60 GEOLOGY OF THE EUREKA DISTRICT. 



They have a wide range and occur nearly 1,500 feet above the summit of 

 the Eureka quartzite. The same coral has been obtained from Lone Moun- 

 tain and White Pine, and in both these latter localities associated with the 

 genus Zaphrentis. 



Lone Mountain. This isolated mass rises abruptly out of the broad plain 

 lying between the Wahweah and Pifion ranges and about 15 miles north- 

 west of the Eureka Mountains, which shut in the plain to the south- 

 west. Its isolation, its great altitude as compared with the length of the 

 uplift in strong contrast with the neighboring ranges, and its steep slope to 

 the eastward make the mountain a most conspicuous object. In its geolog- 

 ical structure the mountain appears to be a monoclinal ridge of great sim- 

 plicity and uniformity, remarkably free from any great faults and folds and 

 presenting a block of strata about 4,000 feet in thickness and reaching- an 

 altitude nearly 2,000 feet above the plain. The beds have all the appear- 

 ance of being cut off by a sharp fault at the south end of the block, evi- 

 dence of which may be found in the body of Carboniferous limestone rest- 

 ing against the Devonian at the southeast base of the uplifted mass. The 

 dip of the strata upon Lone Mountain is uniformly to the east at an angle 

 of 30 to 50, with a strike a little east of north. To the geologist a 

 series of beds like this at Lone Mountain would at all times command 

 attention, but in this exposure of 4,000 feet of strata is represented a sec- 

 tion of the Paleozoic rocks rarely seen in the Great Basin and so far as 

 known nowhere else so well shown as here. The value of the exposure 

 consists in the simplicity with which the three divisions of the Silurian are 

 brought out in the same continuous section. At the western base of the 

 mountain the upper members of the Pogonip come to the surface, but. 

 with an exposure of only about 375 feet of beds. Within this belt, how- 

 ever, a fauna strikingly characteristic of this horizon is found and almost 

 identical with that occurring in the corresponding Pogonip beds at Eureka. 

 A few hours' search yielded the following: 



Receptaculites mammillaris. Modiolopsi.s occidens. 



Monticulopora sp. ? Modiolopsis pogouipeiisis. 



Cystidian plates. Hellicotoina? 



Acrotreta (like A. subconica). Plenrotomaria loneusis. 



Stropboineua neraea. Murchisonia sp. I 



