Excerpt from The Geology of Central and Western Minnesota: A Preliminary Report The gently undulating contour of most of this region appears to mark areas over which the ice-sheet moved in a continuous current, and from which it disappeared by melting that was extended at the same time over a wide field. The inequalities of surface are very slight in comparison with the thickness of the drift, and the average height generally rises or falls imperceptibly, its slope being often not more than 50 or 100 feet in as many miles. These general changes in altitude, which affect the whole country and give direction to its drainage, are doubtless produced by differences in height of the bed-rock upon which the drift lies as a sheet, probably some what uniform in depth; but the small elevations and depressions appear to be due to the accumulation of different amounts of till in and beneath adjoining portions of the moving ice-sheet. This unequal deposition of the drift has produced the multitude of lakes which dot the map of Minnesota. The lapse of time since the ice-age has been insufficient for rains and streams to fill these basins with sediment, or to cut outlets low enough to drain them though in many instances we can see such changes slowly going forward. 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.