236 ON THE DETRITAL TIN-ORE OF CORNWALL. 
state of pyrites* only, and more than one compound of iron ;} but 
all in much smaller quantities and less frequently than in the lodes. 
Indeed the proportion of tin-ore in the fin-ground of one of the 
largest and richest stream-works in Cornwall} scarcely exceeded 
that contained in vein-stones of the very poorest odes when culled 
and made ready for the stamping-mill.§ Whether substances 
with which the tin-ore was associated in the Jodes were separated 
from it whilst passing from its original, to its latest, repositories, 
or that the lighter and more soluble impurities were afterwards 
removed, in suspension or solution, by the streams, of spring and 
rain water, percolating through the tin-grownd, is scarcely within 
compass of this enquiry ;|| but that the ( grain-tin) metal obtained 
from stream-ore is of better quality than the metal afforded by 
mine-ore has been long and generally known. 
(b-1). Gold has been culled from amongst the detritus of every tin- 
producing district in Cornwall ; viz:—at Saint Just,** Wendron,t}t} 
* Colenso, /bid, p. 31. 
“‘ Native copper is frequently found in our mines, near the surface, or 
‘“‘ commonly but a few fathoms deep.” Pryce, Mineralogia Cornubiensis, p. 61. 
+ Colenso, Cornwall Geol: Trans: iv, p. 31. Henwood, /bid, p. 59. 
t “The quantity of tin-ground opened at Pentuan has been seven 
‘ hundred fathoms in length, averaging about twenty six fathoms in breadth, 
‘“‘ making a total of eighteen thousand two hundred square fathoms. The 
‘“‘average quantity of black-tin [ore] gotten per square fathom has been one 
‘hundred and eighty pounds” [or about 0°00500 its weight.] ConENso, 
Cornwall Geol: Trans: iv, p. 32, Note. 
In Banca “the quantity [of ground] worked over per man yearly, on an 
‘“‘ average from 10,000 to 16,000 cubic feet, must contain 19 to 20 cwt. [from 
«¢ 0:00076 to 0:00128 its weight] of tin-ore:” Van Diust, Banca and its Tin 
Stream-works, (Translated by CLement Le Neve Foster, B.A., D.S., F.G.8.) 
p. 84. 
§ Quarterly Journal of Science, iii, (1866,) p. 108. Henwood, Cornwall 
Geol: Trans: viii, p. 472 
The proportion of tin-ore obtained from the tin-ground at Carnon varies 
from 0-150 to 0-001 the weight of the mass. Taytor, (C. DyKE), Proceedings 
of the Institution of Mechanical Engineers, (Cornwall Meeting), p. 161. 
|| ‘The metalliferous substances obtained from washings, are such as 
‘care not liable to undergo decomposition when exposed to air and moisture.” 
Watney, Metallic Wealth of the United States, p. 200. 
q Carne, Cornwall Geol: Trans: ii, p. 332. Henwood, Ibid, iv, p. 65. 
** Carne, Cornwall Geol: Trans: ii, pp. 293, 300. 
++ Henwood, Ante, p. 201, Note. 
