LONK MOUNTAIN LIMESTONE. 57 



different horizons of tlii' Lone Mountain linicstone, hnt even of tlie Devon- 

 ian, are seen to repose directh- njjon and to overlap the quartzite. Under 

 any circunistanees the (juartzite would be dilficult to measure, inasmuch as 

 over the greater part of the area stratitieation lines are wanting-, and the 

 beds are frequently brokt'ii up b}' a sueeession of small paiallcl faults not 

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

 difficult to estimate. These minor dis])lacements, when the rocks lie nearly 

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

 the surtace rock. In nearly all such instances the Togoni]) beds are exposed 

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

 indineil 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 lloosac 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 Inroad a development. No fossils have been ol)tained from this horizon, 

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

 complete an alteration has taken j)lace since the original sand deposits were 

 laid down, so that all traces of fossils, if any existed, nui.st have lieen 

 obliterated. 



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

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

 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 (^f the Eureka District, where it is seen in its full development better 

 than in the immiMliate 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 membei's of the Silurian period and with the overlying body of 

 Devonian limestone. The section at Lone Mountain is g-iven in detail at 

 the end of this chapter. 



The Lone Mountain epoch may be divided ujion paleontological 

 grounds into two horizons, which, for convenience, are pro\dsionally desig- 

 nated as the Trenton and Niagara. The lowe.stbeds resting- imnKKliatel yon 

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



