of the Bear River Formation. 103 



No recognizable fossils had been found 'in the broad space 

 between No. 12 and No. 28, and the visible structural and topo- 

 graphic features gave no indication of the presence of folds or 

 faults there. On careful search in this space it was found that 

 the fossiliferous layer in No. 15 mentioned by Professor Meek 

 contains characteristic Jurassic species and that No. 13 is in 

 part occupied by fossiliferous Bear River shales, showing that 

 between these two zones there is a fault the existence of which 

 had not before been suspected. 



In the space No. 13 several species of Bear River fossils 

 were found on the surface and less than half a mile northeast 

 along the strike the same forms were found in place in cal- 

 careous and argillaceous shale of which about 250 feet are ex- 

 posed. The following forms were obtained : 



Pyrgxdifera humerosa Meek. 



Corbula pyriformis Meek. 



Goniobasis chrysalis Meek. 



Goniobasis chrysaloidea White. 



Goniobasis macilenta White. 



These are all characteristic and easily recognizable Bear 

 River forms, all of which occur in No. 28 of Meek's section. 

 The zone was traced by means of small exposures and of fos- 

 sils on the surface, north-northeast along the strike, to Stowe 

 Creek, a distance of two miles. 



500 or 600. feet west of these Bear River strata the fossilif- 

 erous layer in No. 15 mentioned by Professor Meek, yielded 

 the following Jurassic species : 



Belemnites clensus M. and H. 



Trigonia quadrangularis Hall and Whitf. 



Myacites (Pleuromya) weberensis Meek ?. 



Numerous examples of the first named species were found. 

 It is one of the most common and characteristic forms of the 

 Jurassic of the Rocky Mountain region. Trigonia quadran- 

 gularis is not so well known, but the type is from Jurassic 

 strata near Como, Wyoming. The Myacites is abundant 

 though not well preserved and there is some doubt as to the 

 stratigraphic position of the type specimen which was referred 

 to the Jurassic for paleontologic reasons. The evidence of the 

 Jurassic age of this layer furnished by the first two species is, 

 however, regarded as conclusive. The fossils were found for 

 about half a mile along the strike. The other associated beds 

 that are referred to the same age were so assigned because no 

 reasons were found for separating them. 



From No. 14 to No. 27 inclusive only the harder beds are 

 exposed and the descriptions of the others are based on the 

 character of the surface debris. It is evident, however, that 

 none of these strata are duplicated as they would be if the 



