96 C. A. White — On the Bear River Formation, etc. 



covery to the 43d parallel of north latitude, a distance of about 

 100 miles. Besides this he reported the existence of a nar- 

 rower and shorter belt lying parallel with the other, a few 

 miles farther eastward. 



Most of the strata throughout the district examined by Dr. 

 Peale have been much displaced by orogenic movements and 

 the structural geology there is therefore often found to be 

 obscure. Doubtless because of this obscurity he failed to see 

 any reason to oppose the then prevalent opinion that the Bear 

 River formation is referable to the Laramie epoch, and re- 

 ported that formation as overlying a series of strata which he 

 assigned to the Cretaceous, but admitted that he found no 

 paleontological evidence of their Cretaceous age. 



In 1877 and' 1878 Prof. Orestes St. John examined the 

 geology of a portion of western Wyoming, his district lying 

 immediately north of the one examined by Dr. Peale, but the 

 results of his work were not published until 1882. In this 

 report* he shows that the Bear River strata which, following 

 the then prevalent custom he assigned to the Laramie, occupy 

 considerable areas in the district examined by him, one of 

 them being a northward continuation of the principal belt 

 reported on by Dr. Peale. These areas show a northward con- 

 tinuation of the Bear River formation of about 40 miles more 

 than was shown by the results of Dr. Peale's observations, 

 and they seem to mark the extreme northern limit of the 

 formation. * 



The structural geology of Prof. St. John's district is even 

 more obscure than that of Dr. Peale's but his report appears 

 to indicate that no marine Cretaceous strata have been depos- 

 ited in the immediate neighborhood of the Bear River strata 

 which he found there. Furthermore a proper interpretation 

 of the reports which have been made by various geologists 

 upon western Wyoming and adjoining parts of tltah and 

 Idaho indicate that no true Laramie strata exist within the 

 district where those of the Bear River formation occur. This 

 fact seems to have favored the erroneous identification of the 

 Bear River formation with the Laramie. 



From 1881 to 1885 inclusive I published several articles in 

 which reference is made to certain of the characteristic fossils 

 of the Bear River formation. f In all of those articles the 



* Twelfth Ann. Rep. U. S. Geol. Surv. Terr., Part I, pp. 175-269 and map. 



f The following statement of the titles and places of publication of these articles, 

 in addition to similar references in preceding foot notes, is given for the purpose of 

 making bibliographical reference to the subject of this article as complete as prac- 

 ticable. 



Tanganyika Shells. Nature, vol. xxv, pp 10 J, 102. 



On certain conditions attending the geological descend of some North American 

 types of Fresh-water gill-bearing Mollusks. This Journal, vol. xxiii. pp. 382-386. 



New Molluscan forms from the Laramie and Green River groups, with discussion 



