174 
GEOLOGY OF THE FIRST DISTRICT. 
About half or three quarters of a mile from Plandome, on the road to Hempstead court¬ 
house, is an enormous block of granite, undoubtedly an erratic block, which was estimated 
by the eye to contain eight hundred cubic yards above the surface of the ground, and must 
weigh near, two thousand tons. Blocks like this, of fifty to five hundred tons weight, are not 
uncommon ; but this block is the largest I have seen that was solid, and had not been cracked 
into fragments by natural causes. This block may be the same described by Dr. Mitchill ? 
in Bruce’s Mineralogical Journal, as containing 20,400 cubic feet.* 
About two and a half miles north of Plandome, on the shore of Cow bay, I found a large 
block of tremolite containing pargasite and talc. It had been blasted for making a stone fence. 
It is somewhat similar to a rock found at Warwick and Edenville, Orange county. A speci¬ 
men may be seen in the case containing the drift of Long island, in the State Museum at 
Albany. 
Granite and gneiss form the largest portion of the boulders and erratic blocks of Great neck, 
in the northwest part of North-Hempstead. Much of the gneiss is hornblendic gneiss, and 
the hornblende may be considered as the basis, it being the predominating ingredient. In 
some of these masses, granular epidote is very abundant, forming nearly one-half the mass, 
and its proper descriptive name would be epidotic hornblendic gneiss. A large nest of these 
blocks, containing perhaps one hundred tons, maybe seen at high-water mark, on the north¬ 
east shore of Great neck, near the outlet of a salt pond. Another nest of hornblendic gneiss 
blocks, (which may possibly be in place,) may be seen at high-water mark on the north¬ 
west shore, near Hewlet’s point. Boulders of tremolite, like that on Cow neck, were seen 
in several places on Great neck. Boulders and blocks of white granular limestone, like the 
Westchester limestone, were observed on the northwest shore, between Hewlet’s point and 
the ferry. Some of them contained an abundance of white tremolite, in bladed crystals and 
large masses. 
In Flushing township, boulders of greenstone trap predominate from Flushing to Little- 
neck bay. Two miles from Flushing village, on the road to Little-neck bay, some small 
boulders of serpentine were observed. Three miles from Flushing, many boulders of grey 
sandstone, with grains from the size of mustard seed to gravel, were noticed. They are 
composed of grains of quartz and feldspar, most of which are rounded, and the latter are in 
a state of decomposition, forming white, pulverulent or crumbling grains, which give a whitish 
color to the masses of rock. This rock slightly resembles a crumbling feldspathic granite, 
for which it has been sometimes mistaken. Dr. J. F. DeKay, the Zoologist of the Geologi¬ 
cal Survey, informed me, that a rock of precisely similar aspect underlies the trap rock of 
the Palisades, at or near Bull’s ferry, on the New-Jersey side of the Hudson. It probably 
belongs to the red sandstone formation underlying the trap. 
At two and a half miles from Flushing, a large boulder of greenstone was observed on the 
south side of the road. It was covered with “diluvial” scratches. 
* Bruce’s Mineralogical Journal, Vol. 1, p. 133. I have the reference, but not the book, and there is no library in this vici¬ 
nity that has a copy of the work. 
