528 
TIN. 
to light. In this, however, he differs from Mr. 
Kirvvan, who is fully persuaded that tin exists in a 
native state, and that the great scarcity of the metal 
in general will sufficiently account for its being so 
seldom found. In the Philosophical Transactions 
for the year 1766, notice is taken of a piece of tin 
ore in a mass, inclosed within a kind of quartz- 
stone, or rather in a hard crust of crystallized ar- 
senic. This lump, weighing near twelve pounds, 
was found near Granpont in Cornwall, and was so 
well covered with its crust, that its extraordinary 
weight alone betrayed it. “ The fragments still in 
the possession of Mr. Rosewarne in that place prove 
by the granulated external surface and shotten edge, 
to be native tin.” 
Kirwan tells us that the best tin ores are those 
that are washed down ‘the hills by torrents, and 
thence called stream tin ores ; the tin extracted from 
them is called grain-tin, and not easily procured in 
general. Common block-tin, being extracted from 
ores containing sulphur, is not quite so pure. The 
stream-tin from Pensagillis is said to have gold oc- 
casionally mixed with it, and that this precious metal 
has been found, though very rarely, in pieces of the 
value of two or three pounds sterling. 
Tin, of all the metallic substances, is found nearest 
to the surface of the earth. It is not, however, on 
that account more readily discovered. The veins 
of other metals are easily detected by the different 
stony or slaty substances which accompany them ; 
but the presence of tin is announced only by a 
I 
