58 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



the cave, which at its lowest point was connected with the main incline and 

 at its highest by means of a winze with the ninth level above. Although 

 the atmosphere remained near the dew-point, it was constantly renewed. 

 The observations were conducted very near the center of the cave. 



Roth" says that spathic and fibrous calcium carbonate (calcite or ara- 

 gonite, or both together) are common in the form of stalactites and stalag- 

 mites in the cavities and fissures of limestone, and in the tunnels, shafts, 

 and drifts of- the mines. Dana 6 mentions that it is forming in an old mine 

 in Monte Vasa, Italy, at a temperature below the boiling-point of water. 

 The conditions which govern the formation of aragonite and calcite, re- 

 spectively, are not understood. In Ruby Hill, however, aragonite is form- 

 ing under ordinary pressure at a low temperature. 



Siderite (carbonate of iron and lime) has been frequently noticed. 



Quartz is found in crystals in cavities and mixed through the ore at rare 

 intervals It is not an important mineral in the ore, except that it is neces- 

 sary to its reduction by smelting. 



A silicate of iron has been noticed, but it is not of common occurrence. 



Clays which are more or less mixtures of silicate of alumina, car- 

 bonate of lime, oxide of iron, and other substances, are to be found at 

 the contacts of the different formations, and at numerous places in the ore- 

 chambers. These clays are sometimes merely the products of attrition of 

 the two walls of a fissure, and again have been produced by the decompo- 

 sition of igneous rocks or an infiltration from above. Steatite and talc are 

 occasionally met with, but are unimportant 



Rarer minerals. — Molybdenite has been detected in the quartzite from the 

 bottom of the Richmond shaft, and both carbonates of copper (malachite 

 . and azurite) have been met with in small quantities. As phosphorus has 

 been found in some of the ores it is highly probable that pyromorphite is 

 present, It is, also likely that leadhillite (sulphate and carbonate of lead) 

 as a distinct mineral may occur here (if anywhere), as admixtures of sul- 

 phate and carbonate of lead are very common. Oxide of lead as a mineral 

 .has not been found in the ores in the course of the present examination, 



°Rotk: Algerneine Geologic. I., p. o:>4. Berlin, 1S79. 

 'Dana: System of Mineralogy, p. 696. New York, 1874. 



