OBIGIlSr AND DEVELOPMENT OF ORE-DEPOSITS. 357 



on to speak of "the over-powering contrast between the 

 vast masses of mineral stored in the lodes and the puny 

 sources of the theoretical suppty. See a lode like that of 

 Clifford Amalgamated, sixteen or eighteen feet wide, of cindery 

 copper pyrites from wall to wall, or the thirty or forty feet of 

 dredgy copper ore in the best parts of Devon Consols, or the 

 massive dimensions of the lode at Dolcoath now, at four hundred 

 fathoms deep, larger than ever ; or again the courses of solid 

 crystalline galena which have occurred in several of our more 

 notable lead mines, yielding from five to ten tons to the running 

 fathom, and. such occurrences seem to be inexplicable by the 

 process alleged." * 



Certainly there is no indication that the country rocks ever 

 contained these large quantities of sulphide ores : and for the 

 sulphur at least we seem driven to suppose a deep-seated origin. 

 Sir Warington goes on to our third case, and thus urges the 

 necessity for a similar source for the metallic components. 

 ''Again, look at a rich part of one mining field, at a belt of killas 

 rock extending over eight miles from Cligga Head to the south of 

 G-wennap parish. In that space there are about a hundred 

 parallel lodes, at one time a hundred more or less gaping fissures. f 

 and if these are to be filled up by lateral segregation from the 

 silicate minerals in the country rock, it will go very hard with 

 the long narrow slices of the rock between the successive east 

 and west veins to make up a sufficient quantity." | He then goes 

 on to consider the different contents of the parallel lodes 

 underlying north and those underlying south, which traverse the 

 very same rocks in the St. Agnes and Perran districts, and also 

 to the different contents of right-running and of cross-veins in 

 general, and observes "we should expect that if the sources were 

 the same (viz. : the country rocks immediately contiguous to the 

 deposits) the minerals would be of the same character, and 

 could never exhibit so decided a contrast." He then refers to 



* Smyth's Presidential Address, 1889, Trans. Ro%j. Geol. Soc. Corn., Vol. xi, 

 Part IV. 



f This expression should not be misunderstood, for in the first place the 

 hundred fissures referred to are obviously of three or four widely different ages, 

 and in each " age " it is likely that only a very few of the fissures were even in 

 any sense "gaping" simultaneously. 



X lUd, 



