184 



ON THE MINERAL AND METALLIFEROUS [Ch. IX. 



slate) is heaved by the western flucan*, towards the right 

 hand, and the greater angle, at 



90 fathoms deep, 21 feet, 



120 30 



130 8 



and at 140 fathoms, the two veins are so confused at their 

 point of contact, that neither the quantity nor nature of the 

 heave can be ascertained." At Dolcoath mine (situated on 

 or near the junction of the granite and slate, not far from 

 Camborne) there is an instance of a similar nature; but 

 with the additional interesting circumstance, that the vein 

 which in one part of the mine intersects and heaves the 

 other vein is itself, at another part, intersected by the same 

 vein without experiencing any heave. This fact was first 

 recorded by Mr. Foxf, from whose communication we copy 

 the subjoined diagram. 



Fig. 18. 

 adit 30 fms deep 

 iQfms under adit 



Dolcoath Mine. (Bird's-eye view.) 



* The miners make a distinction between cross-courses and Jlucans, and 

 geologists have followed their example; but there are, in fact, no points of 

 difference sufficiently important to justify such a proceeding; for a vein which, 

 in one spot, is entirely composed of clay, at no great distance often becomes 

 quartzose, thejlucan passing by imperceptible shades into a cross-course. It is 

 certainly right to note this difference of composition when it occurs, but it 

 affords no grounds for instituting distinct classes : nor indeed ought tin and 

 copper lodes to be placed in different classes, for no such separation occurs in 

 nature, the greater number of lodes containing ores of both these metals. 



f Philos. Trans. 1830, p. 404. 



