546 DESCRIPTIVE GEOLOGY. 



Genesee slate ; and although this is the only locality from which it has as 

 yet been recognized in Nevada, it is known in the Wahsatch Range asso- 

 ciated with the interesting groups of fossils from Ogden and Logan Cafions, 

 which show close affinities with the Upper Devonian, and at the same time 

 are allied to the Waverly group of Ohio. 



The black argillaceous shales which form so prominent a feature both 

 in the geological and physical aspect of the district are but indistinctly 

 recognized in other places, and without fossils. This may arise partly from 

 the beds in neighboring ranges becoming more sandy or calcareous, thus 

 losing their marked habit, and in part from offering exposures far less 

 readily studied. There can be little doubt but that the horizon will be 

 clearly identified at some future time in other Palaeozoic uplifts of the 

 Great Basin. Here at White Pine, the black shales have been somewhat 

 roughly separated into two groups, the lower more argillaceous, the upper 

 arenaceous, but divided more sharply by the association of species. 



From the lower strata we have: 



Leiorhynchus quadricostafus. 



Aviculopeden catadus. 



LunuUcardium fragosum (Posidonomyaf). 



NucuUtes triangulus. 



Goniatites Kingii. 



Orthoceras cessator. 



From the upper beds we obtained: 



Streptorhgnchus, sp.l • 



Spirifer, sp.l (resembles S. disjunda). 



Produdus semireticulatus. 



This association of species from the lower beds with Leiorhynchus qua- 

 dricostatiis, a characteristic fossil from the Genesee slate, has naturally led 

 Messrs. Hall and Whitfield to regard the horizon as Devonian, and the 

 overlying upper series with the equally characteristic Spirifer resembling S, 

 disjunda as of Sub-Carboniferous age. 



The sandstone beds are mostly barren of organic remains, their chief 

 interest being derived from the number of impressions of stems and leaves 



