52 GEOLOGY OF THE EUREKA DISTRICT. 



in the fauna from the Hamburg limestone. Many of these genera gradually 

 give way and are replaced by others, until at about 800 or 1,000 feet below 

 the summit the fauna! development is shown by a grouping of fossils made 

 at two widely separated areas, which begin to foreshadow the strongly 

 marked fauna at the summit of the epoch. From the east slope of the 

 ridge east of the Hamburg Ridge there were collected 



Beeeptacolites ellipticus. Maclurea amiulata. 



Cystidian plates. Bellerophon ? 



Orthis perveta. Ortlioceras (like O. mnlticauieratnm). 



Triplesia calcifera. Cypliaspis brevimarginatus. 



Raphistoma? Ilkeruirus eurekeiisis. 



Pleurotomaria loueusis. Asaphus? curiosus. 



And from the long, eastern slope of White Mountain, about 800 feet 

 from the top of the mountain and probably nearly the same distance below 

 the summit of the Pogonip, there were collected as follows : 



Monticulopra. Pleurotomaria lonensis. 



Orthis testudiuaria. Endoceras proteiforme. 



Raphistoma nasoiii. Ortlioceras sp. ? 



Maclurea annulata. Bathyurus similis. 



Maclurea subaimulata. Asaphus cariboueDsis. 



Throughout the upper 600 feet of the Pogonip, wherever organic 

 remains have been observed, the association of genera are much the same, 

 the horizon being well determined both by the fauna and the position of 

 the overlying Eureka quartzite. In many areas where the Eureka quartzite 

 forms the surface rock an underlying limestone several hundred feet in 

 thickness is frequently exposed, which carries paleontological evidences of 

 the upper Pogonip strata. Two localities in these upper Pogonip beds 

 have furnished a rich and varied fauna. From a dark limestone on the 

 summit of White Mountain the following species have been determined : 



Receptaculites ellipticus. Tellinomya contraeta. 



Receptaculites elongatus. Helicotoma sp? 



Receptaculites mammillaris. Orthoceras inulticaineratum. 



Cystidean plates. Eudoceras (like E. inultitubulatum). 



Strophomena uemea. Leperditia bivia. 



Orthis perveta. Leperditia sp? 



Orthis testudiuaria. Beyrichia sp? 



