Art. XII.— The L<araniie Group of Wesitern Wyoiiiiiis' 

 and AdjaceEit Ke§'ioia!>i. 



By A. C. Peale, M. D. 



In this paper I wisli briefly to note a few facts in reference to the oc- 

 currence of the Laramie Group or Post-Cretaceous Formation in Eastern 

 Idaho and Western Wyoming (the district examined by me in the sum- 

 mer of 1877). 



The term Fost- Cretaceous was iirst used by Dr. C. A. White,* although 

 the transitional character of the strata so referred has long been recognized 

 and insisted upon by Dr. Hayden. This transitional character of the La- 

 ramie Group is also acknoATledged by Prof. E, D. Coidc, who says : "In 

 arranging the Laramie Group, its necessary position is between Tertiary 

 and Cretaceous, but on the Cretaceous side of the boimdary, if we retain 

 those grand divisions, which it appears to me to be desirable to do."t 



Professor Cope also gives a table of the faunre of the Laramie Group 

 and the correlated French strata (Sables de Bracheux and Conglomerate 

 de Cerny), and says :t " The result is clear that the French and Ameri- 

 can formations together bridge most completely the interval between 

 the Cretaceous and Tertiary series, as has been anticipated by Haj'den, 

 in America, on geological grounds." 



It is well known that the evidence of palseobotany is in favor of the 

 Tertiary age of the group, while invertebrate palfcontology is negative 

 in its evidence. 



It is unnecessary to enter into any discussion on the subject at this 

 place. As long as the evidence presented by the various organic re- 

 mains is so conflicting, being partly Tertiary and partly Cretaceous in 

 its testimony, ij seems advisable to retain the name Post- Cretaceous for 

 the Lararnie Grouji. 



In the district assigned me for examination in 1877, there were two 

 areas in which the Laramie Group formed a considerable portion of the 

 surface rocks, viz, on the western side of the Green Eiver Basin in 

 Western Wyoming,, and in the region of Bear Eiver and Smith's Fork. 

 I shall now briefly describe these two areas. 



Green Eiver Basin. — In going westward from Green Eiver, in the north- 

 ern part of the Green Eiver Basin, the sandstones and shales of the 

 Green Eiver Group and the variegated beds of the underlying Wahsatch 



* Bulletin U. S. Geol. aud Geograijli. Survey of the Territories, \o\. iii, Xo. 3, p. G08. 



t Bulletin U. S. Geol. aud Geograpli. Survey of tlje Terr., vol. v, Xo. 1, pp. ;>8, 39. 



t Ibid., pp. 37, 38. 



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