176 SILVER-LEAD DEPOSITS OF EUKEKA, NEVADA. 



but a reference to his results is necessary to a clear conception of the rela- 

 tions of the mines to the different formations. 



The Cambrian, Silurian, Devonian, and Carboniferous are all repre- 

 sented in this district, though it is only in the rocks of the first two that 

 metalliferous deposits of any kind have been found. 



Formations. — Mr. Hague distinguishes the following beds in the Cambrian, 

 beginning with the oldest : Prospect Mountain quartzite, Prospect Mount- 

 ain limestone, Secret Canon shale, Hamburg limestone, Hamburg shale. 

 Those five formations have all been laid down conformably. The rocks of 

 the Silurian in the order of succession are Pogonip limestone, Eureka quartz- 

 ite, and Lone Mountain limestone. The rocks of the Devonian in this 

 neighborhood are the White Pine shale and Nevada limestone. 



Relations of the mines to the formations. — With the exception of the Hoosac mine 

 in the Eureka quartzite, and the Bullwhacker and other mines in the Pogo- 

 nip limestone on the slope north of Adams Hill, all the mines which have 

 been discussed in this memoir are found in the Prospect Mountain and 

 Hamburg limestones. No deposits whatever have been found in the Secret 

 Canon shale which separates these two beds, and although it is true that 

 pyrite, both as impregnations and in masses, as well as distinctly-defined 

 veins of quartz accompanied by calcite, have been found in the Prospect 

 Mountain quartzite, the lowest of the sedimentary beds "of the district, it 

 has had no economic value. These occurrences, moreover, do not seem to 

 be in any way connected with the deposits in limestone, and, as far as is 

 known, there is no ore in the Hamburg shale. 



Massive rocks. — The only massive rocks which make their appearance in 

 the metalliferous zone which is occupied by Prospect Mountain and its off- 

 shoots are granite, quartz-porphyry, and rhyolite, but hornblende-andesite 

 is found in its neighborhood. Quartz -porphyry, probably Mesozoic, ap- 

 pears in two places north of Adams Hill, and seems to be of earlier origin 

 than the ore. Rhyolite is abundant in the neighborhood of the mines, as 

 well as in immediate proximity to the ore. In some portions of the district 

 it covers large areas, but in the mines it is only found in the form of dikes. 

 Hornblende-andesite occurs near Hoosac Mountain, where it covers con- 

 siderable territory, and basalt is found within three miles. 



