Page:Popular Science Monthly Volume 13.djvu/677

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GEOLOGICAL HISTORY OF NEW YORK.

ation of this long line of drainage. As has been remarked, it is of great and yet unknown depth. The clay by which it is partially filled has been penetrated to a depth of about 100 feet along its margins. How deep it is in the middle portion can only be conjectured; but Hell Gate channel, which has been kept comparatively free by the force of the tides, is in places known to be nearly 200 feet deep; and, since this is a channel of erosion formed by a stream draining into the Hudson, the ancient bed of the Hudson must be still lower.

From the depth and distinctness of the old river-course on the submerged plain outside of the Narrows, we may reasonably infer that the old channel at New York is not much less than 300 feet deep.

We are compelled to conclude from these and other facts of similar import: 1. That the topographical features of the vicinity of New York were for the most part fashioned by the erosion of a system of watercourses which, in preglacial times, when the continent was higher than now, cut their valleys much deeper than would now be possible.

2. That there was here a group of hills composed of crystalline rocks, a sort of spur from the Alleghany belt, and that this range of hills was then seventy or eighty miles inland from the ocean, separated from it by a plain similar in its topographical relations to that which lies between the highlands of our Southern States and the present shore of the Atlantic.

3. At the period under consideration a river draining the basin of the Great Lakes, and in size the second on the continent, followed the course of the Mohawk and Hudson, and, passing through the New York hills, there left the highlands and flowed quietly on to the ocean.

4. Where New York Harbor now is, this great river received two important tributaries—one from the east through Hell Gate channel, which joined it at the Battery, the other from the west through the gorge of the Kill van Kull. Of these, the first is now represented by the Housatonic, then a larger stream, with a longer course and more tributaries; the second was formed by the Passaic and Hackensack, which united at the head of what is now Newark Bay, arid emptied into the Hudson at the entrance to the Narrows. The junction of these two considerable branches so near each other seems to have produced the expansion of the valley which is now New York Harbor. This must then have been a very picturesque spot, as its outlet oceanward was a narrow pass bordered by the hills of Staten and Long Island, 500 feet in height. On the north, it was overlooked on one hand by the great wall of the Palisades, which rose 700 feet above the river; on the other, by a bold shoulder or headland, 400 feet in height, now New York Island, then a promontory, which separated the Housatonic and the Hudson to their junction at its southern extremity.

5. After the lapse of unnumbered ages, during which this nook among the hills was slowly prepared for the important part it was to play in the history of the yet unborn being—man—a quiet subsidence