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.