130 ORIGIN' AND DEVELOPMENT OF ORE-DEPOSITS. 



the time of Henry VII, for tlie sake of the two chief "lodes" 

 and the impregnated "country" between. Early in the 

 present century regular mining operations were commenced on 

 these two lodes, which were only 5 or 6 fathoms apart, but 

 diverged somewhat in depth. The lodes bear from 16°tol8"N. 

 of E., and vary from a few inches to 6 feet in width, dipping 

 steeply to the northward. They are composed of quartz, schorl, 

 and tin-ore, with a little wolfram and black copper-ore, and much 

 clay and gilbertite ; they have also yielded small quantities of 

 iron ore at certain points. The mine was worked to the 82 

 fathom level, by Messrs. Williams of Scorrier, until about 1830, 

 when it was abandoned " on account of its poverty," accord- 

 ing to Mr. Hawkins,''^ having yielded about £30,000 profit 

 to its owners Subsequent workings carried the mine a few 

 fathoms deeper, but no large amount of work was ever done 

 below the 92 fathom level. 



The lodes were always richer where the country was soft. 

 When the lodes were small they often consisted of almost solid 

 tin ore, but if large, a central " pith " or "' leader " of tin occurred 

 as a double crystallized coating upon crystallized quartz.f 



A very similar association of " lodes " with tin impregnated 

 country was also worked on a considerable scale at the Bunny 

 Mine, about half-way between Beam and St. Austell, but no 

 record of the results is obtainable, and the "lodes " seemed to 

 die out at a moderate depth. 



Birch Tor. The deposits of this mine seem to have been 

 pretty much of the character just described. Mr. Henwood says 

 that the veins united in depth, that the works were very ancient, 

 and that specular iron-ore occurred with the tin. J 



Two things have been especially noted in connexion with 

 these deposits, first, that the stanniferous belts of the surface 

 became more concentrated into definite " lodes " in depth, and 

 second, that as a whole the deposits were, as in the corresponding 

 cases of killas stockworks, much richer than the stockworks 

 properly so-called, which are not connected with definite lodes. 



*Trans. Eoy. Geol. Soc, Corn., iv, p. 477. 



+ "The Henslbarrow granite district." — Truro, Lake and Lake, 1878. 



JTrans. Roy. Geol. See., Corn., v, p. 132. 



