The deposits of the useful minerals & rocks; their origin, form, and content . rans. Amer. Inst. Min. Eng., 1877, VI.—.J. S. Curtis. Silver-Lead Deposits of Eureka, Nevada Geol. Survey, Mon., 1884,VII.—A. Hague. Geology of the Eureka District, Nevada, Mon. XX., 1892. The Eureka mountains consist of limestone, quartzite, sandstone, andslate, of Cambrian, Silurian, Devonian, and Carboniferous age. Theseformations, having a total thickness of many thousands of feet, have beensubdivided in a most detailed manner by Hague. The Cambrian system,which here is of particular interest, is represente
The deposits of the useful minerals & rocks; their origin, form, and content . rans. Amer. Inst. Min. Eng., 1877, VI.—.J. S. Curtis. Silver-Lead Deposits of Eureka, Nevada Geol. Survey, Mon., 1884,VII.—A. Hague. Geology of the Eureka District, Nevada, Mon. XX., 1892. The Eureka mountains consist of limestone, quartzite, sandstone, andslate, of Cambrian, Silurian, Devonian, and Carboniferous age. Theseformations, having a total thickness of many thousands of feet, have beensubdivided in a most detailed manner by Hague. The Cambrian system,which here is of particular interest, is represented by the following sequence ;first a brownish-white quartzite 1500 feet in thickness with intercalatedargillaceous beds, this quartzite being known as the Prospect Mountainquartzite ; then an overlying grey compact limestone more than 3000 feetthick, the Prospect Mountain Hmestone ; then yellow and grey shales,known as the Secret Canon shales, among the upper members of which thinbeds of limestone are fomid ; next the Hamburg limestone 1200 feet thick ; 766 OEE-DEPOSITS. Quarter- Eureka Pogonip Hamburg Hamburg Secret Prosp. Jit. Prosp. Mt. Rhyo- Rhyo. Granite,nary. Quartzite. Limestone. Shale. Limestone. Caiion. Limestone. Quartzite. lite. lite. Silur. Cambrian. Eruptive rocks. Fig. 354. Geological map of the Eureka district. Hague. and finally a yellow shale. All these are cut by a large number offaults. The ore-deposits in their occurrence are limited to the Cambrian lime-stones, none being known below the Prospect Mountain Umestone. In that THE METASOMATIC LEAD-SILVEK-ZINC DEPOSITS 767 limestone however, from its lowest sections right to the Secret Canonshales above, deposits are numerous. On the slope of Prospect Mountain,from Mineral Hill southwards to Surprise Peak, the limestone is traversedby fissures and irregular cavities of varpng mdth and extent. Many ofthese run parallel to the bedding, while others cross it apparently at anyangle. In the cavities oxidized ore-
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