220 SCIENCE PROGRESS 



deposits of the Rand. He believes that the numerous diabase 

 dykes in the Rand were the means of opening up the channels 

 by which the gold-bearing solutions ascended. A new point 

 advanced by Horwood relates to the fact that the Rand bankets 

 are really gold-silver deposits, as the bullion contains 10-12 

 per cent, of silver. This tells against the placer theory, for 

 placer gold is always exceptionally pure. 



Prof. Young, on the other hand, is a supporter of the placer 

 theory of origin, and has arrived at his conclusions from a 

 close petrographical study of the banket and its metasomatism. 

 He points out that the metasomatic changes which have been 

 appealed to in support of the infiltration theory, took place 

 subsequent to the cementation of the rock by quartz, and 

 therefore after the banket had lost its original permeability. 

 He considers that the placer theory has been greatly strengthened 

 by the recent stratigraphical work of E. T. Mellor bf the Trans- 

 vaal Geological Survey. 



Waterhouse's description of the South Heemskirk tin-field 

 in Tasmania contains a very full account of the igneous, strati- 

 graphical, and economic geology of an interesting district. 

 The ore deposition was associated with intense igneous action 

 in the Devonian, the dominant tin ores being introduced with 

 the granites, and the subordinate nickel ores with the basic 

 intrusions. 



While antimony ore is known at sixty-seven localities in 

 Alaska, the prospects for profitable antimony mining under 

 normal conditions is not encouraging. The great war demand 

 for the metal, however, has stimulated production, and has led 

 to the publication of Brook's memoir, which summarises 

 present knowledge of the Alaskan antimony deposits. 



In his interesting Presidential Address to the Geological 

 Society of Glasgow, Prof. J. W. Gregory reviews and classifies 

 the phosphate deposits of the world, including therewith an 

 account of the phosphatic lenticles in the Scottish Torridonian 

 sandstone. He shows that the history of coal, iron, and phos- 

 phate mining in Britain illustrates the truth of the economic 

 principle of using an asset while you can. From an examina- 

 tion of the world's phosphate production statistics, Prof. 

 Gregory concludes that there is no reasonable danger of a 

 phosphate famine as predicted by some alarmists ; " and we 

 are no more blameworthy for using as much as we need than 



