ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. ] 17 



of seven or eight miles. The beds of ore, locally termed lodes, 

 consist of garnet rock, mostly crystalline, containing large quan- 

 tities of iron-pyrites and mispickel, with some disseminated 

 copper-pyrites. These beds are interstratified with "perfectly 

 conformable " dark siliceous slates, and the whole series dips 

 pretty regularly away from the granite * The economic import- 

 ance of these beds might, I think, be greatly enhanced by a 

 system of raw-smelting before export, so producing a matte which 

 would better bear the cost of carriage, and which would be more 

 readily saleable than such low-grade ores as are usually met 

 with in this district. 



The dark slates extending from Launccston to Lew Trench- 

 ard are everywhere permeated with manganese, which at many 

 points seems to be gathered into lenticular or irregular masses 

 having their greatest extensions mainly conforming to the strike 

 and dip of the beds, so forming what have been termed "bedded 

 veins," but sometimes so regular in form as to appear true beds 

 — at others expanding into irregular masses or "pockets." Many 

 of these have been worked very extensively and have in former 

 times, when manganese was high in price, yielded large profits 

 to their owners. 



That the Haytor, Bideford, Luckham, Treluswell, and 

 Botallack iron-ores, the copper-ores of Belstone and Sourton, 

 and the manganese ores of Launceston, Lifton, and Lew 

 Trenchard, are truly contemporaneous in their first origin, 

 there is, I think, no reason to doubt ; of mineral infiltration into 

 the rock substance since its consolidation, other than in some 

 instances an infiltration of silica, there seems to be no evidence 

 whatever. It is equally certain however, that the ore-matter in 

 them has been re-arranged and concentrated since the beds were 

 first formed. This is in fact usually the case with contemporaneous 

 ore-beds whenever their age is considerable — as for instance the 

 concretionary iron-ores of the English coal measures, and 

 notably the well-known bituminous copper-schists of Mansfeld;f 



* The workings on these cupriferous beds at Belstone, which seem to greatly 

 resemble many metalliferous deposits in South Norway were described by Sir 

 W. W. Smyth, in the year 1868. See Trans. Roy. Geol. Soc, Corn., ix, p. 38. 



f For a clear though condensed account of the deposits, see the admirable 

 treatise on " Ore-deposits," by the late Mr. J. A. Phillips, P.B.S. 



