OLENELLCS SHALE. 45 



This horizon has yielded the following species: 



Lingulepis inaera. Dicellocephalus angnstifrons. 



Lingulepis miuutu. Dicellocephalus inarica. 



Lingula manticula. Dicellocepbalus bilobatus. 



Obolella discoidea. Dicellocephalns oswola. 



Acrotreta gemma. Ptychoparia aflinis. 



Kntorgiua minutissima. Ptychoparia oweni. 



Hyolithes primordialis. Ptychoparia bagnei. 



Aguostus coinmunis. Ptychoparia granulosa. 



Agnostus bidens. Ptychoparia simulata. 



Aguostus neon. Ptychoparia nuisulcata. 



Aguostus prolongus. Ptychoparia breviceps. 



Agnostus tumidosus. Arethusina americana. 



Agnostus tuimfrons. Ptychaspis minitta. 

 Dicellocephalus nasutus. 



The Olenellus shales lie not only at the base of the fossiliferous rocks 

 at Eureka, but are equivalent to the lowest fossiliferous strata as yet 

 recognized in the Great Basin. Their known stratigraphies! position 

 overlying the Prospect Mountain quartzite and at the base of a conform- 

 able series of limestone and shale of Cambrian and Silurian age, measuring 

 9,000 feet in thickness, renders the question still a matter of some doubt 

 whether older fossil bearing strata will ever be found in Utah or Nevada. 

 Wherever the Olenellus shale is known to occur, it is always found resting 

 upon siliceous beds, and in no single instance, where they occur -together, 

 is the thickness of the lower quartzite so great as at Eureka. Unfortunately 

 no sedimentary beds are known to come to the surface below the Prospect 

 Mountain quartzite, and of the latter we are wholly ignorant as to its thick- 

 ness. What is needed in working out the stratigraphy of the Great Basin 

 ranges is a locality exposing a section of Lower Cambrian rocks still lower 

 than those at Eureka, but at the same time showing their relations with 

 the Olenellus shale and Prospect Mountain limestone above. In the many 

 uplifts of quartzose strata which have been provisionally assigned to the 

 Cambrian upon theoretical grounds, investigation may yet furnish proof 

 that certain iuterstratified shale bands carry either a similar or still lower 

 fauna, and if their structural relations with the Olenellus horizon can be 

 shown, it will make a Cambrian section much to be desired. Organic 



