156 
GEOLOGY OF THE FIRST DISTRICT. 
the great accumulation of the sandy materials on the coast of Long and Staten islands ; and 
the causes of the deposition of these materials there has already been given. 
It has long been supposed that a great lake formerly existed above the Highlands, and many 
speculations have been made concerning it, and the rending of the mountains so as to drain it 
off; but the quaternary and drift deposits found in the valleys undisturbed, demonstrate that 
the channel through the Highlands existed nearly the same during those two epochs, as it is 
at present; so that from these circumstances we know it has been an open channel of commu¬ 
nication between the Atlantic and the St. Lawrence basin, during, and since those two epochs. 
The coarse deposits of gravel and pebbles, and even boulders, in the valleys near the nar¬ 
row passes of the Highlands, of Little-Falls, the Noses, and wherever the current was 
confined, seems strongly to favor the view, that the elevation by which these formations were 
raised above the level of the sea, was not so slow an operation as that of the elevation of the 
coast of Sweden, and it may have been sudden. 
I have seen but two classes of facts that afford evidence of a shifting of the position of 
rocks^, that can be referred to this geological period, that might not have been produced pre¬ 
viously. 
1. One of these is a fault in the clay and gravel beds near Newburgh, where the clay and 
sand horizontally stratified were separated by a vertical line on the surface exposed, each 
abutting against the other, with little disturbance of either, and covered by beds of coarse 
gravel, evidently deposited after the fault had been formed. This locality was where there 
had been no slide or derangement of the strata since the deposit of the gravel beds, and where 
no present causes could wash the gravel, which was the top of the hill, and on a high bank 
where excavations had been made for clay, and sand, about one-half or three-fourths of a mile 
below Newburgh on the shore of the Hudson. It was observed when making a geological 
exploration with a class of my pupils, from the U. S. Military Academy at West-Point, in 
1834. Other facts of this class have been observed on Long island and in the Hudson valley, 
but less conclusive. 
2. The other class is where the slate rocks on the east side of the Hudson valley had been 
ground down, smoothed, deeply grooved and scratched across their edges ;* and since the 
action that had produced these effects, the masses of slate had been shifted a few inches in a 
vertical direction by a slight fault, so that the grooves and scratches on the lower part of the 
mass were continued quite up to that part that had been elevated ; and on the upper mass, the 
same grooves that had been once continuous, were prolonged in their former direction, with 
the same breadth and depth. This shift of position, or slight fault, must have been subsequent 
to the period when the scratches were made, or the scratches could not have been continued 
close up to the vertical surface of the more elevated portion, and without wearing the sharp 
edge of the slate on the upper portion of the shifted mass. This locality was where the 
* Most of the rocks in place in the Hudson valley, when uncovered from the drift or quaternary that covers them in many 
places, show their surfaces to have been ground off, as if by the attrition of heavy moving masses of rock, and are scratched 
and grooved. 
