500 CLARK AND BIBBINS 
ery of vertebrate remains of Jurassic affinities in these forma- 
tions is not, however, sufficient grounds for the reference of the 
entire Potomac group to the Jurassic period. 
The Patapsco formation has afforded a rich flora in which 
dicotyledonous types are not uncommon. The fact that dicoty- 
ledonous forms have never been found elsewhere in rocks earlier 
than the Cretaceous is strong presumptive evidence of the 
Cretaceous age of these deposits; at the same time the fact that 
many other forms are identical or closely related to those of 
European horizons, generally referred to the Cretaceous, further 
substantiates this view. It is the opinion of Professor Ward, 
who has exhaustively studied the flora of this formation, that it 
is equivalent to the lower divisions of the Lower Cretaceous of 
Europe. Professor Ward has divided what the authors here 
recognize as a single stratigraphic unit into several zones, each 
with its characteristic plant forms, which, he states, give evi- 
dence of constantly progressive types in passing from the lowest 
to the highest members of the series. Whether these different 
zones represent a sequence of floras, or to a considerable extent 
local aggregations of forms under different physical conditions 
but of equivalent age, the authors are unable to determine, 
although they strongly incline to the latter view. The abun- 
dance of vegetation having a prominent cycadean element sug- 
gests a repetition of the mild climatic conditions which prevailed 
during the Arundel deposition. 
The fossils of the Raritan formation are in the main distinct 
from those of the Patapsco and include a large assemblage of 
dicotyledonous types with much more modern affinities. Simi- 
lar forms are found in the Tuscaloosa beds of the south, and 
it is the belief of Professor Ward that these deposits repre- 
sent the Raritan formation in the north. The Raritan beds 
show strong floral affinities with the upper portions of the lower 
Cretaceous of Europe (Albian), and, according to Professor 
Ward, it is not impossible that the higher members of this for- 
mation to the north of New Jersey may even represent the basal 
portions of the upper Cretaceous as well (Cenomanian). 
