Review of Rece?it Geological Literature. 319 
In arguing for the upper Cretaceous age of the Comanche Bose 
considers "of much value the occurrence of Vola qninqiiecostata, 
Protocardia hillana, Exogyra flabellata, Ostrea carinata and Ostrea 
dituviana,iovms that are typical for the Cenomanian and the Turo- 
nian; they are found in Mexico partly in the Comanche series, partly 
in the equivalent limestone of Orizaba." But these forms are all of 
types that have a great stratigraphic range and unless identified with 
the greatest care should be used with much caution in correlation un- 
less they are supported by more distinctly characteristic species. Un- 
fortunately when such names once get into the literature as identified 
from a certain formation they are just as good as any others to juggle 
wilh in making up percentages and other devices that are supposed 
to indicate homotaxy or relationship. 
The presence of the ammonite genus Engonoceras is also consid- 
ered significant as it is said to occur only in the Cenomanian in Eu- 
rope. This fact loses \veight when it is known that Engonoceras 
pedernalis, which may properly be considered the type of the genus 
is a Coirianche (Fredericksburg) species and that some, and probably 
all of the European species referred to Engonoceras do not belong to 
it as properly restricted. 
It is not possible nor desirable at the present time to attempt a 
strict correlation of the Comanche series wnth the European Creta- 
ceous. It is hoped that within a few months the invertebrate fauna 
will be published in such a form that it will afTord a more substantial 
basis for comparisons. Meanwhile it should be remembered that dur- 
ing the past fifteen years the geological work in Texas, in which Mr. 
R. T. Hill was the pioneer, has established many im.portant facts that 
must be considered in all such comparisons. No American geologist 
or paleontologist claims that the Comanche series as a whole corre- 
sponds to the lower Cretaceous of Europe, but that it does form a 
natural and very important distinct series in the American Cretaceous. 
It is overlain by an immense thickness of upper Cretaceous beds of 
which an upper portion is easily referred to the Senonian, while a 
lower portion — the Fort Benton and its equivalent, the Eagle Ford, 
■with Inoceramtis labiatns — is well correlated with the Turonian. Still 
lower and immediately above the Comanche series comes the Da- 
kota sandstone and its equivalents. Its relationship with the Co- 
manche is proving closer than had been supposed, and it may eventu- 
ally be assigned to it. Its flora is usually regarded as Cenomanian 
by the American paleobotanists. It is evident, therefore, that the 
upper part of the Comanche — the Washita division — can not be 
younger than the Cenomanian. It is interesting to note in this con- 
nection that the Washita contains an abundant ammonite fauna of the 
general type of Schloenbachia inflata, which in Europe characterizes 
a zone (the Flammenmergel) that is by some authors put in the basal 
Cenomanian and by others in the Gault. Beneath this comes the great 
thickness of the Fredericksburg and Trinity divisions with their varied 
faunas which must find their places in the Cretaceous system and evi- 
dently cannot all be assigned to one horizon. 
