Page:Popular Science Monthly Volume 13.djvu/675

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the Coast Survey, to be distinctly marked upon the sea-bottom out to a point some eighty miles southeast of New York, and where the water is now over 500 feet deep. Here we reach the true margin of the continent, where the shore plunges rapidly down into the depths of the ocean; and here was for ages the mouth of the Hudson River; for the channel which leads to it could not possibly have been excavated except upon a land-surface.

2. Explorations made over a large part of the territory lying between the Atlantic and the Mississippi show that many of the draining streams are now flowing far above their ancient beds, and that these sometimes lie below the present ocean-level. For example, the Ohio flows in a valley the bottom of which is occupied by sand and gravel at least 100 feet thick. The rock-bottoms of the streams which empty into the Great Lakes are at their mouths sometimes 200 feet below the water-level. The Mohawk Valley is filled to a great depth with loose materials, the surface of which forms for long distances a nearly level plain, through which the present river meanders.

Innumerable instances of this kind could be cited, all of which go to prove that for ages the eastern half, at least, of this continent stood 500 to 600 feet higher above the ocean than now, and that during this time the draining streams with swiftly-flowing currents cut the surface into a network of deep channels not unlike the canons of some of the rivers of the far West.

There seems to be good reasons for believing also that in this period of elevation the stream which drains the basin of the Great Lakes, called in different parts of its course the St. Mary's, the Detroit, the Niagara, and the St. Lawrence, flowed not through the modern channel, which passes the Thousand Islands and the Lachine Rapids, but, leaving the basin of Lake Ontario at its southeastern corner, traversed the now deeply-buried channel of the Mohawk, and entered the present valley of the Hudson somewhere near Albany—precisely where has not yet been determined, as heavy beds of drift cover and conceal its course for many miles in that vicinity. From Albany this ancient Hudson River flowed through a deeper and wilder valley than the present one, which is half filled with water, passed what is now New York Island, far below the present water-surface, was joined at the Battery by a large tributary from the east, issued from the highlands by a picturesque gate at the Narrows, and, traversing a littoral plain, emptied into the ocean eighty miles southeast from New York.

The limits of this article will not permit the presentation of all the facts which sustain this view, but a few of them will suffice to show that it hardly admits of doubt. These are briefly as follows:

An ancient connected line of drainage passes through the basin of the Great Lakes at least 200 feet below the present water-surface, deepening eastward, and reaching a level much below that of the bed of the St. Lawrence.