The Geological History of Lake Superior

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Excerpt from The Geological History of Lake Superior: Read Before the Canadian Institute, Toronto, April 15th, 1899 Before the advent of the glacial period a great part of North America stood at an elevation of 3000 feet or more above its present level, and the disintegration and removal of the rocks due to rainfall alone, which was facilitated by the greater elevation, went on for a vast length of time. This is proved by the existence of long and deep river valleys, some of them running down from the central parts of the continent to the present sea coasts, and beyond them into the depths of the ocean. The old valley of the St. Lawrence can be traced for 800 miles. The ancient bed of the Hudson has been followed by soundings, from its present mouth, down the slope of the bottom of the ocean far out to sea, The canon of the Saguenay, and those of the Grand or Hamilton and other rivers of Labrador, as well as the channels of many of the long straight lakes and river stretches in the Archaean country to the north and northwest of us, are due partly to atmospheric and aqueous erosion during a long geological period while the land stood at higher levels. It can be shown that the grade of the Mississippi from its source to the sea was much steeper formerly than now, the present modification or lowering of the slope amounting to some feet. The valleys thus excavated guided, to a considerable extent, the movements of the great glaciers which ploughed the surface of hill and dale, excavating and carrying forward vast quantities of the softened surface rock, together with harder portions in the shape of fragments, boulders and pebbles, which together constitute our till or hard-pan and other deposits, collectively called drift. The general tendency of the glacial action would be to enlarge the main valleys of the preglacial surface and to fill up or modify the smaller ones. The geological structure and the relative resisting powers of the rocks were the primary or fundamental causes which predetermined the loca tion, direction, extent, etc., of the valleys and basins thus formed by the combined action of aqueous denudation and glacial action. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.