52 GEOLOGICAL SURVEY OF THE TERRITORIES. 
such a reference, especially as the strata immediately overlying that 
group contain an abundance of mammalian remains of Hocene-Tertiary 
types, while no such mainmalian types occur in the Laramie Group. 
The following facts, however, favor the view which I have advocated, 
that the Laramie is really a transitional group between the Cretaceous 
beneath and the Tertiary above. 
We have yet no knowledge of the existence of any Cretaceous strata 
in North America which, according to Huropean standards, are equiva- 
lent with any part of the Lower Cretaceous of Europe; all known Cre- 
taceous strata of this continent being usually regarded as of the age of 
the Upper Cretaceous of that part of the world. 
The Fox Hills Group has consequently been regarded as equivalent 
with the latest Cretaceous of Hurope, a conclusion which is sustained 
by the character of its fossil fauna. The Fox Hills Group of Western 
North America is evidently exactly equivalent with the upper portion 
of the Cretaceous deposits of the Gulf and Atlantic States, where the 
marine Hocene deposits rest directly and conformably upon the Creta- 
ceous, with no intervening strata that can be regarded as paleontologic- 
ally equivalent with the Laramie Group. If, therefore, these parallel- 
isms are correctly drawn, asthey appear to be, the Laramie, as a complete 
group, cannot be as old as the latest recognized Cretaceous strata in 
either this or any other part of the world. Again, if those three groups 
of fresh-water strata which immediately overlie the Laramie Group, 
namely, the Wahsatch, Green River, and Bridger Groups, are really of 
Hocene-Tertiary age, as they are accepted by all paleontologists to be, 
then is there additional evidence of the correctness of the view that the 
Laramie is a transitional group between the Cretaceous and the Ter- 
tiary, partaking of the faunal characteristics of both periods. It should 
also be stated that paleontologists have generally agreed in referring 
the Wasatch, Green River, and Bridger Groups to the earlier Hocene. 
In the two publications before cited I have shown that the strata of 
the Judith River and Fort Union series of the Upper Missouri River 
region; the lignitiec series east of the Rocky Mountains in Colorado 
and the adjacent region, and the Bitter Creek series and its equivalents 
west of the Rocky Mountains in Wyoming and Colorado, which were 
formerly treated as separate groups, are all merely regional divisions of 
the great Laramie Group, all being faunally connected together by the 
specific identity of a considerable proportion of their fossil remains.* 
In those publications I also included in the great Laramie Group that 
series of strata which have become well known as the Bear River series, 
its best known development being in the valley of Bear River, in the 
southwestern part of Wyoming, but equivalent strata being known 
many miles to the northward of that valley, and also at intervals in the 
region of the Wahsateh range of mountains as far south as Southwestern 
Utah. That portion of this Bear River series, that is, the lower portion, 
which is of brackish water origin, contains a molluscan fauna, every 
known species of which is distinet, not only from those of other forma- 
tions, but different from any that are found in any of the other portions 
or regional divisions of the Laramie Group, before mentioned. This 
difference is evidently too great to be considered as a mere regional 
variation of the prevailing fauna of that period, and it becomes a serious 
question whether we ought not to regard that Bear River series and its 
* Professor Cope’s investigations of the vertebrate remains in these various regions 
have also shown that these regional divisions of the strata which are here referred to 
the Laramie Group all belong to one great and important geological period. 
