Page:Popular Science Monthly Volume 10.djvu/460

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444
THE POPULAR SCIENCE MONTHLY.

the Ice age is shown in the interesting fact revealed by the United States Coast Survey, and noticed by Prof. Dana, that the old valley of the Hudson River exists a well-defined depression in the bed of the ocean through a distance of 89 miles southeastward from Sandy Hook. It is termed on the Coast Survey chart "a remarkable gorge." The soundings show that it comprises a continuous series of deep depressions in the ocean's bottom. Some of these are eight miles long and from one and a half to two and a half miles wide. The map (Fig. 4), kindly furnished by the publishers of Prof. Dana's "Manual of Geology," shows how the dotted lines of equal depths bend toward Sandy Hook, indicating the line of deepest water, or the old river-valley in question.

PSM V10 D460 Continental shelf off long island and new jersey.jpg
Fig. 4.—Map of the Submerged Border of the Continent off Long Island and New Jersey, with Lines of Equal Soundings in Fathoms. (From Dana's "Manual of Geology," p. 422.)

The Coast Survey chart shows us that at 28 miles from Sandy Hook the depression is 90 feet below the banks or ocean-bottom on either side. At 39 miles and at 51 miles the depression is 60 feet, and at 74 miles it is 72 feet, and at 89 miles it is 492 feet.

The average depth of the ocean over this depression is about one-third greater than on either side.