296 University of California Publications. [Geology 



The formation to the northwest of Pilot Knob is traversed 

 by a heavy bed of light gray limestone about 150 feet thick, the 

 shale above and below it being not essentially different. The 

 total thickness of the shale is about 850 feet or with the included 

 limestone bed about 1,000 feet. 



This shale formation, with its included limestone bed, agrees 

 well with the descriptions that have been given by Hague* for 

 the White Pine shale of the neighboring "White Pine and Dia- 

 mond Ranges to the west of the Egan Range, and it is, there- 

 fore, tentatively correlated with that. This correlation is, more- 

 over, sustained by the fact that no other formation of similar 

 character has been described, so far as the writer is aware, from 

 the Basin Ranges for this portion of the geological scale. As 

 the White Pine shale is a fairly persistent formation in the 

 ranges to the west, it is quite probable that it should extend into 

 the Egan Range. Even the thick bed of limestone in the midst 

 of the shale has its analogue in the White Pine shale of the 

 Eureka and White Pine sections. f There is one lack of agree- 

 ment between the Eureka section and the one here described 

 which seems to militate against the correlation suggested, and 

 that is the absence at the Robinson Mining District of the Dia- 

 mond Peak quartzite. At Eureka this formation has a thick- 

 ness of 3,000 feet and lies immediately above the White Pine 

 shale. It is to be noted, however, that in passing southeastward 

 from Eureka to White Pine, the Diamond Peak quartzite dimin- 

 ishes from 3,000 feet to a few hundred feet,+ and that at this 

 rate of diminution of volume it would feather out before reach- 

 ing the Egan Range. 



The Nevada Limestone. — The correlation of the shale forma- 

 tion of the district with the White Pine shale of the Eureka and 

 White Pine sections is the chief justification for suggesting that 

 the next lower formation is the equivalent of the Nevada lime- 

 stone of the standard section. This formation is a rather mas- 

 sive, gray limestone which agrees in petrographic character with 

 the description of the Nevada limestone ; but no fossils were 

 found in it by the writer, doubtless due to the lack of oppor- 



* U. S. G. S. Mon. XX. 

 t Hague, Op. Cit., p. 193. 

 } Hague, Op. cit., p. 192. 



