TIN DEPOSITS OF THE MALA Y PENINSULA 1 49 



the surrounding hills and carrying cassiterite, are found in the 

 alluvium. 



4. The cassiterite in the alluvium, though in a fragmental 

 condition, is of the same character as that in the granite and 

 limestone. 



5. The alluvium is as a rule richest in tin, and the fragments 

 of ore are largest, near the areas of tin-bearing rocks. 



6. The characteristic minerals associated with the tin in the 

 alluvium are the same as those associated with it in the rock, 

 except in the case of the easily altered minerals, such as the iron 

 and copper sulphides, which have usually been decomposed in 

 the decay of the rocks, and therefore do not often appear in the 

 alluvium, though partly altered masses of these minerals are 

 sometimes found in the alluvium. 



Such facts as these leave no doubt as to the origin of the tin 

 in the alluvium. As regards the tin in the rocks, it may be said 

 that in the granite, the occurrence of the cassiterite in veins, 

 stringers, networks, etc., along lines of fracturing, are strong 

 evidences of aqueous deposition of the ore; while the occurrence 

 as an irnpregnation in the rock where no marked Assuring occurs 

 may be due either to segregation during a more or less molten 

 condition of the rock or to aqueous concentration in a solidified 

 rock. It is possible that the tin was originally a disseminated 

 constituent of the granitic rocks ; and in places its concentration 

 may have been due to segregation from a molten mass, but there 

 can be no doubt that some of the concentration, as at present 

 seen, was due to water action after the solidification of the rock. 



The tin in the limestone was probably also deposited from 

 solution. It does not seem probable that it was derived mechan- 

 ically from the erosion of the granite during the deposition of 

 the limestone formation, as it does not occur in the manner of a 

 fragmental deposit, but in seams and clusters along lines of 

 fracturing. Moreover, it is accompanied by iron pyrites, chal- 

 copyrite, arsenical pyrites, etc., just as in the granite, and this 

 would probably not be the case had the tin been detrital, as the 

 iron sulphides in the granite would have been largely decom- 

 posed before being enveloped in the limestone. It seems prob- 



