210 . ON THE DETRITAL TIN-ORE OF CORNWALL. 
as well on the Continent as throughout the United Kingdom, 
procure most of their materials.* Throughout the granitic tract 
schorl is more or less abundant ; and, here and there, it prevails ;t 
generally, however, associated with quartz or with felspar, and 
sometimes with both. Nor are associations of schorl with quartz 
and felspar peculiar to rocks of massive structure; for the same 
substances—especially the first two—are not uncommon, in their 
alternations displaying every imaginable involution and displace- 
ment, amongst the slates which adjoin the granite.{ Westward 
the schistose rocks are mostly of dark blue and greenish grey hue, 
and their structure is thick lamellar, but occasionally they cleave 
rather imperfectly.§ Eastward, however, they assume various 
shades of pale-blue, greenish-grey, red, and dark brown, and here 
their cleavage is more decided, and their texture softer.|| To-— 
* The following columns show the enormous increase in the export of 
China-stone and China-clay which has lately taken place. 
Years. China-stone. China-clay. 
WO scooccoocccocc0a. ILA Wom) cocoodaco000n00 see 1,757 tons. 
WSUS Gocodegocooocc00 All 4G oo oad ood 0060 ADS. 95 
USPABodic6g5o0006b00Kd000 OHO 0455. cocoodadcoc0cdc00 7,490 ,, 
IEEIS55 500000 o0000000 Ups op ooooocco 0K KD S000 20,784 ,, 
ISGB5G5000000o000000 CILGES 45 adoocodoocoooome eEyIlIs 5, 
USCS rrepeleetedevellolers hateiele OO OO mavrsuinmstetatetelors te pDO000 2-100,000 ,, 
ISHOcocosacpoe0do000 BENNO 5. coOD0KO0DD Od 06 sells 2.0 ies 
Lysons, Cornwall, p. ccxi. Cornwall Geol: Trans: i, p. 233; iii, p. 
360; v, p.478. Hunt, Mineral Statistics, 1858, p. 2; 1868, p. 139; 1871, p. 
443, 
+ Deluc, Geological Travels, iii, p. 343. Conybeare, (J. J.), Annals of 
Philosophy, v, p. 188. Von Oeynhausen and Von Dechen, Phil: Mag: and 
Annals, v, p. 241. Sedgwick, Proceedings of the Geological Society, i, p. 283. 
Boase, Cornwall Geol: Trans : iv, p. 238. Hawkins, /bid, iv, p. 476. Henwood, 
Ibid, v, p. 122. Dela Beche, Report, p. 159. 
+ “On the confines of the granite.. .alternate layers generally of great 
“tenuity, of very minutely granular quartz and schorl, have all the aspect 
‘‘of a stratified mass.” Conypearn, (J. J.), Annals of Philosophy, v, p. 189. 
“A very interesting form of this rock consists of alternating layers of 
‘‘ black and white minerals, exhibiting the most complicated curves and con- 
‘¢tortions....The black are of...schorl-rock, the white of quartz which is 
‘“‘ generally more or less combined with felspar....This kind of schorl-rock 
‘is very abundant in the diluvium on Tregoss Moors.” Boasz, Cornwall 
Geol: Trans: iv, p. 245. 
§ Boase, Ibid, iv, pp. 275, 278. Henwood, /bid, v, p. 125. Phillips, 
(J. A.), London, Edin: and Dublin Phil: Mag., xii, p. 90. 
|| Boase, Cornwall Geol: Trans: iv, p. 286. Henwood, [bid, v, p. 
125. Dela Beche, Report, pp. 80, 82. 
