352 Mhieralogical Olservations on Cornwall. [Nor. 



the great tin veins extend over the whole length of Cornwall 

 and Devon, and lose themselves at both extremities in the sea. 



Tin has been raised in Cornwall from time immemorial. 

 It is well known that the Phenicians traded to this county 

 for tin at least 3000 years ago. Indeed, if we believe Camden, 

 the name Britain was given to our island on account of the tin 

 which it yielded ; for it signifies, he says, the land nf tin. 

 Remains of the old tin mines are now and then found in Corn- 

 wall. They are never deep : and it would appear, from the way 

 in which they are constructed, that the mode of raising the ore 

 was to throw it. by means of shovels, to a recess cut in the shaft 

 for that purpose ; from this it was thrown to another recess ; and 

 this was continued till it reached the top of the mine. The 

 copper mines constitute at present by far the most important 

 mines- in Cornwall. Prodigious quantities of copper are raised 

 there annually. It is not much more than 100 years since the 

 mining for copper commenced ; and during the last 30 years it 

 has been carried to a much greater extent than before. 



As far as I had the means of observing, the Cornish mines are 

 managed with very considerable skill. The machinery is all 

 good, and in many places excellent. They are obliged almost 

 every where to use steam-engines, on account of the scarcity of 

 water. A regular monthly statement of the work done by these 

 steam-engines is collected, a plan which has been attended with 

 much good effect already. The best steam-engines, with the 

 consumption of one bushel of coals, raise 2/, 000,000 of gallons 

 of water one foot high. The little water which can be collected 

 is applied to drive machinery with great skill ; but the expense 

 of procuring water is generally so great as to render steam- 

 engines preferable. 



If I were to presume to find fault with any part of the process 

 followed by the Cornish miners, it would be the manner of 

 washing the tin ore after roasting it. The tin ore is always mixed 

 with copper pyrites, iron pyrites, and arsenical pyrites. To get 

 rid of the arsenic (or mundic, as they term it,) this mixed ore 

 is roasted in a reverberatory furnace. The powc!«r after this 

 process is washed in water ; and by that means the tin ore, which 

 is heavy, is easily separated from the copper ore, which is light. 

 Now it appears to me that, by this roastinir, a considerable portion 

 of the copper pyrites must be changed into sulphate of copper. 

 All this portion will be dissolved by the water used in washing, 

 and entirely lost. I should propose to throw the roasted ore into 

 a kind of pit, to cover it with water, stir it about, and after a 

 few days draw off the water into a separate pit. Old iron thrown 

 into this water would precipitate the copper : and I am persuaded 

 that the quantity of copper thus saved would much more thai* 



