30 



1869. Cope, Transactions of the American Philosophical Society, pp. 40, 9S, 

 243 ; supposed mammalian i-emains proven to be reptilian, and the 

 formation referred to the Cretaceous. 



1871. Newberry, in Hayden's Annual Report, pp. 95-96 ; Lignite flora 

 regarded as Miocene. 



1874. Dawson, Report of Progress of the British North American Boundary 



Commission : on tlie Tertiary Lignite Formation, p. 20 ; Milk River 

 beds regarded as lowest American Tertiary. 

 Cope, Bulletin of the United States Geological Survey of the Territo- 

 ries, No. 2 (April) : Fort Union beds of Colorado referred to the 

 Cretaceous. 



1875. Cope, Proceedings of the Academy of Natural Sciences, Philadelphia 



(January) ; Milk River beds regarded as Cretaceous. 



From the above, it appears that both paleontologists and stratigraphers, 

 excepting the writer, have maintained the Tertiary age of the beds of the 

 Fort Union epoch. 



Whether the Bitter Creek and Bear River groups of Hayden present 

 much ditlerence of horizon remains to be determined. For the present, they 

 are retained as distinct. 



VII. — THE BITTEE CREEK SERIES, 



mentioned by the writer as a distinct group, in the Proceedings of the Amer- 

 ican Philosophical Society, 1872 (pubUshed on August 12), is apparently 

 regarded by Mr. Meek also as representing a distinct epoch.' He says, " The 

 invertebrate fossils yet known from this formation are, in their specific rela- 

 tions, with possibly two or three exceptions, new to science, and diflferent 

 from those yet found either at Bear River, Coalville, or indeed elsewhere in 

 any established horizon,' so that we can scarcely more than conjecture, from 

 their specific affinities to known forms, as to the probable age of the rocks in 

 which we find them." On this account, and because of the great stratigraph- 

 ical diflferences exhibited by the Bear River and Evanston coal-strata, I have 

 followed Hayden in regarding the Bear River group, on the west side of the 

 Bridger basin, as representing a distinct series of rocks, with present knowl- 

 edge. On this account I omit, as heretofore, allusion to determinations 



I Ilajdcn'M Animal Rciioi't for 1872, pp. 4S9-4G1 ; piiblihliod April, 1873. 



