Lf. D. Chester— Distribution of Delaware Gravels. 171 
20 feet is found to rest directly upon the Cretaceous with an 
entire absence of the Red Gravel. Also between Gravelly 
Hill and Charleston the same features are prominent; the 
Philadelphia stratum varies from a refractory white clay to a 
coarse yellow and white gravel, while the surface is literally 
strewn with cobble stones and bowlders, making the country 
unusually barren, : 
Near the neighborhood of Christiana, and from there to New 
Castle, the clay rises in high hills along the creek, where it is, 
In places, entirely replaced by bowlders and cobble stones, rep- 
Tesenting the Potsdam, Millstone Grit, and Trias. 
he true brick clay is confined to the low flat lands along 
the border of the Archean hills, where the extensive brick 
yards of Wihnington, Newark and Elkton obtain material for 
the best variety of brick; but traveling to the south, especially 
between Kirkwood and the Canal, or to’ the southwestern 
limits of the region, the clay changes to a sandy loam or even 
& yellow and gray sand, which is always mixed with its due 
Proportion of gravel. eee 
Th ed Gravel varies still more than the clay in its litho- 
logical characters, and consists of coarse red, yellow and gray . 
Sands, mixed with very characteristic white oval quartzose 
pebbles varying in size from a bean toahen’segg. 
From the similarity between widely separated sections, the - 
Red Gravel seems to have a rough arrangement into three dis- 
Unct strata with quite constant lithological differences. This 
alTangement is no doubt continuous, although there are local 
€Xceptions where only two out of the group of three are repre- 
Sented. In all cases, however, the order of superposition re- 
Mains the same, while each stratum maintains its own In ividu- 
ality. Beginning with the base of the Philadelphia clay, the 
following is the order, with the characters of each stratum. 
"4,77 ted sand mixed with characteristic oval quartzose pe 
bles, varying in thickness from 8 to 10 feet. ‘'he amount of 
