190 F. D. Chester—Distribution of Delaware Gravels. 
physical importance of these morainic gravels that one is imme- 
diately led to the study of them in their relation to the Dela- 
ware flood history. 
_ Generally speaking, we may say that the whole region is 
covered with an upper stratum of yellow brick clay, sand, 
loam or loamy gravel, having an average thickness of about 
three feet, which is underlaid by a thicker stratum or series of 
strata of gravel and sand, varying largely in its characters and 
degrees of coarseness, and having a usual thickness of from 3 
to 20 feet. The former homogeneous stratum we shall call, . 
after Professor H. C. Lewis, the Philadelphia Clay, and the 
latter less homogeneous deposit, after the same author, the 
Red Gravel. Although the Philadelphia Clay-and the Red 
Gravel are generally distinct deposits, with their well marked 
characters, such is not always the case, for the two often run 
into each other indistinctly, the underlying gravel becoming 
slowly argillaceous as the surface is reached, or again the june- 
tion between the two being entirely obscured, or at best but aa 
indistinct wavy line. We therefore regard the two as contem- 
poraneous deposits, with little or no break in the deposition, 
the one requiring quiet and the other troubled conditions of 
sedimentation. Considering these facts it seems proper that the 
two indistinct deposits, i. e, the Philadelphia Clay and the — 
Red Gravel should be included under one head, which we — 
shall hereafter cal] the Delaware Gravels. Bs 
The Philadelphia Clay—The Philadelphia Clay or loam 8 
micaceous, and although sometimes entirely free from gravel 18 — 
upon the 
So true is this latter statement that often the deposit assumes 
the characters of a true bowlder clay, which fact has led other 
geologists to regard it as the same material transported — 
i facie 
clay, and rising in high hills with intervening bowl-like depres: 
sions. This diluvial stratum which ranges in depth from = 
