OKI GIN AND DEVELOPMENT OF ORE-DEPOSITS. 373 



Fifty stockworks, averaging 250 yards long and 20 yards 



wide, and yielding an average of a quarter per cent. 



of metallic tin, 1,250 tons per yard. Together 21,250 



tons of metallic tin per yard of depth. 



The whole area thus indicated would be a little less than 



half a square mile ; outside of this area tin can hardly be said 



to exist at all as a rock or vein constituent. 



Tungsten. This element is far less widely distributed than 

 tin. From all the lead veins, most of the copper-veins, and 

 even many of the tin- veins it is altogether absent ; while it 

 hardly exists at all as a rock constituent outside the veins. Yet 

 in the form of wolfram, which contains about 60 per cent, of 

 tungsten, it is locally abundant, as for instance at East Pool, 

 Great Beam, and Drakewalls Mines. Small quantities of 

 tungsten also occur as scheelite and as zippseite. Still it is 

 probable that on the whole tungsten is not more than one-tenth, 

 perhaps not more than one-twentieth as abundant in Cornwall 

 as tin. 



Here then we ha-ve four elements, each occurring in 

 considerable abundance, though limited to very small actual 

 areas in a not very large mining district, and all four are 

 peculiarly and intimately associated with each other. For if we 

 take the area which contains the whole of the tourmaline, in 

 other words that which contains all the boron and nearly all the 

 fluorine, we shall find that it includes also both the tin and the 

 tungsten. But as the tourmaline area is much larger than the 

 tin area, we may have tourmaline without tin, but not tin without 

 tourmaline. Similarly there may be tin without tungsten, but 

 not tungsten without tin. 



These mutual associations have been fully discussed 

 elsewhere,* and the conclusion seems irresiistible that fluorine in 

 solution has been the tin-carrier, bringing tin up from consider- 

 able depths to what may be called workable depth, and even to 

 the actual present surface in some instances. 



Whether boron aided in this or not is perhaps doubtful, 

 since the direct combinations of boron with tin are little if at 

 all known. It would seem, however, that when once locked up 



* Cornish Tin-stones and Tin-capels, p. 38, et. seq. 



