ALLUVIAL DIVISION. 
33 
cliffs, conjointly with land springs, which in some localities convert the beds of sand into a 
quicksand, cause the mass of superimposed materials to flow off from the slippery clay beds. 
Land slides on a small scale, are of very common occurrence on many parts of the north 
coast of Long Island. They are in some places caused by the sea undermining the cliffs, so 
that the superincumbent masses crack at a short distance from their edges, and slide down to 
a lower level, carrying with them trees and shrubs, and sometimes even without changing 
their relative position. These phenomena are common along the north shore in Suffolk 
county, but they are more striking and numerous where there are clay-beds, and particularly 
so, where the clay slightly inclines towards the sea. Where the cliffs are high, they present 
an appearance of steps, in consequence of the successive slides. (Vide fig. 1.) 
Another cause of slides is, the undermining action of land springs, which often convert sand 
into quicksand, so that it flows from the cliffs, and bears along with it the superincumbent 
masses; but in most instances they are caused by springs, rendering the upper surface of 
clay beds slippery, so that large masses from the cliffs slide down upon the shore, and even 
into the sea. Several acres have thus slidden off at once, and sunk in level from twenty to 
one hundred and fifty feet. By this means ravines of considerable extent are frequently 
formed. (Vide fig. 2.) 
c Quicksand. Island, 
d Clay beds. 
Small slides have been observed about Albany, caused by springs rendering the clay slip¬ 
pery next the rock, which is frequently smooth, and allows large masses to slide into the 
ravines and valleys below. 
The slides at Troy during the summer of 1836, and on the 1st of January, 1837, were also 
caused by springs of water. The locality at which these slides took place, presented a nearly 
vertical face of gravel and clay beds, of two hundred and twenty-seven feet in height. The 
upper part of the cliff probably cracked, and the land spring (which forms a considerable 
stream of water, and which from some unknovm cause had been stopped,) filled the fissure, 
Geol. 1st Dist. 5 
