

ILLUSTRATIONS OF THE 



quently interfea: the metallic, and are remarkable 

 for producing Ihifts in them, or for throwing thenj 



of their natural dired 



The 



particularly thofe that yield copper ai)d tin, ruii 

 nearly from call to weft, having the fame di- 

 redtion with the beds of the rock itfelf, which 



very hard fchift 



^Ifo thof 

 are at i 

 it is rei 



The granite lodes 



as 



f porphyry, called ehan in Cornwall 



gles 



rly to the former : and 



m 



larked, that they generally hea 

 veins, but that the 



or never heave the 



mi 



ofs- 



the 



veins fel- 

 In this 



untry, therefore, the veins of granite and por- 



are poilerior in formation to the metallic 

 Thefe veins of granite may perhaps be 

 ponneaed with the great granitic mafs that run^ 

 longifudinally through Cornwall, from Dart- 



phyry 



r 



veins. 



the Land's End. This much 



th 



th 



dired: 



in general are fuch, that 



» 



J 



II 



y 



produced, they would interfed that mafs 

 3 rly at right angles, 



77. The granite veins in Glentilt, where Dr 



made his firft obfervations on this fub- 

 jecl:, are not, I believe, vifibly conneded with any 

 large mafs of the fame rock =^. The bed of the ri- 



Tilt, in the diftance of little more th 



IS 



* 



Tranf. Royal Society Edin. vol, iii. p. 77, ^c 



