128 ORIGIN AND DEVELOPMENT OF OEE-DEPOSITS. 



Other stanniferous masses of scliorl-rock occur at Boscaswell 

 Downs in St. Just, while the famous Eoehe Eock itself contains 

 small quantities of tin. 



Gonamena. A most remarkable mass of stanniferous granite 

 was formerly worked at Gonamena, at the foot of Caradon 

 Hill ; the excavation is stated by Mr. Hen wood to be 11 acres 

 in extent, and 8 fathoms deep.* He also mentions a similar but 

 smaller excavation near the Cheesewring. These have not, I 

 think, ever been worked for china clay, but the working of the tin 

 has certainly been facilitated by the partial kaolinization of the 

 felspar. The same may be said of the rather extensive excava- 

 tions at Kit Hill, and at Two Bridges on Dartmoor. f Others 

 occur at Eaggy Eowel, on the east side of Tregoning Hill, in 

 Breage, and many other places ; want of water alone prevents 

 very many of these from being profitably worked. 



The aggregate area of these " granite " stockworks can 

 hardly be less than 250,000 cubic fathoms, or, considering the 

 abundance of schorl which increases the specific gravity of the 

 rock, over 4 million tons — averaging little, if at all, less than 8 

 lbs. of tin to the ton, or, say 14,000 tons of black tin. 



4. — TIN STOCKWORKS IN GRANITE CONNECTED WITH DEFINITE LODES. 



These have been very much richer than the deposits just 

 described. A very common mode of occurrence is as a pair of 

 well-defined lodes, enclosing a belt of highly stanniferous country 

 between them. The famous deposits at Balleswidden, Beam, 

 Bunny, and Birch Tor, are of this character. 



Balleswidden, Parish of St. Just. At this mine Awboys lode 

 and the south lode ran parallel, about 20 fathoms apart, for a 

 distance of nearly a mile. There were other lodes crossing these 

 obliquely at various points, the situations of all of them being 

 clearly explained in the paper of Messrs. Eov/e and Foster, in 

 1878.;]: It must not be supposed, however, that these lodes were 

 at all like the great master lodes of the Carn Brea district ; they 



*Traiis. Eoy. Geol. Soc, Corn., "Vol. viii, p. 665. 



flbid, V, p. 132. 



JRowe and Foster, "Observations on Balleswidden Mine." Trans. Eoy. Geol. 

 Soc, Corn., x, pp. 10 and 17. A very well illustrated and valuable paper through- 

 out, 



