94 GEOLOGY OF THE EUREKA DISTRICT. 



as if indicating that they had been derived from the underlying Carbon- 

 iferous rocks. The fossils, however, which are all Coal-measure species, 

 might be derived quite as well from the Upper as from the Lower beds. 

 A chemical examination failed to detect any beds of dolomite in the lime- 

 stones, the highest amount of magnesium carbonate obtained being T33 per 

 cent. This is not without interest, as it is the only limestone horizon in the 

 Paleozoic series at Eureka free from dolomitic strata. 



Upper coal-measure Fauna. This epoch has not yielded as large a number 

 of species as the Lower Coal-measures and many of those found in the 

 middle and upper beds of the latter are known to occur in both divisions of 

 the Carboniferous limestone throughout the Great Basin. The following 

 list comprises all those species obtained from the Upper Coal-measures 

 which were not observed in the Lower Coal-measures: 



Zaphrentis, sp. ? Ptilodictya carbonaria. 



Polypora, sp. ? Ptilodictya serrata. 



Orthis pecosi. Productus punctatus. 



Retzia monnoni. Macrodon tenuistriata. 



Terebratula bovidens. Pleurotomaria, sp. ? 

 Myalina subquadrata. 



A further search of the Lower Coal-measures might show several of 

 these species, and in other localities outside the District it is by no means 

 certain that they have not been found lower down. Terebratula bovidens is 

 known to range throughout the Coal-measures; on the other hand Productus 

 punctatus, a common form, seems to be restricted to the Upper Coal-meas- 

 ures in the Great Basin. 



A narrow belt of yellowish gray, somewhat shaly, limestone, near the 

 head of Hunter Creek, carries the following grouping of fossils : 



Fusilina cyliudrica. Productus semireticulatus. 



Fusilina robusta. Spirifera camerata. 



Chaetetes, sp. ? Spirifera rockymoiitana. 



Orthis pecosi. Spiriferina cristata. 



Productus longispinus. Athyris subtilita. 



Productus nebrascensis. Terebratula bovidens. 



Productus prattenianus. Myalina subquadrata. 



Productus punctatus. Pleurotomaria (like P. turbiiiitbrmis). 



