No. 275. j 
191 
eating the mechanical violence to which ihey have been exposed. This 
rock is not found in place on the east side of the Hudson, but is the chief 
rock on the v^estern shore, from Tappan bay on the north to Bergen 
hill on the south; and as all the varieties found in place there can be 
selected amongst the boulders here, the necessary inference is, that this 
locality is also the source of the greenstone. Specimens forwarded. 
2. Red sandstone^ like the greenstone, is common to every part of 
the island, being found from Corlear's hook to Kingsbridge, but most 
abundant towards the former place. These boulders vary considerably 
in appearance, as well as in size. Though occasionally consisting of 
coarse pebbles, they are generally fine grained, of a red or grayish red 
colour, and distinctly stratified. I have found some that measured 9 or 
10 feet in diameter. This rock, like the greenstone which it accompa- 
nies along the Jersey shore, is not found on the island, nor on the east 
side of the Hudson nearer than the valley of the Connecticut. 
There are two other varieties which I have referred to the red sand- 
stone formation, but on account of their peculiar character as boulders, 
I will describe them by themselves under the name of ferruginous sand- 
stone and claystone. Specimens forwarded. 
3. Serpeniine^ like that at Hoboken, is common in the southern, but 
rare in the northern parts of the island. In speaking of serpentine, w^e 
shall make a distiction between that variety found in place at Hoboken, 
and that found at the anthophyllite locality on the island, which ap- 
proximates to serpentine in character, but is harder and is mixed with 
limestone. These boulders are much more common in Brooklyn than 
in this city, except perhaps the region of Corlear's hook. This might 
be expected, taking for granted that they were transported from Hobo- 
ken, which seems to be a necessary conclusion, as no other locality of this 
variety is known in the vicinity. Besides, the direction of the diluvial 
grooves being from northwest to southeast is such as would carry the 
materials from Hoboken to Corlear's hook, and the east part of 
Brooklyn. 
4. White or Primary Limestone. Boulders of this material were found 
some years ago in cuttmg away the hills at Corlear's hook, and in a 
number of places on the east side of the island, between the city and 
Kingsbridge; but I have neither seen nor heard of any being found on 
the western side. The principal places where I have found this rock, 
are on the 4th avenue near 120th-street; at the 7th avenue, north of 
the village of Harlem, near I42nd-street; at McCorab^s dam, at the 
