44 GEOLOGY OF THE EUREKA DISTRICT, 



the geological age of the limestone in which the great bodies of ore upon 

 Ruby Hill occur. 



The Prospect Jlountain limestone carrying this fauna passes by grad- 

 ual transition into the Secret Canyon shale, the passage beds being mainly 

 thin interstratiiied layers of limestone and calcareous shale. No fossils have 

 been obtained from the argillaceous strata of the Secret Canyon shale 

 throughout its development, but imperfect fragments more or less obliter- 

 ated have been observed in several of the more calcareous beds. At the 

 to]/ of this group the calcareous shales appear, which must be taken as 

 forming the base of the well known Hamburg limestone, inasmuch as they 

 indicate new conditions of sedimentation. It is the coming in of these cal- 

 careous deposits that renders possible the development and preservation of 

 a higlier fauna. These calcareous shales may be recognized readily all along 

 the line of contact. In places it is well characterized by its grouping of 

 fossils, the same species being observed from both the east base of Ham- 

 burg Ridge and the corresponding beds north of Ruby Hill, presenting a 

 higher Cambrian fauna. The following species have been determined from 

 this horizon : 



Protospougia feiiestrata. Dicelloceplialiis osceola. 



Lingulepi.>s ma;ra. Dicellocei)lialus richmoudensis. 



Lingulcpis miiiuta. Ptychoparia pernasuta. 



Lingula manticula. Ptychoparia laticeps. 



Iphidea depressa. Ptychoparia bella. 



Acrotreta gemma. Ptychoparia linnarssoni. 



Kutorginr^ Diimitissima. Ptychoparia oweni. 



Hyolithes primordialis. Ptychoparia haguei. 



Aguostus communis. Ptychoparia sinulis. 



Agnostus bidens. Ptychoparia uuisulcata. 



Agnostus neon. Ptychoparia heviceps. 



Agnostus seclusus. Chaiiocephahis tumifrons. 



Dicellocephahis nasutus. Ogygia problematica. 



After leaving the calcareous shales, which form the base of the Ham- 

 burg limestone, the next fossil horizon occurs in the shales at the summit 

 of the same group, and in thin interlaminated limestones in the overlying 

 Hamburg: shale. 



