96 GEOLOGY OF THE EUREKA DISTRICT. 



a bed of conglomerate about 25 feet in thickness made up mainly of rounded 

 quartz pebbles followed by another belt of shale quite like the one below, 

 40 feet in thickness. In both series of shale occur beds of carbonaceous 

 material and thin seams of impure coal, but nowhere on the surface are the 

 exposures more than three inches in width. Still higher up is another belt 

 of conglomerate carrying more or less lime and followed by buff colored 

 massive limestone changing to brownish gray limestone followed by a cherty 

 limestone, the latter extending to the top of the mountain. This series of 

 limestones has an estimated thickness of nearly 1,000 feet. Fossils charac- 

 teristic of the Coal-measures are common throughout the limestone, but are 

 more abundant in the lower beds, more especially in those immediately 

 above the coal, although no horizon presents any special faunal peculiarities. 

 Scattered throughout the limestone occur the following species: 



Zaphrentis centralis, 1. Productus costatus 



Diphyphyllum, sp. I. Productus semireticulatus. 



Chaetetes, n. sp. Spirifera camerata. 



Discina, sp. ?. Spirifera rockymontana. 



Orthis pecosi. Spiriferina kentuckiensis. 



Qrthis resupinata. Retzia mormcnii. 



Streptorhynchus crenistria. Athyris roissyi. 



Chonetes grauulifera. Athyris subtilita. 



Productus cora. Terebratula bovidens. 



This grouping may be said to present some distinctive features con- 

 taining forms regarded as belonging to the Lower Carboniferous, mingled 

 with others typical of the Coal-measures. Zapl/rattix mitm/ix, Dipliyphyllum 

 and Athyris roissyi give to the horizon a Lower Carboniferous aspect, 

 while the relatively large number of Coal-measure species would ordinarily 

 determine the position of the beds. Not only do the Coal-measure species 

 outnumber the others, but several of them happen to be those forms like 

 Orthis pecosi and Reteia mormoni, which have as yet been recognized only 

 in the Upper Coal-measures. Nevertheless, the evidence of the fauna is 

 strongly in favor of the lower horizon for these coal beds, as certain species 

 are elsewhere unknown higher up in the Carboniferous, whereas it is a 

 feature of the Coal-measure fauna of the Great Basin that" it presents a wide 

 vertical range. 



Lithologically the evidence is not specially decisive. The series of 



