Review of Recent Geological Literature. 375 
corner of Noxontown mill-pond in Delaware while the 
other end reached the shore of the Potomac river near the 
mouth of Potomac creek. 
While the upper and lower portions of the Eocene dififer 
in the character of their fauna and in lithological composition 
sufficient to separate the formation into two divisions there 
is no doubt but that deposition went on continuously through- 
out the entire Eocene period and the increasing thickness 
southward is doubtless to be accounted for by supposing that 
the Cretaceous shore-line was more nearly stationary in cen- 
tral Delaware while the region farther south was undergoing 
more rapid and prolonged subsidence. In this way it was 
possible for the young of Terebratula harlani and of Gryphaea 
vesicularis to migrate southward and, passing beyond the Cre- 
taceous limit, to continue its existence in the warm and deeper 
waters of southern Maryland. Whether the few feet of Eo- 
cene marl in New Jersey represents the entire period or not 
we cannot say, but inasmuch as there is a line of non-deposi- 
tion in Delaware where the Miocene rests directly on the 
Cretaceous this line was either stationary or elevated 
while deposition was going on both to the north and to the 
south of this area. If this is not the case then there was a 
period of erosion in some stage of the Eocene, for the Miocene 
rests uniformly along the entire region from Shark river in 
New Jersey to southern Maryland. It is possible that more 
detailed study of the region of central Delaware will yield ad- 
ditional facts, though the author of this paper has made a 
pretty careful examination of all the available exposures in 
that state. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Maryland Geological Survey, \o\. I, iSg/. VVm. Bullock Clark, 
State Geologist. The Johns Hopkins Press, Baltimore, Md. 
The first report issued by the Maryland Geological Survey is of a 
preliminary character and the subjects treated are largely historical 
and introductory. Part I. discusses the establishment, plan of opera- 
