references: geology 447 



partial rigidity, the composite country rock was broken by persistent 

 fractures in northeast-southwest directions; that aqueous solutions of 

 alkaline nature and some gases arising from the deep-lying* still molten 

 portion of the magma transported ore-making elements outward toward 

 the surface; that these were deposited, on attaining suitably lower tem- 

 peratures and pressures, as lead-silver ores with associated copper and 

 gold in the form of bedded deposits in limestone and lode deposits in 

 fissures, by replacing certain more nearly pure limestone members along 

 and adjacent to feeding fissures and partly by filling fissures, partly by 

 replacing their walls; that movement recurred along these northeast - 

 southwest fissures brecciating and faulting the ore and was followed by 

 fracturing in a northwest-southeast direction; and that along the path- 

 ways thus formed waters descending from the surface have altered the 

 superficial portions of the primary sulfide ores to rich oxide and carbon- 

 ate ores, and that this process is still in progress. J. M. B. 



REFERENCES 



GEOLOGY.— T/ie mining districts of the western United States. James M. Hill, 

 with geologic introduction by Waldemar Lindgren. U. S. Geological Sur- 

 vey Bulletin .507. Pp. 309, with maps, views, and sections. 1912. 

 .Bibliography of North American Geology for 1911. John M. Nickles. U. S. 

 Geological Survey Bulletin 524. Pp. 162, including subject index. 1912. 

 Thirty-third Annual Report of Director of the United States Geological Survey 

 to the Secretary of the Interior. Pp. 175, with maps and sections. 1912. 



ENGINEERING.— i^esiiZ^.s of spirit leveling in New York, 1906 to 1911, inclusive. 

 R. B. Marshall, Chief Geographer. Work done in cooperation with State 

 of New York. U. S. Geological Survey Bulletin 514. Pp. 139. 1912. 

 Results of spirit leveling in Pennsylvania, 1899 to 1911, inclusive. R. B. Mar- 

 shall, Chief Geographer. Work done in cooperation with State of Pennsyl- 

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 Results of spirit leveling in Florida, 1911. R. B. Marshall, Chief Geographer. 

 U. S. Geological Survey Bulletin 516. Pp. 23. 1912. 



Results of spirit leveling in Alabama, 1911, R. B. Marshall, Chief Geogra- 

 pher. U. S. Geological Survey Bulletin 517. Pp. 38. 1912. 

 Results of spirit leveling in Ohio, 1911. R. B. Marshall, Chief Geographer. 

 Work done in cooperation with the State of Ohio. U. S. Geological Survey 

 Bulletin 518. Pp. 108. 1912. 



Results of spirit leveling in Tennessee, 1910 and 1911. R. B. Marshall, Chief 

 Geographer. U. S. Geological Survey Bulletin 519. Pp. 45. 1912. 



B.YT>ROhOGY .—Surf ace-water supply of the United States, 1910. Part XI. 

 Pacific Coast in California. Prepared by W. B. Clapp, F. F. Henshaw, and 

 H. D. McGlashan. U. S. Geological Survey Water-Supply Paper 291. Pp. 

 218, views, and sections. 1912. 



