Page:Popular Science Monthly Volume 10.djvu/454

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438
THE POPULAR SCIENCE MONTHLY.

marsh abounds in stumps; a great number of large size, some of them three feet in diameter, have been seen by the writer at the verge of low water, and we have found them many rods from the shore where the water was ten feet deep.[1] This area was certainly a portion of the original swamp when the land was sufficiently elevated to lift it above the level of the sea.

It is not necessary to further illustrate the present subsidence of this coast, but evidence of the extent of the movement will be of interest.

PSM V10 D454 Section through dyker meadows.png
Fig. 1.—Section through the Dyker Meadows.
Horizontal scale, four inches to the mile; vertical scale, twenty feet to the inch.

In constructing the Erie Basin at Brooklyn in New York Harbor, Mr. George B. Brainerd, engineer, found the following series of deposits, the water being ten feet deep at low tide: Three and a half feet of mud, sand, etc.; ten feet compact peaty meadow. This gives twenty-three and a half feet of depression since the bottom of that meadow was the surface, and covered with vegetation at the level of the sea.

In 1867 John Nadir, Esq., United States Engineer at Fort Hamilton, carefully examined, by boring, the underlying formation around Fort Lafayette. The earth was penetrated to a depth of 53 feet at points between 800 and 1,000 feet from the shore, where the water at low tide was ten feet deep. The deposits passed through were as follows: twenty feet coarse sand and gravel, with few broken shells; three feet decayed meadow, with shells and, Diatomaceæ; seventeen feet gravel and sand, with broken shells; thirteen feet mud, quite compact, which appears to have been a marsh with scanty vegetation, and shells.[2] This indicates a subsidence of the coast of at least sixty-three feet, or, in other words, the land of the coast was that number of feet higher than it now is, when the subsidence began. But there is reason to conclude that the elevation was much greater than sixty-three feet. If we take a step backward in the order of events, we find that, immediately previous to the elevation mentioned, there occurred a great depression of the coast. Possibly the highest hills of the

  1. "Cedar-swamps, buried beneath the meadows on the New Jersey coast, have yielded logs six feet in diameter, and some with 1,000 rings of growth."—Prof. Cook's Report.
  2. The shells were identified by Mr. A. R. Young, of Brooklyn, as follows: Nassa obsoleta, Anomia ephippium, Mya arenaria, Crepidula fornicata, Solen ensis, and Mytilus edulis.