RECENT ADVANCES IN SCIENCE 567 



Mining District," Geol. Survey of South Australia, 191 7, Bull. 

 6, pp. 135). The lodes are contained in a pre-Cambrian com- 

 plex of sediments, acid lavas, and granite intrusions, the 

 introduction of the ore being due to the latter. 



The ore deposits of three areas in the western United States 

 are exhaustively described in the memoirs referred to (E. S. 

 Bastin and J. M. Hill, " Economic Geology of Gilpin Co. and 

 Adjacent Parts of Clear Creek and Boulder Co., Col.," U.S. 

 Geol. Survey, Prof. Paper 94, 191 7, pp. 379 : J. B. Umpleby, 

 " Geology and Ore Deposits of the Mackay Region, Idaho," 

 ibid. Prof. Paper 97, 191 7, pp. 129; F. C. Schrader, "The 

 Geological Distribution and Genesis of the Metals in the Santa 

 Rita-Patagonia Mountains, Ariz.," Econ. Geol. 191 7, 12, 237-69). 

 The two Professional Papers contain complete and valuable 

 discussions of the principles of ore-deposition in the areas 

 described. The Colorado deposits carry primarily gold-silver 

 ores, but uranium, tungsten, copper, and iron ores also occur. 

 The structural types include veins, stockworks, and magmatic 

 segregations. All are believed to have been formed in Tertiary 

 times, and to be genetically related to the Tertiary igneous rocks 

 of the region. The Mackay region of Idaho carries contact 

 deposits of copper ore and veins representing two periods of 

 mineralisation, the earlier of which includes copper, lead-silver, 

 and tungsten deposits, and the later being worked primarily for 

 silver and associated lead. A discussion of the contact deposits 

 shows clearly that a granite magma has supplied large quantities 

 of iron, alumina, and silica to the adjacent limestones, as well 

 as sulphide ores. 



A reprint of Chapter IV of the great Report of the Royal 

 Ontario Nickel Commission forms a publication of the Ontario 

 Bureau of Mines (W. G. Miller and C. W. Knight, " Nickel 

 Deposits of the World," Ont. Bur. Mines, 1917, pp. 286). This 

 of course contains a full description of Sudbury, Ont., the 

 greatest nickel-mining district of the world. A lively contro- 

 versy is proceeding between the advocates of contrasted 

 theories of the origin of the Sudbury ores. Coleman and 

 numerous other investigators ascribe the deposits to magmatic 

 segregation followed by re-arrangement of the material through 

 solution and re-deposition in certain places ; the authors of 

 this report, however, support the theory of deposition by heated 

 waters circulating through brecciated and sheared zones. 



