Page:Popular Science Monthly Volume 45.djvu/209

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the present gorge of the Ohio just below Cincinnati, the river would at once begin the process of cutting down its new channel. A waterfall of far larger proportions than Niagara must have been at once developed in the lower portion of this short cut, near the junction with the Great Miami, which would steadily wear back toward the old channel at Cincinnati, when, if the ice had not reached so far, the water level above the dam would be speedily lowered, but only to be raised again at a later time when the advancing ice reached its farthest extent and obstructed the newer channel. It is altogether probable, however, that this new channel below Cincinnati had not been lowered to its full extent before the maximum advance of the ice. If this were the case the final retreat of the ice across the river would leave a rocky barrier below Cincinnati, such as to maintain the water for a while at a level much higher than that maintained at the present time. There are some deposits up the river indicating that this was the case, as, for instance, some in Teazes Valley extending from the Kanawha River to Huntington. By reference to the first map it will be perceived that this valley is less than seven hundred feet above tide, but it is covered with several feet of very fine sediment, distributed evenly over the bottom of the valley, which must have been deposited in still water during the later stages of the Glacial period.

A glance at the first map will also show some other most interesting problems of change in drainage systems caused by the Glacial period which have not been adequately studied; for example, it will be noticed that a stream rising near Madison, Ind., pursues a very singular course with reference to the contour lines. This is the Muscatatuck River, which rises within less than a mile of the Ohio River and four hundred feet above it; but instead of following the strike of the strata, as it naturally would, around to Louisville, it cuts across a broad north-and-south valley of erosion to join the East Branch of the White River, when both together, continuing on in a westerly course, follow a gorge several hundred feet deep through the highest portion of the State till they unite with the West Branch of the White River to reach the Ohio through the Wabash. It is extremely difficult to explain the course of this stream, except by some such process of reasoning as has been adopted with respect to the Ohio below Cincinnati. The projection of the tongue of ice which extended below Madison deflected the drainage of a considerable region through a partially formed pass across the elevated plateau to the west, while the morainic deposits about the farthest extension of the ice lobe permanently obstructed the channels in that direction, so that upon the withdrawal of the ice the Muscatatuck still continued to run into the Ohio by way of the Wabash.