WAiiD.J m.STORICAL REVIEW OF OPINION. 423 



dispute during the last few years, mainly in consequence ')f the uncer- 

 tain geological bearings of the fossil plants found near this horizon. 

 The accompanying invertebrate fossils have thrown little light on the 

 question, which is essentially, whether the great lignite series of the 

 West is uppermost Cretaceous or lowest Eocene. The evidence of the 

 numerous vertebrate remains is, in my judgment, decisive, and in favor 

 of the former view." ' 



At about this time the researches of Dr. C. A. White, who had be- 

 come deeply interested in this formation, began to bring forth important 

 results. Ilis "Paleontological Papers" commenced to ai)i)ear in 1877, 

 as contributions to the Bulletins of Dr. Hayden's Survey, in the third of 

 which he drew up tables of the groups of the Green River and Upper 

 Missouri River regions. It was here that he employed the term " Post- 

 Cretaceous," to include the Laramie group of the King Reports and the 

 lower third of the Wasatch group, and correlating the Judith River 

 with the Laramie and the Fort Union with the Wasatch group. In 

 the fifth of these papers, published the same year, he enters more 

 fully into the discussion of the age of these groups and remarks : 

 " With a few doubtful exceptions, none of the strata of the Laramie 

 group were deposited in open sea waters ; and, with equally few excep- 

 tions, none have yet furnished invertebrate fossils that indicate the 

 Cretaceous rather than the Tertiary age of the group. These latter 

 exceptions are some Iiiocerami that have been obtained ujiou the lower 

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

 Fox Hills group below; and also a species of Odontohasis from strata 

 near the top of the group, two miles west of Point of Rocks Station, 

 Wyoming. The latter genus, established by Mr. Meek, is compara- 

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

 Cretaceous period. This constitutes the slender evidence of the Cre- 

 taceous age of the Laramie group that invertebrate paleontology has 

 yet afforded. 



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

 afforded 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 characteris- 

 tics that it is often difiScult to say in what respect they materially differ. 

 Aloreover, they give the same uncertain indication as to their geologi- 

 cal 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 

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



' Proceedings of the American Association for the Advancement of Science, 1877, 

 page 229. 



