Page:Popular Science Monthly Volume 10.djvu/459

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443
THE LONG ISLAND COAST.

ness of the upper portions may suggest a shoaling of the coast from an upward movement of the land as the Ice period came on.

That an elevation occurred during the progress of the Ice period is evident from the contour, as well as structure, of the drift of Long Island. On the north side of the island are numerous fiord valleys, constituting a series of harbors of unsurpassed beauty. They extend

PSM V10 D459 Gas well section in brooklyn.jpg
Fig. 3.—Section of the Nassau Gas-Light Company's Well in Brooklyn.

into the island from two to six miles, having depths of water from tan to thirty, and in some instances fifty feet. Beneath the water is a deep deposit of ooze or sediment, known to be in one case forty feet thick. The banks on either side are from a few feet to 200 feet high.

It is apparent that these enormous valleys were not wholly cut into the drift after it was deposited, but rather were maintained while the deposit of drift was in progress, as valleys or water-courses, through which glacial streams may have been discharged into the ocean. These became filled, however, by an excessive accumulation of drift, as from rapid wasting of the ice, causing the outflowing streams to be arrested, and the waters to be discharged eastward or westward from Long Island Sound. But whether they were formed as we suggest, or were cut into the drift after it was deposited, it is quite certain that the coast was sufficiently elevated to permit the glacial floods to sweep the bottom of those valleys.

The 70 feet of drift of the Nassau Gas-Light Company's well is wholly below tide, and its unmodified structure shows that it was deposited above the sea-level, or out of the reach of waves, and further confirms the elevation of the coast in the glacial period.

But evidence of the elevation of the coast during the progress of