570 REVIEWS AND BOOK NOTICES 



malachite, calcite, quartz, kaolinite, and ankerite. Fluorite is the main 

 product of the mines, and lead and zinc might almost be regarded as by- 

 products. Much of the ore must be cleaned before shipping, because the 

 mines are working in the oxidized zone. The mining industry will grow 

 more rapidly when a deeper zone is reached and the ore becomes cleaner, 

 and when transportation facilities improve. E. W. S. 



Climatic Features of the Pleistocene Ice Age. By Professor Al- 



BRECHT Penck. (Reprint from the Geographical Journal, 



February, 1906, pp. 182-87.) 



Professor Penck, in this paper, approaches the problem of the climate 



of the Pleistocene Ice Age from the data of physio-geographical research. 



He thinks it likely that the pluvial periods, of which there is evidence in 



many of the deserts of the world, were contemporaneous with ice-advances, 



and that desiccation phenomena accompanied interglacial epochs. The 



world-wide parallelism of such events points to a common origin, which 



he thinks to be a very slight change of temperature. E. W. S. 



The Transvaal Formation in Prieska, Cape Colony. By E. H. L. 



ScHWARZ. (Reprint from Transactions of the Geological Society 



of South Africa, Vol. VIII, 1905, pp. 88-103; ^ plate.) 



This paper describes the parts of the Transvaal system and sums up 



what is known of it. A number of suggestions are made as to correlation 



with other formations in South Africa and formations in other countries. 



There is a very striking resemblance, both in lithological character and 



sequence, to the Huronian of the Lake Superior region. E. W. S. 



Iron Ore Reserves. By Charles Kenneth Leith. (Reprint from 



Economic Geology, Vol. I, No. 4, February-March, 1906, pp. 



360-68.) 



The exhaustion of the world's supply of iron ore has been put by many 



authorities at less than a century hence. Professor Leith holds that these 



estimates do not take the low grade ores suflficiently into account. Before 



the high-grade ores are exhausted the price of iron will have so advanced 



as to make profitable the working of immense bodies of ore which are not 



worked now. Accompanying this change will be widespread economic 



changes in matters related to the iron industrv. E. W. S. 



