Tin, 
353 
Germans, and is nothing else but decayed granite, in 
which the feltspar has been broken down to clay. 
The zinngraupen, or brown crystallized tin-stone, from 
Cornwall, consists of quadrangular prisms, or double 
quadrangular pyramids, joined by their bases, so that 
these crystals are octoedral; these are found atTrwaun- 
ance and Soil-hole, in the parish of St. Agnes. Similar 
prismatic crystals, but of as small a size as a hair, are 
found in tin-stone upon killas, at Polgooth, one of the 
richest tin mines, which produces sometimes a clear pro- 
fit from 100 to 1200/. sterling per month. 
The stream-tin is collected in the valiies of the tin 
mountains in Cornwall, and yields a considerable quan- 
tity of this metal. The soil is dug several feet deep, and 
washed by water going over it, till the heavier particles of 
the ore remain at the bottom. These are nothing else 
but the abrasions of the tin ores over the mountain^, 
which are rolled down the declivities of the hills to lower 
grounds. 
The stream-tin from Pensagillis is remarkable on ac- 
count of the native gold now and then met with in it ; 
and found, though very rarely, in pieces of the value of 
two or three pounds sterling. It principally consists of 
round, oval, and somewhat smooth pieces, from the size 
of a bean to that of a pea, and less, the polished surfaces 
of which show n variety of reddish, gray, light- brown, and 
dark yellow colours. 
The wood-tin ore looks like hematites, and is found ik 
the parishes of St. Columb, Roach, and St. Denis. This 
is without any crystallized form, and has a very inconsi- 
derable quantity of iron with it* 
Another wood- like tin ore, described by professor 
Rrunnich, shows various fine fibres converging to differ- 
ent centres, like a radiated zeolyte ; but is so compact 
and hard, as to strike fire with steel. Its specific gravity. 
