Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/176

 164 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.

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