Page:Popular Science Monthly Volume 68.djvu/321

Rh Canadian geologists. Singularly enough, the views are, if anything, less original than those of the workers on this side of the line. The establishment of a geological survey of Canada under Logan led to the publication of the now well-known volume of 1863. The views here expressed may be accepted as a summary of the knowledge relating to the glaciation on Canadian territory, as it then existed.

Concerning the region of the lake basins of western Canada, Logan wrote:

These great lake basins are depressions, not of geological structure, but of denudation, and the grooves of the surface rocks which descend under their waters appear to point to glacial action as one of the great causes which have produced these depressions. This hypothesis points to a glacial period when the whole region was elevated far above its present level and when the Laurentides, the Adirondacks, and the Green Mountains were lofty Alpine ranges covered with perpetual snow from which great frozen rivers or glaciers extended over the plains below, producing by their movements the glacial drift and scooping out the river valleys and the basins of the great lakes.

In his address before the Natural History Society of Montreal in 1864 J. W. Dawson took occasion to combat vigorously these ideas of Logan, and this on the ground that 'it requires a series of suppositions unlikely in themselves and not warranted by facts'; that it seems physically impossible for a sheet of ice to move over an even surface striating it in uniform directions over vast areas; that glaciers could not have transported the large boulders and left them in the positions found, having no source of supply; that the peat deposits, fossils, etc., show that the sea at that period had much the same temperature as the present arctic currents, and that the land was not covered by ice.

In describing the course of the rock stria? he announced that he had no hesitation in asserting that the force which produced those having a westerly direction was from the ocean into the interior against the slope of the St. Lawrence Valley, and as he could not conceive of a glacier moving from the Atlantic up into the interior, he considered this as at once disposing of the glacial theory. He conceived, rather, that a subsidence took place sufficient to convert all the plains of Canada, New York, and New England into seas. This, he felt, would determine the direction of the Arctic current which moved up the slope. He would account for the excavations of the basins of the Great Lakes by supposing the land so far submerged that an Arctic current from the northeast would pour over the Laurentian rocks on the northern side of Lake Superior and Lake Huron, cutting out the softer strata and at the same time transporting the debris in the form of drift to the southwest. Glaciers were not wholly dispensed with, but limited to regions of mountainous elevation.

J. S. Newberry, while director of the geological survey of Ohio (1869-78) had frequent occasion to discuss glacial phenomena, and a