1881 .] 
139 
[Wright. 
over this ground and in extending investigations to the upper waters 
of the Delaware, I will now endeavor to put into intelligible 
shape the facts, both new and old, which bear upon the inter- 
esting question announced as the subject of this paper. 
The city of Trenton is built upon a horse-shoe shaped gravel 
deposit which is about three miles in diameter, extending back 
about that distance to the east from the present river. This 
deposit is somewhat lower along its inland boundary than along 
the river. The prongs of this horse-shoe rest, one at Trenton, 
and the other about two miles below, just this side the house 
of Dr. Abbott. 
The characteristics of this gravel are thus accurately described 
by Professor Shaler : 
The general structure of this mass is neither that of ordinary boulder 
clay nor of stratified gravels, such as are formed by the complete rearrange- 
ment by water of the elements of simple drift deposits. It is made up of 
boulders, pebbles, and sand, varying in size from masses containing one 
hundred cubic feet or more to the finest sand of the ordinary sea beaches. 
There is little trace of true clay in the deposit. There is rarely enough to 
give the least trace of cementation to the masses. The various elements 
are rather confusedly arranged ; the large boulders not being grouped on 
any particular level, and their major axes not always distinctly coinciding 
with the horizon. All the pebbles and boulders, so far as observed, are 
smooth and water- worn ; a careful search having failed to show evidence of 
distinct glacial scratching or polishing on their surfaces. The type of 
pebble is the sub-ovate or discoidal, and though many depart from this 
form, yet nearly all observed by me had been worn so as to show that their 
shape had been determined by running water. The materials comprising 
the deposit are very varied, but all I observed could apparently with reason 
be supposed to have come from the extensive valley of the river near which 
they lie, except, perhaps, the fragments of some rather rare hypogene rocks.” 
It is now settled beyond controversy that the rocks from which 
these beds were derived are all in place in the upper Delaware 
valley. (See N. J. Rep., 1877, p. 21 ; Lewis on Trenton Gravel, 
p- 5 -) 
The distinction between the river gravel and that which 
overlies the larger part of southern New Jersey is marked in 
several ways. The Trenton gravel is much coarser than the 
