* 
196 FD. Chester—Distribution of Delaware Gravels. 
hand, when a few steps beyond would bring me into a regiom 
of angular fragments again, while still further beyond, the un- 
broken expanse of gravel would be reached. | 
But the best evidence bearing upon this point is to be found 
near Newark. I have said that there the gravel only rises- 
about 100 feet above tide, where the rock is a very friable mica 
schist and plagioclase gneiss, both of which are now decaying 
with great rapidity. Iron Hill, as will be seen by the map, is. 
situated about three miles due south, and here I have found a 
few of the characteristic quartzose cobble stones within about 
30 feet of the summit or at a height of about 225 feet above 
tide, instead of 100 as is the case at Newark. These facts 
are enough to convince us that the present shore line is not the 
original one, which would, in many cases, considering the topo 
graphy, have to be several miles to the north. Taking the — 
facts as a whole, however, the depth of the estuary waters, oF 
depression of the land, must have been at least 350 feet, which 
depression would have sufficed to cover the whole peninsula 
with water, uniting the Delaware with the Chesapeake. 
glacial arm of the sea we shall most fittingly call the Delaware 
stuary. . 
The floor of the Estuary.—The base of the Delaware gravels, 
which is both the: plastic clay of the Cretaceous, and the up- 
turned edges of the gneiss, has everywhere suffered erosion. 
The red clay is generally a wavy irregular line, while the gneiss 
when not decomposed has been well worn. Clearly marked 
diluvial grooves have in several cases been seen running wit?” 
the direction of the current, whenever the upper edges of the 
rocks happened to be freshly exposed, while again the edges 
have undergone a rough polishing as from the corrasive action 
of transported sand. i 
Bowiders.—Besides the Delaware gravels, a most charactel! — 
itself, although they are contemporaneous and have the same — 
rock representatives. They are usually quartzose, including : 
the glassy, flinty and quartzitic varieties, and vary in size from 
several hundred pounds to a ton or more in weight. Great c 
piles of these have been collected from numerous fields. The — 
uartzose varieties, even those of several hundred pounds — 
weight, are all well rounded, evidently by water, and show ele 
glacial scratches. Those made up of coarse constituents tet 
more angular, and in some cases have shown obscure @VF 
dences of glacial markings, though as a general thing they . 
