</p> - -<p>The method referred to as being now generally in use may be briefly -described as follows: requisites, a good contoured map; a hachured map -in addition, if possible; a clear conception on the part of the modeler -of the country to be represented; and a fair amount of skill. -Materials: a base-board of wood or other suitable material; card-board -or wood of the thickness required by the contour interval and the -scale; and modeling wax or clay. Procedure: reproduce the contours in -the wood or other material; mount these upon the base-board in their -proper relationship; then fill in the intervening spaces, and the space -above the topmost contour, with the modeling material.</p> - -<p>In a series of models of the Grand Divisions of the earth, made about a -year and a half ago, the contours of card-board were made as follows: -the map was photographed up to the required scale, and as many prints -were made as there were contour intervals to be represented—in a model -of the United States of 1,000 feet contour interval there were fourteen -prints. Thirteen of these were mounted upon card-board of the exact -thickness required by the vertical scale, and one upon the base-board. -All large paper companies use a micrometer gauge, and card-board can -easily be obtained of the exact thickness required—even to less than -the thousandth part of an inch. The lowest contour was then sawed out -upon a scroll saw, and placed upon the corresponding line of the map -mounted upon the base-board. This process was repeated with each of the -succeeding contours until all were placed and glued into their proper -positions. At this stage the model presents the relief in a series of -steps, each step representing a rise corresponding to the contour -interval. The disadvantages of the method lie in the fact that unless -the greatest care is exercised in making the photographic prints there -will be considerable distortion, owing to the stretching of the paper -in different directions, and consequently much trouble in fitting the -contours. If care be exercised in having the grain of the paper run in -the same direction in all the prints, trouble in fitting the contours -will be much reduced, but the distortion in one direction will remain. -In our experience this distortion amounts to about two per cent.; in -other words, a model that should be fifty inches long will in reality -be fifty-one inches; but, as this error is distributed over the whole -fifty inches, it is not too great for an ordinary model. If greater -accuracy be required, it can be secured by transferring the contours to -the card-board by means of tracing or transfer paper. The great -advantage of the photographic method lies in the fact that when the -model has been built up, with all the contours in position, it presents -a copy of the map itself, with all the details, drainage, etc., in -position, instead of blank intervals between the contours. Such details -and drainage are a great help in the subsequent modeling.</p> - -<p>The next step in the process is to fill in with clay or wax the -intervals between the contours. I have always found wax more convenient -than clay for this purpose as, unless the surface coating is a thick -one, the clay is difficult to keep moist. To obviate this difficulty, -some modelers have used clay mixed with glycerine instead of water; -this, of course, does not become dry, but the material is, at its best, -unsatisfactory. The filling-in process is the most important one in -relief map making, for it is here that the modeler must show his -knowledge of, and feeling for, topographic forms. Some models seem to -have been constructed with the idea that when the contours have been -accurately placed the work of the modeler is practically done. This is -a great mistake. The card-board contours are only a means of control, -occupying somewhat the same relation to the relief map that a core or -base of bricks, or a frame of wood, does to other constructions as, for -example, an architectural ornament or a bust. It is sometimes necessary -to cut away the contour card; for, as has been already explained, a map -is more or less generalized, and a contour is frequently carried across -a ravine, instead of following it up, as it would do if the map were on -a larger scale. Such generalizing is of course perfectly proper in a -map, but, with the same scale, we expect more detail in a model. The -modeler must have judgment enough and skill enough to read between the -lines, and to undo the generalizing of the topographer and draughtsman, -thus supplying the material omitted from the map. This can be done -without materially affecting the accuracy of the model, considered even -as a copy of the contoured map.</p> - -<p>The contours of card-board or other material are, let me repeat, only a -means of control. The perfect modeler—a variety, by the way, yet to be -evolved—would be able to make an accurate relief map without them, in -the same way that other subjects are made; as, for example, a flower -panel, an architectural ornament, or any other subject in low relief, -where the object sought is artistic effect and great accuracy is not a -desideratum. It is the converse of this idea that has produced the -numerous models that one sees; accurate enough, perhaps, but wholly -expressionless and absolutely without feeling. This is the great fault -of nearly all models made by building up the contours in wood and then -carving down the shoulders. It is then necessary to sand-paper them, -and what little character they might otherwise have had is completely -obliterated by the sand-paper. Such models almost invariably <i>look</i> -wooden. Let the modeler, then, have a clear conception of his subject -and not depend wholly on the contours, and let him work out that -conception in his model, "controlled" and helped by the contours, but -not bound by them; the resulting model will thus be far more -satisfactory and a far better representation of his subject, in other -words, it will be more life-like—more nearly true to nature.</p> - -<p>The model, provided it be not of clay, is sometimes used in the state -in which it is left when finished. It is much more common, however, to -make a plaster mould, and from this a plaster cast. For this purpose a -moulder is usually called in; but moulders as a rule are ignorant men, -accustomed to one line of work only, and the result is not always -satisfactory. It is much better for the modeler himself to do this -work, though to obtain good results from plaster it is necessary to -know the material thoroughly, and this knowledge comes only from -experience. The mould is generally made quite heavy, in order to stand -the subsequent hard treatment that it may receive, and should be -retouched and thoroughly dried before being prepared for the cast. The -method used by some modelers of placing a frame about the model and -pouring in the plaster, filling the frame to the top, is a crude and -very wasteful one and not at all to be recommended. In a model of large -size—say seven or eight feet square—it would require a derrick to -move the mould. It is wholly unnecessary, as, with a small amount of -care, a good mould can be made not more than an inch thick, or, at -most, an inch and a half. The drying of the mould before use can -sometimes be dispensed with, but is always desirable.</p> - -<p>Nearly all American moulders (as distinguished from French and Italian -ones) varnish the mould, and thus lose some of the finest detail and -sharpness. This is unnecessary. The mould can be easily prepared with a -solution of soap so as to leave nothing on the surface but a very thin -coating of oil, which is taken up and replaced by the plaster of the -cast. Of course, if the model has been sand-papered, no fine work in -moulding or casting is necessary, as there is nothing to save. If the -subject is a very intricate one, with "undercuts" (as they are called), -it is customary to make a waste mould; as this is very seldom necessary -in relief map work, however, the process need not be described.</p> - -<p>To make the cast it is only necessary to repeat the processes used in -making the mould. With great care and some skill a cast can be produced -but little inferior in point of sharpness and detail to the original -model. It is customary to make the cast very thick, and, consequently, -very heavy; this is unnecessary. In our work we seldom make a cast -thicker than one inch, and yet are never troubled with changes in the -model after it is finished. Even in a very large cast (now in the -National Museum), weighing nearly 1,500 pounds and presenting a surface -of over 160 square feet, the average thickness is less than one inch, -although it required over five barrels of plaster to make it. The cast, -after being thoroughly dried, should be finished—all its imperfections -being carefully repaired. The surface, however, should be touched as -little as possible, as the slight roughness of surface that comes from -the original model, through the mould, is removed by any tooling. This -roughness adds much to the effect of the model; in fact, where the -scale is large enough, it is sometimes desirable to emphasize it.</p> - -<p>The proper way to paint a model is a matter that must rest principally -upon the judgment of the modeler, depending to some extent, also, on -the use to which the model is to be put. The plain cast is sometimes -used, drainage, lettering, etc., being put directly upon it. This has -the advantage of preserving all the detail that comes from the mould, -but it has also the disadvantage of a surface easily soiled and -impossible to clean. If the model is to be photographed, the surface -should be nearly white—in our practice we use a small amount of yellow -with the white. This yellow is hardly appreciable by the eye, but its -effect upon the photographic negative is quite marked. Yellow becomes -grey in a photograph, and, in a photograph of a model colored as -described, a grey tint is given to the whole surface. The high lights -are not pure white, and there is no harsh contrast between light and -shade. There is another point of great importance in photographing -models: the surface should have a dead finish—that is, should have no -gloss, or, at most, should have only what is known among painters as an -egg-shell gloss. It is almost impossible satisfactorily to photograph a -model that has a shiny surface. Any portion of a model that it is -desired to separate from the rest should be painted a different -color—the water, for example, should be painted a light blue; not a -blue composed of indigo, however, or any of the grey blues, as these -produce in the photograph a dead grey, and are not pleasant to the eye. -The most satisfactory color that we have used is a mixture of -cobalt—the purest of the blues—with Antwerp blue—which is quite -green—and white. This gives a color that is pleasant to the eye, has -the retreating quality to perfection, and photographs well.</p> - -<p>Models intended for exhibition as such should be painted realistically. -There is room here for an immense improvement in the usual practice, -which is to paint the model either in some conventional scheme of light -and shade, or else to put a single flat tint upon it. If the model is -to be colored conventionally it is, in my opinion, much better to use a -flat tint, light in tone, and with a dead surface. The use of a variety -of colors upon the face of a model interferes materially with the -relief, especially if the relief is finely modeled. For this reason -models colored to indicate geologic formations should always be -accompanied by duplicates representing topography only, colored -realistically, if possible, and without lettering. Well-defined lines -other than those pertaining to the model itself, such, for example, as -those used to define the boundaries of geologic formations, should not -be allowed upon a model when it is desired to bring out all the relief. -The lettering on such models should be kept down as small as possible, -or wholly dispensed with. The latter is much the better method.</p> - -<p>The cheap reproduction of models is the most important problem -connected with the art, and the one that is attracting most attention -among those engaged in it; as, until models can be reproduced cheaply, -they will never have any wide distribution and there will be far less -incentive to the modeler. Various materials have been suggested and -experimented on, but nine-tenths of the models that are made to-day are -made of plaster of Paris. Although this material was the first to be -used for this purpose, it has not yet been superseded. A plaster cast -is heavy, expensive and easily injured; but plaster gives an accurate -copy of the original, retains permanently the form given it, and is -easily finished and repaired. The weight is an obstacle that can be -easily overcome. By the incorporation in the plaster of fine tow, or of -bagging or netting of various kinds, the cast can be made very light -and at the same time strong, but the expense is increased rather than -diminished by this method. Models made in this way, however, have the -advantage that when broken the pieces do not fall out, they are, -however, fully as liable to surface injury as the other kind. The large -cast in the National Museum, before referred to, was made in this way. -It weighed nearly 2,000 pounds when boxed—not an easy thing to -handle—but it stood shipment to New Orleans and back without suffering -any material injury. This would hardly have been possible had the cast -been made from plaster alone.</p> - -<p>Paper seems, at first sight, to be the material best adapted for the -reproduction of models; but no one has succeeded well enough with it to -bring it into use. Like nearly all those who have given this subject -attention, I have experimented with paper, but the only positive result -has been a loss of a large part of the confidence that I once had in -the suitability of the material. Paper has been used extensively for -large scale models of pueblos, ruins, etc., but I have never obtained a -satisfactory result with subjects in low relief and fine detail. A -paper cast may look well when first made, but it absorbs moisture from -the atmosphere, and contracts and expands with the weather. The -contraction is apt to flatten out the model and the expansion to make -it buckle up.</p> - -<p>Casts of models have been made in iron; but this, while suitable -perhaps for models of mounds and subjects of like character, would -hardly be applicable to small scale models with fine detail; such casts -require too much surface finishing. The material known as -Lincrusta-Walton seems to me to be the ideal material for this purpose. -It is tougher than rubber, will take the finest detail, and its surface -can be treated in any way desired. Unfortunately the manufacture of -models in this material would require expensive machinery, and is -outside the scope of a modeling room. Should it ever become -commercially advantageous, however, casts of a model of ordinary size, -in every way equal to the original, can be turned out in this material -at a very small cost.</p> - -<p>It remains to speak of the reproduction of models by -process-engravings—a method that will probably receive much more -attention in the future than it has in the past. It is perhaps along -this line that the cheap reproduction of models will develop; but the -subject is too large a one to be adequately treated here, and must be -postponed until some future occasion.</p> - -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 27"> - <tr> - <td width="702"> - <img src="images/27.jpg" alt="Fig 27"> - </td> - </tr> - <tr> - <td width="702" align="center"> - HACHURED AND CONTOURED MAPS.<br><br> - <small>REPRESENTATION OF A HILL ACCORDING TO THE TWO SYSTEMS AND - ON DIFFERENT SCALES.<br><br> - From Supplement to Enthoffer's Topographical Atlas by permission of Mr. - Enthoffer.</small> - </td> - </tr> -</table><br> -<br> -<br><a name="figure28"></a> -<br> -<br> -<table align="center" border="0" cellspacing="0" cellpadding="6" summary="Figure 28"> - <tr> - <td width="699" align="center"> - FROM BUTLER'S COMPLETE GEOGRAPHY. - </td> - </tr> - <tr> - <td width="699"> - <img src="images/28.jpg" alt="Fig 28"> - </td> - </tr> - <tr> - <td width="699" align="center"> - <small>C<small>OPYRIGHT</small>, 1888, <small>BY</small> - E. H. B<small>UTLER</small> & C<small>O</small>.</small> - </td> - </tr> - <tr> - <td width="699"> - <small>Printed by permission.</small> - </td> - </tr> -</table><br> -<br> -<br><a name="chap3"></a> -<br> -<br> -<h2>NATIONAL GEOGRAPHIC SOCIETY.</h2> - -<h3>ABSTRACT OF MINUTES.</h3> -<hr align="center" width="25%"> -<br> -<center><i>October 5, 1888, Ninth Meeting</i>.</center> - -<p>A paper was read entitled, "Topographic Models," by Mr. Cosmos -Mindeleff. Published in the "National Geographic Magazine," <a href="#chap2">Vol. I, No. 3.</a></p> -<br> -<center><i>October 19, 1888, Tenth Meeting</i>.</center> -<p>The attendance being very small, no paper was read.</p> -<br> -<center><i>November 2, 1888, Eleventh Meeting</i>.</center> -<p>The paper of the evening was entitled, "Surveys, their Kinds and -Purposes," by Mr. Marcus Baker. The paper was discussed by Messrs. -Ogden, Goodfellow, Gannett and Baker. Published in "Science," Vol. XII, -No. 304.</p> -<br> -<center><i>November 16, 1888, Twelfth Meeting</i>.</center> -<p>A paper was read by Mr. Henry Gannett, giving certain "Physical -Statistics Relating to Massachusetts," derived from the map of that -State recently prepared by the United States Geological Survey. A -discussion followed which was participated in by Messrs. Baker, -Kenaston, Fernow, Weed, and the author. A second paper entitled, -"Something about Tornadoes," was read by Lieut. J. P. Finley, U. S. -Signal Corps.</p> -<br> -<center><i>November 30, 1888, Thirteenth Meeting</i>.</center> -<p>The annual reports of vice-Presidents Herbert G. Ogden and Gen. A. W. -Greely were delivered. Published in the "National Geographic Magazine," -Vol. I, No. 2.</p> -<br> -<center><i>December 20, 1888, Fourteenth Meeting</i>.</center> -<p>Held in the Law Lecture Room of the Columbian University. The President -delivered his Annual Address, entitled, "Africa." Published in the -"National Geographic Magazine," Vol. I, No. 2.</p> -<br> -<center><i>December 28, 1888, Fifteenth Meeting</i>.</center> -<p>The Society met in the Society Hall of the Cosmos Club, President -Hubbard in the chair. Owing to the absence from the city of the -Secretaries, Mr. O. H. Tittmann was requested to act as Secretary of -the meeting. The minutes of the first and fourteenth meetings were read -and approved. The report of the Secretaries was read, in their absence, -by the temporary Secretary, and was approved. The Treasurer's report, -showing a balance on hand of $626.70, was read and approved, as was -also that of the auditing committee.</p> - -<p>The President announced that vacancies caused by the resignation of two -of the managers, Messrs. W. D. Johnson and Henry Mitchell, had been -filled by the Board on the 15th of November, by the election of Messrs. -O. H. Tittmann and C. A. Kenaston; and that a vacancy caused by the -resignation of Vice-President John R. Bartlett, had been filled by the -election of Lieut. George L. Dyer, on November 30th.</p> - -<p>The Society then proceeded to the election of officers, with following -result:</p> - -<blockquote><i>President</i>—G<small>ARDINER</small> G. H<small>UBBARD</small>.<br> -<i>Vice-Presidents</i>—H<small>ERBERT</small> G. O<small>GDEN</small>, -[land]; G<small>EORGE</small> L. D<small>YER</small>, [sea]; -A. W. G<small>REELY</small>, [air]; C. H<small>ART</small> M<small>ERRIAM</small>, -[life]; A. H. T<small>HOMPSON</small>, [art].<br> -<i>Treasurer</i>—C<small>HARLES</small> J. B<small>ELL</small>.<br> -<i>Recording Secretary</i>—H<small>ENRY</small> G<small>ANNETT</small>.<br> -<i>Corresponding Secretary</i>—G<small>EORGE</small> K<small>ENNAN</small>.<br> -<i>Managers</i>—C<small>LEVELAND</small> A<small>BBE</small>, M<small>ARCUS</small> B<small>AKER</small>, R<small>OGERS</small> B<small>IRNIE</small>, J<small>R</small>., -G. B<small>ROWNE</small> G<small>OODE</small>, W. B. P<small>OWELL</small>, J. C. W<small>ELLING</small>, C. A. K<small>ENASTON</small>, -O. H. T<small>ITTMANN</small>.</blockquote> - -<br> -<center><i>January 11, 1889, Sixteenth Meeting</i>.</center> - -<p>The paper of the evening was entitled, "The Great Plains of Canada," -and was presented by Professor C. A. Kenaston, of Howard University.</p> -<br> -<center><i>January 25, 1889, Seventeenth Meeting</i>.</center> -<p>The paper of the evening was entitled, "Irrigation in California," by -Mr. William Hammond Hall, State Engineer of California. To be published -in the "National Geographic Magazine," Vol. I, No. 4.</p> -<br> -<center><i>February 8, 1889, Eighteenth Meeting</i>.</center> -<p>The following papers were read by Prof. W. M. Davis, of Harvard -University: "Topographic Models," and "Certain Peculiarities of the -Rivers of Pennsylvania." Published in the "National Geographic -Magazine," <a href="#chap1">Vol. I, No. 3.</a></p> -<br> -<center><i>February 22, 1889, Nineteenth Meeting</i>.</center> -<p>The paper of the evening was entitled, "Round about Asheville, N. C.," -by Mr. Bailey Willis. The paper was illustrated by charcoal sketches -and lantern slides. Discussion followed, which was participated in by -Messrs. Baker, Merriam and McGee. To be published in the "National -Geographic Magazine," Vol. I, No. 4.</p> -<br> -<center><i>March 8, 1889, Twentieth Meeting</i>.</center> -<p>The following amendments to the By-Laws were adopted.</p> - -<p>[For Article VI substitute the following]:</p> - -<center>ARTICLE VI.<br> -<br> -<small>MEETINGS</small>.</center> - -<p>"Regular meetings of the Society shall be held on alternate Fridays, -from November until May, and excepting the annual meeting, they shall -be devoted to communications. The Board of Managers shall, however, -have power to postpone or omit meetings, when deemed desirable. Special -meetings may be called by the President.</p> - -<p>"The annual meeting for the election of officers shall be the last -regular meeting in December.</p> - -<p>"The meeting preceding the annual meeting shall be devoted to the -President's annual address.</p> - -<p>"The reports of the retiring Vice-Presidents shall be presented at the -meetings in January.</p> - -<p>"A quorum for the transaction of business shall consist of twenty-five -active members."</p> -<br> -<p>In Article V, the following paragraph was introduced immediately after -the first paragraph of the article:</p> - -<p>"The dues of members elected in November and December shall be credited -to the succeeding year."</p> -<br> -<p>The following papers were then presented: "A Trip to Panama and -Darien," by Mr. R. U. Goode, and "Survey of Mason and Dixon's Line," by -Mr. Mark B. Kerr.</p> - -<p>A Trip to Panama and Darien, to be published in the "National -Geographic Magazine," Vol. I, No. 4.</p> -<br> -<center><i>March 22, 1889, Twenty-first Meeting</i>.</center> -<p>The paper of the evening was entitled, "Recent Events in the U. S. of -Columbia," by Mr. W. E. Curtis. The discussion which followed was -participated in by Messrs. Baker, Gannett, and others.</p> -<br> -<center><i>April 5, 1889, Twenty-second Meeting</i>.</center> -<p>The paper of the evening was entitled, "House Life in Mexico," by Mr. -A. B. Johnson.</p> -<br> -<center><i>April 19, 1889, Twenty-third Meeting</i>.</center> -<p>This meeting was devoted to papers upon the Samoan Islands. The -following programme was presented:</p> - -<p>"Samoa; the General Geography and Hydrography of the Islands and -Adjacent Seas," by Mr. Everett Hayden.</p> - -<p>"Climate," by Prof. Cleveland Abbe.</p> - -<p>"Narrative of a Cruise Among the Islands," by Capt. R. W. Meade, U. S. N.</p> - -<p>"The Home Life of the Samoans and the Botany of the Islands," by Mr. W. -E. Safford, U. S. N.</p> -<br> -<center><i>May 3, 1889, Twenty-fourth Meeting</i>.</center> -<p>The paper of the evening was entitled, "Across Nicaragua with Transit -and Machéte," by Mr. R. E. Peary, U. S. N. To be published in the -"National Geographic Magazine," Vol. I, No. 4.</p> -<br> -<center><i>May 17, 1889, Twenty-fifth Meeting</i>.</center> -<p>The paper of the evening was entitled, "The Krakatoa Eruption," by Dr. -A. Graham Bell. The paper was discussed by Captain C. E. Dutton.</p> -<br> -<br><a name="chap4"></a> -<br> -<br> -<center>(Translated by Mr. R. L. Lerch.)</center> - -<h3>INTERNATIONAL LITERARY CONTEST</h3> - -<p>To be held at Madrid, Spain, under the auspices of the Commission in -charge of the celebration of the Fourth Centennial Anniversary of the -Discovery of America.</p> -<br> - -<center>P<small>ROGRAM</small>.</center> - -<p>The work for which a prize is offered is to be a prose essay, a true -historic picture giving a just estimate of the grandeur of the occasion -to be celebrated.</p> - -<p>So much has been written on this subject since the opening of the XVIth -century that it would seem difficult to say anything new and good. -Perhaps the details, perhaps the circumstances in the life and acts of -Columbus are worthy of no little research; but already the Royal -Academy of History is engaged in the erudite and diligent task of -bringing together and publishing the un-edited or little known papers -bearing on this question.</p> - -<p>The book required by this contest must be of a different nature: it -must be comprehensive and synoptic, and must be sufficiently concise -without being either obscure or dry.</p> - -<p>Although there is an abundance of histories of America, of voyages and -discoveries, of geographic science, and of the establishment of -Europeans in remote regions of the earth, there is no book that sets -forth as it can be done the combined efforts of the nations of the -Iberian peninsula, who, since the commencement of the XVth century, -have, with a fixity of purpose and marvelous tenacity, in almost a -single century of silent efforts brought about the exploration of vast -continents and islands, traversed seas never before cut by Christian -prows, and in emulous strife obtained almost a complete knowledge of -the planet on which we live.</p> - -<p>There is a growing interest and manifest unity in all those more -important events; not to mention the circumstantial evidence borne by -the charts of 1375 and the semi-fabulous voyages, such as that of Doria -y Vivaldi and others less apocryphal though isolated and barren of -results, like that of Ferrer, begun in 1434, when Gil Eannes doubled -Cape Bojador, discovered Guinea, and dispelled the terror inspired by -the unknown ocean, and ended in 1522 with Elcano's arrival at Sanlucar -after circumnavigating the globe.</p> - -<p>In all this activity very little occurs by chance. The progressive -series of geographic discoveries, due to persistent premeditation and -not to accident, was inaugurated at Sagres by the Infante D. Enrique -and his illustrious pilot Jaime de Mallorca.</p> - -<p>Well might Pedro Nuñes exclaim that from that time forth until the form -and size of the terraqueous globe were thoroughly known, the most to be -obtained would not be firmly established, "unless our mariners sailed -away better instructed and provided with better instruments and rules -of Astronomy and Geography than the things with which cosmographers -supplied them."</p> - -<p>The culmination in the progress of that beautiful history falls on the -12th of October, 1492, when Columbus was the first European to set foot -upon the intertropical shores of the New World. But this act, -considered apart from its intrinsic value, as purely the individual -inspiration of a mariner and the generous enthusiasm of a patron Queen, -derives a higher value when regarded as part of a summation of efforts, -a grand development of an idea, a purpose to explore and know the whole -globe, to spread the name and the law of Christ together with the -civilization of Europe, and to reap a harvest of gold, spices, and all -the riches of which costly samples and exaggerated reports were -furnished by the traffic of the Venetians, Genoese and Catalonians, who -in turn got them from Mussulmans.</p> - -<p>Doubtless the moving cause, whose gorgeous banner so many men of our -peninsula followed, was clothed in great sentiments, good or bad; their -hearts were filled with religious fervor, thirst for glory, ambition, -Christian love, cupidity, curiosity, and violent dissatisfaction (even -during the Renaissance), to seek and undergo real adventures that -should surpass the vain, fruitless, and fanciful adventures of -chivalry; and to make voyages and conquests eclipsing those of the -Greeks and Romans, many of which, recorded in classic histories and -fables, were now disinterred by the learned.</p> - -<p>What must be described is the complete picture in all its sumptuousness -so that its magnificent meaning may stand out distinctly, without which -the conviction would be lacking that the studies, voyages, and happy -audacity of Bartolomé Diaz, Gama, Alburquerque, Cabral, Balboa, -Magallanes, Cortes, Pizarro, Orellana, and a host of others, do not dim -the glory of the hero whose centennary is to be celebrated, even though -it heighten and add greater luster to the work of civilization begun by -Portugal....</p> - -<p>The book here vaguely outlined must also contain a compendious -introduction, notices of voyages, ideas, and geographic progress up to -the date of D. Enrique's establishment at Sagres, and an epilogue or -conclusion of greater extent, in which are examined and weighed the -changes and progress that our subject has made, collectively, in the -civilization of the world—in the commerce, economics and politics of -the peoples, in regard to the broad field opened to the intelligent -activity of Europe, over which it could spread and dominate; the -abundance of data, sunken hopes, and more secure basis lent to the -studious and wise for the extension of our knowledge of Nature, the -unraveling of her laws, and penetration of her mysteries.</p> - -<p>The vast, elevated argument of the book requires it be a finished work -of art, not in fullness and richness of diction, but in plan and order, -in sobriety and unity of style, whose nobility and beauty must lie in -simplicity of phrase, correctness of judgment and richness of thought.</p> - -<p>There may enter into this contest any unpublished work written to this -end in Spanish, Portuguese, English, German, French or Italian.</p> - -<p>The tribunal that is to award the prize will be composed of two members -of the R. Acad. of History, and one member from each of the Spanish R. -Academies of Moral Sciences and Politics, and Exact and Natural -Sciences—all to be chosen by the Academies themselves.</p> - -<p>Furthermore, there will be included in the tribunal the diplomatic -representative of every power whose subject or subjects wish to enter -the contest, which is to be done through said representative or some -person duly appointed to act in his place.</p> - -<p>The tribunal will elect its presiding officer and will decide on the -best works by an absolute majority of all the jurors who take part in -the vote.</p> - -<p>Each work submitted in this contest must be neatly copied, in legible -writing, on good paper, without the author's name but with a quotation -to identify him afterwards.</p> - -<p>Each author will inclose a separate folded sheet on whose exterior is -written the quotation he has chosen and the opening sentence of his -work; within, he will write his name and residence.</p> - -<p>The folded sheets corresponding to the works that did not get a prize -will be burnt publicly without being opened.</p> - -<p>Though it is difficult to set a limit as to size, the works should not -have more reading matter than is contained in two volumes of the shape -and size of the complete works of Cervantes issued by Rivadeneyra in -1863-4.</p> - -<p>If the plan or purpose of any of the works require it, there may be -added another volume of documents, maps, or other illustrations.</p> - -<p>As it will take time to examine and judge the works, they should be -sent to the Secretary of the R. Acad. of Hist. prior to January 1, 1892.</p> - -<p>There will be first prize of 30,000 pesetas ($5,790) and a second of -15,000 pesetas ($2,895).</p> - -<p>Besides this, each of the two successful authors will receive 500 -copies of the printed edition of his work.</p> - -<p>It rests with the Centennial Commission to determine the number of -copies in the edition of each of the two prize works, and what -disposition is to be made of the copies that are not given to the -authors.</p> - -<p>These (the authors) keep the right to re-print and to sell their works, -and to translate them into other tongues.</p> - -<p>The Commission, however, will have the right, if either or both prize -works are in a foreign tongue, to have them translated and published in -Castilian.</p> - -<p>The Commission affix their seal to the preceding directions for the -information of the public and government of those persons who desire to -participate in the contest.</p> - -<blockquote>Madrid, June 19, 1889.</blockquote> - -<div align="right">The Vice President, D<small>UKE OF</small> -V<small>ERAGUA</small>. <br> -Secretaries, J<small>UAN</small> V<small>ALERA</small>, J<small>UAN</small> -F. R<small>IAÑO</small>. </div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The National Geographic Magazine, Vol. -I., No. 3, July, 1889, by Various - -*** END OF THIS PROJECT GUTENBERG EBOOK NATIONAL GEOGRAPHIC MAG., JULY 1889 *** - -***** This file should be named 50383-h.htm or 50383-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/0/3/8/50383/ - -Produced by Ron Swanson -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law 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. 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