778 REVIEWS 



The principal points which the memoir dwells upon are : 

 i. The main feature wherein the scheme of classification offered 

 differs from others is in the prominence given to geological occurrence 

 and the direct operation of the geological processes as essential factors 

 in the genesis of ore bodies. 



2. The nearest approach to a purely genetic classification of ore 

 deposits is believed to be found in their geological relationships, as 

 determined by the great groups of geological processes, and not in 

 their direct chemical formation or physical, shapes. 



3. The chemical reactions so widely used as criteria of ore classifi- 

 cation are to be regarded as general agencies, and therefore they are 

 not available in the specific determinations of the various classes of ore 

 bodies. 



4. In the discovery and exploitation of ores, structure is of first 

 importance, that is, the structure of the inclosing country rocks. 



5. The primary groupings of ore bodies appear to be best indicated 

 when based upon their geological occurrence, as governed by the nature 

 of geological processes operating. 



6. The secondary groupings appear to be best based upon the 

 general form of the ore bodies as geological formations produced by 

 the grander geological agencies. 



7. The ternary groupings are best based upon the specific phases 

 of the geological processes involved in the formation of ores as ore 

 bodies. 



8. The source of the ore materials is an unessential factor in their 

 classification, the great practical question being, how are ores best 

 exploited? In this connection it matters little what was the original 

 condition of the ores. Nor have we to do very much with the detailed, 

 complex, and usually fanciful chemical reactions that are supposed to 

 take place before the final stage of the ore, as we find it, is reached. 



9. Ore bodies of very similar appearance may be formed by very 

 different methods — a fact which, while apparent in all classifications, 

 does not necessarily vitiate any. 



10. Finally, the proposed scheme is merely suggestive. It is the 

 barest outline of what is believed to be capable of much farther expan- 

 sion and development into a comprehensive, rational, and practical 

 general plan. 



C. F. M. 



