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 Western63 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 the64 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 Neuchatel. 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 different65 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,66 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 passed67 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.68 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.69 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 Ca............