DRIFT DIVISION. 
185 
satin spar; slaty rocks of various textures and colors, as fine-grained slaty grits ; slate like 
roofing slate, of a blue colour, others red and mottled, coarse and fine ; and siliceous slate 
and basanite, are those that rank second in relative numbers. Limestones like the various 
limestones and calciferous rocks of all the Hudson valley, blue, grey, black, compact, crys¬ 
talline, and fossiliferous ; conglomerate like that of the Shawangunk mountains ; opalescent 
feldspar rock like that of Schroon in Essex county, and pebbles of the Potsdam sandstone, 
are next in relative numbers. Specimens of these rocks can all be referred to their proper 
strata, without much chance of error, and all are evidently and undoubtedly derived from a 
northwardly source. 
The rocks mentioned are now well known in 'place, their localities and extent, and will be 
described under their proper heads. The deposits of drift may be seen well developed at 
West-Point, and along the gravel terrace from the base of the Crow’s Nest to three miles 
below West-Point, and also on the opposite bank of the Pludson one-fourth to one-half of a 
mile from the river. The boulders and erratic blocks have been mentioned as attaining to a 
height of about one thousand feet; and there the mass in some places seems to stop suddenly 
on the northern flanks of the mountains, as if an ancient shore had there existed.* 
The valley of Smith’s clove contains boulders of conglomerate like that of Skunnemunk 
mountain; of granite, gneiss, etc. like the Highlands ; grits and slates like those of the 
Hudson valley, and pebbles of the Potsdam sandstone. Boulders of other rocks are found, 
but those of the vicinity are most numerous. 
Dr. W. Horton, who made the geological examination of Orange county, and who has 
been many years an attentive observer of its geology, speaking of its boulders and erratic 
blocks, says: 
“ These are found in the county in the greatest profusion. Most of the surface is thickly 
dotted by them, and in many places they are so numerous as to prevent cultivation. Under 
this term, however, it is not intended to comprehend any rocks or stones, except such as have 
been removed to considerable distances from the place of their formation. Over the whole 
surface, from the Highlands on the southeast, to the Shawangunk mountain on the northwest, 
perhaps nine-tenths of the loose stones are greywacke. Many of them are unlike any rock 
of this description in the county, while others resemble and no doubt were broken up from 
the layers upon and near which they now lie. The parent rock of the former is to be sought 
for beyond the bounds of the county ; but where, has not fallen under my observation. 
‘“Boulders of greywacke similar to that of the Catskill, Shawangunk and Helderberg mountains, are very numerous in many 
places in the Highlands of New-York. They are found on the summits of the mountains, on their sides, and in the valleys ; 
but they are far more numerous in certain localities than in others. On the northwest slope of the Highlands towards the great 
valley, and in the upper part of the high lateral, transversal and longitudinal valleys, they are most numerous, and in some 
instances seem almost to form a kind of horizontal belt encircling the irregularities of the ground, similar in figure to that which 
would be cut out by a plane passed horizontally, or nearly so, through the hills at the level where they are most abundant.” 
(Mather on Diluvion, West-Point, 1835, pp, 14, 15.) 
Geol. 1st Dist. 
24 
