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Updated: May 23, 2025
The variety we find, both as to the contours and the collocation of the islands, is due chiefly to differences in the structure and composition of their rocks, and the unequal glacial denudation different portions of the coast were subjected to. This influence must have been especially heavy toward the end of the glacial period, when the main ice-sheet began to break up into separate glaciers.
He was a bold man who first conceived the idea of the great continental ice-sheet which in Pleistocene times covered most of the northern part of the continent, and played such a part in shaping the land as we know it. That bold man was Agassiz, who, however, was not bold enough to accept the theory of evolution as propounded by Darwin.
Traces of an ice-sheet, thousands of feet in thickness, beneath whose heavy folds the present landscapes have been molded, may be found everywhere, though glaciers now exist only among the peaks of the High Sierra. No other mountain chain on this or any other of the continents that I have seen is so rich as the Sierra in bold, striking, well-preserved glacial monuments.
Elias, together with the multitude of separate river-like glaciers that load the slopes of the coast mountains, evidently once formed part of a continuous ice-sheet that flowed over all the region hereabouts, and only a comparatively short time ago extended as far southward as the mouth of the Strait of Juan de Fuca, probably farther.
The idea of the great glacier did not conflict with Agassiz's religious predilections, and the theory of evolution did. It was a bold generalization, this of the continental ice-sheet, one of the master-strokes of the scientific imagination.
Notwithstanding the absence of lofty mountain-chains in America, we are not wholly without the means of measuring the thickness of the ice-sheet, by comparing it, as in Europe, with some of our highest elevations.
The flowing or the creeping of this old ice-sheet, so that it could transport large boulders hundreds of miles, is one of the most remarkable things about it: as slow or slower than the hour-hand of the clock, yet an actual progression, carrying it, in the course of thousands of years, from its apex in Labrador well down into New Jersey, where its terminal moraine is still clearly traceable.
Now this great valley, extending for more than twenty-five degrees of latitude, is a CONTINUOUS GLACIER BOTTOM, showing plainly that for its whole length the great southern ice-sheet has been retreating southward in it. I could find nowhere any indication that glaciers descending from the Andes had crossed this valley and reached the shores of the Pacific.
Whether they date from our driving back by the polar ice-sheet, together with our titanic Big Game, the woolly rhinoceros, the mammoth, and the sabre-toothed tiger, from our hunting-grounds in Siberia and Norway, or from recollections of hunting parties pushing north from our tropical birth-lands, and getting trapped and stormbound by the advance of the strange giant, Winter, certain it is that our subconsciousness is full of ancestral memories which send a shiver through our very marrow at the mere mention of "cold" or "sleet" or "wintry blasts."
This Palaeolithic race seemed to come to a mysterious end, and Europe was then invaded by the higher Neolithic race. England was probably detached from the Continent about the end of the Magdalenian period. It was thought that some great devastation the last ice-sheet, a submersion of the land, or a plague then set in, and men were unable to retreat south.
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