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diff --git a/old/60195-0.txt b/old/60195-0.txt deleted file mode 100644 index c854d60..0000000 --- a/old/60195-0.txt +++ /dev/null @@ -1,3594 +0,0 @@ -The Project Gutenberg EBook of The Coming Ice Age, by C. A. M. Taber - -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 Coming Ice Age - -Author: C. A. M. Taber - -Release Date: August 29, 2019 [EBook #60195] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE COMING ICE AGE *** - - - - -Produced by Tim Lindell, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - - - - - - - - -[Illustration: No. 1. - -THIS MAP SHOWS THE SPREAD OF GLACIERS AND ICEBERGS, AND THE EXTENSION -OF SOUTHERN LANDS DURING ICE AGE AND ALSO THE DIRECTION OF WINDS AND -OCEAN CURRENTS.] - -[Illustration: No. 2. - -THIS MAP SHOWS THE SPREAD OF GLACIERS AND ICEBERGS AND THE DIRECTION -OF WINDS AND CURRENTS AT THIS DATE.] - - - - - THE - COMING ICE AGE. - - - BY - C. A. M. TABER. - - - BOSTON: - GEO. H. ELLIS, 141 FRANKLIN STREET. - 1896. - - - - - COPYRIGHT, 1896. - BY C. A. M. TABER. - - - GEO. H. ELLIS, PRINTER, 141 FRANKLIN STREET, BOSTON. - - - - -PREFACE. - - -The explanations given in the following pages, in which I have sought -to show the manner in which an ice age is being brought about, is an -extension of a treatise on “The Cause of Warm and Frigid Periods,” -which I published in a small edition in 1894. And, from the small -number of copies circulated, only a few came to the hands of persons -particularly interested in such matter. Yet there were instances of -its having proved of special interest to persons celebrated for their -geological attainments, and also to instructors in physical geography. -Besides, it received considerate notice in some of the leading reviews. -Being thus somewhat encouraged, and thinking that the subject was too -important to be neglected, I have given it further study during the -last year, and meanwhile have obtained additional information from -recent discoveries which has served to corroborate my views. Hence I -have been able to be more explicit in my explanations in the present -volume than in my earlier writings. Still, while acting as a pioneer in -the matter, it will be seen that I have only attempted to expose the -main outlines, as my age and failing health will not permit me to enter -into the voluminous details necessary for a full explanation. In order -to show why my attention has been turned to the great climatic changes -which have taken place during past ages, and now threaten the future, I -will repeat the introduction of my earlier publication, wherein I wrote -that “the reason why I have undertaken to explain the causes which have -brought about the warm and cold epochs is because of my being unable -to harmonize the several theories that have been published with the -general mode of action which nature pursues to-day. Having in the early -part of my life been employed for a score of years in the whaling -service, during which time my sea voyages were passed in cruising over -the North and South Atlantic, and over the Indian Ocean, from latitudes -north of the equator to the southern shores of Kerguelen Land, and -along the seas of Southern Australia, I also, in my searching, cruised -over the Pacific Ocean from the icy seas south of Cape Horn to the -northern latitudes of Alaska, and, from New Zealand in the Western -Pacific to the numerous islands in the tropical zone. And it may be -said that among the chief things to be learned on such voyages was the -direction of the prevailing winds and surface currents of the sea. Thus -the impressions then received were in mind when, in after years, I had -my attention drawn to the several theories advanced for explaining the -causes which produced the warm and frigid epochs. But, so far as my -marine experience goes, such theories have not harmonized with nature’s -mode of operating at this age of the world. Therefore, I have conceived -views which, to my mind, are more agreeable to the simple operations of -nature of which I have long been witness. Consequently, I have written -several short essays on climatic changes since 1880, and also letters -relating to the same subject, which have been published in _Science_ -and _Scientific American_. But the space allowed for the introduction of -such matter was necessarily too limited for so wide an explanation as -the subject required. The views then advanced I have again repeated, -with the addition of several facts pertaining to physical geography, -which, so far as I know, have never before been published.” - - WAKEFIELD, MASS., U.S.A. - June, 1896. - - - - -CONTENTS. - - - CHAPTER I. - - PAGE - - CAUSE OF COLD AND MILD PERIODS, 9–36 - - Traces of ancient glaciers in temperate zones, 9; - prevailing winds the main cause of the circulation of - the ocean waters between the tropical and temperate - zones, 10; general direction of prevailing winds, and - how, in connection with continents, they circulate the - surface waters of the sea, 11; high and low sea-levels; - separation of antarctic lands from South America, 12; - Captain Larsen’s discoveries in antarctic regions, - 13; how low lands south of Cape Horn were submerged, - 13; how the winds move more surface water southward - than northward, 14; Dr. Croll’s views on winds and - ocean currents, 16; under-currents of the ocean, and - how caused, 16; Gulf Stream currents, 17; antarctic - under-currents, 18; why the winds were able to force - more of the ocean waters southward than northward - at the close of the Tertiary age, 19; Mr. Alfred R. - Wallace’s views on Tertiary seas, 20; how the Cape Horn - channel affects the ocean currents, 21; cause of the - increase of cold in southern latitudes, 22; how the - Cape Horn channel is closed during ice age, and its - effect on ocean currents and temperature of southern - latitudes, 24; the melting of glaciers from southern - lands, 27; a salt sea requisite for circulation during - ice age, 28; direction of surface currents in southern - seas, 29; Humboldt current, 30; Agulhas current, 32; - temperature of arctic ice, 34; movement of southern - icebergs, 35; glaciers south of Cape Horn, 36. - - - CHAPTER II. - - HOW ICE PERIODS IN THE NORTHERN HEMISPHERE ARE BROUGHT - ABOUT, 37–54 - - Northern seas during Tertiary age, 37; Gulf Stream during - Tertiary times, 38; the origin of a cold period in the - northern hemisphere, 38; remarks on Gulf Stream and - arctic currents, 39; circulation of arctic waters, 40; - arctic channels during ice age, 41; how the weight of - glaciers in the northern hemisphere attracts the waters - of the southern seas during ice age, 42; Professor - Prestwich on the submergence of European lands, 43; - the great Atlantic tide rips the head-waters of the - Gulf Stream, 44; high sea-level of Atlantic calm - region, 45; tropical Atlantic currents, 46; Sargasso - Sea, 48; arctic and Gulf Stream currents, 49; Pacific - Ocean currents, 50; slow growth of an ice period, 52; - reduction of Cape Horn channel, 53; permanence of - antarctic glaciers elevated above the snow-line during - mild periods, 54. - - - CHAPTER III. - - SPREAD OF GLACIERS DURING COLD EPOCHS, 54–61 - - Spread of glaciers in tropical zone, 54; Professor Agassiz - on the origin of Galapagos Islands, 55; the bowlders - of Hood’s Island and rookery of Albatross, 56; alpine - flora of Galapagos and tropical America, 57; Mr. J. - Crawford on ancient glaciers in Nicaragua, 58; Cuba and - Republic of Colombia during ice age, 58; destruction - of animal life during glacial age, 59; temperature - of North Atlantic and Mediterranean Sea during ice - age, 60; temperature of ocean during warm epochs, 61; - generative age ascribed to warm eras; Professor Wright - on pre-glacial man, 61. - - - CHAPTER IV. - - THE GLACIERS OF THE TEMPERATE ZONE, 62–75 - - Professor Hitchcock on the early history of North America, - 62; glacial deposits of Nantucket and Martha’s - Vineyard, 63; Professor James Geikie on the glacial - deposits of Northern Italy, 64; California coast ranges - the work of Sierra glaciers, 65; ancient glaciers on - the Pacific slope north of California, 67; Professor - Geikie’s views on the ancient glaciers in the Salt - Lake region, 68; Colorado Cañon, 69; the conglomerate - deposits in the Appalachian district, 69; remarks on - the glacial boundaries in United States during ice age, - 70; sands of Florida, 71; ancient ice-sheets of the - plains west of the Mississippi River, 73; the driftless - region of Wisconsin, 74; tropical waters of North - Atlantic chilled during ice age, 75; the drifted snow - of British America and Siberia during ice age, 75. - - - CHAPTER V. - - REMARKS ON THEORIES ADVANCED FOR EXPLAINING ICE PERIODS, 76–93 - - Professor Geikie on supposed causes of the glacial period, - 76; change in the relative level of the land and sea - during glacial and post-glacial times, 77; submergence - of northern lands at close of ice age, 78; the main - cause of the movement of water from the northern seas - at the close of glacial age, 79; why the earth-movement - hypothesis should be rejected, 79; glaciers of Europe - and Alaska, 80; North Pacific currents, 81; why the - Pacific waters are growing cool, 82; the lowering - temperature of the northern seas, 83; the increase of - cold in Europe and Asia, 84; falling temperature of - the Andean region, 85; General Drayson’s astronomical - discoveries for explaining the cause of ice periods, - 87; why the Gulf Stream was always confined to the - North Atlantic, 89; the improbability of the Indian - Ocean currents entering the arctic seas, 90; why the - increase of glaciers must continue while the Cape Horn - channel maintains its present capacity, 91; comments on - the coming ice age, 92; tropical zone the abode of man - during ice age, 93; preservation of the tropical ocean - fauna through the glacial period, 93. - - - - -CHAPTER I. - -CAUSE OF COLD AND MILD PERIODS. - - -It is now generally conceded by those who have given the subject much -attention that the greater portion of North America above the latitude -of 39° north to the shores of the Arctic Ocean has been furrowed and -scoured by the action of ice. - -Vast traces of ancient glaciers are also found in Europe; for it is -reported that ice-sheets have left unmistakable marks of having overrun -the greater part of the lands lying between the arctic seas and the -latitude of the Pyrenees. - -In Asia evidences of glacial action have been noticed from Northern -Siberia to the mountains of Syria. - -The great glaciers of Himalaya have in times past attained gigantic -proportions. In Northern China huge bowlders are found scattered over -the valleys, and a long distance from the mountains. - -The southern hemisphere, in proportion to the extent of its land -surface, shows ample traces of former ice action. From the latitude of -38° south to the southern extremity of the western continent there is -said to be the clearest evidence of former glacial action in numerous -bowlders scattered over the land. - -On the shores of the South Pacific, from the Island of Chiloe to -Cape Horn, the coast is fringed with deep fiords, which appear to be -channelled out by ice, like the fiords of Norway and Greenland. And at -this date the mountains of that southern region are covered with snow, -and the glaciers which flow down the valleys are said to reach the -tide-water as far north as the latitude of 47° south. The glaciers of -New Zealand, now of Alpine proportions, during the ice age descended -to the sea, and channelled the deep fiords on its south-western coast; -and certain traces of glacial action have been observed in Southern -Australia, and also in the province of Natal, South Africa. - -Kerguelen Land is pierced with deep, narrow fiords, which have the -appearance of having been the work of ancient glaciers. - -The lands south of the antarctic circle are to-day supposed to be -covered by an ice-sheet, of which the great ice barrier surrounding -that region furnishes ample proof. - -While impressed with the above reports of the work of ancient -glaciers, in connection with my own observations along the shores of -the several oceans, I have been led to seek for the physical causes -which brought about the great climatic changes of past geological -ages. And, while having the subject under consideration, I have had my -attention directed to the manner in which the great prevailing winds in -connection with continental lands are able to move the heated surface -waters of the tropical oceans into the colder zones, and also transfer -the cold waters of the higher latitudes into the tropical zones. - -And it is through this grand movement of the ocean waters that we are -enabled to account for the difference in the temperature of places now -lying in the same parallels of latitude. - -The natural methods for conveying tropical heat into the higher -latitudes, and also for excluding it therefrom, are so simple and -efficient that on due consideration we are able to conceive how epochs -possessing mild climates have been succeeded by periods of frigidity. - -It has been admitted by several writers on climatic changes that, -should the tropical surface waters of the ocean be moved into the -high latitudes in large volume, thus adding their warmth to the heat -imparted by the sun, such combined heat would cause a mild climate. -And it has been estimated that the amount of equatorial heat moved -into the temperate and polar regions of the northern hemisphere by -the Gulf Stream alone is equal to one-fourth of all the heat received -from the sun by the North Atlantic from the tropic of Cancer to the -arctic circle. Still, it appears to me, while viewing the subject from -a marine standpoint, that the explainers of climatic changes have never -fully comprehended the manner in which the surface waters of the ocean -are moved from the tropics into the high latitudes, and returned from -the high latitudes to the tropics. Consequently, they have neglected -necessary and efficient natural agents in their explanatory theories, -and with much learning and ingenuity have laboriously sought to show -how great changes of climate could be brought about through other -causes. - -But when we notice the simple methods employed by nature to-day for -transferring the heat of the tropics into the higher latitudes, and -also the manner of excluding such heat therefrom, they appear to afford -an explanation for the great changes of climate which have taken place -during past ages; for it appears that the natural manner of proceeding -by which heat is moved from the torrid zone into the high latitudes -sufficient to cause a mild climate is through the ocean currents which -are constantly set in motion by the great prevailing winds of the -globe. These winds, as is well known, blow mostly from the east toward -the west in the tropics, and from the west toward the east in the high -latitudes. - -This counter-movement of the winds, in connection with a continent -extending both northward and southward from the equator over many -degrees of latitude, such as obtains on the western continent, is -abundantly able to create extensive depressions and elevations on -the ocean’s surface, and thus cause vast streams of water to move by -gravity from the high sea-levels to the low sea-levels; and in this -way the tropical waters have been moved during past ages, and to a -considerable extent are now moved far into the northern and southern -seas. - -This transfer of the ocean waters is the main cause of a temperate -climate being enjoyed by countries situated in the high latitudes at -this age. - -But, in order that the tropical currents should be able to flow into -the high latitudes, in quantities sufficient to cause all lands and -seas situated in such latitudes to enjoy a mild climate, it would be -necessary that the land should extend unbroken, or nearly so, from -the arctic to the antarctic circles. Thus, with a continent of such -vast extent, the westerly winds would blow the surface waters of the -ocean away from the eastern shores in the high latitudes, and so cause -extensive low sea-levels; while the easterly winds of the torrid zone -would heap the surface waters of the ocean against the eastern tropical -shores of the continent. Consequently, the warm waters of the tropical -high sea-level would be moved by gravity to the low sea-levels of the -high latitudes, even to the arctic and antarctic regions, and thus -afford them a mild climate. In this way we account for the mild climate -enjoyed on lands and seas within the high latitudes during the warm -epochs anterior to the glacial periods. - -As the western continent is the only land that extends unbroken from -the equator to the cold latitudes of both hemispheres, thus affording -an opportunity for the prevailing winds to move the tropical waters -into the high latitudes, I will call attention to that portion of the -continent which extends far southward into the southern ocean, where -the winds and ocean currents have the greatest range and power to -affect the climate on different parts of the globe. Here we see South -America separated from the antarctic continent by a wide channel of -deep water, where the westerly winds blow with great force. The space -now covered by this interesting channel, owing to its being situated in -the high southern latitudes, must have been occupied by a channel of -comparatively small capacity, or else an isthmus of low land uniting -the southern portion of South America with the antarctic continent -during the warm epochs when the beds of the ancient seas of the -northern hemisphere contained a considerable portion of the water now -swelling the southern ocean. - -Therefore, the obstructions which separated the Pacific Ocean from -the South Atlantic furnished opportunity for the westerly winds to -force the surface waters of the sea away from the leeward side of such -obstructions, causing a vast low sea-level, sufficient to attract the -tropical waters heaped against Brazil by the trade winds into the -southern seas in adequate quantity to cause a mild climate throughout -the antarctic regions through long periods of time. - -Recent discoveries have proved that these high southern latitudes have -been subject to great changes of climate. According to the reports -from the Dundee whalers, while searching for seal in the icy seas that -surround the South Shetlands, they met with the Norwegian ship “Jason,” -Captain Larsen, who had traced the eastern shore of Graham Land to 68° -south latitude, noting two active volcanoes. - -The same mariner brought from Seymour Island fossil shells and -coniferous wood of the Tertiary epoch. - -These furnish sufficient evidence to show that a warmer climate once -prevailed there. - -At the commencement of the glacial age the obstructions which separated -the South Pacific from the South Atlantic had become deeply submerged -by the sea, which may have been caused by a tendency of the ocean’s -waters to move southward or by a comparative small movement in the -earth’s crust. But, on account of the stability of the crust of the -earth during times so late as the glacial epochs, the submergence of -this southern region was probably owing to the movement of the ocean’s -waters from the northern hemisphere into the southern hemisphere, -which appears to have been brought about mostly through the agency of -the great prevailing winds; for it seems to have happened that the -prevailing winds on account of the disposition of the lands and seas -were able to move more of the ocean waters southward than they moved -northward during the age preceding the glacial periods. The waters -thus slowly and gradually forced into the high southern latitudes -must have deprived the northern hemisphere of their heaviness, and -added their weight to the southern hemisphere. Therefore, the waters -moved southward could not all be returned to the seas of the northern -hemisphere by gravity, for the reason that the earth’s centre of -attraction would change in accordance with the weight of water moved -from the northern hemisphere into the southern. It will thus be seen -that, while the northern seas were drained or became shallow, the -augmented southern oceans deeply submerged the region south of Cape -Horn, thus widely separating the western continent from the antarctic -lands. - -Although the south-east trade winds on the eastern sides of the -Atlantic and Pacific Oceans extend further northward than the -north-east trade winds extend southward, owing to the heated tropical -shores north of the equator being more extensive than such lands -south of the equator, still, on account of the general weakness of -the south-east trade winds at the equator, and also because of the -obstructing northern lands, they have during remote times, and at this -age, been largely prevented from impelling the surface waters of the -sea into the northern latitudes in opposition to the brisk north-east -trades. Furthermore, on account of the widening of the oceans as they -extend southward, the surface currents setting in the latter direction -have more broad and easy passages than the great currents setting -northward. - -Moreover, the great currents setting southward on the western sides -of the oceans south of the equator are also much assisted during the -southern summer months by the strong north-east monsoons which prevail -along the east coast of equatorial Africa and the east coast of South -America as far as the latitude of 30° south. - -The South African current is impelled northward by the trade winds down -the south-western coast of Africa; but it is debarred from entering -the northern latitudes by the Guinea currents, and so turned away into -the south equatorial current which flows into the Brazilian stream. - -The Gulf Stream is much obstructed in its northern movement by the -narrow Florida channel and the opposing arctic currents, and also -by the trend of the North American coast eastward; while its return -current on the eastern side of the Atlantic has a much less obstructed -passage in its southern movement, and, while on its way past the Azores -and Madeira Islands, is largely assisted by the prevailing winds. - -The Brazil current, with the impelling force of a strong north-east -monsoon during the summer season, has no obstruction whatever in its -southern passage until it meets with an offshoot from the great drift -current of the southern ocean. - -And the same favorable conditions are obtained by the great currents -setting southward on the western sides of the South Pacific while on -their way to the low sea-levels east of Southern Australia and New -Zealand. That portion of the equatorial stream of the Pacific which -continues west across the Indian Ocean finds no open passage to the -northern seas. Consequently, it turns south along the east coast of -Africa into the southern seas. - -Therefore, this current, in connection with the great currents setting -southward east of Australia, offsets the great Humboldt current setting -north along the coast of Peru. - -In the North Pacific the Japanese current setting northward is -obstructed by the narrowing of the ocean; while its return current -on the American side has a constantly widening ocean on its passage -southward, and also favorable winds to impel the surface waters toward -the equator. Still, with all the facilities above mentioned for the -movement of the ocean waters into the southern latitudes, it is -probable that since the shallow seas of the northern hemisphere were -drained, or much diminished, the prevailing winds have not possessed -sufficient force to further augment the southern seas, because of the -superior weight of the land in the northern hemisphere compared with -the lands south of the equator. - -It will appear to those who attribute the rotation of the earth as -being the main cause of ocean currents that I am too much given -over to the wind theory. But I have reason to believe, as Dr. Croll -has asserted, that “the winds are the principal cause of the ocean -currents, and are not due to the trade winds alone, but to the general -impulse of the prevailing winds of the globe.” - -Dr. Croll also declares that “all of the principal currents of the -globe are moving in the exact direction which they ought to move, -assuming the winds to be the sole impelling cause.” - -Those who think that the rotation of the earth is the real cause of -the movement of the great surface currents of the sea should explain -in some reasonable way why the Agulhas current turns west into the -Atlantic from the Mozambique stream, and why the Guinea current turns -to the east from the main tropical current of the North Atlantic; for -it seems that these two great currents move in direct opposition to the -rotation theory, while at the same time many things go to show that -they receive their motion from the winds. This view of the question -will receive further attention in succeeding pages. - -It is the opinion of some writers that a difference of temperature -and density between the waters of the polar latitudes and the torrid -zone is the principal cause of the movement of the surface waters of -the ocean from the equatorial latitudes toward the polar seas, and -so returned in under-currents; and this is a favorable factor for -assisting the winds on some parts of the sea, especially in aiding the -Brazil current in moving the surface waters from the high sea-levels -abreast Brazil, and the equatorial calm belt of the Atlantic into the -southern ocean, and also for favoring the surface currents setting -southward on the western sides of the South Pacific and Indian Oceans. - -Yet, whatever gravitating force it may possess for assisting the -above-named currents, it would also act against the impelling force of -the trade winds, while they were drifting the surface waters northward -toward the equator on the eastern sides of the several oceans, and also -to retard the returning surface currents, while being drifted by the -winds southward on the eastern sides of the North Atlantic and North -Pacific. Therefore, while it would seem to favor the winds in their -work on the one hand, it would act as an opposing agent on other parts -of the ocean. Still, the difference of temperature between the tropical -and antarctic seas probably does act in opposition to the wide and -brisk trade winds on the eastern sides of the great oceans south of the -equator, and so prevents their impelling the surface waters northward -to a great extent; and this seems to be one great cause of there being -less surface water moved northward than southward over the greatest -oceans of the globe. - -The theory that the difference of density caused by the difference -of temperature between the polar seas and the equatorial oceans made -under-currents to flow from the polar latitudes, and meet in the -equatorial seas, can only be carried on in the Atlantic Ocean, and in a -comparatively less perfect way in the Pacific Ocean, and not at all in -the Indian Ocean. - -The North Atlantic being open to the Arctic Ocean, a portion of the -Gulf Stream waters that enter it from the north-west of Europe do sink -and return southward in under-currents; and the cold waters which pass -down the east and west coast of Greenland also sink under the Gulf -Stream while on their southern movement. The meeting of these arctic -currents with the cold under-currents from the antarctic seas in the -tropical zone is probably one cause of their cold waters rising near -the surface of the sea in the torrid latitudes of the Atlantic; and -the same conditions probably obtain in a somewhat less degree in the -Pacific Ocean. - -Yet it appears that the cold waters of the Antarctic occupy the largest -space in the tropical zone, even in the North Atlantic. Dr. Carpenter, -in his lectures on Ocean Currents, speaks of meeting with antarctic -water so far north as the latitudes of the West India Islands; and -he also says that all of the Pacific Ocean at its depths is supplied -from the Antarctic Ocean, as are the cold under-waters of the tropical -Indian Ocean, which extend over twenty degrees north of the equator. - -Thus, from what we can learn of the antarctic under-currents, they seem -to show that they are not wholly attracted northward on account of -the difference of temperature between the antarctic and the tropical -oceans, but partly because of more surface water being moved southward -by the prevailing winds than they are able to move northward. - -And it appears that, if through the winds, combined with the difference -of temperature between the antarctic seas and the equatorial waters, -and also because of the oceans widening toward the south, more surface -water is being carried southward than northward, the waters of the -under-currents so caused must rise toward the surface in the latitudes -from which they were first removed. Having called attention to the -fact that the prevailing winds are not able at this date to augment -the southern ocean waters from the scanty northern seas, because of -the preponderance of northern lands, still there is reason to believe -that even now, owing to the form of continents and oceans, and the -attraction of the tropical surface waters into the Antarctic Ocean -because of the difference of density between the warm and cold seas, -the prevailing winds of this age are able to force more of the surface -waters of the sea southward than they force northward; but, owing to -the superior weight of the land in the northern hemisphere, the surplus -surface water forced into the southern seas is returned by gravity -after being cooled by the antarctic ice, and so adding to the deep -under-currents which flow with a sluggish movement over the bottom of -the sea into the tropical and northern temperate latitudes. And in this -way the northern oceans are maintained at their present sea-level. - -The cold under-currents are probably assisted in their northern -movement by whatever difference there may be in the density of the -antarctic waters over the bottom waters of the equatorial seas. But, -as such currents extend into the northern tropical latitudes of the -northern hemisphere, it seems that the winds are the main cause of the -under-currents which carry so much antarctic cold into the northern -tropical seas, because the winds have forced an undue proportion -of ocean surface water southward, to be attracted northward in -under-currents by the preponderating northern lands. - -Yet, notwithstanding the superior weight of land in the northern -hemisphere, it appears that there have been periods when there was -somewhat more water in the oceans of the southern hemisphere than now; -for it is reported that a portion of the low lands of Australia show -traces of having been submerged during late geological times. - -This may have happened through an increased weight in the antarctic -glaciers, which have in past ages, and probably may in future epochs, -cause more of the ocean waters to be attracted southward than now -obtains. But it is probable that an increase of southern ice would be -largely counterbalanced by the accumulation of ice on northern lands. - -Yet it appears certain that since the Tertiary epoch the waters of -vast shallow seas have been moved from the northern hemisphere into -the southern. The dry beds of the ancient northern seas encourage this -opinion, while the comparatively small area of southern lands serves to -support such views. - -Still, during the ages prior to the glacial periods, while the low -lands of the northern hemisphere were covered by the sea, the wide -shoal channels which submerged the lower portion of North America -afforded convenient passages for the surface waters of the ocean in -their northern movement, and so prevented the oceans of the southern -hemisphere from gaining undue preponderance. - -Hence long geological ages passed away before the winds were able -to force more of the ocean waters southward than they could move -northward, and thus augment the southern ocean from the waters of the -northern seas. But the slow growth of such immense marine deposits -in the shallow seas as are found in the Florida Peninsula and other -portions of that region was at length sufficient to greatly obstruct -the passage of the Gulf currents in their northern movement, and thus -cause conditions which enabled the winds to force more of the ocean -waters southward than they could move northward after the close of the -Tertiary epoch. - -Mr. Alfred R. Wallace says in “Island Life” that the seas in the -northern hemisphere during the Tertiary period covered a much larger -area than now, and extended across Central Europe and portions of -Western Asia, and the Arctic Ocean was enlarged. - -As it is not likely that any portion of the waters of the sea have been -absorbed by the earth during the late epochs in the world’s history, -therefore the ocean waters have not diminished except during cold -periods, when the water evaporated from the sea was converted into ice, -and, eventually, again returned to the sea. - -Thus it necessarily follows that, when the seas of the northern -hemisphere contained a much larger portion of the waters of the globe -than at this age, the seas of the southern hemisphere must have -contained proportionally less. Consequently, during such times a -portion of the shoal seas of the high southern latitudes must have been -dry land. Therefore, this must have been the condition of the shallow -sea basins in the region of Cape Horn. - -Mr. Wallace also says that “many peculiarities in the distribution of -plants and some groups of animals in the southern hemisphere render it -almost certain that there has sometimes been a greater extension of -antarctic lands during Tertiary times.” - -And he also asserts that the great ocean basins have not changed, and -that the form of continents has been permanent. It will thus be seen -that it was through the movement of the ocean’s waters southward that -the low lands south of Cape Horn were covered with water previous to -the frigid periods, and so caused the wide separation between the -western continent and the antarctic lands. - -The Cape Horn channel thus enlarged, the continuous mildness of the -high southern latitudes which possessed the earlier ages came to an -end, and gave place to alternate epochs of frigid and mild weather. -For it appears that it is owing to the creation or enlargement of the -Cape Horn channel that it is possible for frigid periods to be brought -about, for the reason that its enlarged space of water prevents the -westerly winds from maintaining a great low sea-level in the higher -latitudes of the southern ocean; for, whenever the capacity of the Cape -Horn channel is enlarged, the westerly winds, instead of maintaining a -low sea-level on the South Atlantic, employ their force in impelling -the surface water of the southern seas around the globe. And this work -the strong westerly winds of the high southern latitudes have always -accomplished whenever the Cape Horn channel was widely open, and this -is what the winds are doing at this date. - -Therefore, such waters of the torrid zone as are moved southward from -their high sea-level, caused by the trade winds abreast the Brazilian -coast, are largely turned away from the high southern latitudes. It is -true, even with an enlarged Cape Horn channel, they can always flow -along the South American coast to an inferior low sea-level, caused by -the westerly winds blowing the surface waters of the sea away from the -coast of Argentine and Patagonia; but on gaining that region they meet -the cold ice-bearing currents which turn away east of Cape Horn from -the great southern drift current to gain the same low sea-level which -attracts the Brazil water. Consequently, the ice-bearing currents from -the south, which branch off from the great southern drift current, are -able to largely turn away the warm Brazil current from the higher -southern latitudes; and, furthermore, the great southern drift current -which passes through the Cape Horn channel, and so onward around the -globe, also partly turns away the Mozambique current as well as the -East Australian current, and so largely prevents their waters from -warming the southern seas. - -Therefore, it is evident that, whenever the Cape Horn channel obtains -sufficient capacity to give an independent circulation to the southern -ocean, the conditions are favorable for the increase of cold in the -southern latitudes. For it is because of the large exclusion of the -tropical waters from the southern seas that ice-sheets have been -able to form in early periods and in later epochs on the antarctic -lands, and store away the annual frosts for thousands of years, and -at the same time furnish icebergs sufficient to chill the waters of -the southern temperate oceans, and consequently make cold such of the -surface waters of the sea as are forced into the southern latitudes by -the winds in surface currents, and so returned to warmer seas in cold -under-currents, and thus with such frigid combinations bring about cold -periods. - -Thus it appears, as I have previously shown, that it is owing partly -to there being more of the surface waters of the sea forced southward -by the prevailing winds than they impel northward that the cold -under-currents are maintained; but it also requires an independent -circulation of the southern ocean, such as I have pointed out, to cool -its surface waters before they can sink and form cold under-currents. - -And there is reason to believe that such cold under-currents are more -efficient in lowering the temperature of the temperate and tropical -oceans than even the icebergs which such under-currents move into the -temperate seas. And, when it is considered that the cold antarctic -under-currents fill the depths of the Pacific and Indian Oceans in the -northern hemisphere, and also largely the tropical depths of the North -Atlantic, I am led to believe that the frigid conditions of the ice -age were concurrent in the northern and southern hemispheres. The main -reasons for such belief I will explain in the following chapter. - -After the foregoing explanations, showing how frigid periods are -brought about through the independent circulation of the southern ocean -surface waters, it is evident that, whenever through a slow natural -process the Cape Horn channel is closed, a great change is wrought in -the circulation of the southern ocean. - -For instead of the westerly winds blowing the surface waters of the -southern seas constantly around the globe, and so turning away and -preventing the entrance of the tropical currents into the high southern -latitudes, the strong westerly winds, whenever the Cape Horn channel -is closed or greatly obstructed, would blow the surface waters away -from the Atlantic side of the closed channel, and so cause a great low -sea-level, sufficient to attract the ocean waters of the tropical high -sea-level abreast Brazil well into the southern seas. Therefore, it is -important to trace nature’s slow methods of closing the wide Cape Horn -channel at the perfection of an ice age. - -In my previous explanations on the subject I have thought that, should -the southern seas have remained at or near the same sea-level as now, -through an ice period brought about in the manner I have described, -ice-sheets would accumulate on the antarctic continent, and also on the -southern lands of South America, sufficient to flow out into the sea -and close the Cape Horn channel. - -But further consideration shows the impossibility of the southern seas -having maintained their present sea-level during the growth of frigid -epochs which have left such ample traces of glaciers having extended -widely over the lands of the high latitudes of both the northern and -southern hemispheres. For it appears that the larger areas of land in -the northern latitudes, embracing wide continents and large islands, -must, during the growth of a frigid age, have increased the spread of -glaciers many times greater in extent than could be obtained on the -smaller lands of the high latitudes of the southern hemisphere. - -For it is evident that the water evaporated from the sea and deposited -in snow on the large continents and islands of the high northern -latitudes during the growth of an ice period would, while thus -diminishing the ocean waters, greatly increase the weight of northern -lands. Therefore, the waters of the diminishing seas of the southern -latitudes would be attracted into the northern oceans in opposition to -the prevailing winds. - -Thus it appears that the Cape Horn channel would be too much reduced at -the perfection of an ice age to afford an independent circulation for -the southern ocean, even without being filled by glaciers to the extent -I have pointed out in previous essays. Still, to whatever dimensions -the Cape Horn channel might be reduced at the perfection of a frigid -period, the enlarged shores bordering its diminished waters would be -covered by heavy glaciers that would flow into the shrunken strait, and -so close it effectually. Thus the reduction of the Cape Horn channel -during the advance of an ice age seems, on close consideration, to be a -simple operation of nature, which in the normal course of events must -have taken place. - -As the closing of the Cape Horn channel has been considered by -reviewers the weak and questionable point in preventing my views from -gaining acceptance, it becomes necessary to be explicit concerning the -manner in which the Cape Horn channel has in past ages been obstructed. - -According to the charts prepared by John James Wild, the middle portion -of the strait is represented as being over a thousand fathoms in depth; -but, as far as I know, its true soundings have never been determined. -The deep portion of the mid-channel is described as being narrow -when compared with its whole breadth from Cape Horn to the antarctic -continent. - -And, when it is considered, with the growth of an ice age, how much of -the ocean waters would be stored in the vast ice-sheets of the northern -hemisphere, and consequently because of their weight a large portion of -the diminished southern oceans would be attracted into the northern -seas, it seems that the bottom of the shoaler waters of the Cape Horn -channel, which now comprise so large a portion of its breadth, would be -raised above the surface of the sea. - -The one-hundred-fathom depth south of Cape Horn, now supposed to extend -from longitude 70° west to 55° west, and southward to the latitude of -57°, would be a land supporting heavy glaciers for six hundred miles -along the north side of the reduced channel during the advanced growth -of a frigid age; and the same conditions would be obtained in the -vicinity of the South Shetland. And when, in addition, we contemplate -the great snow-fall of that region, and the consequent gathering of -glaciers which would occur on the widened shores of the lessened -channel, and the certainty of their flowing into the diminished strait, -together with the immense icebergs of such an age grounding in the -shoaled waters, it seems that the complete obstruction of the reduced -channel would be accomplished. - -While contemplating the conditions that would obtain while the Cape -Horn channel was being reduced, it will be seen that the independent -circulation of the icy southern ocean would be carried on to a -considerable extent even after the narrowing strait was no longer -able to afford space for wide drift currents, for the reason of the -strong current that would be caused on account of the high ocean-level -maintained by the westerly winds on the Pacific side of the diminishing -channel, and the great low sea-level that would take place on its -Atlantic side. - -Still, as previously shown, it seems that during an advanced stage of -the frigid epoch, the heavy glaciers from the enlarged northern and -southern shores of the shrunken channel, together with the ponderous -icebergs, blocking its waters, the closing process would at last be -speedy and effective. - -And on further consideration it might be said that a channel of much -less width and depth would not have been of sufficient capacity to -have caused ice periods so wide-spread as those that have left their -traces on the continents and islands of the globe, for the reason -that the independent circulation of the southern ocean would not have -been sufficiently complete and long continued to have brought such -world-wide cold periods to perfection. - -With the Cape Horn channel closed, as above explained, there would be, -as I have asserted, a great change wrought in the circulation of the -southern ocean; for instead of the westerly winds blowing its surface -waters constantly around the globe, and so turning away and preventing -the entrance of tropical currents into the higher latitudes, the strong -prevailing westerly winds would blow the surface waters of the sea from -the Atlantic side of the closed Cape Horn channel, and so cause a great -low sea-level, sufficient to attract the ocean waters of the tropical -high sea-level abreast Brazil well into the southern seas. - -The winds of the southern westerly wind-belt being stronger in that -region than on any other portion of the globe, consequently they are -able to do nearly as much work while drifting surface water as the belt -of westerly wind of greater width on other parts of the southern seas. -Thus a person who has had a long experience with the forcible westerly -winds of the southern ocean can well understand their ability for -disturbing the ocean waters in the latitudes of the Cape Horn channel. - -The drift currents of this region are moved by the winds and waves -from one to four miles an hour. Therefore, with the Cape Horn channel -closed, there is nothing more certain than that the westerly winds -would be able to cause a vast low sea-level on the Atlantic side of -the closed Cape Horn strait, and that the waters of the high tropical -sea-level abreast Brazil would be attracted to its wide depression, as -shown on map No. 1. - -The tropical waters thus attracted far southward would be cooler -than the tropical waters of to-day, owing to the great amount of -cold imparted to the ocean by the numerous icebergs of a frigid age. -Still, they would begin the slow process of raising the temperature -of the southern ocean, and would in time carry sufficient heat into -the southern regions to melt the ice from all southern lands; for, in -addition to the Brazil currents, the waters of the high sea-level of -the tropical Indian Ocean which pass southward down the Mozambique -channel would reach a much higher latitude than during periods when the -Cape Horn channel was open. - -The ice periods of the northern and southern hemispheres being -concurrent, a condition which I shall explain in another chapter, makes -it obvious that during the melting of the glaciers from the antarctic -continent and other southern lands the depleted Cape Horn channel -could not gain sufficient capacity to give an independent circulation -to the southern ocean during the melting of the southern ice-sheets, -on account of the diminishing heaviness of the antarctic ice and the -greater weight of the extensive glaciers and augmented seas of the -northern latitudes. Consequently, it seems that the southern seas would -continue in a lessened state while the glaciers were being melted from -the northern hemisphere, as was the case during the melting of the ice -from the southern hemisphere; and, furthermore, during such times the -glaciers which overrun all the low lands and shoal waters of the Cape -Horn region would, on account of their position being to the windward -of the tropical currents, be the last great mass of ice to melt from -the southern hemisphere. - -Therefore, it seems that the Cape Horn channel would continue closed -or greatly obstructed while the glaciers were being melted from the -lands of both hemispheres. Thus at length a mild climate would extend -over the globe, and so remain until the prevailing winds slowly forced -the surface waters of the sea into the southern ocean in the manner -explained in previous pages, thus filling the Cape Horn channel to its -present capacity, and again restoring the independent circulation of -the southern ocean. - -While contemplating the conditions that would obtain during the melting -of the ice from the antarctic lands, it will be seen that the tropical -waters attracted to the great low sea-level to the leeward of the -closed Cape Horn channel would eventually enter the great bight of -the antarctic continent to the eastward of Graham Land, where Captain -Weddell sailed to the latitude of 74° south. This deep gulf, owing to -its situation, would receive the full impact of the southern movement -of the tropical currents; and, as the warm waters spread over the -wide sea-level, the westerly winds would convert them into a drift -current, and under such conditions would be driven along the shores -of the antarctic continent, past the South Indian and Pacific Oceans, -and eventually, after undergoing a cooling process from the long icy -passage, be forced against the Pacific side of the closed Cape Horn -channel and the western Patagonian coast. - -While regarding the circulation of the sea during an ice age, it may -be said that the ocean’s being composed of brine was the cause of its -waters being able to circulate in frigid latitudes where fresh water -would congeal. Consequently, this is one of the reasons why successive -periods of frigidity and mildness have been brought about; for with an -ocean of fresh water, repeated epochs of cold and warmth could not have -occurred, because a sea composed of fresh water would have congealed -while circulating in the high latitudes during a frigid age. Therefore, -it required a sea of brine to maintain a liquid state during the low -temperature of an ice period. - -For, while the cold of a glacial age increased, the saltness of the sea -increased also, because of the great amount of fresh water evaporated -from the ocean, and stored in ice-sheets on the great continents and -islands of the globe. Thus the briny sea was maintained in a liquid -state, while washing vast ice-fields and glaciated shores and floating -the numerous icebergs of a freezing age. The cold which radiated -from such ice-bound seas must have been severe; but meanwhile the -evaporation from the ocean was much reduced, while the saltness and -coldness of the sea increased, and so prevented the ice of a glacial -period from gaining invincible proportions before the independent -circulation of the southern ocean was arrested. Therefore, the -remaining warmth of the tropical waters after gaining free access to -the antarctic latitudes was able to overcome the accumulated cold of -that frigid region. - -At this date the observant navigators who have visited the antarctic -seas report that the surface currents above the latitude of Cape Horn, -while being drifted eastward by the prevailing westerly winds, also set -toward the antarctic ice cliffs, as shown on map No. 2. - -The reason why this southerly set of the surface currents becomes -noticeable above the latitude of 55° south is because the tropical -currents which set southward from the torrid latitudes on the western -sides of the Atlantic, Indian, and Pacific Oceans, although largely -turned away from the high latitudes by the westerly winds and drift -currents, are also able to send sufficient water into the great -belt of westerly winds to furnish water for the deep under-currents -setting northward from the antarctic shores. Thus the surface waters -moving from the north in order to gain the higher latitudes, after -entering the westerly wind-belt, are moved in drift currents by the -impelling winds easterly over many degrees of longitude, and also at -the same time slowly southward among the cooling icebergs, because of -the attraction caused by the difference of temperature and density -between the northern drift waters and the icy seas of the antarctic ice -barrier. Consequently, the gradual movement of the surface waters of -the westerly wind-belt southward before entering the higher latitudes -is not generally apparent; for it is after they enter latitudes where -the globe becomes much reduced in circumference that their southern -movement in the contracted seas becomes more noticeable. The impact of -this southerly current, which finds its outlet in deep under-currents, -and retards somewhat the increase of ice on the southern continent at -this date, also largely prevents the small icebergs and field-ice from -floating northward, away from the antarctic ice barrier; for it is such -large icebergs as penetrate the deep under-currents that are the best -able to move into the more temperate latitudes. - -From the above explanations it will be seen that the impact of surface -water against the antarctic ice barrier when the Cape Horn channel -was closed would greatly assist the tropical waters attracted to the -great low sea-level to the leeward of the obstructed strait to wash the -antarctic shores while being drifted eastward by the westerly winds -over the southern ocean against the Patagonian coast and the Pacific -side of the closed channel, and there causing a high sea-level. This -movement of the winds and currents encircling the antarctic continent -is shown on map No. 1. - -The vast, high sea-level caused by the westerly winds drifting the -surface waters against the Patagonian coast would obtain a much higher -plain, were it not that so much of the water of the great drift current -was required to feed the antarctic under-current which constantly sets -northward from the antarctic shores; yet it would be sufficient to -greatly increase the volume of the Humboldt current, which would flow -in the same direction it now flows, down the South American coast to -the equatorial latitudes, where it would become the main source of the -great equatorial stream, and thus offset the increased southward flow -of the equatorial waters through the Brazil and Mozambique streams. - -The equatorial stream, with its increased volume, would also move, as -it moves to-day, across the Pacific; and, on gaining the western side, -after sending off large streams to the northern and southern latitudes, -it would pass through the East India passages into the Indian Ocean, -where it would be drifted westward by the trade winds and cause a high -sea-level abreast the east coast of Africa, and so become the source -of the great Mozambique current, which would flow southward along the -east coast of Africa, and, with the Cape Horn channel closed, would -gain a much higher latitude than it would with the channel open. At -this age, when the continuation of this great equatorial stream gains -the latitude of the Cape of Good Hope, its waters are largely turned -eastward by the great drift current of the southern ocean. - -Still, a considerable portion of its waters turns toward the west, -forming the Agulhas current, which flows around the Cape of Good Hope -into the Atlantic, where it mingles with the cooler currents which -branch off from the great southern drift current; and so, in connection -with the latter, it is attracted to the low sea-level caused by the -south-east trade winds abreast the south-western coast of Africa, -and from thence moved as a drift current by the trade winds to the -equatorial Atlantic and coast of Brazil. Thus it will be seen that the -Agulhas current, even with the Cape Horn channel in possession of its -present wide capacity, serves to retard somewhat the advance of a cold -period. - -The Agulhas current at this date also partly serves to replenish the -water which is forced from the South Atlantic by strong westerly winds -into the Southern Indian and Southern Pacific Oceans. For it appears -that more water is now removed by such winds from the South Atlantic -than enters it from the South Pacific, even through the enlarged Cape -Horn channel of this date; and this fact seems to favor an impression -that a portion of this enlarged channel existed prior to the glacial -periods, but with its waters so much reduced as to be unable to give -the southern ocean an independent circulation sufficient to exclude the -tropical currents from reaching the high southern latitudes in adequate -volume to maintain a mild climate in the southern hemisphere. - -For previous to the glacial age, with little or no ice gathered on -the antarctic lands, it seems that a strait possessing one-half the -capacity of the Cape Horn channel of the present age could not prevent -the Brazil current and the Agulhas stream from flowing into the -southern ocean in quantities sufficient to make it impossible for -glaciers to form on southern lands. - -Thus it is probable that a reduced channel separated the western -continent from the antarctic lands even in the mild eras previous to -the glacial epochs. - -The Cape Horn channel, at the present age, with a capacity sufficient -to largely maintain an independent circulation for the southern ocean, -is still only one-third of the breadth of the westerly wind-belt of the -southern seas. Therefore, the drift currents do not all pass through -it from the Pacific into the Atlantic. Consequently, a considerable -portion of the drifted water turns northward west of Cape Horn, and so -forms the Humboldt current. - -The Agulhas stream, which even now assists in replenishing the South -Atlantic with tropical water, would, during the perfection of a glacial -period, with the Cape channel closed, be a much stronger stream than -it now obtains with the Cape channel possessing its present enlarged -capacity, for the reason that the South Atlantic waters would continue -as now to be forced eastward by the westerly winds, while they could -not be replenished, as they are to-day, directly from the South Pacific. - -Consequently, the waters of the South Atlantic Ocean would be -correspondingly reduced. - -Such conditions alone would greatly increase the volume of the Agulhas -stream at the culmination of a frigid age. Therefore, the work of -subduing a frigid period in the southern hemisphere after the Cape Horn -channel was closed would not rest on the Brazil current alone, but also -on the great equatorial stream of the Pacific and Indian Oceans. - -Yet during such frigid times the sources of the equatorial stream would -be greatly chilled by its two great feeders, the Humboldt current and -the returning Japanese current, both of which flow down from the high -latitudes and meet in the equatorial latitudes on the eastern side of -the Pacific, thus cooling the source of the great equatorial current. - -But this latter stream, while on its long western passage across -the Pacific and Indian Oceans, beneath a torrid sun, with only -one cold feeder from the south which approaches it along the west -side of Australia, would, on its long tropical journey, be able to -obtain considerable warmth, even during an ice period, to supply the -Mozambique and Agulhas streams, and so greatly assist the Atlantic -waters in bringing about a mild period. Still, the process of subduing -the cold of the southern latitudes would be slow, even with the Cape -Horn channel closed, because of the vast collection of ice burdening -the sea and land. - -Yet there were conditions that were naturally brought about to favor -the process of returning warmth; for it appears that, when the southern -ocean was made shallow because of a considerable portion of its waters -having been moved into the northern hemisphere, it will be seen that -the conditions were more favorable for the westerly winds to create -drift currents than would be the case on deeper seas. Therefore, -the high and low sea-levels caused by such winds would be greater -on a shallow ocean than would occur on deeper waters. Thus the low -sea-levels of the shallow southern sea would have strong attraction -for tropical surface waters, and so increase the thickness of its warm -drift currents, and at the same time its lessened depths would have -less capacity for the storage of cold water to reduce the temperature -of the under-waters of the tropical zone. - -And, furthermore, when the southern ocean was shallow, New Zealand -acquired a longer extension of land to the north and south. -Consequently, the enlarged low sea-level on its eastern side attracted -more tropical water into the southern latitudes than now. - -So, according to the conditions I have pointed out, the ice-sheets -would at length melt away, and a long period of mildness would succeed -on account of the length of time it would require after the ice -disappeared from the earth for the prevailing winds to move the surface -waters of the augmented northern seas into the southern ocean, and -again restore its independent circulation, and so, after a considerable -lapse of time, bring about the geographical and climatic conditions -existing at the present date, which can be seen on map No. 2, which -shows that a cold period has already made considerable advance in the -southern hemisphere, the southern continent and islands being covered -with glaciers, and the prevalence of icebergs as far north as the -latitude of 35° south. - -Moreover, when we consider that the independent circulation of the -southern ocean is caused by the westerly winds blowing its surface -waters constantly around the globe through the open Cape Horn channel, -and so largely preventing the tropical currents from entering the -high southern latitudes, and how, in consequence, the cold is slowly -on the increase through the constant accumulation of ice on the lands -and in seas of the southern latitudes, it appears that a frigid age -is slowly progressing in the southern hemisphere. For it seems that -continental ice-sheets should not only be able to retain their freezing -temperature, but also the mean of the low temperature in which they -were formed, for a considerable length of time, and so impart their -extreme coldness in the shape of icebergs into such seas as border on -the glaciated lands. - -It has been proved at Point Barrow that strata of ice and gravel can -maintain a wintry temperature through the summer months. Captain -G. B. Borden, keeper of the refuge station in that region, states -that Lieutenant Ray, of the Signal Service, excavated through ice and -gravel to a depth of forty-one feet, and that the lower portion of the -excavation maintains a temperature 15° Fahrenheit above zero the year -around. Therefore, with the probability of southern glaciers obtaining -a temperature of over 15° Fahrenheit below the freezing point, we -can well realize the frigidity imparted to the southern oceans while -melting numerous immense icebergs, and consequently will conclude that -the temperature of the southern latitudes is gradually lowering. - -The icebergs of the antarctic seas would not move northward into the -temperature latitudes so readily as they now do, were it not that the -general southward set of the southern ocean currents were interrupted -by the movement of northerly surface currents in the longitudes of -the low sea-levels, caused by the westerly winds drifting the surface -waters of the sea from the eastern coasts of Southern South America and -New Zealand. For it is owing to the low sea-levels thus created, in -connection with the deep under-currents which set northward from the -ice cliffs of the antarctic lands, that many icebergs are enabled to -move into the temperate latitudes, especially to seas north-east of the -Falkland Islands. - -On other portions of the southern ocean above the latitude of 55° south -the surface waters, while being drifted eastward by the strong westerly -winds, also set toward the antarctic shores, and so furnish water for -the cold under-currents which set northward from that frigid region. -Thus from such parts of the coast only the largest bergs, which require -a deep sea to float them, are moved by the under-currents into the -temperate latitudes. Therefore, it happens that, while an ice period -progresses, and the antarctic icebergs increase in size, the more -readily the cold, deep under-currents force them into the temperate -zone, in opposition to the winds and surface currents. - -The icebergs, after gaining the temperate latitudes, are moved more -or less eastward by the westerly winds and drift currents, and so are -scattered over the southern temperate oceans, where the melting bergs -impart whatever coldness they were able to store up while forming in -the antarctic regions. - -The low sea-levels caused by the westerly winds to the leeward of New -Zealand and to the leeward of Argentine, not only cause the ice-bearing -currents to set northward, but they also cause the tropical currents to -make considerable inroads into the high southern latitudes. This is the -reason why the lands are less burdened with ice on the antarctic shores -opposite Cape Horn than on other parts of that glaciated continent. - -The tropical currents which turn southward east of New Zealand largely -mingle their waters with the great southern drift current, and so -are carried through the Cape Horn channel. Owing to this cause, the -antarctic lands abreast Cape Horn are less burdened with ice than other -portions of the antarctic shores. - -Thus, were it not for this penetration of warm waters southward, the -antarctic coasts south of Cape Horn, because of the great snow-fall of -that region, would obtain heavier glaciers than other portions of the -southern continent. But the time is slowly coming when, with a lower -temperature, the ice-sheets on the lands in the vicinity of the South -Shetlands will attain greater thickness than the glaciers on other -shores of the antarctic continent. - -Hence it appears that, when the several agents for producing -and distributing cold in the southern latitudes are taken into -consideration, the immense and continuous storage of ice on the -southern lands, which adds to the wide-spread fleet of icebergs that -float the southern temperate seas, and also the vast movement of -cold antarctic water into the temperate and tropical oceans in deep -under-currents, combined with the increasing coldness of the westerly -winds, are now slowly bringing about in the southern hemisphere a -period of frigidity. - - - - -CHAPTER II. - -HOW ICE PERIODS IN THE NORTHERN HEMISPHERE ARE BROUGHT ABOUT. - - -A large number of geologists are of the opinion that during the whole -of the Tertiary period the climate of the northern temperate and arctic -latitudes was uniformly warm, without a trace of intervening frigid -periods. I have before explained why the climate was made warm in the -southern hemisphere during the Tertiary epoch, and how on the closing -of that age, and subsequently, a considerable portion of the ocean -waters had moved from the northern hemisphere into the southern. - -Therefore, the northern seas during Tertiary times covered a much -larger area than have obtained during periods following that mild -epoch. So, when the low lands of Europe were submerged, the Baltic, -Caspian, and other neighboring seas, now land-locked, were a portion of -an enlarged Atlantic. Consequently, the westerly winds blew over a much -wider North Atlantic than during the later periods. - -Thus the high sea-level caused by such winds on its European side was -greater than has since been obtained with the Atlantic of less breadth. -This high sea-level, composed largely of drift water from the ancient -Gulf Stream, had convenient access to the enlarged Arctic Ocean, which -then covered the low plains of Northern Europe and Siberia. And owing -to the trend of elevated lands north-eastward, which then formed the -southern shores of the Arctic Ocean in those regions, the warm waters -of the high sea-level of the Eastern North Atlantic found an easy -passage into the arctic seas; for, while they moved over the European -and Siberian seas to the north-east, they had the assistance of the -westerly winds well into the arctic seas, from which position they -were attracted across the Arctic Ocean to the low sea-level abreast -Labrador and Davis Strait. - -The Gulf Stream of Tertiary times comprised a much larger area than it -now obtains; for with Florida and a large portion of the Gulf States -submerged, and a wide, shallow sea covering the Mississippi valley -and the Great Lake region, the tropical waters of the enlarged Gulf -of Mexico moved from their vast high sea-level to the low sea-level -abreast British America and Labrador, without being confined to the -narrow Florida channel. Thus with an enlarged Gulf Stream in possession -of a wide and clear passage leading northward, in connection with a -mild period in the southern hemisphere, giving warmth to the southern -oceans, the resources of the ancient Gulf currents for warming the -northern regions were so ample and inexhaustive they were fully able to -maintain a mild climate on the shores of the European seas, and also on -the shores bordering the Arctic Ocean, during the Tertiary epoch. - -Furthermore, the Humboldt current, which had its rise in the mild -southern seas of that age, mingled its warmth with the equatorial -current of the Pacific, which in turn gave its warmth to the Japanese -current. Therefore, the latter stream under such conditions was -competent to maintain a mild climate on the North Pacific coasts. - -The origin of a cold period in the northern hemisphere was largely -owing to the changed condition of the northern oceans following the -close of the Tertiary epoch. The movement of the ocean waters into the -southern hemisphere lessened the area of the Arctic and North Atlantic -Oceans, and brought them to their present reduced limits, and also -diminished the volume of the Gulf currents. - -This great geographical change, in connection with a cold period -progressing in the southern hemisphere, and so increasing the coldness -of the Japanese current, and the cold antarctic currents, previously -explained, which set northward on the bottom of the sea through the -torrid latitudes even into the North Pacific and North Atlantic -Oceans, were altogether sufficient to cause conditions favorable for -the advancement of a cold period in northern latitudes. Besides, with -reduced northern oceans and a diminished Gulf current, conditions were -favorable for an independent circulation of the arctic waters, such as -is being carried out at the present time. Hence an explanation of the -movements of the ocean waters of to-day will explain the conditions -which caused the northern ice periods in times past, as well as -those to come in a future age. Although the conditions are such that -the independent circulation of the arctic waters cannot be so well -performed as the independent circulation of the southern ocean, still -the open arctic channels are able to prevent the tropical Gulf Stream -water from largely entering the higher northern latitudes. For it is -certain that the prevailing westerly winds blow the surface waters of -the North Atlantic away from the eastern shores of North America from -Georgia to Labrador. - -Consequently, the low sea-level thus caused attracts the waters of -the Arctic Ocean southward through Baffin’s Bay and Davis Strait, and -likewise down the east coast of Greenland, thus surrounding that large -island with an arctic temperature, and so causing it to become a land -of glaciers, which are constantly launching icebergs into the sea to -cool the waters of the northern oceans. The tropical waters of the high -sea-level of the Gulf of Mexico also seek the low sea-level abreast the -American coast, thus causing the Gulf Stream. This great ocean current, -being the main conveyer of tropical heat into the high latitudes of -the North Atlantic, calls for particular notice. The great gravity -currents, of which the Gulf Stream is one of the most conspicuous, are -moved by small gradients. - -Hence the gradient which causes the Gulf Stream waters to move out -of the Florida passage is small. The levellings which have been made -place the surface waters of the Gulf of Mexico as being about one -metre higher than the Atlantic abreast New York, the pressure of the -higher Gulf waters toward the low level of the Atlantic being nearly -equal in the narrow Florida channel from the surface to the bottom of -the stream. Therefore, according to descriptions given by Commander -Bartlett, the warm stream moves like a river over the hard level floor -of the channel; but to the northward of the Bahamas, abreast Cape -Hatteras, the stream spreads out in fanlike form, and flows over a bed -of cold water of great depth. - -A bed of cold water is found to cover the bottom of all the deep oceans -that are accessible to the antarctic seas, through which the cold water -is mostly supplied, as I have before pointed out. - -But the cold water which underruns the Gulf Stream is probably -furnished by the arctic waters which move down Davis Strait and the -east coast of Greenland. The Gulf Stream, as it widens and becomes more -shallow, is, through its exposure to the westerly winds, gradually -converted into a drift current; and in this way its surface waters are -forced over abreast the shores of Western Europe, where it imparts its -warmth to a wide region, and also causes a high sea-level. A portion -of the waters of this high sea-level turn southward to replenish the -waters which have been moved by the trade winds from the eastern -tropical North Atlantic over into the Caribbean Sea and Gulf of Mexico, -while its northern and smaller portion mingles with the Arctic Ocean -waters north of Europe. These latter waters, having escaped from the -westerly wind-belt, and acquired a high sea-level, and also made cool -on mingling with the icy arctic seas, lose a part of their bulk on -becoming chilled by sinking and returning in under-currents to the seas -from which they were forced by the south-westerly winds; while the -larger remaining surface waters set across the Arctic Ocean over to -the northern coast of Greenland, and so down the east and west coasts -of that large island to the low sea-level abreast the American coast, -where the cold waters not only crowd the Gulf Stream from the shore, -but they also sink under it, and form the vast bed of cold water over -which the Gulf currents flow. This cold underflow of water southward -probably joins the deep antarctic currents south and south-east of the -Bermuda Islands, and returns to the tropical latitudes a portion of the -water that is carried into the Arctic Ocean by the Gulf Stream. - -There are times during the late summer and early fall months when the -arctic channels are considerably obstructed by icebergs, and the low -sea-level of Davis Strait and Baffin’s Bay, with the assistance of -occasional south-east winds, is able to attract the temperate waters -of the Atlantic as far north as the Arctic Circle. Also from the same -cause the icy waters which flow down the east coast of Greenland are -attracted along its southern and south-western shores into Davis Strait. - -Yet at the same time the icy waters which flow from Smith’s Sound and -other arctic channels move in a counter-current down the westerly -side of Baffin’s Bay and Davis Strait, and so carry the icebergs and -field-ice past Labrador and Newfoundland well on to the borders of the -Gulf Stream. And, according to Lieutenant Maury, the westerly gales of -the winter months force the temperate waters of the Atlantic, which -pertain to the Gulf Stream, several degrees away from the south-east -coast of Greenland. Therefore, during such seasons the surface waters -of the returned arctic currents, which flow down the east coast of -Greenland and Davis Strait, are drifted past Southern Greenland and -Iceland, and so onward into the arctic seas, north of Europe. Thus the -arctic waters maintain an independent circulation sufficient to largely -exclude the Gulf Stream from the arctic seas, and surround Greenland -with an arctic temperature; and it is on this account glaciers have -formed on Greenland and other arctic shores, and such glaciers are -probably increasing, as every iceberg launched from the frigid lands -and floated to the lower latitudes lowers somewhat the temperature -of the North Atlantic, and so causes conditions favorable for larger -accumulations of ice on the arctic shores. - -Yet it is probable that an ice period extending over the northern -temperate zone could not be perfected by this process alone, should the -tropical and southern oceans maintain their present temperature. But, -with the assistance of a frigid period in the southern hemisphere to -cool the ocean waters, and thus lower the temperature of all tropical -currents, including the Gulf Stream and Japan currents, an ice age -could be brought about in the northern hemisphere equal in intensity to -the glacial periods of the past. - -And, when we know that a considerable portion of the heat carried into -the northern latitudes by tropical streams is largely derived through -the mingling of the waters of such currents with the warm waters of -the southern tropical oceans, it is evident that the ice periods of -the northern and southern hemispheres were concurrent; although the -culmination of the northern frigid period would be somewhat later -than the perfected southern ice age, on account of the northern seas -requiring the assistance of the cold oceans of the southern hemisphere -to perfect a northern ice age. - -The small area of the northern seas, compared with the southern oceans, -and the wide mingling of the ocean waters of the hemispheres, make it -evident that the comparatively scanty northern seas could not bring -about or maintain either a frigid or mild period in opposition to the -superior oceans of the southern hemisphere. - -On the consummation of an ice period in the northern hemisphere heavy -glaciers covered the larger portion of its continents and islands, -which added so much weight to the northern lands as to attract the -waters of the southern oceans into the northern latitudes, as I have -before explained. - -Thus, when the ice was mostly melted from the lands of the southern -hemisphere, the heavy ice-sheets that remained on the extensive -northern lands would still continue to attract the warm waters of the -southern seas into the northern oceans; and in this way the Japanese -and Gulf currents would gain a higher temperature and greater volume, -and thus add to their ability for melting the northern glaciers -wherever they were able to flow, and so hasten the growth of a mild era -in the northern hemisphere. - -And it seems reasonable to suppose that there was more water in the -northern hemisphere on the ending of its ice period than at this age; -yet it appears that it was returned to the southern hemisphere during -a short period by the prevailing winds in the manner which I have -previously explained. - -Therefore, there are but few traces of such flowage to be found in the -glacial drift, especially with the scarcity of marine life after the -rigor of a frigid age. - -An article in _Science_, July 5, 1895, written by Agnes Crane, states -that Professor Joseph Prestwich has recently contributed a suggestive -memoir on this subject to the Philosophical Transactions of the Royal -Society. It treats of the evidence of a submergence of Western Europe -and the Mediterranean coasts at the close of the glacial period; and in -a previous paper communicated to the Geological Society of London, in -1892, the author gave evidence, deduced from personal observation, of -the submergence of the south of England not less than a thousand feet, -at the close of the glacial epoch. - -Since that time the flood of water which flowed all of the low lands -of the high northern latitudes has been returned to the southern seas, -because of the force of the prevailing winds in connection with the -great oceans which open so widely toward the south, the force of the -winds being assisted through the attraction caused by the difference -of temperature in the surface waters of the vast southern temperate -oceans and the antarctic seas, and in this manner bringing about the -geographical conditions of to-day which favor the return of another ice -age. - -It is said by those who attribute the great currents of the ocean to -the rotation of the earth that the winds have little to do in causing -such currents as the Gulf Stream. But my impression is that the -southern portion of the Gulf Stream waters, after being drifted by -westerly winds over abreast Europe, are attracted to the low sea-level -in the vicinity of the Canary Islands, to be moved by the trade winds -toward the equatorial calm belt and the West India Islands. And during -my many months’ cruising over these seas I have had my attention -directed to the singular action of the surface waters, while being -impelled by the trade winds toward the West India sea; for during the -first fifteen hundred miles of their passage they are moved by the -prevailing easterly winds without much apparent resistance or unusual -disturbance. But on nearing the longitude of Cape St. Roque, and -having acquired a high sea-level from which there is no easy or wide -outlet, the impelled surface waters begin to rebel against the forceful -winds, and cause a remarkable commotion in the shape of tide-rips and -white-capped ripples, which extend from the equator in a northerly -direction to the latitude of about 19° north, thus crossing the central -portion of the north-east trade-wind belt, with a breadth of over three -hundred miles, as shown on map No. 2. - -This disturbed region where the winds and waters conflict is the -probable fountain-head of the Gulf Stream. The reason why the surface -waters of this disturbed portion of the Atlantic do not flow peacefully -along through the West India passages into the Caribbean Sea and Gulf -of Mexico is because of their narrow outlet at the Florida channel. For -it is mainly through this narrow channel that the vast waters of the -tropical high sea-level are attracted to the low ocean-level of the -Western North Atlantic. - -Thus it seems that the great fountain-head of the Gulf Stream is -situated between the wide tide-rips and the Caribbean Islands. The -waters from this high ocean-level enter the Caribbean Sea mainly -through the several passages south of Guadeloupe; while the northern -portion of the raised waters set mostly toward the north-west, and so -unite with the eastern portion of the Gulf currents after they enter -the Atlantic. Still, the great high sea-level which presses against -the Windward Islands, being somewhat higher than the Caribbean Sea, -forces its waters through the island passages in quantities sufficient -to supply the Gulf Stream; and there are times when the winds are so -strong and favorable that all of the passages east of Cuba conduct -water into the Caribbean Sea, the cold under-waters entering the deeper -channels as well as the warm surface waters. Yet the currents setting -through these numerous channels are subject to fluctuations, and so -also is the Gulf Stream which they supply. - -That portion of the high sea-level south of Guadeloupe receives -considerable assistance as a feeder for the Gulf Stream through being -connected on the south by the great high sea-level abreast Brazil and -the great high sea-level of the equatorial calm belt. The latter high -level is caused by the trade winds, which generally blow briskly down -the coast of Sahara, and also further off shore, and ending south of -the Cape Verde Islands somewhat abruptly in the equatorial calm belt. - -The south-east trades which blow over the Eastern and Middle South -Atlantic terminate on the southern side of the calm region. Therefore, -the two trade winds impel the surface waters of the tropical Atlantic -from opposite directions directly toward the calm belt, and so raise -its waters above the common level of the sea. - -This is the opinion of the writers of the South Atlantic Directory. -Still, it is probable that the high ocean-level of the calm belt is -but slightly raised above the common level of the sea, on account of -the trade winds having to contend against the tendency of the warm -tropical surface waters to move toward the polar latitudes. The calm -belt expanse which extends from Africa, where it attains its greatest -width, gradually narrows as it extends westward to the longitude of -Cape St. Roque, where it attains its highest sea-level, on account of -the borders of its narrowing space being impelled westward by the trade -winds. - -The movement of the waters of this high ocean-level is mostly toward -the west, forming a portion of the equatorial current of the Atlantic. -The reason of its western movement is on account of its raised waters -being able to supply a portion of the Gulf Stream with water which is -sent off in a westerly current along the South American coast, west of -Cape St. Roque into the Caribbean Sea; while, on the other hand, it -joins with the great high sea-level abreast Brazil, and so unites with -its great southern current. The gradient of the high sea-level of the -calm belt on its southern side probably extends south of the equator, -on account of the south-east trades being weak in latitudes near the -equator; while on the north side the north-east trades generally blow -brisk and end more abruptly, so producing a gradient of less width than -that of the South Atlantic side. - -It does not appear that the seas of the high northern latitudes gain -an undue proportion of the tropical Atlantic waters, because of the -south-east trades extending north of the equator, on account of such -winds being weak, and the waters of the high sea-level of the Western -North Atlantic having narrow and otherwise obstructed passages leading -to its northern seas. Yet the high sea-level of the equatorial calm -belt is always ready, whenever a favorable grade is formed by a monsoon -or otherwise, to run off its surplus water obtained by winds and rain; -and I have noticed, while cruising in these seas, that it happens at -times during the northern winter months when the north-westerly gales -drive the surface waters of the North-western Atlantic toward the -tropical zone, and at the same time a strong north-east monsoon is -prevailing along the southern coast of Brazil, the westerly currents -setting past the Amazon River are reversed, and set to the south-east, -while such conditions last. - -For, when the summer solstice is in the south, and the north-east -monsoon moves southward along the coast of Brazil, much equatorial -water moves off in that direction; and during the same season the -cooled Sahara has an outward flow of air toward the south, which -moves more or less water from the coast of Guinea, which is easily -accomplished, because the warm surface waters of that coast are -inclined to join with the south equatorial stream. Consequently, the -waters move from their high sea-level north of Cape Palmas, and so form -the Guinea current. - -The high sea-level of the equatorial calm belt of the Atlantic contains -a large portion of the conserved heat of the tropical Atlantic, which -at this age sends off a somewhat limited supply of warm water to -the Gulf Stream, and also to the Brazil current. But, whenever the -Cape Horn channel is closed or much obstructed, so causing a great -low sea-level in the Southern Atlantic, the tropical waters heaped -against Brazil, and the raised waters of the great calm region being -one continuous high sea-level, would mostly be attracted to the vast -low sea-level of the southern ocean. Hence it will be seen how large a -portion of the conserved heat of the tropical Atlantic would be used to -warm the high southern latitudes during a warm period in the southern -hemisphere, and at the same time the head-waters of the Gulf Stream -would obtain the same height as now. For we now see much of the force -of the north-east trade winds lost, while maintaining so large a high -sea-level to the windward of the West India Islands, which is probably -capable of supplying a stream of double the capacity of the gulf -current which passes through the Florida channel. - -And it appears, while viewing the vast reservoirs of warm water -apparently gathered by trade winds to subdue the cold of the high -latitudes, that much of the energy of such winds is now lost to the -world, while maintaining a vast and pent-up high sea-level which has -a difficult outlet to the northern seas, and no strongly attractive -low sea-level to move its waters into the oceans of the high southern -latitudes. The wide waters which are banked up to the windward of -the West India Islands, and cause the wide tide-rips, set mostly -to the westward into the Caribbean Sea through the passages south -of Guadeloupe, while the northern portion of the raised waters set -mostly toward the north, and thus form the eastern boundary of the -Gulf Stream, and comprise the inner circle of the great current that -encircles the Sargasso Sea. - -I have been informed by an old Barbuda fisherman that “the weeds which -float on the surface of the Sargasso Sea grow in large quantities -on the bottom of the shoal waters to the north and eastward of that -island and Antigua.” Consequently, the currents of that region carry -such weeds as become detached from their places of growth into the -higher latitudes, where the westerly winds in the winter season drift -them eastward south of Bermuda, until finally the central area of -their gathering, where the most dense collection of weeds is found, is -situated near the tropic of Cancer, and about 55° west longitude, as -shown on map No. 2. - -This position is also the centre of the great circular currents which -encompass the Sargasso Sea. The comparatively few weeds which enter -the Gulf Stream abreast Florida are currented to the northward of -the Bermuda Islands, and from thence drifted by the westerly winds -to the south-west of the Azores before entering the trade-wind belt. -The weeds, on their long drift from their native shoals, hold their -freshness, and continue to grow while floating on the sea for a -considerable time, but at length lose their renovating properties, and -in certain areas of the sea acquire an appearance of age and decay. - -The Gulf Stream, and such other tropical waters as are attracted -northward to the low sea-level abreast the North American coast, pass -into the westerly wind-belt, and so gradually become drift currents, -while being forced by the winds over to the European side of the ocean, -as we have previously shown. - -The vast movement of the North Atlantic waters encircling the great -Sargasso Sea has often been pointed out by writers on the subject. But -the central and most dense portion of the vast sea of weeds has always -been placed on the charts several degrees of longitude east of its true -position. - -It is fifteen years since I wrote of the Gulf Stream and arctic -currents as being attracted to a low sea-level caused by the westerly -winds. But, as far as I know, writers on the Atlantic currents have -had nothing to say of the great low sea-level caused by the westerly -winds blowing the surface waters of the North Atlantic away from the -eastern coast of North America, from Georgia to Newfoundland, and thus -attracting the arctic and Gulf Stream waters in opposite directions, -fifteen hundred miles along the North American coast. For, were it -not for this low sea-level, the Gulf Stream would not be able to move -so far northward as it now flows, but would spread out, were there no -unevenness in the sea-level of the Atlantic, and become a drift current -far south of its present northern limits. The United States government -has caused surveys to be made of the Gulf Stream, and the interesting -discoveries thus obtained have all been laid before the public. Still, -such surveys cover but a portion of the whole round of the vast -movement of the Gulf Stream water, and do not refer to the vast high -sea-level of the calm belt as being one of its feeders, or to the wide -disturbance of the surface waters of the tropical North Atlantic in -their conflict with the trade winds, while being forced to the vast -high sea-level of the Caribbean Sea and Gulf of Mexico, and so giving -head to the Gulf Stream. - -Thus from the foregoing explanations it will be seen that the ability -of the prevailing winds to move the surface waters of the ocean away -from the weather shores of continents over against the opposite leeward -shores in the different wind-belts of the globe, and so cause both high -and low sea-levels, is the main reason why there is an interchange of -surface water between the tropical and colder zones sufficient to carry -heat from the tropics to the cooler regions, and thus largely affect -the temperature of the higher latitudes. - -The unmistakable traces of cold periods having occurred in both -hemispheres have given rise to an ingenious astronomical theory to -account for their origin. According to this theory the ice periods -in the two hemispheres were consecutive; and it is admitted by its -supporters that, should it be shown that the frigid periods in the -northern and southern hemispheres were concurrent, the astronomical -doctrine would have to be abandoned. - -It is impossible for a person who is acquainted with the great surface -currents of the several oceans to conceive how a mild period could be -maintained in the northern hemisphere with a frigid period existing -in the southern hemisphere. A frigid period in the latter hemisphere -necessitates a cold temperature for the superior oceans of the globe -south of the equator. With this vast area of water reduced to a -chilling temperature, it seems impossible for the inferior waters of -the northern latitudes to maintain sufficient warmth to favor a mild -period in the northern hemisphere, especially with both hemispheres -receiving an equal annual amount of the sun’s rays. The great Humboldt -current, having its rise in the southern ocean west of Cape Horn, -would during a southern frigid period greatly lower the temperature -of the vast equatorial stream in the Pacific Ocean. Consequently, the -Japanese stream, which branches off from the equatorial current into -the North Pacific, would be cooled to such a degree that it would be -unable to maintain the mild climate on the shores of the North Pacific -which extensive lands now enjoy. Furthermore, during a cold period in -the southern hemisphere the temperature of the Gulf Stream would also -be greatly lowered by the great South-eastern Atlantic return current, -which is caused by the south-east trade winds impelling the surface -waters of that region into the equatorial latitudes, such waters -being replenished from the common level of the southern ocean, and so -mingling the cool waters of that sea with the equatorial waters of the -Atlantic during a frigid period in the southern latitudes. And it may -be said that during such times the frigid Antarctic Ocean would send -its cold under-currents to cool the inferior northern oceans. Even -to-day the northern and southern hemispheres, through the intermingling -of the waters of the northern and southern oceans, largely maintain -a like temperature in their temperate zones. Therefore, when we -consider the certain traces of ice-sheets having formed on South -Africa and Southern Australia, and to have overrun South America above -the latitude of 40° south, thus strewing the oceans of the southern -temperate zone with ice that are now largely free from it, it seems -that the maintenance of warm oceans in the northern hemisphere during -the time of a frigid period in the southern hemisphere would be -impossible. - -In order to make this statement more plain, I will again refer to the -importance of the great Humboldt current for cooling the waters of -the North Pacific during the perfection of a southern ice age. For -during such times the ocean strewed with ice west of Cape Horn, where -the Humboldt current takes its rise, would impart its coldness to the -Humboldt stream, while it was floating icebergs toward the equator. The -equatorial current of the Pacific being a continuation of the Humboldt -stream, its waters would partake of its coldness. The Japanese current, -being a large offshoot from the equatorial stream, would also possess a -lower temperature than it obtains at this age. Yet at this date, with -the southern ice-sheets confined to the antarctic lands, it does not -possess heat sufficient to prevent glaciers from flowing down to the -tide-water from mountains in Alaska. - -Consequently, the Japanese stream could not maintain a mild climate on -the North Pacific coasts while a cold period was being completed in the -southern hemispheres. Therefore, under the conditions above set forth -the support of a mild period in the northern hemisphere during the -existence of a frigid period in the southern hemisphere could not be -carried out. - -From what has been explained, it will be seen that the growth of an -ice period is necessarily slow, especially in its early stage, and also -that the storage of ice is carried on in both hemispheres at the same -time; but I will call further attention to the southern hemisphere, -because it possesses greater resources than the northern for the -production of an ice age. - -The independent circulation of the southern ocean waters, as before -shown, turns away the tropical currents, and thus largely prevents -their warm waters from entering the high southern latitudes. -Consequently, the heat from the sun’s rays, and all other sources of -heat included, are not sufficient to prevent ice from gathering on -lands within the antarctic circle. This increasing storage of ice is -only another name for the accumulation and spreading of cold, and so -the increasing chillness goes on. The snow falls, and thus adds to the -extension and thickness of the ice-sheets; and at the same time the -spreading snow-fields reflect the heat received from the sun’s rays -into space, while the cold is retained and increased in the growing -glaciers. - -The spreading ice-sheets having covered the land are able to flow into -the surrounding seas, where their outer edges become detached and form -icebergs, which float out to sea, and so scatter over the adjoining -oceans. Thus their coldness is mingled with and largely preserved by -the sea, while the surface water, which is carried into the southern -latitudes from the northern oceans by the prevailing winds, and also -such surface waters as are attracted into the antarctic seas because -of the difference of temperature of the antarctic waters and the -more northern seas, are on gaining the frigid latitudes made cool, -and returned to the more northern seas in cold under-currents, and -so chilling the vast under-waters of the great oceans of the globe, -and eventually their wide surface waters also; and so the coldness -increases until the ice-sheets which at first formed on polar lands are -enabled to spread slowly toward the equatorial regions so long as the -independent circulation of the southern ocean is maintained. - -But at length the depth of the great southern ocean is diminished -because of the water evaporated from its surface, and precipitated in -the shape of hail and snow over the vast continents and islands of the -high northern latitudes, thus adding sufficient weight to the northern -lands to attract the waters of the southern seas and still further -lessen their depth. Thus during such times the Cape Horn channel is so -reduced as to be obstructed by the heavy glaciers and icebergs of an -ice age. - -Consequently, a great change is wrought in the circulation of the -southern seas. For, when the Cape Horn channel is closed, the westerly -winds employ their strength to force the ocean’s surface waters away -from the glaciers which have filled the diminished channel. This -potent action of the winds necessarily creates a great low sea-level -on the Atlantic side of the obstructed strait, sufficient to attract -the tropical waters heaped against Brazil by the trade winds, and the -waters of the high sea-level of the equatorial calm belt, and also the -equatorial waters which set along the east coast of Africa, well into -the southern seas. - -It will thus be seen that the conditions for the circulation of the -tropical ocean waters have met with a great change. - -But the temperature of the waters has been lowered by the coldness of a -frigid period; and, consequently, their capability for conveying heat -to the high latitudes has largely diminished. Therefore, their first -inroads in the higher latitudes make small impression on the icy seas, -so the early process for melting ice is exceedingly slow. But the icy -southern ocean, deprived of its independent circulation, in the course -of time yields to the warming invasion of the tropical waters, whose -wide and increasing spread is eventually able to bring about a mild -period, according to the natural methods which I have explained in the -preceding pages. - -And it may be said that a mild period succeeding a glacial age gained -sufficient warmth to melt the ice-sheets from all lands excepting the -highest mountains. For it is probable that there are lands situated in -the antarctic circle sufficiently elevated even during late Tertiary -times to have been above the snow-line. Therefore, the glaciers on -such lands could not have melted away during mild periods succeeding -an ice age. For, as has been explained, a portion of the waters of the -southern seas had moved into the northern hemisphere. Consequently, the -antarctic lands were raised higher above the sea-level than at this -age. Hence the area of lofty land was increased above the snow-line. -And, according to Dr. James Croll’s estimate, the ice-sheet at the -south pole is at this age several miles in thickness. Therefore, its -upper surface is above the line of perpetual snow, and could not be -melted away during the warm eras succeeding glacial periods. - - - - -CHAPTER III. - -THE SPREAD OF GLACIERS DURING COLD EPOCHS. - - -I have before explained that the conditions are such that the cold -periods of the northern and southern hemispheres were concurrent. -Through this cause, while the glacial epoch was being perfected, the -ice followed down the mountain ranges of both hemispheres; and, while -gathering on the lands of the temperate latitudes, it also spread -over a portion of the tropical zone. It is reported that traces of -ancient glaciers are found in India, and also in Central America and -in tropical South America. In fact, the denudation caused by ancient -glaciers on the elevated lands of the tropics are too well defined to -be attributed to any process of weathering, while Alpine plants of the -same species are found near the summits of mountains in the tropics as -well as in the high latitudes of both hemispheres. - -This fact goes to show that a portion of the lowlands of the tropical -zone have experienced a temperature favorable for the growth of Alpine -plants. And, judging from the tropical islands I have visited, situated -in the cold currents which flow down the eastern sides of the oceans -from the high latitudes, I think they show strong traces of having -during some remote period been subject to the action of glaciers. The -island of St. Helena, situated in the southern tropical Atlantic, has -the appearance of having been heavily iced during a frigid age. Its -steep ravines, which deepen as they approach the sea, recall to the -southern voyager the ice-worn islands of the high latitudes. It seems -improbable that these deep ravines which penetrate the hard volcanic -rock, on their short course to the sea, could have been caused by their -scanty brooklets. - -The bowlders scattered over the island are not in harmony with the -weathering process, while the obliteration of its craters seems to -point to a more rapid process of erosion than could be attributed to -weathering. - -Professor Agassiz, in his “General Sketch of the Expedition of the -‘Albatross,’” states that the Galapagos Islands are of volcanic origin, -and that their age does not reach beyond the earliest Tertiary period; -and his report seems to favor the impression of their having undergone -denudation sufficient to slough off large portions of the rims of the -older craters, and also the eastern face of Wenman Island. On Hood’s -Island, at the time of my visit, its crater had entirely disappeared. - -The highest portion of the island, which was the probable site of -its ancient crater, showed no trace of its former existence; yet at -the foot of this low mountain, on its southern side, I saw a large -collection of loose bowlders, composed of hard volcanic rock, which -were mostly free from soil and other débris, and easily moved from -their places, while the spaces afforded by the loose piles of dark -basaltic rocks afforded a secure retreat for numerous owls and lizards. -Beyond the rocky piles to the southward a horizontal area of land was -strewn with bowlders to the sea, which was some two miles distant from -the higher land. The bowlders which covered the plain were somewhat -smaller than those at the foot of the mountain, as none of the former -were more than three or four feet in their longest measurement. - -They seem to have been formed from thin strata of lava, which were -broken in pieces from pressure, such as the action of ice could -perform. In fact, the crowded and angular and somewhat worn blocks -of lava presented a different appearance from stones thrown from the -crater of a volcano, while no such bowlders are found among the recent -volcanic eruptions on the islands. - -The plain so thickly strewn with bowlders, and partly shaded by a tall -growth of shrubs, fell off abruptly at the seaside, forming a steep -cliff some two hundred feet in height. - -The rocky floor at the foot of the cliff received such débris as fell -from the sea-washed land; yet it contained few bowlders, they having -been washed away by the waves soon after falling. - -At one place a steep, dry ravine penetrated the land from the seashore, -which was dangerous to cross on account of the loose stones resting -on its sides. Two or three miles further west, on the level land -bordering the sea, a large rookery of albatross were brooding their -eggs and chicklings. The land on the south side of Albemarle, near the -sea, consists of débris from the eroded high lands; and, judging from -the crumbling cliffs by the sea, it seems that the land at one time -extended further seaward. - -Besides the excessive denudation which appears to have taken place on -portions of these bowlder-strewn lands, we have other unmistakable -testimony of their having formerly possessed a frigid temperature. The -characteristic Alpine flora of these islands points to a time when they -were exposed to a cold climate. Furthermore, rookeries of seal and -albatross, which naturally belong to shores situated in cold latitudes, -still exist on these equatorial islands; and, when we consider the -favorable position of the Galapagos for the reception of cold during a -frigid period, we can well account for the lingering signs which point -to their former cold climate. - -During the perfection of an ice period the western shore of South -America was covered with an ice-sheet from the summits of its mountain -range to the sea, extending northward as far as the latitude of 38° -south. - -This vast ice-sheet, situated in a region of great snow-fall, was -constantly sending icebergs into the sea, where they were borne -northward by the cold Humboldt current directly toward the Galapagos -Islands; while, on the other hand, in the northern latitudes, in -regions of great snow-fall, such as Alaska and British America, -numerous icebergs were launched into the ocean, to be currented -southward to the Galapagos seas. Thus during the frigid epoch the -equatorial waters surrounding the Galapagos group was one of the -greatest gathering places for floating ice to be found on the globe. - -And here the frigidity stored up in the glaciers of the higher -latitudes was set free, thus chilling the waters as well as the -atmosphere of that region. The Alpine flora of the American coast -mountains was probably carried by floating ice to the Galapagos, while -its rookeries of albatross and seal date back to a cold period. And -it seems that these cold-weather animals, with the assistance of the -cool Humboldt current, may be able to preserve their rookeries at the -equator until the advent of another ice period. In connection with the -evidences of a cold climate having possessed the Galapagos, there are -ample traces of ice-sheets having flowed over a large portion of the -high lands of tropical America, and in some places the ice may have -flowed down to the sea, especially where the large rivers now empty; -and it is said that masses of clay, mixed with sub-angular stones, have -been found in Brazil, which goes to prove the glaciation of portions of -that tropical land during a remote age. Professor Louis J. R. Agassiz, -during his research in the Amazon valley, found bowlders resting near -the summits of the low hills of that region, which he attributed to -the action of ice. The spread of glaciers on southern continents and -islands is shown on map No. 1. - -In _Science_, Nov. 17, 1893, Mr. J. Crawford published a summary of -his discoveries in Nicaragua, during ten months of nearly continuous -exploration since August, 1892. - -The author of this report says: “The numerous eroded mountain -ridges and lateral terminal moraines of that tropical region give -unquestionable evidences of the former existence of a glacial epoch, -which covered an area of several thousand square miles in Nicaragua -with glacial ice. The ice-sheet covered a large part of the existing -narrow divide of land (containing about 48,000 square miles) between -the Pacific and Caribbean Sea.” And it is likely that other large areas -of tropical America were glaciated at the same time, especially in -regions of great precipitation. - -The island of Cuba, during a portion of the ice age, probably -supported heavy glaciers, and obtained an average temperature as low -as South-western New Zealand at this age. According to the description -given by J. W. Spencer, of the Cuban land, great valleys have been -excavated, the lower portion of which are now fiords, reaching in one -case at least to seven thousand feet in depth before gaining the sea -beyond. Thus, while keeping in view the glacial condition of Central -America during the frigid period, it seems that the great Cuban -excavations were partly the work of glaciers of the same cold epoch.* -Judging from such reliable statements, it is probable that the climate -of tropical America during the frigid age was somewhat colder than -obtained in the tropical regions of the eastern continent, owing to -the wide connection of the Atlantic with the Arctic Ocean as well as -with the antarctic seas, and because of its shores possessing a larger -area of glaciated lands in proportion to its size than the Pacific and -Indian Oceans, and also owing to the tropical Atlantic containing so -small a portion of the world’s waters which lie within the torrid zone, -and its equatorial current being separated by continental lands from -the great equatorial stream of the Pacific and Indian Oceans. - - *The meeting of the British Association for the Advancement - of Science, September, 1895, was reported in _Science_ of - October 18, where mention is made of an interesting paper by - Mr. R. B. White, on “The Glacial Age of Tropical America,” in - which he described a number of apparently glacial deposits in - the Republic of Colombia, almost under the equator. He spoke - of moraines forming veritable mountains, immense thicknesses - of bowlder clay, breccias, cement beds, sand, gravels, and - clays, beds of loess, valleys scooped, grooved, and terraced, - monstrous erratics, and traces of great avalanches. - -Therefore, the tropical Atlantic waters must have been reduced to a -lower temperature during a frigid age than the tropical waters of the -Indian Ocean or the western part of the tropical Pacific, as a large -portion of the great equatorial current of the latter oceans, during -its western movement, was exposed to the rays of a tropical sun for a -much longer time, after being replenished by the cold waters of the -high latitudes, than the tropical currents of the Atlantic; and it -is probable that, on account of tropical America possessing a colder -climate than the tropical lands of the eastern continent during the -frigid epoch, the cold of the western continent was more destructive -to its fauna and flora than was the case in the tropical regions of -the eastern continent. Professor Wright, in his valuable work on “The -Ice Age of North America,” gives a good description of the “flight -of plants and animals during the glacial epoch,” and also of the -extermination of many superior species because of the frigid climate. - -The high lands of tropical Africa, above the altitude of three thousand -feet, and situated in places of great precipitation, were probably -covered with snow and ice during the glacial age. Travellers have -reported that islands composed partly of granite bowlders are found -in the lakes at the head-waters of the Nile. But the glaciers that -invaded the tropical latitudes were of short duration compared with the -ice-sheets that burdened the lands of the temperate zones. Besides, -such tropical ice as flowed to the low lands was so near a melting -condition that it made small impression on the rocks; but on steep -mountain slopes, where the movement of the ice was comparatively rapid, -it possessed considerable eroding power. The climate of the tropical -zone on both continents during the perfection of an ice period was so -cold that such animals as could not endure a low temperature retreated -into the warmest regions of the equatorial latitudes, while many -species who failed to reach such places perished. And especially was -this the case with the pre-glacial fauna of the western continent. Mr. -W. B. M. Davidson, in his treatise on Florida phosphates, says: “The -great mammal hordes of the glacial epoch were driven into Florida in -their flight southward for life and warmth, and there perished because -of the deadly cold which ever moved southward. The Florida waters -grew so icy cold, fishes, reptiles, and mammoth animals died, and -added their frames and teeth to the valley of bones now found in that -southern region.” - -Such species of the tropical fauna of the ocean as survived the ice age -could have existed only in torrid seas with small connection with the -cold oceans during the frigid epochs. For, with the diminished oceans -of a cold period, it seems that the conditions were favorable for the -maintenance of such seas in the region of the East India Islands. - -Such parts of Southern Europe and Northern Africa as bordered on the -Mediterranean Sea probably possessed a milder climate during the ice -age than regions in the same latitudes on the Atlantic coast, for the -reason that the North Atlantic was proportionally a greater receptacle -for icebergs which were launched into it from the numerous glaciers of -North-eastern America, Greenland, Iceland, and North-western Europe -than the great inland sea obtained from its less frigid shores. And it -may have happened that during such times the tropical waters of the -Indian Ocean had some connection with the Mediterranean through the -Red Sea and Suez, and so during portions of the year the waters of the -tropical Indian Ocean were forced by the periodical winds into the -inland sea. It is the opinion of several writers that man, along with -other species of animal life, existed previous to the glacial period; -for, since the seas and lands of the globe were chilled, the conditions -seem to have been less favorable for the spontaneous generation of -animate bodies than during the previous warm ages. Therefore, it -appears that the generative ages should be ascribed to the long genial -eras prior to the glacial epochs. For it is probable that the lower -parts of the ocean, which now possess a low temperature even in the -tropical latitudes, were, during the warm eras, wholly composed of warm -water, because the surface waters of the antarctic seas of that age, -which supply the great under-currents of the ocean, would possess a -high temperature; and it is probable that the temperature of a large -portion of the seas of the torrid zone was for a long time maintained -at blood heat. For it should be considered that the waters which moved -from the torrid seas, after making their journey through the warm -regions of the high latitudes, would on their return to the tropics -retain a large portion of the heat they acquired in the torrid zone -before making their journey to the mild polar regions. - -And, when we reflect how the heat of the sun’s rays was conserved by -the ocean waters, and that their circulation during such times was -almost wholly performed by the winds, as the difference of temperature -between the polar latitudes and the equator was small, it appears -that during the eras previous to the glacial age the oceans must have -obtained a higher temperature than possessed by the warmest seas of -to-day. - -According to the discoveries of Professor Wright and others, ancient -stone implements have been found beneath the glacial drift, as well -as the bones of animals whose descendants are now living, which goes -to prove that man, with other species of fauna which now inhabit the -earth, existed anterior to the glacial epoch. - -And on consideration it seems unreasonable to suppose that any of the -superior species of animals could have been brought into existence -since the waters and lands of the earth were chilled by the cold of -a glacial age. And it appears that many species of animals which -are known to have survived the cold periods were indebted for such -survivals to the slow process through which a frigid period is brought -about, thus affording time for evolutionary inurement to the slow -increase of cold which at length perfects a glacial epoch. - -The inurement to cold acquired by animals during the glacial age is -still an attribute possessed by many species of fauna to-day. For, when -a warm climate took possession of the tropical zone, it was deserted -by a large portion of the animals that found refuge there during the -glacial age. - -Thus, while the seas and shores of the cooler latitudes swarm with -animate bodies, the torrid latitudes seem comparatively lonely to the -voyagers on the tropical oceans. - - - - -CHAPTER IV. - -THE GLACIERS OF THE TEMPERATE ZONES. - - -Having asserted that during the culmination of a frigid period the -ice-sheets spread over a portion of the lands of the tropical zone, -I will give my views, with those of several writers, on the spread -of ice-sheets within the now temperate latitudes; and meanwhile I -will repeat a portion of my former essays on the subject. Professor -Hitchcock, in his lectures on the early history of North America, -says that “the history opens with igneous agency in the ascendant, -aqueous and organic forces become conspicuous later on, and ice has -put on the finishing touches to the terrestrial contours.” But there -appear to be various opinions held by geologists respecting the changes -brought about on the earth’s surface during the glacial period. Some -think that glaciers have never been an important geological agent, -while others assert that during the glacial epoch heavy ice-sheets -covered the elevated portions of Western North America as far south -as the thirty-sixth parallel of latitude, and Eastern North America -was overspread with ice-sheets, which attained a depth of five or six -thousand feet, and were able to move their débris over wide lands of -little declivity toward the sea, their immense deposits forming the -lands of Cape Cod, and also the islands of Nantucket and Martha’s -Vineyard. - -But it is now said that this implied magnitude of the glacial deposits -on the lands skirting the New England coast is without foundation, -since the larger bulk of these islands consists of upturned Cretaceous -and Tertiary strata, which are only thinly covered with glacial débris, -such as bowlders, gravel, clay, and sand, from the eroded shores of the -mainland of New England. But it appears that the dislocated and folded -cretaceous strata which underlie the glacial drift of Nantucket and -Martha’s Vineyard were during an early period deposited on the bottom -of a shallow sea, which then covered the Vineyard Sound, Buzzard’s Bay, -and their surrounding lowlands. Thus the ice-sheets of the frigid age -which moved over New England displaced the yielding stratified deposits -of the shallow sea, and forced them southward in a disturbed condition -to the position which they now occupy. - -Still, it is apparent that only a small portion of the glacial drift is -found on these islands, which, according to appearances, must have been -eroded and moved southward from the rocky lands of New England during -the ice age; but there is sufficient to show that large quantities -of such débris were carried over the islands into the Atlantic. And, -judging from the eroded rocky New England lands, there must have been -sufficient glacial drift moved over Nantucket and Martha’s Vineyard -into the ocean beyond to far exceed in bulk the deranged Tertiary and -Cretaceous deposits which now form so large a portion of the islands. - -For, when we look over lands bearing traces of the ice age, where -the glaciers did not move their drift into the sea, so the terminal -moraines of such glaciers can be better estimated, we can realize the -great work that has been performed by the ice-sheet that overran New -England during a frigid age. - -Professor James Geikie states, in his discussion on the glacial -deposits of Northern Italy, that the deposits from Alpine glaciers of a -frigid period “rise out of the plains of Piedmont as steep hills to a -height of fifteen hundred feet, and in one place to nearly two thousand -feet. Measured along its outer circumference, this great morainic mass -is found to have a frontage of fifty miles, while the plain which it -encloses extends some fifteen miles from Andrate southward.” And it -is reported that there are found on the southern flank of the Jura -numerous scattered bowlders, all of which have been carried from the -Alps across the intervening plains, and left where they now rest. Many -contain thousands of cubic feet, and not a few are quite as large as -cottages. - -Such blocks are found on the Jura, at a height of no less than two -thousand feet above the Lake of Neuchâtel. The Jura Mountains being -formed of limestone, it is easy to distinguish the débris deposited -by Alpine glaciers; and, from what I can learn of extensive glacial -work, it appears that intervening plains, lakes, and sounds are so -often found separating the source of ancient glaciers from their -deposits that their existence becomes almost necessary to represent -the general outlines of disturbance performed during an ice period. In -consideration of such facts and the foregoing statements of reliable -observers, I am prompted to offer my views on glacial work performed on -a portion of the Pacific shores of North America, which seems to me to -be much more extensive than hitherto supposed. - -Professor Whitney describes the coast mountains of California as being -made up of great disturbances, which have been brought about within -geologically recent times; and this statement I found to be so obvious -in my travels over that region that it appears to me that the coast -ranges originated in a different manner from the older Sierras. The -western sides of the latter mountains everywhere show the great eroding -power of ancient glaciers; and, when I considered their favorable -position for the accumulation of snow during a glacial period, I was -led to seek for the glacial deposits adequate to represent the great -gathering of ice which an age of frigid temperature would produce. - -But it seemed to me that such deposits could not be found in the -foot-hills of the Sierras, which contain the moraine of inferior -ice-sheets that terminated at the base of the mountains. - -Under these conditions I came to the conclusion that during the earlier -ice period the immense glaciers which must have formed on the western -slopes of the Sierra range moved their gigantic accumulation of débris -so far seaward as to form the range of hills now existing next the -coast line, and perhaps the islands abreast the Santa Barbara coast, -the Contra Costa, or eastern range, being formed during a subsequent -ice period, in the same manner as the hills next the coast line. - -Still, it may be that neither of the coast ranges was the work of a -single cold epoch; but the western range must necessarily have been the -earliest deposit. Although the coast ranges differ from the Sierras -in their make up, yet it does not disagree with the glacial origin -of the former inferior mountains, from the fact that the ice-sheets, -while moving their bulk westward, displaced the deposits of such bays, -lakes, rivers, and marshes as lay abreast of the Sierra slopes. The -advancing ice-sheets, thousands of feet in depth, moving from a lofty -and steep incline, pressed and ploughed below the somewhat superficial -cretaceous and alluvial strata which lay in their course. The disturbed -strata, while forced along in confused heaps in front of the ice, were -amassed in ridges sufficient to form the hills of the coast ranges. -The bowlders found imbedded in several of the coast hills must have -been moved by the ice from the Sierras on account of the coast ranges -not having a rocky core of sufficient firmness to give shape to such -bowlders. Moreover, the temperature of the Pacific waters would not be -favorable for glaciers to form on the coast ranges, with the ice-sheets -of the Sierras terminating at the foot-hills. - -The Sacramento and San Joaquin Valleys are now covered by recent river -deposits. Therefore, the glacial drift which should be traced from the -Sierras to the coast ranges is concealed. - -Yet the abraded appearance of exposed solid rocks at the base of the -foot-hills, and also the scattered bowlders which gradually disappear -beneath the diluvial deposits of the plains, indicate that the Sierra -ice-sheets could not have ended at the foot-hills, but must have moved -further westward, while gathering immense accumulations in their front, -sufficient to form the coast hills, the débris thus amassed being able -to arrest the further movement of the ice seaward. - -The coast ranges in several places have been subject to igneous action, -which may have been brought about through heat generated from pressure -exerted on the interior masses after the ice had melted away, the heat -thus produced being sufficient to cause outbursts of lava, where the -nature of the material favored combustion. The low plains, lakes, and -bays which separate the Sierras from the coast hills are in a position -similar to the shallow sounds which separate Nantucket, Martha’s -Vineyard, and Long Island from the inferior slopes of the mountains of -New England. Therefore, while agreeing with glacialists, who believe -that great geological changes have been wrought by ice-sheets in Italy -and New England, it appears to me that the ancient glaciers of the -Sierra Nevada have accomplished more extensive work, owing to the -Sierras being situated in a more favorable position to receive the -humidity of the ocean. - -Hence, with a low temperature, vast quantities of snow must have -collected on their lofty sides; and at the same time their great -height and declivity would cause the ice to move down their steeps -with greater force than the glaciers which passed over New England. -Writers who have given the subject considerable study think that the -deep valleys of the Sierra Nevada were produced by disruptive rather -than erosive agencies. This conclusion has been formed from the lack -of large accumulations of débris about their lower extremities, which -would not be the case if such valleys were the result of glacial -erosion. But, should the coast ranges be attributed to glacial action, -as has been stated, we can well account for the débris that should -accumulate from the erosion of the deep valleys. - -The only thing that could prevent the ice from gathering on the Sierra -Nevada range during an ice period in greater masses than on any -mountains in the northern hemisphere would be the lack of cold; for, -with a low temperature, the fall of snow would be enormous. This is -shown by the great snow-fall during the short mild winters of to-day. -Therefore, with ice-sheets covering a large portion of the lands of -the high northern latitudes, and with the Japanese current which -tempers the north Pacific waters made cold in the manner described -in the foregoing pages, and while the sea along the north-west coast -of America was strewn with icebergs launched from Alaska and British -Columbia, it seems that California must also have obtained a frigid -climate during the ice age. Therefore, on account of its exposure to -the ocean winds, and the consequent heavy snow-fall, the accumulation -of ice on its lands must have been immense. For, when it is considered -that the glaciers of North America extended southward even into the -torrid zone sufficient to cover a large portion of Central America, -it is unreasonable to suppose that any portion of California could -escape being covered by heavy ice-sheets during the glacial epoch. The -comparatively scant fall of rain and snow over Greenland is known to -form ice-sheets hundreds of feet in thickness. - -Therefore, what must have been the depth of ice over the high lands of -the Pacific coast north of California at the culmination of a frigid -period? The descriptions given by Dr. Dawson and others, of glacial -phenomena along that coast, favor the impression that an immense -ice-sheet at one time deeply covered the whole region from the top of -the mountain range to the ocean. - -Thus all the deep channels were filled and all the islands deeply -overrun with ice, while the immense bergs launched from the shore -and carried by the winds and currents southward were probably not -melted until they reached the tropical latitudes. Thus, when the -whole circulation of the Pacific waters are taken into account, it -will be seen that their temperature during the ice age must have been -considerably lowered. The movement of ice-sheets on the Pacific slope -was probably local in character, and not connected with the movement of -ice on the eastern sides of the mountains. - -From what I have seen of the vast territory lying between the Sierra -Nevada and the Rocky Mountains it appears that it obtained much heavier -ice-fields than generally supposed. Professor Geikie in his lectures -says of this region that during the glacial age, “in the Second -Colorado Canyon, the sides were completely glaciated from bottom to -top. These walls are from 800 to 1,000 feet high, and at the thickest -point the glacier was 1,700 feet thick”; and he says that “the country -around Salt Lake was covered with ice, for the rocks about there show -the action of ice, and that the bones of the musk-ox are found there.” -This vast area of ancient ice, although subject to little movement in -its interior basin, still, in whatever movement it may have had, must -have found its main outlet through the Grand Canyon of the Colorado. - -For in no other way can we account for the erosive forces necessary to -excavate that immense chasm. Not even the mighty torrent that carried -off the waters of the melting ice-sheets that covered the interior -portion of the continent could accomplish work of such magnitude. - -According to Professor Geikie’s observations the Second Colorado Canyon -was filled with glaciers during the ice age. Therefore, it seems that -these glaciers must have flowed down into the Grand Canyon, and there -united with glaciers flowing from more northern regions. - -An account of a collecting expedition to Lower California by G. Eison, -in 1895, describes ancient moraines at the extremity of the peninsula -as being prominent, large, and steep. This region lies under the tropic -of Cancer, and 8° south of the mouth of the Colorado River where -it empties into the Gulf of California. Hence it appears that the -temperature of that portion of North America during the ice age was -favorable for the great glacier of the Colorado Canyon to have flowed -into the Gulf of California. - -The wide, shallow basins of Utah and Nevada were filled with the water -from the melting ice-sheet on the breaking up of the ice period, -and the lakes so caused remained for a considerable time after the -disappearance of the ice. But, owing to the great evaporation and light -rain-fall of that region, the lakes gradually shrank away, the filling -and emptying of the lake basins being governed by the cold and mild -epochs. - -The conglomerate deposits in the Appalachian district of North America -are known as occurring on a large scale. Professor Shaler is inclined -to attribute them to glacial action, because he knows of no other force -that could bring together such masses of pebbles from a wide-spread -surface. In Eastern Kentucky and East Tennessee these deposits are -found to be several hundred feet in thickness. Such accumulations of -apparent glacial origin are to be found from New Brunswick to Alabama. - -Hence it seems that the ice during a frigid period followed down the -Alleghany range even so far south as Georgia and Alabama; and for a -time, when the ice attained its greatest spread, it flowed over the -central portion of the Gulf States. For how else can we account for the -clay mixed with gravel and pebbles and stony fragments being spread -broadcast over that region? - -I know that such statements do not agree with the views of glacialists -who have written on the subject, and have drawn the glacial boundary -from seven to ten degrees further north, where a line of bowlders with -other glacial débris is plainly traced. Still, it appears to me that a -line of bowlders deposited by an ice-sheet spreading over a continent -and across many degrees of latitude cannot be compared to the moraines -of inferior mountain glaciers of the temperate latitudes of the present -age. - -An ice-sheet moving from a high latitude to a lower would, while in the -colder latitude, freeze firmly to the rocky ledges, and hold them so -strong in its frigid grasp as to break off the weaker portions of the -rocks, and drag them toward a milder region, as far as the freezing -grip of the ice-sheet would permit; but, on gaining lower and milder -latitudes, the holding and dragging power of the ice would be lost on -account of the increased warmth of the earth over which the glacier -must pass, and also because of the ice-sheet having lost a portion of -the low temperature acquired in the higher latitudes. Therefore, on -such lines the bowlders would be released, while the ice-sheet would -still move on, although largely deprived of its eroding power. - -This is the probable reason why a line of glacial débris, largely -composed of bowlders, is found to extend across the Middle and Western -States, and so generally supposed to be the glacial boundary of a -frigid period. But there is no reason to suppose that an ice-sheet, -although deprived of its eroding power, was arrested in its southern -movement on the line of its stony débris, because there could be no -sudden change of temperature in a particular latitude on the eastern -lands of North America to cause an abrupt ending of the ice-sheets. -And there appears to be nothing to hinder the ice from gathering and -flowing over lands warm enough to loosen its implements of erosion; -for there is much to show that the ice-sheets flowed much further -southward, even into the middle portion of the Gulf States, and there -spread the clay mixed with gravel and pebbles, with now and then a -bowlder, over the land. The scattered bowlders, found in numerous -instances many miles south of the bowlder line, were so deeply imbedded -in the ice-sheet that they could not be dropped on the usual releasing -ground. The ice-sheet, when deprived of its rocky, eroding implements, -would, while flowing over the land, leave few or no imprints on the -rocks; but it would probably move and spread a large amount of clay, -gravel, pebbles, and sand over its wide course, especially if the ice -moved from a region abounding with such material. - -Should we place the glacial boundary on the line of the rocky débris, -how could we account for the glaciated stones found on the hills and -plains situated far southward of the bowlder-strewn regions of the -Middle and Western States? The clay mixed with gravel and sand, and -spread so broadcast over a large portion of Georgia and even into -Northern Florida, makes it appear that the ice of a cold period must -have covered that southern region. - -Moreover, it seems to have been through the great abrasion which only -ice-sheets could perform that the sands of the Florida peninsula were -produced; for on examination they seem to have resulted from the -abrasion and weathering of crystalline rocks. - -The worn remnants of such rocks are now found in the southern -Appalachian range. In fact, the hills and mountains of that region at -the present time are supposed to be a small remnant of the ancient -highlands. Thus, on consideration, it appears that the sands caused by -the action of glaciers were, on the disappearance of ice-sheets, blown -by the strong north-west winds toward the Florida peninsula as fast -as the receding waters of the ocean which flowed the lowlands on the -breaking up of the ice age would permit; and in this way the sand was -spread over the lowland region, which was largely composed of coral -sea shells and other marine matter. And it seems that the sand must -have been blown over large areas in Florida soon after the ending of -the frigid period, because the sand, in order to be moved by the winds, -must have spread over a country nearly destitute of vegetation; and -such would be the condition of that region during times which succeeded -the ice period and the subsequent brief flowage of the lowlands on the -ending of the frigid age, which would not be the case if such sands -resulted entirely from water erosion and weathering, because with -such a state of things the country would be covered with forests and -grasses, which would prevent the sand from being moved by the winds to -any great extent. - -This goes to show that the region of the Gulf States was so much -affected by the cold of the glacial period, together with the -submergence of the lowlands at its close, its flora and also its -animals were exterminated; for how else can we account for the abundant -fossil remains of animals now found buried in the Florida sands? It -appears also that, when Florida was being covered with drifting sands, -many of the lake basins now formed did not exist, as the wind-blown -sand could not have crossed a continuous chain of lakes like the St. -John’s River; and it is an easy matter to-day to trace the beds of the -ancient lakes that prevented the sands from drifting over certain lands -now nearly destitute of it. And it is probable that the sea flowed the -lowest lands during the period when the winds were drifting the greater -portion of the sands over the peninsula. Therefore, regions which -embrace the Everglades and portions of the Indian River territory are -quite free from heavy sand deposits, and so also are the extensive flat -woods of the peninsula. - -Since the sands blew over the ancient desert of Florida, many lake -basins have been formed because of the sinking of the ground. This -sinking of the ground is a common occurrence in limestone regions, -where a great amount of material is moved in solution, leaving caverns -whose roofs often fall in. The great amount of sand blown upon Florida -caused the marine strata to give way in the weaker places under its -burden. The sinks thus formed, probably of frequent occurrence at one -time, have now nearly ceased. Still, there are depressions to be seen -to-day where the tops of large pine-trees, which grew on dry, sandy -land, are barely above the surface of the water which partly fills -the basins so recently formed. Yet I would not assert that all of the -depressions where Florida lakes exist were caused by the sinking of the -ground; for the winds may have caused shallow basins in the sand, where -the decayed vegetation has formed mud sufficient to hold the water -which now partly fills such basins. - -The mobility of Florida sands can be seen to good advantage when -exposed to a strong, dry north-west wind, where the ground happens -to be destitute of vegetation. An observer can then realize what the -result would be, should the whole land be deprived of vegetation and -laid bare to the action of the winds. - -Under such conditions, not only would the winds be much stronger than -now, but the air near the ground would be filled with sand, moving like -drifting snow in a Dakota blizzard. And, furthermore, it is probable -that the rainfall was very light while Florida was void of vegetation; -and, even if shallow basins were formed, there would be a lack of rain -to supply them with water. - -The wide plains west of the Mississippi River, extending southward into -Texas, during the frigid period must have been covered with a sheet -of ice and snow. And it is probable that it was not wholly a product -of more northern latitudes, but was mostly produced by the snow which -fell on the plains during the long winters of that period, which could -not be melted away during the cold summers of an ice age, when it is -considered that an ice-sheet, with a temperature sufficiently low as to -carry glacial drift, covered the lands of Missouri as far as latitude -38° south; and it may have been through the pressure from an ice-sheet -in its south-eastern movement that we are to account for the numerous -ore-bearing faulting fissures traversing the limestone strata. - -The ice-sheet was also the probable cause of the erosion of the -horizontal bedded stones, yet it appears that the ice did not greatly -change the contour of the ground; for it is well known that glaciers -do move over lands that are not frozen to the ice without causing much -disturbance, especially where the gradient is small, and this was the -probable condition of the Western plains during the ice age. Thus it -seems that whatever disturbance this region has undergone could be -partly attributed to ice-sheets without the presence of bowlder drift, -because the temperature and texture of the ground in the limestone -region were unfavorable for such accumulations; yet it may be owing to -the action of ice that minerals once diffused are now found collected -in fissures. The deep valleys through which the large rivers now pass -on their way toward the sea were once filled with glaciers which flowed -into them from their tributaries. Thus the deep trenches of the plains -are largely the work of glaciers. It is generally supposed that the -driftless region of Wisconsin was free from ice during the frigid -period. But it seems impossible for this region to have escaped being -covered by ice and snow, with the great lakes filled with glaciers, and -the regions on all sides of the driftless area covered with ice. - -The reason why this territory escaped the drift from the north was on -account of the hindrance which the drift-bearing ice-sheet encountered -in the deep basin of Lake Superior. In this great depression the -ice-sheet from the north was relieved of bowlders and other glacial -drift, as well as obstructed in its southern movement. - -Therefore, the snow and ice which gathered on the driftless region had -little movement in any direction, while the temperature and consistency -of the ground under the ice were not favorable for the production -of bowlder drift; and, when we consider that the Mississippi valley -was deprived of great sources of warmth during the culmination of a -glacial period, we are forced to the conclusion that its wide lands -were also covered with snow and ice. - -The tropical waters of the North Atlantic were so much chilled by the -floating icebergs of North-eastern America, Greenland, Iceland, and -Northern Europe that the Caribbean Sea, its warmest reservoir, was -reduced to a temperature so low that the easterly winds which blew over -its waters were unable to prevent ice-sheets from gathering on Eastern -Nicaragua. - -Therefore, during such frigid times it appears that, with the waters of -the Caribbean Sea and Gulf of Mexico reduced to a low temperature, it -was impossible for the great Mississippi valley to escape glaciation, -while being surrounded by cold seas and glaciated lands which extended -even into the tropical latitudes. The broad, level lands of British -America and Siberia during the ice age must have been thickly covered -by the snow which fell on the deeply frozen plains, besides the large -amount of snow that the cold westerly winds must have drifted over -their icy surface from lands of greater snow-fall on their western -borders. This snow during such freezing times could not be melted away. - -The great ice-sheets thus formed over wide, level lands could have -but little motion in any direction, certainly not sufficient to cause -glacial drift of much magnitude; yet the ice-sheet, at one stage of -its existence, probably served to widen and deepen the channels of the -great rivers which empty into the Arctic Ocean from these vast regions, -and the glacial débris from such erosion was deposited in the arctic -seas. - - - - -CHAPTER V. - -REMARKS ON THEORIES ADVANCED FOR EXPLAINING ICE PERIODS. - - -On Nov. 12, 1891, Professor Geikie made his presidential address before -the Edinburgh Geological Society, the subject being “Supposed Causes of -the Glacial Period.” - -Many of his views advanced in this lecture were so much in accordance -with my own that I am induced to repeat them. He said that the glacial -period was a general phenomenon due to some widely acting cause, and -that where we now have the greatest rain-fall the greatest snow-fall -took place, and that the Pleistocene period was characterized by great -oscillations of climate, extremely cold and very genial conditions -alternating. He also said that in glacial and post-glacial times -changes in the relative level of the land and sea had taken place, and -any suggested explanation which did not fully account for these various -climatic and geographical conditions could not be satisfactory. And, -while examining the earth-movement hypothesis, he pointed out that in -the first place there was not the least evidence of great continental -elevations and depressions in the northern hemisphere, such as the -hypothesis postulated. Next he showed that, even if the diserrated -earth-movements were admitted, they would not account for the phenomena. - -Such changes, no doubt, would profoundly affect the maritime regions of -North America and Europe; but they would not bring about the conditions -that obtained at the climax of the ice age. - -Another objection to the earth-movement hypothesis was this: it did not -account for interglacial conditions. The advocates of that hypothesis -imagined that these conditions would supervene when the highly elevated -northern regions were depressed to their present level. But these -were the conditions that obtained at the present time; and yet in -spite of them the climate was neither so equable nor so genial as that -which obtained in interglacial times and during the mild stage of the -necessary post-glacial period. - -Therefore, he said that the earth-movement hypothesis should be -rejected, not only because it was highly improbable that such -wonderfully rhythmic elevations and depressions of northern lands could -have taken place, but chiefly because it did not explain the conditions -of the glacial periods and interglacial times. - -Still, Professor Geikie says that in glacial and in post-glacial times -changes in the relative level of the land and sea had taken place; and -it is reasonable to suppose that such changes were obtained in the high -latitudes of both hemispheres during the breaking up of the last ice -age. - -We have previously pointed out that much of the ice of the glacial -period in the southern hemisphere was melted away, and its waters -warmed sufficiently to assist the Gulf Stream and Japanese current to -bring about a mild period in the northern hemisphere; for without such -assistance they would be unable to disperse the vast ice-sheets of the -northern latitudes. - -Still, the attraction of the southern ocean waters into the northern -seas must have commenced as soon as the growing ice-sheets of the large -continents and islands of the high northern latitudes surpassed the -growth and weight of the glaciers on the smaller lands of the southern -hemisphere. - -Hence the attraction of the ocean waters northward overcomes the force -of the prevailing winds from moving an undue portion of the ocean’s -surface waters southward. Consequently, the movement of water from the -southern seas into the northern latitudes continued so long as the -vast northern ice-sheets increased in weight greater than the glaciers -of the southern hemisphere. Therefore, at the perfection of a frigid -age straits and channels situated so far southward as the Magellan and -Cape Horn channels were much diminished in width and depth or entirely -deprived of their waters. Through this cause such reduced channels were -readily filled with glaciers in a region of great snow-fall. The depth -of water on the submerged northern lands at the close of the glacial -period is not known. - -According to Professor Dawson, in the township of Montague in Ontario -the skeleton of a whale was found in post-glacial deposits 440 feet -above tide-water, and marine shells are known to occur on Montreal -mountain at an elevation of 520 feet above the ocean; and it is said -that there are traces of submergence of over one thousand feet in the -higher latitudes, including the islands of Great Britain. - -According to the researches of Dr. J. W. Spencer, one great sheet of -water covered most of the great lake region about the close of the -ice age; and the lower strands of these inland seas are known to be -connected with old marine shore lines. The probable reason why so few -sea-shells collected on the glacial drift during such times was because -of so much marine life having been exterminated in the high northern -latitudes during the frigid age. Therefore, the sea, in the short -period of northern submergence, left but few traces on the glacial -drift it once flowed. - -Thus it will be seen that, if the ocean waters were attracted northward -through the preponderance of northern ice-sheets, they not only -assisted in melting the northern ice, but also served to greatly reduce -the waters in the Cape Horn channel, and so largely prevented the -independent circulation of the southern ocean, thus furthering a mild -climate in the southern hemisphere until the prevailing winds, after -the northern ice-sheets were melted, were able to move more of the -ocean waters southward than they could move northward, owing to the -ocean currents setting southward being less obstructed than the lesser -currents setting northward. This tendency of the ocean waters to move -southward I have before explained in the preceding pages. - -But I will say in addition that, on further consideration, it seems -that one of the main causes of the waters of the augmented northern -oceans moving southward so soon after the melting of the ice from -the northern lands was on account of so much water being attracted -southward to the great low sea-level east of Cape Horn. This vast low -sea-level remained a great area of attraction for the northern seas -until so much northern water was moved into the southern ocean as to -reduce the seas of the northern hemisphere and augment the southern -ocean sufficiently to enlarge the Cape Horn channel, thus causing -the extinction of the vast low sea-level that furnished such great -attraction for the waters of the more northern latitudes. - -If the earth-movement hypothesis, so wholly rejected by Professor -Geikie, fails to explain the cause or causes of a northern ice age, it -seems to be still more inadequate for explaining the occurrence of ice -periods extending over both hemispheres. For it is not probable that -portions of continents and large islands rose above the snow-line in -both temperate zones during the same period of time, and then again -obtained their present level with the occurrence of a mild era. - -Those who maintain that the continents of North America and Europe -rose to great elevations during the ice age, in order to prove their -assertions, point to the fiords which indent the eastern and western -coasts of North America, and also to the fiords of Norway, as having -been eroded by streams of ice that flowed along the bottom of such -gorges when they were above the sea. - -But it appears that such erosion could be performed by heavy glaciers -with the lands at their present level. A glacier three thousand feet -thick would fill and press heavily on the bottom of a gorge fifteen -hundred feet in depth. Therefore, should the bottom of a fiord sink -hundreds of feet below the sea-level, a glacier several thousand feet -thick flowing through and over it into a sea of much greater depth, the -erosion at the bottom of the sunken channel would be greater than on -the land above the sea, where the ice possessed less weight. - -Therefore, it is not necessary that lands pierced by deep fiords -should have acquired a higher level during the ice age than they now -maintain. And it is probable that on the antarctic continent ice -erosion may be going on at much greater depths below the sea-level than -the deepest channels in the high northern latitudes. For it is likely -that the temperature of a glacier is so low in such frigid regions -that it holds firmly in its freezing grasp such bowlders as may become -detached from the rocks, thus giving it great erosive power. - -But this great eroding ability could not be maintained by glaciers in -the lower latitudes, where a higher temperature would largely deprive -the ice of its abrading properties except on the steep slopes of -mountainous lands. - -There are deposits of ice on the North American coast bordering the -arctic shores, and also on Northern Siberia, that are supposed to have -existed since the last frigid period, and are likely to be preserved -into a future cold age, which now appears to have made considerable -progress on Greenland and other ice-clad arctic shores on account of -the independent circulation of the Arctic Ocean waters, which largely -excludes the Gulf Stream from the polar seas; and it is for this reason -that the glaciers on the elevated lands of Iceland are being enlarged -and rapidly advancing. Yet, notwithstanding the gathering of ice -and increasing coldness of lands largely removed from the warm Gulf -currents, there are still mountain regions where glaciers may have been -preserved through post-glacial times, although directly to the leeward -and under the influence of the Gulf Stream and Japanese currents. -These glaciers are situated in the Alpine districts of Europe and on -the mountain ranges of Alaska. It would appear that, were the climate -growing gradually colder in the northern temperate zones, such glaciers -should be increasing in size. - -Yet it is said that such is not always the case. This is probably -owing to their being subject to the genial influence of the tropical -currents. For, although the climate of Europe and Alaska may have been -slowly growing colder for centuries, still the slow shrinkage of these -once immense glaciers may still be going on, although at a much slower -rate than formerly, even if the tender plants of these latitudes, -because of the growing coldness, have gradually moved southward. - -As to the Alpine glaciers, M. Forel reports from data he has collected -that there have been several enlargements and diminutions during the -last century. And since 1875 enlargements have taken place, their -shrinkage being caused by warm and dry weather, while their enlargement -was brought about during cold and rainy seasons. The glaciers of -Alaska cannot attain much extension until the waters of the great -Japanese stream acquire a lower temperature. There is at this date a -small current setting down through the eastern side of Bering Strait, -bearing field-ice in the spring season down to Anadyr Gulf. The Okhotsk -Sea in the spring season furnishes considerable field-ice to cool the -north Pacific waters, and the wintry winds which sweep down from the -high lands of Northern Asia also serve to chill the Pacific seas; but -all such sources of cold combined at this age have but little general -effect on the vast Japanese current, which still has warmth sufficient -to prevent the increase of glaciers on Alaska. - -This great ocean stream in its impact against the shores of Oregon -causes a high sea-level, which is mostly turned southward by the -prevailing north-west winds. Still, a comparatively small stream -sets along the shore of the Alaska Gulf, and also through the island -passages toward a slight low sea-level, to the leeward of the Alaska -peninsula; and it is probable that this current which warms these -in-shore waters is favored by the difference of temperature and density -between the waters abreast Oregon and the Gulf of Alaska, and it may be -owing to the same cause that a small stream is sent along the eastern -shore of Bering Strait into the deep portions of the Arctic Ocean. Thus -because of the warm waters that proceed from the great Japanese current -the glaciers of Alaska are prevented from increasing their bulk. - -The only way to furnish the Japanese stream with colder water, and -so cause glaciers to increase on the north-west coast of America, is -through the great Humboldt current, which has its rise in the southern -ocean west of Patagonia and the Cape Horn channel, where a moderate but -vast high sea-level is formed on account of the great drift current of -the southern ocean being somewhat obstructed on its passage through the -Cape Horn channel, which is about one-third the breadth of the westerly -wind-belt. - -Therefore, the northern portion of the waters of the high sea-level -so caused are attracted northward to the low sea-level abreast Peru, -from whence they are moved by the south-east trade winds as a drift -current to the equatorial latitudes, thus meeting and mingling with the -returning Japanese current abreast Central America, and so giving head -to the great equatorial stream which moves westward over the Pacific -Ocean, partly impelled by the trade winds, and, on gaining the western -side of the ocean, sends off from a moderate high sea-level a large -stream to the low sea-level caused by the westerly winds abreast Japan, -from whence it is drifted by the same winds over to the north-west -coast of America, thus forming the great Japanese current. - -Meanwhile the temperature of the Humboldt current, being governed by -the temperature of the southern ocean from which it takes its rise, is -cooling at a slow rate through the enlargement of ice-sheets in the -antarctic regions, while the increase of glaciers on Patagonia will -in time greatly add to its coolness, and so lower the temperature of -the equatorial current from which the Japanese current branches, the -latter current being made cooler through the increase of coldness of -the former streams. Therefore, the temperature of Alaska, which is -governed by the Japanese current, will slowly acquire a colder climate; -and, consequently, its glaciers will increase in size sufficient to -launch icebergs into the Pacific to be currented southward, and so -still further lower the temperature of the Eastern Pacific waters, -and consequently the equatorial current from which the Japanese stream -branches, and so eventually, under the above conditions, cause heavy -ice-sheets to spread widely over the north-west coast of North America. - -It will be seen from the above explanations how an increase of cold -in the southern hemisphere is necessary to cause a wider spread of -ice-sheets on lands in the northern hemisphere. - -Especially is this the case to promote the gathering of glaciers on the -west coast of North America. The great equatorial current while on its -way to the Indian Ocean not only sends off the Japanese stream, but -also the East Australian current, which is like the Japanese current, -having its temperature lowered in proportion as the equatorial stream -is cooled. Therefore, the southern ocean is slowly being deprived of -equatorial heat from this source. - -I have explained how the increasing coldness of the superior oceans of -the southern hemisphere affects more or less the temperature of the -Gulf Stream, which meanwhile is only able to enter a small portion -of its waters into the Arctic Ocean after undergoing a long cooling -process as a drift current; and, while thus mingling with the arctic -waters, it is not able to prevent the gathering of ice-sheets on -Greenland, where glaciers are launching bergs to float southward as far -as the latitude of 40° north. Consequently, the northern seas are now -being cooled as well as the seas of the southern hemisphere. - -Yet this cooling process is so slow there is a lack of data to -show that the temperature of the high latitudes is lowering. Our -thermometrical observations are of such recent date they cannot be used -to determine climatic changes which requires centuries to bring about. -Still, it is generally known that the climate of Northern Europe has -been accused of growing colder. The vine no longer flourishes on the -shores of Bristol Channel or in Flanders or Brittany; and vineyards -are no longer planted on the elevated shores of France where they -flourished three hundred years ago. Arago did not refuse to believe -that the laws regulating the temperature of Western Europe had notably -altered. This is proved, he said, by the general retrogradation of the -vineyards southward. - -The recent deadly freezing of the orange groves of Florida makes it -uncertain whether the cultivation of the orange can again be successful -in the counties where during this generation it has been very -profitable. - -Travellers visiting Iceland say that the old accounts of its prosperity -seem strange to those who now visit its shores; and it is narrated in -the Sagas that in early times sheep could shift for themselves during -winter, and that there were large forests and that corn ripened. -Several years ago a correspondent of the _Spectator_, writing from -Northern Russia where the Volga is locked with ice for six months in -the year, stated that “the people were beginning to show increased -resentment at the climate, and that there was reason to believe that -the northern government of Russia would be abandoned to the desert. The -people silently glide south by the tens of thousands every year, so the -life of Russia was concentrating in the south.” - -It is now the opinion of travellers in arctic lands that the -inhabitants of the Esquimaux regions are decreasing, as are also the -inhabitants of Northern Siberia. - -A writer in the North China _Herald_, of Shanghai, says that “the -climate of Asia is becoming colder than it formerly was, and its -tropical animals and plants are retreating southward at a slow rate. -In the time of Confucius elephants were in use on the Yangtse River. -A hundred and fifty years after this Mencius speaks of the tiger, the -leopard, the rhinoceros, and the elephant as being in many parts of -China. - -“It is also said that the ferocious alligator, that formerly infested -the rivers of South China, has retreated southward. - -“The flora of the country is also affected by the increasing coldness -of the climate. The bamboo is not found in the forests of North China, -where it grew naturally two thousand years ago, but is still grown in -Pekin, with the aid of good shelter, as a sort of garden plant only.” - -A letter from Hong Kong, published in the London _Standard_, reports -that on the 15th of January, 1893, the temperature of Hong Kong, a -tropical seaport of China, was below freezing for three days, and was -colder than ever before known. The rocks and also vegetation were -covered with a coating of ice. The thermometer at times stood at 23° -and 26° Fahrenheit. - -I have previously explained how the slow increasing coldness of the -northern temperate zone is also being carried out in the southern -hemisphere. The meteorological records for the lofty table lands of -Ecuador, although very incomplete, furnish strong evidence to show that -the mean temperature of that region is gradually lowering. - -Observations made by Boussingault at Quito in 1831, compared with those -from 1878 to 1881, showed a decrease from 15.2° Centigrade to 13.27° -Centigrade. - -Records made by Hall from 1825 to 1827 give averages of 16.1° -Centigrade, 15.52° Centigrade, and 15.6° Centigrade. This decrease -holds good for all points in the inter-Andean region where records have -been kept. - -Yet we know that the falling temperature in the northern temperate -latitudes is not brought about by a yearly increase of cold, because, -when the arctic channels are somewhat obstructed with icebergs, the -movement of arctic waters through them is lessened; and, therefore, -during such times the Gulf Stream, meeting with less opposition from -arctic currents while flowing northward, is able to move a larger -volume of its waters into the arctic seas, thus warming their waters -sufficiently in a few seasons to clear the obstructed channels, and -also somewhat soften for several successive years the temperature of -such lands as border on the seas of that region. - -And in this way we account for the mild seasons which at times follow -those of lower temperature in high northern latitudes. - -But, when the detained icebergs are set adrift, and currented into the -temperate North Atlantic, the heat consumed while melting such numerous -bodies of ice is able to more than overcome the warmth gained during -the temporary detention of ice in the northern seas. Thus, under such -considerations, it appears that the conditions are favorable for the -growth of glaciers in the high northern latitudes. - -I have pointed out the manner in which the superior oceans in the -southern hemisphere are obtaining a lower temperature, and how -they impart their coldness to the tropical currents, and in this -way slowly cool the waters of all oceans. Thus it appears that the -northern temperate zone, with all other parts of the earth, is slowly -approaching a cold epoch. - -Several writers on climatic changes have expressed their views as to -the number of glacial and mild periods that have been perfected since -the conditions have been favorable for their appearance on the globe. -According to my views, while considering the reasons for the occurrence -of the great glacial periods which have left such extensive traces on -the land, it seems certain that two very cold epochs have possessed -the earth, separated by a warm period; and, possibly, other preceding -cold epochs of less intensity have possessed the high latitudes, with -intervening periods of mildness. But the earlier cold periods, if they -ever existed, were comparatively short, because the Cape Horn channel -during such times possessed less capacity than in the later periods, -and, therefore, was more easily and quickly obstructed by the natural -methods previously explained. - -Consequently, the independent circulation of the southern ocean was -sooner arrested than during the later epoch, when the channel had -become enlarged by erosion from heavy glaciers and icebergs; and -meanwhile the same conditions may have governed the arctic channels -which give an independent circulation to the arctic waters which -surround Greenland, and thus, in connection with cold epochs in the -southern hemisphere, have caused periods of cold of small intensity to -occur in the high northern latitudes, and it may happen in the future -that more ice periods will be perfected than the one now progressing. - -Still, it is well to bear in mind that the Cape Horn channel, which -is the real cause of glacial periods having occurred in both the -northern and southern hemispheres, in the manner previously explained, -is being made wider and deeper during each succeeding ice age. For -this reason the latest cold epoch will require a longer continuance -of cold to obstruct the channel than the cold period preceding. -Therefore, it appears that the time will come when there will be such -great accumulations of ice stored on the land and in the sea before -the enlarged Cape Horn channel can be closed that, when it is closed, -there will not be sufficient warmth remaining in the tropical seas to -unite with the sun’s rays to subdue the intense cold stored in the -immense gatherings of ice. And thus the earth, which began its career -with a warm temperature, and so continued for long ages, will finally -terminate in an endless glacial age. - -The statements made by General Cowell in _Science_ of Nov. 25, 1892, in -reference to the alleged discovery of the second rotation of the earth -by Major-general Drayson, represents the discovery as affording a new -solution for the cause or causes of an ice age. - -The second rotation as defined consists in the pole of the heavens -describing a circle around a point which is ascertained to be -situated six degrees distant from the pole of the ecliptic. And it -is asserted that by a knowledge of the second rotation it is proved -that a variation of twelve degrees in the extent of the arctic circle -and the tropics occurred not later than 13,500 B.C., “the tropics -varying in distance from the equator from the minimum of 23° 25′ -47″ to the maximum of 35° 25′ 47″, thus extending the torrid zone -during its widest expansion from Cape Hatteras to the river Plate.... -It is calculated that at this date we are about 403 years distant -from the time when the pole of the heavens in its revolution, the -pole of the ecliptic and that of the second rotation, will be in -the same colure,--that is, in the year 2,295 A.D.; and then the -least differences in temperature between summer and winter will be -experienced. From that time forward this difference will increase, and -about 6,000 years later, or about the year 8,300 A.D., the earth will -enter the next glacial period, and attain its greatest severity about -the year 18,136 of our era.” General Cowell does not state how the -widening of the tropical zone, as above set forth, would bring about -a glacial period. The winters of the temperate zones would evidently -be colder than now; but, on the other hand, the summers would be -proportionally warmer, while the westerly winds above the latitudes of -40° would prevail the same as now. - -Therefore, their general effect on the surface waters of the ocean -in the high latitudes would not be changed with such an extension of -the tropical zone, neither would the trade winds change their general -direction with a wider torrid zone; yet the boundaries of the trade -winds and also the westerly winds would be more shifting according to -the declination of the sun, such winds being governed as now by the -position of the sun during the summer and winter solstice. Yet the -natural process for moving tropical water into the high latitudes, or -excluding it therefrom, would not be greatly changed. - -Consequently, the expansion of the torrid zone to the latitudes named -by General Drayson would not affect the climate of the hemispheres -sufficiently to cause a frigid epoch. On the contrary, the summer -monsoons, which now blow from the north-east, along the shores of -Eastern Africa, and also along the coast of Southern Brazil, would be -much stronger with a vertical sun in midsummer as far south as river -Plate, thus forcing the surface waters of the tropical oceans into the -higher latitudes with greater facility than at this age. - -Moreover, according to the statements of General Cowell, the present -period of mildness should be on the increase, and obtain perfection -in the year 2,295, or about 400 years hence; while, on the contrary, -according to the explanations we have given in the preceding pages, -there is much to show that an ice age is advancing, and has made -considerable progress in the high latitudes of both hemispheres. -Furthermore, if the second rotation, as claimed by General Cowell, -is able to perfect a glacial period at regular intervals of 31,600 -years, it seems that traces of frigid epochs should not be confined to -late geological records, as there appear to be little or no traces of -glacial work prior to the Quaternary or Post-tertiary periods. - -It appears that explanations so far given, which depend on the -astronomical theory to account for the ice age, are not in harmony with -well-known geographical facts. The explainers neglect the attention due -to the great prevailing winds which since the earlier geological ages -have, in connection with continents, moved the surface waters of the -ocean from torrid latitudes to colder zones, and from the colder zones -to the warmer latitudes. - -This exchange of ocean waters between the zones is as old as the -continents which shape their courses. The important change wrought in -the ocean currents sufficient to have caused the glacial age which -ended the early warm epochs was brought about through the action of the -prevailing winds, which, in connection with the form of continents, -became able to move the ocean waters from the northern hemisphere into -the southern sufficient to submerge the low lands of the southern -hemisphere, causing a great diversion of the tropical currents from -the high southern latitudes, such as I have pointed out in preceding -chapters. - -Those writers who believe that ocean currents have been the cause of -great climatic changes have suggested that the existence of an ancient -channel through the isthmus of Panama would have caused a frigid period -on lands bordering on the northern shores of the Atlantic by turning -the head-waters of the Gulf Stream into the Pacific Ocean. - -Professor Agassiz thinks that such a channel existed during some remote -geological age, judging from the semblance of the fauna pertaining to -the Caribbean Sea and Pacific Ocean. - -Yet it may be said that an open channel through Central America would -have connected two high sea-levels. - -For this reason there would be little or no exchange of water between -the Caribbean Sea and the Pacific Ocean. - -The high sea-level on the Pacific side is caused by the prevailing -north-west winds which blow down the North American coast past -California as far south as Central America; while, on the other hand, -the south-east trade winds impel the surface waters of the South -Pacific along the coast of Peru down to the equator, and so onward 5° -to 8° north latitude. Thus the space between the ending of the two -ocean winds obtains a high sea-level, corresponding to the high level -of the Caribbean Sea. This has been proved from levellings for the -Nicaragua ship canal. - -Consequently, the Atlantic waters would not run into the Pacific Ocean, -even if a channel opened through Central America. - -Therefore, the Gulf Stream has never been turned away from the North -Atlantic. - -Writers, while seeking a cause for the mild climate of ages preceding -the glacial epochs, have thought that during such times channels -opening through Asia from the Indian Ocean by the way of the Persian -Gulf into the arctic seas would be the means of furnishing the Arctic -Ocean with warm water. But it is evident that such a movement of water -could not be brought about, because the winds would not be favorable -for it. For, when we reflect that the prevailing winds would blow in -the same direction as now, and that the seas of Eastern Europe and -Western Asia were enlarged during the warm epochs, it seems that they -would obtain high levels superior to the high level seas of the Indian -Ocean. - -Besides, we should consider that there is a continuous range of high -land separating the Persian Gulf from the northern seas, which probably -existed anterior to the ice age. Still, during later periods, while -the ice-sheets were being melted from the northern hemisphere and also -on the ending of the last ice age, the Isthmus of Suez was submerged, -as were all other low lands in that latitude; but it is probable that -the waters of the high sea-level of the Indian Ocean abreast tropical -Africa did not flow largely into the Mediterranean Sea for the reason -that the enlarged European seas, being within the westerly wind-belt, -maintained a high sea-level, while at the same time the high level -tropical Indian Ocean waters were strongly attracted into the southern -oceans through the Mozambique and Agulhas currents in the manner I -have previously explained. Yet the waters of the high sea-level of the -southern European seas must have been strongly attracted to the low -sea-level abreast the Canary Islands. - -While considering the causes which brought about the glacial periods, -it is well to reflect that the natural mode of action which could have -produced a frigid age was as extensive as the surface of the globe; -and, therefore, any geographical change that would affect only a -comparatively small portion of the earth cannot serve to account for -ages of warmth which extended over the globe, or for glacial epochs -which were separated by warm periods of time, which seem to have -affected all lands and seas. - -And it appears from the geographical explanations given in preceding -pages of the general movements of the winds and currents of the sea how -impossible it is for heat to be conveyed to the antarctic latitudes -sufficient to prevent the growth of glaciers on their lands while the -Cape Horn channel is in possession of its present capacity. - -For, as has been shown, this channel furnishes opportunity for the -westerly winds to impel the surface waters of the great southern ocean -constantly around the globe, and so largely turns away the tropical -currents from the high southern latitudes. - -Consequently, there seems to be no method yet devised through nature’s -mode of action that can carry sufficient heat into the antarctic -latitudes to melt the ice-sheets from the southern continent, or even -arrest their growth, while the Cape Horn channel maintains its present -width and depth. - -Therefore, the increase of glaciers and icebergs will slowly continue -until a glacial epoch is perfected. - -And it seems that this arrangement for bringing about a frigid age -made slower progress in its early stage than at this date, owing to -there having been a lack of glacial ice in the polar regions to produce -icebergs for cooling the ocean waters. But the independent circulation -of the great southern ocean, after turning away the tropical currents -from the high southern latitudes for thousands of years, did at length -cause glaciers to form on the antarctic lands, which have been slowly, -but constantly increasing; and, consequently, the cooling of the ocean -has been accelerated proportionate to the increase of ice-sheets. -Therefore, with the cooling process so well advanced as it now appears -to be, it seems that more than half of the time required to bring a -frigid age to perfection has been expended since ice-sheets began to -gather on the antarctic shores. For, when we realise how the facilities -for making ice have advanced through the increase of glaciers in both -hemispheres, and how large a portion of the ocean waters have been -cooled below a temperate or tropical temperature even in the torrid -latitudes where the warm upper waters of the ocean have been reduced -to a comparatively thin stratum when compared to the vast bulk of the -cooled under-waters, it appears that the cold will increase at a faster -rate for the next thousand years than was the case during the last ten -centuries. Therefore, the climate will be less favorable for plants and -animals existing on lands in the high latitudes for the next thousand -years than during the ten centuries preceding; and, when we take into -consideration the accelerative growth of a frigid epoch, it seems that -the increasing cold will in a few thousand years drive the greater -portion of both plants and animals from the now temperate latitudes to -maintain an existence in the tropical zone, where a large part of the -existing species of such life must have taken refuge during the last -ice period. - -And, from what can be learned from the relics of man’s prehistoric -life, it seems to point to the lands of the tropical latitudes as -having been his home during the frigid ages; and, because of his long -undisturbed residence in favored portions of the tropics, he there -attained his earliest civilization. For it appears that the tropical -zone was not only less burdened with ice in glacial times than the -higher latitudes of the globe, but was also more exempt from the -great flooding of lands which obtained in the more northern latitudes -through the shifting of the ocean waters, from causes set forth in the -preceding pages. Yet it may be said that the low lands of the tropical -zone south of the equator during cold epochs were much more extensive -than at this age, on account of the shrinkage of the sea, because of -the great amount of water evaporated from its surface, and stored in -ice-sheets on the great continents and islands. Hence the reefs and -shallows which surround such tropical islands as include the Seychelles -Archipelago, and also the extensive banks covered with shoal water -in that portion of the Indian Ocean, were during the glacial period -elevated above the surface of the sea, possessing a climate favorable -for vegetable and animal life. But, owing to the great rain-fall of -that region, it is probable that the highest lands were glaciated, -as it is reported that granite bowlders still rest on the mountain -slopes of the highest island. The numerous islands and shoals of the -south-western tropical Pacific must also have afforded wide land areas, -with a temperate climate, owing to their having been situated on one of -the warmest regions of the earth during the ice age. - -Moreover, it is probable that these tropical lands afforded space for -numerous lagoons which had little connection with the surrounding -oceans, and consequently were able to maintain, in their secluded -shallow basins, a warmer temperature than obtained in the open seas; -and at the same time, owing to the great rainfall in such tropical -portions of the Indian and Pacific regions, the waters of the lagoons -were rendered less salt than the briny depths of the shrunken oceans -of a cold period. Hence because of such conditions the fauna of the -tropical seas were preserved from the destructive rigor which beset the -earth during the frigid epochs. - - - - -Transcriber’s Notes - - -Punctuation, hyphenation, and spelling were made consistent when a -predominant preference was found in the original book; otherwise they -were not changed. - -Simple typographical errors were corrected; unbalanced quotation -marks were remedied when the change was obvious, and otherwise left -unbalanced. - - - - - -End of the Project Gutenberg EBook of The Coming Ice Age, by C. A. M. 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