522 Reviews — Zinc Ores. 



IX. — Impeeial Institute Monographs: Zinc Oees. pp. 64. Published 



by the Imperial Institute, 1917. Price 2s. 

 f nmS monograph is the first of a series now in preparation, under 

 J_ the auspices of the Mineral Resources Committee of the 

 Imperial Institute. Its object is to give a general account of the 

 world's production and resources of zinc ores, with special reference 

 to the British Empire. The compilation is chiefly due to Messrs. S. J. 

 Johnstone and T. Crook, who have carried out their work very 

 thoroughly ; all available sources of information have been effectively 

 sifted and the results condensed into a handy form. The memoir 

 contains sections on zinc minerals, the world's production of zinc 

 ores, the ore deposits of the British Empire and of foreign countries, 

 the valuation, concentration, smelting, and price of the ores, 

 commercial spelter, and on the properties and uses of the metal. 

 The treatment adopted is partly geological and partly statistical, 

 together with references to the methods of mining and degree of 

 development of the individual deposits. The descriptions of the 

 actual manner of occurrence of the ores are often somewhat slight, 

 but this is probably not the fault of the authors, since such information 

 is usually very diflScult to obtain from the scattered literature of 

 mining geology. Furthermore, at the present time many new 

 developments are taking place in this and other branches of mining 

 as to which details are not yet available. However, the difficulties 

 inherent in a work of this sort have been successfully surmounted, and 

 the Committee are to be congratulated on having made an excellent 

 beginning of a series which cannot fail to be of great permanent value 

 to the mineral industries of the Empire. 



X. — The Limestones of South Africa. 



THE Geological Survey of South Africa has published a memoir 

 on the Limestone Resources of the Union, by W. Wybergh 

 (Pretoria, 1918), containing a very full account of the known 

 occurrences of limestone of various grades in the Transvaal and 

 portions of Bechuanaland and Zululand. The total production of 

 lime for the year 1916 is given as 78,222 short tons, and the demand 

 is likely to increase in the near future. In the district under review 

 the most widespread calcareous rock is dolomite, which occurs in 

 enormous quantities both in the crystalline rocks of earliest date 

 and in the Potchefstroom System. Both of these types, however, 

 contain too much magnesia for many purposes, so that the most 

 valuable deposits from the economic point of view are the surface 

 limestones so common in many parts of the Union. 



The memoir also contains a special chapter hy Dr. A. L. du Toit 

 on the crystalline limestones or marbles of Port Shepstone and 

 Herraansburg, Natal. Detailed mapping has shown that the marble 

 of Port Shepstone is a bent and twisted mass, enveloped and 

 penetrated by sheets of igneous material ; the limestone must have 

 a thickness of several thousand feet, and the metamorphism produced 

 in it is of extraordinary theoretical interest. A detailed description 

 is promised in a future publication. 



R. H. R. 



