New York, March, 1842. — The island on which New York stands is composed of gneiss, as are the cliffs on the left bank of the Hudson, for many miles above. At Hoboken, on the opposite side of the river, cliffs are seen of serpentine, a rock which appears to be subordinate to the gneiss, as in many parts of Norway and Sweden. All these formations, as well as the syenite of Staten Island, correspond very closely with European rocks of the same order.

Long Island is about 130 miles in length, and the town of Brooklyn, on its western extremity, may be considered as a suburb of New York. This low island is every where covered with an enormous mass of drift or diluvium, and is the most southern point in the United States, where I saw large erratic blocks in great numbers. Excavations recently made in the Navy Yard at Brooklyn have exposed the boulder formation to the depth of thirty feet; the lowest portion there seen consisting of red clay and loam, with boulders of trap and sandstone, is evidently the detritus of the New Red Sandstone formation of New Jersey. This mass, in the sections where I observed it, was about eighteen feet thick, and rudely stratified. Above it lay an unstratified grey loam, partly of coarse and partly of fine materials, with boulders and angular blocks of gneiss, syenitic greenstone, and other crystalline rocks, dispersed at random through the loamy base, the whole being covered with loam eight feet thick.