WHITE ON PALEONTOLOGY. 629 



Cretaceous rather than the Tertiary age of the group. These hitter ex- 

 ceptions are some Inocerami that have beeu obtaiued upon the lower 

 confines of the group, and doubtfully referred to it rather than to the Fox 

 Hills group below ; and also a species of Odontobasis from strata near 

 the top of the group, two miles west of Point of Rocks Station, Wyom- 

 ing. The latter genus, established by Mr. Meek, is comparatively little 

 known, but it was, regarded by him as characteristic of the Cretaceous 

 period. This constitutes the slender evidence of the Cretaceous age of 

 the Laramie group that invertebrate paleontology has yet afforded. 



Again, the brackish- and fresh-water types of Mollusca that are afford- 

 ed by the Laramie and the lower portion of the Wahsatch group are in 

 most cases remarkably similar, and some of the species of each group 

 respectively approach each other so nearly in their characteristics that 

 it is often difficult to say in what respect they materially diifer. More- 

 over, they give the same uncertain indication as to their geological age 

 that all fossils of fresh- and brackish- water origin are known to do. 

 ■It is in view of the facts here stated, and also because I believe that 

 a proper interpretation of them shows the strata of the Laramie group 

 and the base of the Wahsatch to be of later date than any others that 

 have hitherto been referred to the Cretaceous period, and also earlier 

 than the Eocene epoch, that I have decided to designate those strata as 

 Post-Cretaceous, at least provisionally. 



