ON THE DETRITAL TIN-ORE OF CORNWALL. 213 
river from those of the Fal ;* but both flow southward into the 
British Channel.t A similar, but perhaps a rather lower range, 
of like character extends—perhaps 25° E. of N.—W. of S.—from 
the granite near the Indian Queens to that of Castle an Dinas ;* 
thus separating the tributaries of the Ladock rivulet—a branch of. 
the Fal—from those of the Gannel and of the (Saint Columb- 
minor) Porth brook; both which run northward to the Bristol 
Channel. 
As the Roche river is traced upward through the moors north- 
east of Hensbarrow the stream-works mentioned hereafter are 
passed in succession. 
At Pendelow in Saint Austell the detrital deposits—wrought 
since 1828{—now present the undermentioned section ;— 
(1). Granitic sand and gravel, divided by thin partings of 
hardened silt into many separate beds ........ 6 to 8 feet ;— 
(2). Peat (fen); often mixed with, and sometimes inter- 
laid by microscopic layers of,s granitic sand ....0°3 foot ,, 2 ,, ;— 
(3). Gyranitic sand and gravel in many thin layers; the 
lower of them much mixed with hardened mud. 7,8 » j— 
(4). Peat, very closely resembling No. 2......e.ccseee 1 foot ;— 
(5). Gyranitic sand and gravel, scarcely differing from 
WG Wsedeoscoaca fslorcforetaiorehs cicielsccuelelovioicvoieletevere 90 3 to 6 inches ;— 
(6). Peats ; sometimes mixed with stems of fern, nuts, 
leaves, branches of furze, alder and hazel, and 
trunks of oak. Here and there, but very rarely, Ligh 
a few flints have been discovered.........see0e 1 foot ;— 
(7). The tin-ground, consisting of granitic, schorlaceous 
and quartzose matter mixed with the oxide of 
tin, usually in the state of sand and gravel; but 
sometimes it includes subangular masses of 
various granitic rocks and vein-stones; and—yet 
more rarely—thin scales of slate also.........- 2 to 4 feet ;s— 
The (Shelf) rock beneath is granite of ordinary texture, sometimes 
moderately hard, but usually more or less disintegrated; in such cases, how- 
ever, it is often deeply eroded, and in these erosions the ore is often richer 
than in the tin-ground proper. 
* Polwhele, History of Cornwall, i, p. 183. Lysons, Cornwall, p. 
elxxxvii. Gilbert, (C. S.), Historical Survey of Cornwall, i, p. 405. Hitchens 
and Drew, History of Cornwall, i, p. 521. Ante, p. 212. 
+ Thomas, (R.), History of Falmouth, p. 15. 
t Henwood, Cornwall Geol: Trans: iv, p. 63. 
§ Specimens of this peat were obligingly submitted to microscopic 
examination by Mr. Ralfs, F'.R.C.S. 
