i go REVIEWS 



"Prospecting in the North." By Horace V. Winchell. The 

 Mining Magazine, Vol. Ill, No. 6, p. 436. December, 1910. 



The writer compares the sulphide ore deposits of the western part 

 of the United States and Mexico with those of British Columbia and 

 Alaska and notes the differences in the operations of the processes of 

 superficial alteration and secondary enrichment in the different latitudes. 

 In the more northern deposits the metals have not migrated in cold 

 solutions so extensively, because the colder climatic conditions are less 

 favorable. Further, the secondary ores, where found, have generally 

 been planed off by ice erosion. 



Since glacial times, at some places, a kind of secondary sulphide 

 enrichment has taken place at the very surface, but generally this 

 amounts to little more than a veneer or varnish on the lower-grade 

 material. His conclusions, applied to deposits of sulphide ores of 

 copper, silver, lead, and to some extent, of gold, are: " (1) Boreal 

 regions seldom contain rich and extensive deposits of secondary ore. 

 (2) The surface appearance is often deceptive, and if the ore is high 

 grade, sudden decrease in value may be expected at limited depth. (3) 

 Where large deposits of primary ore are found in glaciated regions, these 

 are likely to extend downward." In the temperate zone,. "(1) Deep 

 superficial alteration and complete oxidation of vein-matter is a common 

 phenomenon in warm countries and is indicative of good ore below; 

 (2) In general, ore deposits are more abundant in the warm and tem- 

 perate zones; and (3) They are not so likely to terminate suddenly or 

 change rapidly in depth." 



W. H. E. 



Geological and Archaeological Notes on Orangia. By J. P. John- 

 son. London: Longmans, Green & Co., 1910. Pp. 99. 



This volume contains chapters on Stratigraphy, Kimberlite Dikes 

 and Pipes, Diamond Mines, and Superficial Deposits and Pans. 



Almost the whole surface is made up of nearly horizontal beds 

 belonging to the Karoo System, with comparatively small outcrops of 

 older formations along the Vaal River. In the area best exposed these 

 older beds dip away from a central core of granite and are overlain 

 unconformably by the Karoo. 



The lowest of the Karoo beds is the Dwyka series, which is described 

 as a band of bowlder shale. The underlying rocks wherever exposed are 

 polished and present the characteristic contours of a glaciated country. 



