PALEONTOLOGY OF THE EUREKA DISTRICT. 



BY CHARLES D. WALCOTT. 



SUMMARY OF RESULTS. 



The general character of the fauna of the Cambrian, Silurian, Devo- 

 nian, and Carboniferous strata of the Eureka and White Pine Mining 

 Districts of Central Nevada is given in this report more to illustrate the 

 stratigraphic succession and equivalency of the geologic horizons with 

 those described elsewhere than as a detailed monograph of the inverte- 

 brate fossils; since, for the latter purpose much more extensive collec- 

 tions are necessary to represent the large fauna of the Paleozoic system of 

 Central Nevada than we have at present. 



As an assistant geologist in the field-work, the writer collected most of 

 the fossils in situ, and studied their mode of occurrence and stratigraphic 

 relations, thus disposing of an element of uncertainty which frequently 

 arises in the mind of the paleontologist when examining collections from a 

 region unfamiliar to him, and which presents, in the strata of the lesser divis- 

 ions of its great geologic series of rocks, associations of species unknown 

 elsewhere or an unusual vertical range of individual species. The presence 

 of the Trenton species Orthis testudinaria in the upper portion of the lower 

 half of the Pogonip Group in association with the genera Ptychoparia, 

 Dicellocephalus, and Asaphus, is a typical example. Other illustrations 

 of unusual association of species will be given in speaking of the Devonian 

 fauna. 



