ON THE DETRITAL TIN-ORE OF CORNWALL. 231 
(3). The tin- -ground generally consists of much the same ingre- 
dients as the deposit (2) directly above it; but perhaps it - 
may sometimes affect smaller and more rounded masses.* 
The tin-ore occurs, mostly, as water-worn sand or gravel ; 
but now and then in perfect (unfractured) crystals ...... 3 ,, j— 
The Shelf is rather coarse-grained granite; moderately hard whilst 
covered, but it rapidly disintegrates when—in progress of the work—it is 
exposed. 
The pits are drained by aid of water-wheels ; respectively— 
6 feet in diameter, and 3 _ feet wide (in breast) at Netherton; and 
7 Dp 5p op AS) KOON oy, x », Penny-snap. 
Trewint-Marsh, also in Alternun, drains into a brook which 
nee the Lynher, a tributary of the (Deane At and near its head, 
operations have been long discontinued ; but an instructive section 
is still visible. The tin-ground was long since gleaned of any ore 
it might have contained; but the remaining portions of it, and 
the whole succeeding deposit—both, consisting of granite, schorl, 
quartz, and felspar, beside fragments of various granitic vein- 
stones—affect, here and there, rude spheroids, and, perhaps more 
frequently, subangular masses; but for the most part they are 
rough angular blocks, which hear no mark of attrition. 
The moors west of Kilmar, Sharp Tor and the Cheese-wring 
decline towards Trewartha-marsh, whence their drainage falls 
into the Lynher. The bed and margin of every tributary} — 
evidence the labours of earlier streamers, who sometimes found 
particles of gold mixed with their tin-ore.} 
* “The stream-works in the valley of the Fowey, on the Bodmin moors 
..show that twice has the surface been clothed with vegetation. The first 
“time, on a granitic soil, grew large timber trees: a flood laid them down... 
‘‘ with their heads directed down the valley...and spread a layer of granite 
‘pebbles and tin over them: another soil was formed supporting a vegeta- 
‘tion of bushes and ferns, the resort of the deer, and upon this a finer gravel, 
“the result of slower and longer diluvial action, accumulated: and lastly, 
“ on this, a third bed of peat has arisen, crowned with no leafy honours, and 
‘‘ whose tallest plant is the low but elegant heath.” Parrigson, Cor nwall 
Geol: Trans: vii, p. 36. 
+ Blight, Journal of the Royal Institution of Cornwall, iii, (Mo. ix,) 
. 13. 
+ Three-quarters of an ounce of gold culled from amongst the stream- ~ 
tin-ore of his domain in North Hill, was—by direction of Mr. Spoure (who 
died in 1696)—made into a signet-ring, which has descended, as an heir-loom, 
to his representative Mr. Rodd of Trebartha, whose muniments comprise a 
contemporary manuscript descriptive of the conditions under which both the 
metal and the ore were discovered. Mr. Hpwarp Huarwe Ropp, of Penzance, 
MS. 
