LONE MOUNTAIN LIMESTONE. 57 



different horizons of the Lone Mountain limestone, but even of the Devon- 

 ian, are seen to repose directly upon and to overlap the quartzite. Under 

 any circumstances the quartzite would be difficult to measure, inasmuch as 

 over the greater part of the area stratification lines are wanting, and the 

 beds are frequently broken up by a succession of small parallel faults not 

 always easy to recognize, rendering the amount of displacement still more 

 difficult to estimate. These minor displacements, when the rocks lie nearly 

 horizontal, produce steps and mural faces wherever the quartzite occurs as 

 the surface rock. In nearly all such instances the Pogonip beds are exposed 

 in the more deeply eroded canyons. On the other hand, where the beds are 

 inclined at high angles, accompanied by numerous faults, the formation fre- 

 quently presents the appearance of a much greater thickness than is really 

 the case, as is seen on Hoosac and Lookout mountains. 



The best estimates place the thickness of the beds at about 500 feet, 

 although no escarpment of the quartzite free from faulting presents quite 

 so broad a development. No fossils have been obtained from this horizon, 

 nor is it likely that they will be found. The microscope shows clearly how 

 complete an alteration has taken place since the original sand deposits were 

 laid down, so that all traces of fossils, if any existed, must have been 

 obliterated. 



Lone Mountain Limestone. Next above the Eureka, quartzite comes a body of 

 limestone without any transition beds, the change in the character of depos- 

 its being unusually abrupt. The designation of the epoch is taken from a 

 bold isolated mountain which rises out of the plain a few miles to the north- 

 west of the Eureka District, where it is seen in its full development better 

 than in the immediate area of the map. Not only is it well shown at Lone 

 Mountain, but in a continuous section its relations are clearly made out with 

 the other members of the Silurian period and with the overlying body of 

 Devonian limestone. The section at Lone Mountain is given in detail at 

 the end of this chapter. 



The Lone Mountain epoch may be divided upon paleontological 

 grounds into two horizons, which, for convenience, are provisionally desig- 

 nated as the Trenton and Niagara. The lowest beds resting immediately on 

 the quartzite are a steel-gray, almost black, gritty limestone, in most places 



