174 (iEOL(^(iY OF THE EUliEKA DLSTKU'T. 



species as Productus semireticulatus, P. lorujispinus, Atliijris subtil ita, and 

 Spirifera camerata are sufficient to establisli tlie Carboniferous age of the 

 limestones, and their j^o.sition beneath the Weber conglomerate assigns 

 them, beyond question, to the Lower Coal-measures. 



On PI. II will be found two cross sections di-awn across the volcanic 

 ntcks th;it stretch between the Hoosac and Pinto faults, se})arating the Car- 

 boniferous strata into distinct areas. Both sections lie between the two gen- 

 eral sections E-F and I-K. They are drawn on due east and west lines 

 and measure a little over 2 miles in length: Section i, atlas slieet viii, passes 

 just south of tlie Spring Hill limestone body and crosses the hornblende 

 andesite nearest its broadest expansion. At the extreme western end occurs 

 a small exposure of Carboniferous limestone, only a few hundred yards in 

 length, completely surrounded by andesite. As shown in the section these 

 andesites extend with a very irregular outline for a long distance, beyond 

 which a body of basalt comes in, followed by limestone, in turn followed 

 by pumices overlain and buried beneath other basalts. These latter basalts 

 give out on the steep slo^^es of Dome Mountain, which is made up of Ne- 

 vada limestone, lying on the west side of the Pinto fault. 



Section ii, atlas sheet x, is drawn so as to show the great body of Pinto 

 Peak rhyolite, and passes just south of the summit of the peak. Along- this 

 section, between the two great meridional lines of displacement, none other 

 than volcanic rocks reach the surface, the pumices all along the east slope 

 resting against the upturned Silurian rocks of English Mountain. In this 

 section the Pogonip limestone is seen beyond the line of the Hoosac fault, 

 but its direct connection with the fault is wholly lost by outbursts of lava. 

 By reference to the atlas sheets the position of this Pogonip limestone on 

 the west side of the fault and the Carboniferous limestone on the east side, 

 will be readily understood. 



