192 
[Assembly 
northern termination of the 7th avenue; and in a number of places in 
the valley of the Harlem river, between McComb's dam and Kings- 
bridge. Now the nearest locality where this rock is found in place, is 
at Kingsbridge, and I have no doubt the boulders in question came from 
this place; but had they been transported in the general direction of the 
current shown to be northwest and southeast, instead of reaching their 
present location, they would have been carried across the Harlem river, 
and have been deposited in the range of grounds lying about midway 
between Harlem and Westfarms. Specimens are forwarded. 
5. Granite and gneiss, especially the latter, being abundant in every 
part of the island except the northern extremity, boulders of these 
might be expected to be more numerous than of any other materials; 
yet I think greenstone boulders are quite as numerous, take the whole 
island together, as granite and gneiss. The largest boulders I have 
seen of the latter kind, measured in diameter 12 and 18 feet, and are 
equally common in all parts south of the Harlem and Manhattanville 
valley. The granite, which exists in veins in the gneiss, is mostly on the 
west side of the island; and this when torn from its place and trans- 
ported by a northwest current would naturally have been distributed 
over the eastern parts, and even as far as Long-Island. A number of 
very large ones were excavated between 1825 and 1830, in the vicinity 
of Corlear's hook, some of which were peculiar in character. One I well 
remember lay many years on the south side of East-Broadway, near its 
junction with Grand-street. It was a gray granite of coarse texture, 
with tabular crystals of black hornblende 3 or 4 inches in diameter in- 
terspersed throughout. It was 18 feet long, 16 broad, Sh high. This 
is the largest boulder I have seen on the island, but those from 10 to 
12 feet diameter are very common. 
A large boulder of granite, 11 feet in diameter, and though somewhat 
rotund, has a rough and angular surface, as though it had suffered little 
from mechanical violence, rests on the gneiss rock on the east side of 
Bloomingdale road, from a quarter to half a mile south of the village 
of Manhattanville, and at the southwest corner of a Mr. Stevens' house^ 
between it and the road. The whole rock on which it rests is covered 
with diluvial grooves, and a very large one 3 inches deep and IS wide 
between the road and the boulder, and terminating at the latter, seems 
to have been the result of the movement of this huge mass. Specimens 
are forwarded. 
