28 GEOLOGY OF THE EUREKA DISTRICT. 



the west side of Newark Mountain. North of Newark Mountain, however, 

 the limestones occupy their true geological position, overlying the quartzite 

 and dipping westerly. 



Alpha Ridge for its entire length is made up of Lower Coal-measure 

 limestones uniformly inclined toward the west and in turn overlain by the 

 Weber conglomerates and Upper Coal-measures. In the Weber conglom- 

 erates there is a synclinal and anticlinal fold, the latter being well shown in 

 long narrow ridges stretching in north and south lines parallel with the 

 bedding. Of the Upper Coal-measures there occurs only a limited expo- 

 sure above the conglomerates, but they are admirably displayed with their 

 stratigraphical position well brought out and their geological age deter- 

 mined from ample paleontological evidence. 



In the area north of Newark Canyon, stretching northward as far as 

 the limit of the map and west of the Alpha fault, a north and south fault 

 011 the west side of Alpha Peak ridge, occurs an inclined table "wholly 

 made up of Upper Coal-measure limestones. Its identity upon both lith- 

 ological and paleontological grounds, with the body of Carboniferous lime- 

 stones overlying the Weber conglomerates south of Newark Canyon seems 

 conclusive, and the finding of Carboniferous species unlike those known to 

 occur in the Lower Coal-measures at Eureka and characteristic of the Upper 

 Coal-Tneasures elsewhere establishes the geological position of these beds. 



Carbon Ridge and Spring Hill Group. This block OCCUpieS a far less COUSpicU- 



ous position than any of the others, and seen from any commanding 

 point of view it would not be in the least likely to attract attention as a 



I 



prominent physical feature of the country. Unlike the adjoining uplifted 

 blocks which rise boldly out of the plain, this one has rather the appear- 

 ance of a depressed region without any persistent or distinctive character- 

 istics. Nevertheless, it is sharply defined, geologically, by parallel lines of 

 displacement, the Hoosac and Pinto faults. On the one side rises Prospect 

 Ridge and on the other rises the broad mass of County Peak and Silverado 

 Mountains. This relatively depressed block measures 6J miles in length, 

 but between the faults has an average width of only If miles. Estimating 

 from the thicknesses of the different epochs given in the Eureka section 

 both faults show profound vertical displacements of 12,000 to 15,000 feet. 



