190 GEOLOGY OF THE EUREKA DISTRICT. 



Silurian and Devonian. Exposures of Silurian and Devonian rocks present- 

 ing a development of strata at all comparable with the Eureka section are 

 known in but few localities in the Great Basin, and nowhere are the struc- 

 tural relations of the Cambrian, Silurian, and Devonian so clearly brought 

 out as here. Nevertheless, numerous mountain uplifts present so many 

 partial exposures of the Eureka section that the evidence is sufficient to de- 

 termine the same succession of strata over a wide area of the Great Basin. 



Geological Section, white Pine. In the year 1872 the writer 1 visited White 

 Pine and Eureka and established the identity of a great thickness of the 

 Pogonip beds at both places. The fossils collected at that time from Pogo- 

 uip Mountain, White Pine, and the hills east of the Jackson Mine at Eureka, 

 were submitted to Messrs. Hall and Whitfield and shown by them to be 

 specifically identical. At that time, however, neither tliu. base nor the 

 summit of the epoch was clearly defined and not until after the thorough 

 survey of the Eureka district were their exact limitations known, nor could 

 they be determined until after the collection of a large amount of paleonto- 

 logical material. Topographically, Pogonip Ridge holds much the same 

 relation to the White Pine Mountains that Prospect Ridge does to the Eu- 

 reka Mountains. It forms the most prominent uplift in that district, occur- 

 ring as a sharp longitudinal ridge, the highest point attaining an elevation 

 of nearly 10,800 feet above sea level. Across this ridge the oldest sedi- 

 mentary beds of the district lie inclined at high angles to the east, the 

 northern end being made up almost wholly of Silurian rocks. The structure 

 is simple, the beds which trend obliquely across the ridge being easily fol- 

 lowed from the summit of the peak to the northern base. 



After the completion of the work at Eureka Mr. C. D. Walcott made a 

 careful examination of the Silurian rocks at White Pine where, according to 

 him, the Pogonip strata measure over 5,000 feet in thickness. The oldest 

 strata identified by their organic remains are the beds at the base of 'the 

 Hamburg limestone, several species being identical with those from the 

 corresponding horizon at Eureka. These Hamburg limestone beds, several 

 hundred feet in thickness, are cut off by a fault bringing them in contact 



1 U. S. Geological Exploration of the Fortieth Parallel, vol. 2, Descriptive Geology, pp. 

 542 and 547. 



