296 GEOLOGY OF THE EUREKA DISTRICT. 



features to those of Prospect Mountain, the resemblance holding equally 

 good for the ore bodies. On Adams Hill the Price and Davies mine lies in 

 this formation in close contact with the Secret Canyon shales, whereas the 

 Wide Wide West occurs near the summit just below the Hamburg shales. 

 Other localities where more or less work has been done were sufficient to 

 indicate the existence of mineral deposits across the intervening belt of 

 limestone from one shale belt to the other. Along Hamburg Ridge the 

 limestones are not so much disturbed as on the steeper mountain slopes, and 

 fissures and seams of ore are by' no means as common, but on the other hand 

 mines like the Duuderberg and Hamburg have produced large bodies of ore, 

 second in quantity to none in the district outside of Ruby Hill, and these 

 stand in the closest connection with intrusive masses of rhyolite. Dikes 

 and irregular shaped bosses of rhyolite along the summit of Hamburg Ridge 

 indicate a network of eruptive rocks between the two great shale belts. 

 Like the underlying Secret Canyon shale horizon, the Hamburg shales, 

 although of much less thickness, are impervious to ascending mineral cur- 

 rents, and neither along the front of the mountain or north of Adams Hill 

 is there the slightest evidence of ore bodies penetrating it. 



Ores of the Silurian. Coming to the Pogonip horizon, ore bodies occur all 

 the way from the north end of Adams Hill southward to Roundtop 

 Mountain, at the extreme southern end of the region, with, however, con- 

 siderable intervals where none have been exposed near the surface. Numer- 

 ous mining claims have from time to time been recorded, but most of the 

 ground proved unprofitable and unproductive. On the other hand, such 

 mines as the Bullwhacker and Williamsburg, northwest of the town of 

 Eureka, and the Page and Corwin, southwest of Pinto Peak, have yielded 

 large quantities of mineral matter and may be said to exhibit well its 

 mode of occurrence in the limestone of this horizon. In the Williams- 

 burg Mine a well defined quartz-porphyry dike penetrates the limestone, 

 and dikes of similar rock come to the surface near the Bullwhacker. The 

 Page and Corwin was not being worked at the time of the writer's visit, 

 and it is impossible to say whether any intrusive dikes have broken 

 through the strata in close connection with the ore, but the limestones are 



