VOL. XII.] PHILOSOPHICAL TRANSACTIONS* 425 



The pits are 40, 50, or sometimes 6o fiithoms deep and more. The load 

 being very rich and good, above that is about 10 fathoms from the grass. And 

 below that there is a large cavity, containing nothing but air, for many fathoms 

 deep. This cavity lies between hard stony walls, about 6 or 9 inches asunder. 



Tin is usually incorporated with the stone, or is found in it. They break 

 every individual stone, and if there be any blackness in the stones, of this black 

 stuff the tin is produced. — Sometimes it is as it were mixed with a small gravelly 

 earth; sometimes white, but for the most part red. From this earth it is easily 

 separated by bare washing^; but from the stone not without much stamping. — 

 This gravelly tin they distinguish from that which is gathered from the stones, 

 calling it pryan tin, and is but about half the richness of the other. — They have 

 another sort of ore, called mundic ore. Being mixed together, the mundic 

 may be easily known by its glittering, yet deep brownness. — The mundic is said 

 to nourish the tin; and yet they say where much mundic is found, there is little 

 or no tin; and where there is little or none of that, much and good tin is found. 

 Certain it is, if there be any mundic left in melting the tin, it does it much pre- 

 judice, making it less ductile. For tin without it will easily bend any way; but 

 mixed with it, becomes very brittle, and will crack and break. 



This mundic seems to be a kind of sulphur. Fire only separates it from the tin, 

 and evaporates it into smoke. Little sprigs or boughs being set in the chimnev, 

 the smoke gathers upon them into a substance, which they call poison, and 

 think it is a kind of arsenic; which being put into water, easily dissolves, and 

 produces very good vitriol. — ^The water in which it is dissolved soon changes 

 small iron rods put into it. — When they burn it to separate it from the tin, it 

 sends forth a very loathsome and dangerous stench. 



Besides the forementioned stones, &c. found in tin mines, and incorporated 

 with the tin ; there occurs a spar, mixed also with this metal, as it is commonly 

 with lead and copper. — This appears frequently of a shiny whitish substance; 

 and casts a white froth on the water in washing it. When first taken out of 

 the earth it is soft and fattish, but soon after grows somewhat hard. The 

 miners call it white spar. 



The Cornish diamonds, so called, lie intermixed with the ore, and sometimes 

 on heaps : some of them large enough to have a coat of arms engraven on them ; 

 and are hard enough to cut glass. Some of them are of a transparent red, and 

 have the lustre of a deep ruby. These diamonds seem to me to be but a finer, 

 purer, and harder sort of spar ; for they are both found together, as on St. 

 Vincent's rocks near Bristol. 



The working of the ore is performed in this manner : The stones, beaten as 

 before said, are brought to the stamping-mill. They are so disposed, as that 



VOL. II. 3 I 



