Xxil 
Tin-lodes when in slate consist mostly of quartzose slate (capel),* 
chlorite, quartz and schor! in thin alternations, frequently mixed 
with quartz, and usually much contorted ;f the tin-ore is inter- 
spersed amongst these substances even more minutely than where 
it is associated with granitic minerals; and is, almost invariably 
mixed with larger proportions of other ores.{ The Jlodes which 
yield copper-ore in granite almost always contain gossan near the 
surface, and sometimes to considerable depths.§ The quartz they 
include is, perhaps, scarcely so (sugary) granular minutely divided 
as in the slate, but it opens in small irregular masses which 
crumble under a slight pressure. The numberless cavities which 
penetrate this slightly coherent ingredient often contain earthy 
brown iron-ore, felspathic clay, earthy black copper-ore and mala- 
chite, at greater depths fluor is not an uncommon vein-stone, 
earthy black copper-ore is frequently succeeded by vitreous copper, 
and this by copper-pyrites || One of the principal districts was 
anciently wrought for the tin-ore it afforded near the surface ; but 
downward the tin was gradually replaced by copper, of which, in 
fact, it proved to be one of the richest and most extensive reposi- 
tories in Cornwall ;§ yet deeper, however, tin-ore re-appeared,** 
and for sometime it has been almost the only product} of the 
neighbourhood. The lodes which yield copper-ore in slate contain— 
large quantities of soft, drusy, yellow or pale-brown, earthy iron- 
ore,—blende occasionally to some amount,—tin-ore frequently, 
though in small proportions,—and masses of galena at intervals ; 
iron-pyrites is often abundant. Their earthy ingredients are 
mostly quartz (which in favourable situations is often friable), 
mixed sometimes with (prian) felspathic clay, less frequently with 
chlorite, and now and then with fluor. Near the surface these 
* Pryce, Mineral: Cornub: p. 90. Phillips. (W.), Geo’: Trans: ii., 
p. 119. Carne, Cornwall Geol: Trans: ii., p. 87. Boase, Ibid, iv., p. 448. 
Henwood, Edin: New Phil: Journal, xxii., p. 156; Cornwall Geol: Trans: 
v., pp. 183, 220. Fox, Reports of the Royal Corn: Pol: Society, iv., p. 87. 
{+ Conybeare, (J. J.), Annals of Philosophy, v., N.S., p. 189. Boase, 
Cornwall Geol: Trans: iv., pp. 244, 250. Henwood, Ibid, v., p. 228. 
+ Ibid, v., p. 228. 
§ Ibid, v., p. 227. 
|| Pryce, Mineral: Cornub: pp. 88, 91. Phillips, (W.), Geol: Trans: 
i., p. 25; i., pp. 117,119 Carne, Cornwall Geol: Trans: ii., p. 95. Fox, 
Reports of the Royal Corn: Pol: Society, iv., pp. 95, 96. Dela Beche, Re- 
port, p. 326. Henwood, Cornwall Geol: Trans: v., pp. 206, 207, 227; viii., 
pp. 678-680. 
4 Cornwall Geol: Trans: i., pp. 252, 256, 259; ii., pp. 428, 430, 432, 
434, 436; iii., pp. 342, 344, 346, 348, 351. 
** Carne, Ibid, ii., p. 102. Henwood, Ibid, v., Table li. 
++ Thomas, (J.) and Henwood, Journal of the Royal Institution of Corn- 
wall, iii., pp. 191-197. Hunt, Mineral Statistics, 1867, p. 5; 1868, p. 5. 
