438 GEOLOGICAL SUEVEY OF THE TEERITOEIES. 



the formation must be accounted as Cretaceous, on account of the pres- 

 ence of the Dinosaurian Agathaumas sylvestris ; and those above it, as I 

 have aheady pointed out. Eocene,* on account of the types of Mamma- 

 lia contained in them. 



The authorities on the Bitter Creek formation have presented views 

 more or less at variance with those entertained by the writer, or of such 

 dubious character as to fall very far short of the requirements of evi- 

 dence. Dr. Hayden has regarded them as Tertiary and as transitional 

 from Cretaceous to Tertiary. Mr. King, in his very full article on the 

 Green River basin, definitely refers the lower part of the series to the 

 Cretaceous, in the following language : t " We have, then, here the upper- 

 most members of the Cretaceous series laid down in the period of the 

 oceanic sway, and quite freely charged with the fossil relics of marine 

 life; then an uninterrupted passage of conformable beds through the 

 brackish period up till the whole Green River basin became a single 

 sheet of fresh water." He regards the line of the upper bed of oysters 

 as the summit of the Cretaceous, and the superimposed beds as Tertiary, 

 in the following language, (p. 453 :) " while the fresh- water species, 

 which are found in connection with the uppermost coal-beds, seem to 

 belong to the early Tertiary period." He thus places the line some dis- 

 tance within what I have regarded as the Cretaceous boundary ; what 

 the significance of this conclusion is will be subsequently considered. 



Mr. Lesquereaux, as is known, regards these beds as Tertiary, not 

 only on account of their vegetable fossils, but also on account of the 

 stratigraphic relations of the formation. His conclusion to this effect is 

 consistent throughout, and is a fact of the highest importance in this 

 connection. 



Mr. Meek has fully discussed the age of this series in his interesting 

 article in Hayden's Annual Report for 1872, the general tenor of which 

 is indicated by the passage I have quoted from the opening of his re- 

 marks in the beginning of the present notice of the Bitter Creek beds. 

 His opinions may be cited as follows: In the Annual Report for 1870, he 

 determined the beds visible at Hallville as Tertiary; in that of 1871, 

 three species of oysters from other parts of the Bitter Creek beds are 

 placed in the Cretaceous list, each one with question as to the identifica- 

 tion of species, a point, it is to be noticed, equivalent in the case of 

 oysters to question of the age of deposit. The remarks in his report, as 

 well as those in Mr. King's report, refer either to the much lower Weber 

 River coal or to the different area of the Bear River group, and are con- 

 sequently noticed under that head. 



In a paper on the age of these beds, published August 12, 1872, the 

 writer asserted the Cretaceous age of the series. On this Dr. Bannis- 

 ter, the companion of Mr. Meek, writes| that " Mr. Meek, and, I believe, 

 Mr. Emmons also, had considered that these beds might be Cretaceous, 

 but this was rather on account of the change in the fossil fauna from 

 purely fresh-water, as in the characteristic Tertiary of this region, to 

 brackish-water marine, and the specific affinities of a few of the fossils 

 to California Cretaceous species, than from any very positive evidence. 

 As far as I know, the only evidence of this kind is the identification by 

 Professor Cope of the saurian remains found by us at Black Butte." 



It only remains to observe that the strata and coal of the Bitter Creek 

 group of the Cretaceous are either wanting on the western and southern 



* On Bathmodon, an extinct genus of ungulates, Feb. 16, 1872, Hayden's Annual 

 Eeport, 1870, p. 431 ; Annual Report, 1872, p. 645. 

 t Exploration of the Fortieth Parallel, p. 458. 

 X Annual Eeport, 1872, p. 534. 



