RECENT ADVANCES IN SCIENCE 377 



Sudbury nickel eruptive M. A. Dresser (Econ. Geol. 191 7, 12, 

 563-80) shows that the norite is frequently schistose and 

 brecciated, but the abundant fractures are found in the early- 

 formed minerals. This is regarded as an indication of de- 

 formation before complete solidification, probably due to the 

 development of the Sudbury syncline. The sulphides, quartz, 

 and micropegmatite were all late in crystallisation, and were 

 still molten at the time of deformation. It is maintained that 

 the sulphides are chiefly of magmatic origin. 



Metalliferous Ores. — The chief factor in the genesis of tung- 

 sten deposits (R. H. Rastall, Geol. Mag. 191 8, 5, 193-203 ; 

 241-6 ; 293-6 ; 367-70) is the differentiation of igneous mag- 

 mas, especially those of granitic composition. Tungsten occurs 

 in association with tin, molybdenum, arsenic, fluorine, and 

 boron, as a concentrate from the final aqueous residuum of 

 granite magmas, and is thus found mainly in pegmatites and 

 quartz veins. While this constitutes the typical paragenesis 

 of tungsten ores, certain other types are characterised by an 

 association with uranium, niobium, and tantalum. In still 

 other occurrences transitions are traceable to groups of ore- 

 deposits containing gold, silver, copper, zinc, and lead. 



According to A. L. Parsons the molybdenite deposits of 

 Ontario (Ont. Bur. Mines, 191 7, 26th Annual Report, 275-313) 

 are contact ores, usually developed in a band of pyroxenite 

 intervening between granite or pegmatite and crystalline 

 limestone. Pyrite and pyrrhotite are almost always present 

 in these deposits. 



Thomson, E., A Pegmatite Origin for Molybdenite Ores, 

 Econ. Geol. 1918, 13, 302-13. 



Dolmage, V., The Copper-Silver Veins of the Telkwa 

 District, British Columbia, ibid. 349-80. 



Ball, L. C, The Arbouin Copper Mines at Cardross, North 

 Queensland, Queensland Geol. Surv., Publ. No. 261, 191 8, 70 pp. 



During 191 7, the Geological Survey of Great Britain (Summ. 

 Prog, for 191 7, 191 8, 55 pp.) carried out an investigation of the 

 iron ore resources of this country. Considerable difficulty was 

 encountered in estimating reserves, especially where the iron 

 ore occupies lodes or pockets ; but of reserves " more or less 

 developed " there is estimated to be 2,883,189,160 tons ; with 

 a " probable additional reserve " of 8,428,361,600 tons. 



Dr. F. H. Hatch has also published an excellent summary 

 25 



