No. 275.] 11?7 
it disappears. A branch of it strikes off about two miles north of Ny- 
ack in a westerly direction, and extends, with perhaps some interrup- 
tions, to near the Highlands. These ranges of trap rock are narrow, from 
one-fourth to one mile, and in some places perhaps one and a half to 
two miles broad. Along the Hudson, and on the north front of the 
range extending west from Haverstraw, the trap rock forms high mural 
columnar escarpments, of 300 to 800 feet in height, with a steep slope 
of debris, which have been crumbled off from the cliffs above by the ac- 
tion of the weather and the frost.* On the western and southern sides 
of this range, the trap rock generally slopes off more gradually, but in 
a few places it is precipitous. It can scarcely be considered otherwise 
than an enormous projecting trap dyke. Dykes were observed in seve- 
ral places cutting through the sandstone, some of which were very large. 
Occasionally it was seen spreading laterally from the dykes between the 
strata of sandstone. Many facts of high scientific interest were observ- 
ed. They will be detailed in the final report on the Geological Survey 
of the State. 
ALLUVIAL DEPOSITS. 
Fluviatile Jllluvions. 
There are no alluvions of importance of this kind above water, that 
may not be classed as salt marshes. Tappan, Haverstraw and Peeks- 
kill bays are becoming more shoal by the deposition of alluvial matter 
in many places, and the larger steam-boats cannot go in to Dobbs' ferry, 
Tappan Slote, Nyack or Haverstraw, in consequence of the shoal water 
over these mud flats. There is a broad channel through these bays of 
considerable depth, but in many places the water is shoal nearer the 
shore, and large areas are becoming gradually more shallow, so that we 
may reasonably anticipate the time when they shall become land. The 
flats along the right bank of the Hudson, opposite West-Point, both 
below Gee's Point and near Camp-Town, have grown sensibly more 
shallow within the last fifteen years, during which time they have been 
under my observation. The same may be said of the flats between 
Constitution island and Gouverneur's landing, opposite West-Point, 
and between Constitution island and Cokl-Spring.f 
* There are several places where valleys pass through the trap range above described, but 
it is believed there are none where this rock is discontinued. The valley west of Nyack is 
perhaps the lowest, but even here the trap is seen at the summit of the valley. 
t In 1822, sloops used to come in at the foundry dock, about half way between Cold-Spring 
and the West-Point foundry, to take in their freight of cannon and other castings from the 
foundry, but the water has become so shoal that for some years past it has not been possible, 
and they now load at Cold-Spring, 
