Reports cO Proceedings — Institution of Mining, etc. 233 



Pays de Bray. The region round Paris. The battlefields of the 

 Marne. The Aisne tablelands and the Cheniin des Dames. A 

 digression on Laon and some other French cathedrals. The battle 

 fronts in Champagne and Argonne. The Cotes de Meuse, the Woevre, 

 and the St. Mihiel salient. Summary and conclusion. 



Institution op Mining and Metallurgy. 

 March 18, 1920.— The President, Mr. H. K. Picard, in the chair. 



■' Tin and Tungsten Deposits : The Economic Significance of 

 their Relative Temperatures of Formation." By W. R. Jones. 



The tin and tungsten deposits of the world, occurring in situ, can 

 be classified according to their mode of occurrence into five classes : 

 I. Segregation Deposits ; II. Contact-metamorphic Deposits ; 

 III. Pegmatoid Deposits (which include deposits in minor igneous 

 intrusions, such as pegmatites, aj^lites, quartz-porphyries, and rhyo- 

 lites) ; IV. Quartz Vein Deposits ; V. Replacement Deposits. 



Evidence is adduced to show that the Segregation and Contact- 

 metamorphic Deposits were formed at higher temperatures than 

 were the Pegmatoid Deposits ; that the latter were formed at 

 Jiigher temperatures than were the Quartz Vein Deposits ; and that 

 the Replacement Deposits, if such exist, were formed at com- 

 paratively low temperatures. 



The author believes that a study of the relative temperatures of 

 formation of these deposits, and in particular of the Pegmatoid and 

 Quartz Vein Deposits (which together are the source of the bulk of 

 the world's supply of tin and tungsten minerals) will be found helpful 

 in investigating the probable persistence or non-persistence of the 

 ore-bodies in depth. 



The world's tin and tungsten deposits have been classified and 

 briefly described, and certain general conclusions are established 

 therefrom. These conclusions appear to support very strongly two 

 hypotheses advanced in this paper, namely, that deposits in which 

 cassiterite and wolframite occur in intimate association were formed 

 in a lower temperature zone than were the bulk of the tin deposits 

 free from wolframite, and that cassiterite is a higher-temperature 

 mineral than wolframite. 



On the assumption that these two hypotheses are correct, and 

 supported by other evidence bearing on the strength, lateral con- 

 tinuity, and mineralization of the lodes and so forth, the author 

 suggests that some of the deposits of Tavoy District, Burma, where 

 cassiterite and wolframite occur in intimate association, will be found 

 in depth to resemble the tin deposits of parts of Siam, of the 

 Federated Malay States, and of Cornwall. 



It is emphasized that this method of investigating the difficult 

 problem of what obtains in depth in a new field is not intended 

 to substitute, but to supplement, any other helpful evidence that 

 may be available. 



