REVIEWS 571 
The Eocene representative, which was at first thought to consist of 
a single formation, and was called the Pamunkey formation, has since 
been differentiated into two stratigraphical units known as the Pamunkey 
group. ‘The lower of these, the Aquia, consists of greensands and green- 
sand marls interbedded with occasional shell layers. Locally the beds 
have been subdivided into zones. The upper member, the Nanjemoy, 
overlies the Aquia conformably and is composed of greensands, but 
differs from it in having a greater argillaceous and less calcareous con- 
tent. The contact is usually represented by a bed of white and pink 
clay. The combined thickness of the two formations is about 200 feet. 
The Eocene fauna is dominated by the presence of countless molluscan 
individuals; a total of 61 gasteropods, 60 pelecypods, and 30 protozoans 
are recorded. ‘There are also five species of reptiles and eleven of fishes. 
Miocene deposits have an extensive outcrop due both to their 
thickness and to their gentle dip. Four formations are recognized, 
known as the Chesapeake group. The basal member, the Calvert, 
rests unconformably upon the Nanjemoy, Aquia, Patuxent, and early 
crystalline rocks, and consists of fine-grained sands, clays, marls, and 
diatomaceous earths. Gypsum and glauconite are common in the clay. 
The width of the outcrop reaches 30 miles and is well shown in the coun- 
ties of King George, Essex, Caroline, and Hanover. Above the Calvert 
the St. Mary’s formaticn is present with an unconformity that represents 
the complete removal of the Choptank member which is present in 
Maryland. The deposits are similar to the Calvert except that dia- 
tomaceous earths are lacking. The upper formation, the Yorktown, is, 
so far as known, conformable upon the St. Mary’s. It is character- 
istically made up of beds of finely comminuted shells apparently accumu- 
lated in shallow water. Layers of clay and sand are also present. The 
faunas are rich and varied and, on the whole, indicate a marine origin 
for the Miocene strata. 
The Lafayette formation is placed tentatively in the Pliocene. It 
consists of unconsolidated sands and gravel, and where the deposits have 
been least eroded the uppermost beds are capped by loam that varies 
from a few inches to ro feet in thickness. It is markedly unconformable 
upon all the underlying formations, and is in contact, at one place or 
another, with almost every older formation in the region. It is prac- 
tically unfossiliferous. Its distribution is coextensive with the Lafayette 
terrace. 
The Pleistocene formations are all surface deposits and are, in general, 
represented by the terraces described in the early pages of the bulletin. 
