F. D, Chester—Gravels of Southern Delaware. 41 
smaller quantity of quartzitic pebbles from one-half to three 
inches in diameter; and in still rarer cases, as at Milford and 
Seaford, cobblestones and small bowlders have been dug out 
of the white and red sand deposit. Bowlders are, furthermore, 
everywhere found covering the surface of the estuary sands to 
even the southernmost limit, some of the largest being found at 
Snow Hill, Md. They therefore must have been dropped by 
ice-rafts borne upon the waters of the Post-Glacial estuary, in 
which were deposited the white sand and gravel upon which 
they lie. In the neighborhood of Seaford, one may readily 
perceive the relation of the dunes to the estuary sand. 
ile the former are extremely loose and fine, free from 
even the smallest pebbles, the latter is a rather coarse loam, 
containing enough clay to hold it together and sometimes to 
pack hard, mixed with a due proportion of fine gravel. In- 
stead of the meridional sand hills having been produced by 
the blowing in of that material from the sea, it seems more 
probable that they were made by the shifting and accumula- 
most on species is the modern oyster (0. Virgintca). 
These have been found in some four or five localities of Sussex 
sie Near Dagsborough a nest of broken fragments of the 
with Venus mercenaria and Fulgur canaliculatus. For an exam- 
ation of these modern shells from the Astuary sands, I am 
indebted to Professor Angelo Heilprin. 
