( e. ) 
REPORT 
Of L. D. Gale, to W. W. Mather, on the Geology 
of New- York county. 
GEOLOGICAL SURVEY OF THE ISLAND OF NEW-YORK, 
This island is about twelve miles long, and from a half of a mile to 
two miles and a quarter broad. 
To give a clear view of the geology of the island, it will be necessary 
to state in general terms the character of the neighboring rocks, boul- 
ders of which there is good evidence to believe are found on almost 
every part of the island. 
Taking the Hudson river as the dividing line, we have on the east, 
the island of New- York, and the southern portions of Westchester 
county, consisting of gneiss and its subordinate rocks, as serpentine, 
hornblende^ primary limestone, anthophyllite rock, and perhaps a few oth- 
ers; while on the west in the contiguous State of New-Jersey, we have 
red sandstone in all its varieties; serpentine, greenstone in all its varieties, 
with the minerals usually accompanying these rocks. 
The basis rock of the island is gneiss, if we except about one mile in 
length of the northern extremity, which is limestone. The middle and 
northern portions are rough and broken from the almost constant expo- 
sure of the rock above the surface; while the southern, although con- 
sisting of the same material, is every where covered, and in some places 
to great depths, with alluvial* and diluvial deposits. 
The gneiss varies considerably in character in different portions of 
the island. For example, the northern part abounds largely in lime- 
* Whether some of these alluvial deposits referred to, especially the beds of sand found un- 
der the diluvium, are as old as the tertiary or not, I will not pretend now to determine. 
[Assem. No. 275.] 23 
