180 Dr. Bet^ger on the physical Structure 



their matrices. Before closing this memoir, I shall venture to ofTer 

 some conjectures on the causes to which some of the great pheno- 

 mena in the physical structure of Cornwall may be attributed, and 

 on the epochs of their occurrence, more particularly with respect to 

 the formation of the veins and the cross-courses. 



It appears to me, that the force which produced the fissures that 

 now contain the veins must have acted upon the northern and 

 southern slope of the chain : that at the time when the waters fell 

 into the British Channel on the one side, and into the Bristol Chan- 

 nel on the other, the granite ridge, as well as the upper part of the 

 strata of grauwacke, being left exposed and in a state of softness, 

 must, when left to their own weight, have yielded on the sides 

 where they were no longer supported, and that owing to this cause, 

 fissures, or empty places, were formed on each slope, parallel to the 

 length and to the direction of the chain, that is to say, from east to 

 west ; and that these spaces, being afterwards filled up with different 

 materials held in solution, formed the veins such as we now see 

 them. 



But the body of water still serving as a support to the strata at 

 the base, while they were deprived of it in the upper parts, it ne- 

 cessarily followed that the fissures were conBned to the parts of the 

 chain which were first left exposed ; and we find, in fact, that the 

 greater number of the mines are situated on a line which is a little 

 be low that of the junction of the granite and the grauwacke. 



Farther, there must have been at an after period some great con- 

 vulsion, which produced the falling down or hanging of the chain 

 towards the west ; the formation of the cross-courses, and conse- 

 quently the breaking across of the true veins ; and lastly, the dislo- 

 cation of some portion of the chain, the fragments of which carried 



