1 64 "Dr. Berger ofi the physical Structure 



are even shorter than those which contain a mixture of copper and 

 tin. This appears, at least, by comparing the number of the workings 

 with the number of the veins. The respective length of the three 

 species of veins may, I believe, be pretty accurately represented by 

 the relative value of the following numbers. 



Copper ... 72 



Copper and Tin G4 



Tin , , , . 5% 



In the parish of St. Agnes, and at other places along the coast, but 

 particularly at St. Agnes' Beacon, the distortion and irregularity in 

 the course of the veins is very remarkable.* The width of the 

 veins varies with the form they assume; when they divide into small 

 ramifications they become poor ; when, on the contrary, several 

 small veins converge, and form a belly, then they become rich. I 

 do not believe that there is any vein in Cornwall more than a fathom 

 in thickness, at least if there are any of greater width, they are very 

 rare. Some of the veins in Cornwall penetrate to a very great 

 depth, to one hundred and forty fathoms in Huel Alfred, and one 

 hundred and eighty-eight in Dolcoath, Cook's Kitchen, and Huel 

 Virgin. The copper veins go deeper than those of tin.* There is 

 another fact pretty well known to the Cornish miners, viz. that a 

 change of the rock in which a vein runs, produces a change in the 



* Pryce's Mineral. Cornub. 



+ It is very seldom that tin continues rich and worth (he working beyond fifty fathoms 

 deep ; and it is absolutely certain, that copper is not often wrought in great abundance, 

 till past that depth, to an hundred fathoms or more. It is also a fact, that most mines 

 with us, both of tin and cojiper, are richer in quality near the surface. The richest state 

 for copper is between forty and eighty fathoms deep, and for tin, between twenty and 

 sixty. Pryce's Miner. Cornub. 



