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 ot 
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. 
