540 
GEOLOGY OF THE FIRST DISTRICT, 
The first of these seems to be similar to the trap of the Pallisades ; the other is a more 
crystalline rock, composed principally of hornblende, with some felspar, and, like granite, 
forms beds, interlaminated masses, veins and irregular intertruded masses among other rocks. 
The trap dykes were observed among the rocks of this class in a few places, the principal 
of which will be enumerated. 
1. The trap dykes and interlaminations among the gneiss, granite and white limestone, 
already described under the white limestone near Duck-cedar pond in Monroe. 
2. The dykes at the Two ponds in Monroe. 
3. The greenstone in gneiss about three-quarters of a mile southwest of West-Point. It 
is near the outlet of a small marsh, and a nitch has been cut in the rock to drain it. It scarce 
shows itself on the surface. Small but perfect crystals of hornblende are sometimes found 
in masses of this trap. In a quartz vein in the gneiss a few rods farther north, small scales 
of sulphuret of molybdenum are occasionally found, but specimens can be procured with 
difficulty. This is not mentioned as a locality for collecting this mineral, but merely to show 
where a few specimens have been obtained. 
4. The dykes through granite on Stony point. 
5. Dykes of trap and serpentine traverse the hornblendic rocks west of the granite on 
Stony point. Prof. Beck, speaking of this place, says, “ On the western side of this point, 
there is a coarsely crystallized hornblende, and with this is associated the mineral usually 
called kerolite or magnesite. Two parallel dykes of trap pass up the northwestern face of 
the point, and are distinctly visible by a coating of white magnesian minerals. The rock 
which has formed the wall of these dykes has disintegrated, and the debris cover the whole 
of the side-hill. The trap is filled with veins of kerolite of different varieties, some of which 
closely resemble those of Hoboken and Staten island. There are also other magnesian mine¬ 
rals, and veins of a beautiful silky amianthus are not uncommon.”* 
The granular greenstone is similar to that described in Putnam and Westchester counties, 
of the texture of a sandstone, , composed of grains of hornblende and felspar • the former 
predominating, and the latter being light colored; and like that rock, it forms interlaminated 
masses and beds, veins, and irregular intertruded bodies of rock among the gneiss, granite, 
hornblende, and other rocks of the Highlands. It may be seen in almost every hill and 
mountain in the Highlands. The Crow’s Nest and Butter hill may be referred to as localities ; 
also the hill on which Fort Putnam is located, near West-Point. 
The rock called “ primitive greenstone,” merely because under this name it has been 
described by various authors, (although the name is inappropriate,) consists of a crystalline 
aggregate of hornblende and feldspar. It passes into the granular greenstone and trap on the 
one hand, and into sienite on the other, and may more properly be included among the horn- 
hlendic rocks. Hornblende predominates and gives character to the rock. 
» Fourth Annual Report of the Geology of New-York, p. 91. 
