134 GEOLOGY OP THE EUREKA DISTRICT. 



northward nearly to Atrypa Peak, and is an excellent locality for studying 

 the Eureka quartzite. A longitudinal fault line follows up Lamoureux 

 Canyon, but the amount of movement is by no means as great as along the 

 Sierra and Lookout faults ; the orographic movements apparently dis- 

 playing less and less force to the westward of Prospect Ridge. Passing up 

 to the head of Lamoureux Canyon, there is an interesting occurrence of an 

 exposure of the underlying limestones brought up by faulting. Here the 

 Pogonip beds are surrounded on all sides unconformably by the quartzite. 

 The hill in the middle of the canyon formed of these limestones is capped 

 by about 100 feet of quartzite resting conformably upon the underlying 

 beds. A careful search in this locality reveals the Receptaculites fauna, 

 associated with Orthis and Maclurea, immediately beneath the quartzite. 



Between Lamoureux Canyon and Castle Mountain the country presents 

 the appearance of a shallow trough or basin with a northwest and southeast 

 trend. This basin is for the most part filled with Nevada limestone, between 

 which and the Eureka quartzite the Lone Mountain beds generally come 

 to the surface, forming a narrow belt around the edge of the basin and in 

 places extending up on to the top of the quartzite rim. Over this area the 

 beds dip east and southeast except immediately next the quartzite of Lam- 

 oureux Canyon, where, conforming with it, they show a westerly dip. But 

 few fossils have been recognized in this area other than an occasional Atrypa 

 reticularis and corals characteristic of the Devonian, but without indicating 

 any special horizon. 



MAHOGANY HILLS. 



Spring Valley extends the entire length of the Eureka Mountains and 

 sharply distinguished Prospect Ridge and the Fish Creek Mountains from 

 Mahogany Hills, all that region lying on the west side of this valley being 

 included within the Mahogany Hills. Strictly speaking, it is not one 

 continuous valley, but rather two valleys, with a low dividing grassy 

 ridge between them, the water draining both to the north and to the 

 south. From the broad plain of Diamond Valley, Spring Valley, only a 

 few hundred yards in width, rises gradually for 1,200 feet to the divide, 

 following the course of a remarkable fault, which brings both the Lone 



