/ 



4"2'2 FLORA or TIIK LARAMIE GROUP. 



Coi)e described a Dinomur found near Black Buttes Station as Creta- 

 ceous. I have verified tlie determination of the stratigrapiiic horizon 

 by examining the phice and Ilnding other l>irwsaiir bones; but tliis liori- 

 zon is above the i)hysical break, and the evidence of the Dinosaur seems 

 to be contradicted by the evidence furnished by many other 8i)ecies 

 described by Professor Cope from about the same horizon." 



Dr. Wliite also discusses this (luestion in the same volume, and states 

 his reasons for regarding the Point of Kocks beds as Cretaceous in the 

 following words (pp. 83, S-t): "There is no physical break between this 

 group and the Salt Wells group below it. Its strata contain at least 

 three species of Inoceramus, which genus has never been known in 

 strata of later date than the Cretaceous period. Odontobasis, a species 

 of which has been obtained from near the summit of the grouj), is re- 

 garded as a Cretaceous genus ; and in view of the facts before stated, 

 that land and fresh- and brackish-water mollusks are comparatively 

 valueless as indices of the passage of geological time, the presence of 

 no known forms in its strata forbids the reference of this group to the 

 Cretaceous period." 



On the other hand, the Bitter Creek series proper is referred to the 

 Eocene, and to the question " Why has the dividing line between the 

 strata of the Tertiary and Cretaceous periods been drawn where it is 

 rather than at some horizon either iibove or below it?" his answer is: 

 " There is no physical break in the Cretaceous strsita from the base of 

 the series to the top of the upper, or Point of Eocks group, at which 

 horizon there is at all observed points, extending over a large region, a 

 considerable unconformability by erosion of the lower strata of the 

 Bitter Creek grouj) upon the upper strata of the Point of Kocks group 

 (p. 87)." 



The second volume of the Eeports of the Geological Exploration of the 

 Fortieth Parallel by Mr. Clarence King, which appeared in 1877, contains 

 exhaustive papers upon the geology of this region by Messrs. Arnold 

 Hague and S. F. Emmons, who had studied the rocks with great care. 

 Both these gentlemen agree in referring the entire lignite-bearing series 

 to the Cretaceous. They do not draw the nice distinction made by 

 Messrs. King, Powell, and White, but Mr. Hague seems to have uo 

 doubt that even the Carbon coals belong there, while Mr. Emmons sim- 

 ilarly disposes of those of Evanston. In this report the term Lk/nitic 

 is abandoned altogether and the term Larumu' is applied to this forma- 

 tion. Mr. Emmons constantly speaks of the " Laramie Cretaceous" and 

 the " Laramie group," the latter of which terms has now been generally 

 adopted and extended over a much wider .irea. 



In his vice-presidential address, delivered before the American Asso- 

 ciation for the Advancement of Science, at Nashville, Tenu., August 30, 

 1877, Prof. O. C. Marsh expressed himself as follows upon the general 

 subject under discussion : "The boundary line between the Cretaceous 

 and Tertiary in the region of the Rocky Mountains has been much iu 



