72 



Featherstonhavgh^s Geological Report. 



nean power frequently interrupt the operations of miners, 

 who, finding the continuity of the beds interrupted by the 

 sinking or rising of one portion of them, have applied the 

 technical term fault to them. Where these occur, a mining 

 district has to be studied very accurately in relation to them, 

 for it is evident that no mining operation upon a large 

 scale can be carried on w^ith proper economy, both as to 

 drainage and arrangement, without their extent and direction 

 being first known. 



By studying the veniferous rocks we perceive that veins 

 are not only earthy or mineral, but metallic in their nature, 

 and that some are posterior to others. This last fact has in- 

 duced some persons to entertain the opinion that metals are of 

 different ages ; and it is certainly true that the rarest are 

 usually found amongst rocks of the highest antiquity. The 

 interesting fact also has been established, that the most pro- 

 ductive veins have a general direction fjom east to west. 

 This is the case, with the tin veins or lodes in Cornwall, as well 

 as those lodes containing copper. The veins which run nearly 

 north and south are not as metalliferous as the others which 

 they intersect. Many of these, called flucan^ in Cornwall, 

 are filled with clay. Clay is sometimes found in the copper 

 veins ; and as other metallic veins which deviate from the east 

 and west course contain increasing quantities of clay, and the 

 flucan or clay veins running from north to south, the evidence 

 seems to be strong that there are different systems of veins, 

 the more minute study of which may hereafter lead to im- 

 portant results respecting their general origin, and the causes 

 which have modified their contents. The ancient Wernerian 

 notion, that minerals and metals settled into fissures, from 

 aqueous solutions, is now exploded, and the more general 

 opinion that they have been injected from below has been 

 substituted for it; still they present themselves occasionally 

 under such circumstances as baffle our judgments. We do 

 not understand wliy veins are sometimes extremely dilated, 



