428 FLORA OF THE LARAMIE GROUP. 



1879. Dr. White had spent the entire season in the exhaustive study 

 of the various outcrops of the liaramie in Colorado and Wyoming on 

 both sides of the Rocky Mountains, and had made large and valuable 

 collections, which he had worked up with care, and wiiich form the sub- 

 stantial basis for his ('oncUisions as here set forth. In his "general 

 discussion," which follows the detailed report, starting with "the unity 

 of all the principal brackish-water deposits hitherto known in the 

 Western Territories, and * * * their recognition as a comprehensive 

 group of strata under the name of the Laramie group, which represents 

 a great period in geological time, and especially such in the geological 

 history of North America," he proceeds to discuss, not so much the a<ie 

 of the group, as the coiulitions of its dei)ositioM and the geological 

 history of the western part of the continent following the close of true 

 Cretaceous time. Into this discussion, though confessing its superior 

 importance, we cannot here enter, but must be content to cite a passage 

 or two to show to what conclusions he had now come relative to the age 

 of the Laramie group, its geographical boundaries, and the thickness 

 of its deposits. Ue says: 



" Kesting directly upon the strata of the Fox Hills group are those 

 of the Laramie group, the latter, as already shown, having been, at 

 least in jjart, deposited continuously with the former. The geographi- 

 cal boundaries of the great Laramie formation are not known, but its 

 area embraces many thousand square miles, for it is known to extend 

 from Southern Colorado and Utah northward beyond the northern 

 boundary of the United States, and from the Wahsatch Mountains east- 

 ward far out on the great plains. It reaches a maximum thickness of 

 about 4,000 feet, and its general lithological characteristics are similar 

 to those of the Fox Hills group, a known marine formation. Its fauna, 

 however, has been shown to be largely of brackish- and partly of fresh- 

 water origin, and not marine. Furthermore, the brackish-water species 

 arc distributed throughout its entire thickness and its whole geograph- 

 ical extent. These facts, together with the absence from all the strata 

 yet examined of anj' true estuary characters, show that the Laramie 

 group was deposited in a great brackish water sea. * * * 



"In the foregoing report I have purposely avoided an expression of 

 opinion as to the true geological age of the Laramie group, because, 

 notwithstanding the positive opinions that have been expressed by oth- 

 ers upon that subject, I regard it as still an open (piestion. * • * The 

 claim that Cretaceous types of vertebrates are found in even the higher 

 strata of the Laramie group is freely conceded, and I have no occasion 

 to question the reference that has been made of its fossil plants, even 

 those of the lowest strata, to Tertiary types. The invertebrate fossils 

 of the group itself, as 1 have elsewhere shown, are silent upon this 

 subject, because the types are either uni(iuc, are known to exist in both 

 .Mesozoic and Tertiary strata, or pertain to living as well as fossil forms. 

 Every species found in the Laramie group is no doubt extinct, but 



