142 ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 



4th. — This complex fissure became filled with mineral matter 

 of a distinctive character, the whole of which is now known as 

 the Cudna Reeth Lode. 



No proper idea of the importance of faults from a geologi- 

 cal point of view can be obtained, if we do not consider the 

 enormous number existing in such a district as Cornwall and 

 West Devon. Probably there is not a square mile in the 

 whole of the mining regions which is not traversed by one or 

 more faults, while in some places there are dozens within 

 such an area. It must not of course be supposed that all are 

 metalliferous, still less that all will pay for working. Still this 

 fact has much to do with the long continuance of the West of 

 England as a mining region, and should give us hope of new 

 discoveries in the future as in the past. Very striking examples 

 of the much fissured St. Agnes region are given in Mr. Davies's 

 excellent little work on heaves and faults.* 



Whatever may be the advantages of a greatly faulted 

 country from a mining point of view, it is evident that the 

 existence of divisional planes in the rock-masses will have con- 

 tributed to the favourable results, in so far as they have favoured 

 the formation of fissures serving as channels for the metalliferous 

 solutions, or loci for the deposition of mineral substances. But 

 it does not follow that a much jointed rock is better than one 

 having comparatively few joints. On the contrary unless the 

 fault movements are concentrated into a comparatively few 

 fissures, it may be that the mineral filling will be too much 

 distributed to be of commercial value. Such stockworks as 

 those of Minear Downs, Mulberry Hill, and Wheal Jennings, can 

 only be worked at a profit because they are at the surface, and 

 workable as open quarries. The much richer underground 

 stockwork at Pednandrea mine, described long since by Mr. H. 

 C. Salmon, could not be made to pay, although if the mineral 

 spread through 50 or 60-ft. had been concentrated in a lode of 5 

 or 6-ft. it would have paid remarkably well.f 



In studying fault phenomena, it is necessary to be on one's 

 guard as to certain phenomena which simulate faulting. Sir 



* Report Miner's Association of Cornwall and Devon, 1879. 

 fSee The Mining and Smelting Magazine, 1862, pp. 143-4, 



