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Published online by Cambridge University Press: 01 May 2009
The hornblendic and associated rocks referred to in the above title cover a large part of the township of Cortland—the north-western of Westchester County, New York—between Croton River on the south and the parallel of Peekskill on the north, an area of about 25 square miles. They differ widely from the ordinary rocks of the county, and may well be designated the Cortland series. In fact, a series so remarkable in constitution, so diversified in kinds, and so full of geological interest, is seldom found together within so small an area anywhere on the globe. They reach the banks of the Hudson just south of the Peekskill railroad station, and at several points beyond; yet considerable portions of the shore region are occupied by narrow strips of common kinds of mica schist and gneiss, and occasionally limestone.
page 59 note 1 This article is one of a series by Prof. Dana on the Limestone belts and associated rocks of Westchester County, New York, published in the American Journal of Science, volume 20. Westchester County is the Southern County of Eastern New York. The Hudson River bounds it on the west, and New York Island—the site of New York City — on the south. Its rocks are, with small exceptions, ordinary gneisses, mica schists, and crystalline limestone.
page 62 note 1 A detailed study of the rocks of the Cortland region has already been begun, at my suggestion, by the accomplished lithologist, Dr. G. W. Hawes.Google Scholar
page 63 note 1 This rock looks like the norite, but contains augite in place of hypersthene. If its felspar is chiefly labradorite (a point yet in doubt), it does not differ in mineral constitution from dolerite or diabase, or a prominent part of the so-called gabbro
page 64 note 1 These chrysolitic rocks usually have, on a fresh fracture, the cleavage surfaces of the hornblende or augite spotted with chrysolite; but the presence of chrysolite, however abundant, cannot be made certain without slicing for microscopic examination, since the chrysolite is slightly altered externally, and such spots on hornblende crystals may be due to small imbedded crystals of augite. If the cleavage of the hornblende has an unbroken surface, it is probable that the rocks contain no chrysolite. The hornblendite has much stronger lustre than the pyroxenite.