Page:Popular Science Monthly Volume 8.djvu/372

358 are small; some of them exceedingly minute. We found, in specimens of drifted sand, 1,920 particles in the weight of a troy grain. This will give, for a pound avoirdupois, more than 13,000,000, and about 1,450,000,000 in a cubic foot of sand. The comparison of a "great multitude" to the "sands of the sea-shore" is wonderfully vivid and impressive. Examined by the aid of a microscope, these delicate grains are seen to have lost the sharp, angular features of broken quartz, and closely resemble pebbles, irregular in form, but smooth and rounded. They are wave-worn bowlders on a small scale.

This beach, which is seldom more than one-third of a mile broad, constitutes the coast-line from Coney Island at the entrance to New York Harbor, to the Nepeague Hills, a distance of about one hundred miles, but broken by occasional inlets through which the tides ebb and flow. Throughout this distance, scarcely a pebble of any considerable size occurs. Mather, in the "Geological Survey of the State of New York," commenting on this magnificent beach-line, says, "In Europe, there is no deposit of a similar character to compare with it in extent."

Eastward from the Nepeague hills, which are of sand, along the ocean-side of Montauk Point, high bluffs of bowlder-drift reach the shore, strewing it with their falling débris. Here may be seen on a grand scale the process by which rocks are transformed into the fine sand of which the beach is composed. The waves throw their whole force upon the shore, carrying forward with tremendous roar tons of bowlders and pebbles which roll back as the waves recede. This process is repeated with every wave. The stones thus rolled and tossed lose something of their volume, and scarcely one can be found that does not show signs of disintegration and decay. All of them are penetrated by moisture, some are fractured by frost, and others, weakened by chemical changes, are dashed in pieces. The sand-beach represents the silicious matters of these comminuted rocks. Its position along the coast is determined by the set of the waters, but its contour of sand-hills is determined by winds. These, in their endless play, have carved it into every form possible to drifting sands. Mather observed that "where the beach is above the reach of the surf, it is covered by a labyrinth of hillocks of drifting sand, imitating almost all the varieties of form which snow-drifts present after a storm." These are sand-dunes, or dunes, as they are termed by Lyell, and their surprising mobility, in the ever-changing direction and force of the winds, is a subject of scientific and popular interest.

Everywhere on the beach, in a dry, windy day, the sand-grains on the surface are in motion. They are not carried through the air like dust, except to a limited extent, when the winds are violent, but roll or bound along the surface. Their motion, therefore, represents to the eye, although less perfectly than snow or dust, the motions of the invisible air.