218 BthiiograpMcal Notices. 



This important mining centre in Central Nevada is in the Great 

 Basin, which consists of Paheozoic rocks (Cambrian to Carboniferous), 

 20,000 feet thick, extensively faulted and affected by Tertiary 

 volcanic eruptions. A complete monograph is being prepared. 



4. The Geology of Leadville, Colorado, by Mr. S. F. Emmons. 

 The Mosquito range is rich with silver-lead ores in a Carboniferous 

 dolomitic limestone, overlain by intrusive sheets of porphyry. They 

 have a gaugue of iron, manganese, and clay, which sometimes re- 

 places nearly all the limestone. The whole has been uplifted, 

 folded, faulted, and shattered, and subsequently greatly denuded. 

 Mr. Emmons thinks that originally the metallic minerals were in 

 the porphyries, and that percolating water took them down into 

 the limestone, as sulphides, before the disturbances took place, 

 dissolving the limestone away with chemical interchanges. He 

 suggests that sulphides will be found to be more abundant lower 

 down, but poorer in silver than near the surface. 



5. The Geology of the Comstock Lode, by Mr. G. F. Becker. The 

 high temperature in the deep sinkings of this wonderful source of 

 silver-ore is referred by Mr. Becker, not to the kaolinization of 

 felspar, as has been suggested, but to a source of underground heat at 

 more than two miles from the surface. The heat has been trans- 

 mitted to the side-rocks by the lode. Some gases also are present ; 

 and the evidences show " that the immediate neighbourhood of the 

 Comstock lode must be considered as a solfatara, now almost ex- 

 tinct." The ore was deposited probably " by ' lateral secretion ' at 

 or near the contact between the diorite (foot-wall) and the diabase 

 (hanging-wall)." This is oflered as the basis for practical guidance 

 in the mine, where much money has been wasted. Mr. Becker 

 finds that the so-called " propylite " and " quartz-propylite " 

 are merely decomposed dioritic and hornblendic rocks. Other re- 

 sults of rock-change, also the structural results of faulting, the 

 electrical activity of ore-bodies, and other interesting physical inves- 

 tigations, are here treated succinctly, and are to be further described 

 in a full Beport on the Comstock Lode and the Washoe District. 



6. The Director mentions a History of the Comstock Lode, as 

 being in course of preparation bj^ Mr. Eliot Lord, not only treating 

 of the discovery and working of these mines, but of the growth of 

 the industries resulting therefrom, and the development of Mining 

 Law, to which these gave rise. 



7. On the Production of the Precious Metals in the United States, 

 by Mr. Clarence King. This concise and valuable resume of the 

 statistics of the bullion production in the United States for the 

 tenth census-year, ending May 31, 1880, precedes the intended, far 

 more elaborate, technical Report on the Distribution and Production 

 of the Precious Metals in the United States. The basis has been 

 2730 reports, from 1967 deep mines, 325 placer-mines, 327 amal- 

 gam ating-mills, concentration -works, and chlorination and leaching 

 establishments, 86 smelting-works, and 2") arrastras. The output 



