61 A. White — On the Bear River Formation, etc. 91 



Aet. XIII. — On the Bear River Formation, a Series of 

 Strata hitherto k?iow?i as the Bear River Laramie; by 

 Charles A. White. 



[Published by permission of the Director of the U. S. Geological Survey.] 



In the year 1859 a series of strata, constituting an important 

 section, was discovered by Mr. Henry Engelmann at a locality 

 in southwestern "Wyoming, upon the bank, and near the 

 mouth of Sulphur Creek, a tributary of Bear River one of the 

 members of which section contain abundant remains of a pecu- 

 liar non-marine molluscan fauna. During the fifteen years 

 following that of their discovery, these non-marine strata were 

 generally spoken of as the Bear River estuary beds, but later 

 explorations have revealed their presence at other localities in 

 Wyoming, Idaho and Utah which shows that they are of more 

 than estuarine extent. During that time also no one expressed 

 any doubt of the Tertiary age of these strata because their fossil 

 fauna, although consisting of new species, included only types 

 which were then regarded as characteristic of the Tertiary, 

 and this view was supposed to be supported by their strati- 

 graphical relation to the other members of the same section 

 and their equivalents in that neighborhood. 



About the year 1876 the various deposits, which are now 

 properly referred to the Laramie, began to be generally recog- 

 nized as constituting one great formation, and these non-marine 

 strata of the Bear River valley district came to be generally 

 known as the Bear River Laramie because they were thought 

 to have been contemporaneous with the true Laramie and to 

 hold the same taxonomic position with relation to other forma- 

 tions, although it was well known that their molluscan fauna is 

 very different from that of the Laramie. They were then 

 also subject to the doubt which certain geologists began to ex- 

 press as to whether the Laramie is properly assignable to the 

 Tertiary or Cretaceous ; but this doubt was confined to the 

 question of their geological age and did not extend to that of 

 their relation to those marine strata of undisputed Cretaceous 

 age which constitute other members of the same section. This 

 statement finds support in the fact that up to the year 1891" 

 none of the publications of the various geologists who have 

 examined these non-marine Bear River strata contain any 

 clearly expressed doubt that they are all of later origin than 

 any of the marine Cretaceous strata which occur in that part 

 of the continent. That is, it was understood by them that the 



* See BulL U. S. Geol. Surv., No. 82, p. 153. 



