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University of California Publications. 



[Geology 



doubt with regard to any. The most dubious as to age in his 

 opinion is the Diphyphyllum n. sp., and even in this case he be- 

 lieves that it may safely be regarded as Upper Carboniferous or 

 Pennsylvania!!. All of these fossils occur in the same stratigraph- 

 ically continuous area of the Ruth limestone, of which Fossil 

 Hill is the most prominent feature, on the south side of the 

 Ruth Mine. The Seminula subtilita appears to be the most com- 

 mon. The Diphyphylum n. sp. also occurs on the Phenix claim 

 in the area of Ruth limestone two-thirds of a mile to the north 

 of the Ruth Mine. It is interesting and satisfactory to observe 

 that the palaeontological determination of the age of the Ruth 

 limestone by Mr. Girty entirely agrees with the conclusions that 

 had been reached by a comparison of the physical characteristics 

 and stratigraphic sequence of the Ruth section with those of the 

 standard section established at Eureka some 80 miles distant.* 



The Arcturus Limestone. — Below the Ruth limestone is a 

 strongly contrasted formation of argillaceous, and in part sandy, 

 limestone which may be designated the Arcturus shaly lime- 

 stone, although the shaly character is not always apparent. This 

 formation is easily distinguished from the other formations of 

 the district by the abundance and yellow color of its regolith. 

 In general it yields to atmospheric erosion smooth slopes strewn 

 with small subangular or rounded residual fragments of yellow 

 limestone. In it there are occasional beds of a massive character, 

 but even these do not project prominently above the general 

 slope. Some of the limestone beds contain a notable proportion 

 of manganese, and when freshly broken present a faint pinkish 

 tint suggestive of rhodochrosite. This formation increases in 

 thickness from east to west, and passes in the country to the 

 northwest of Ruth into yellow, orange and red weathering, soft 

 shales, with thin beds of impure limestone. The formation car- 

 ries Carboniferous fossils but not so abundantly as the Ruth 

 limestone. Species of Zaplirentis and Stenopora were recognized 

 by Mr. G. H. Girty. Its average thickness within the district is 

 about 1,000 feet with a minimum of 900 feet in its more eastern 

 exposures. 



* Hague, A. U. S. G. S., Monograph XX, 1892. 



