216 | ON THE DETRITAL TIN-ORE OF CORNWALL. 
(3). The tin-ground, including small angular and rounded 
bodies of ferruginous and milk-white quartz, 
masses of crystalline felspar, and of granitic 
matter, of quartzose and schorlaceous vein-stones, 
and of tin-stone, all in the state of sand and gravel, 
mixed with minute unfractured crystals of tin-ore. 
Microscopic particles of gold are sometimes scattered 
through the other ingredients .............e00. 5 4 ,, 5 feet ;— 
The roots of marsh plants penetrate the tin-ground. 
The Shelf—of mottled blueish and brownish clay—exhibits frequent and 
deep undulations; in the hollows of which the tin-grownd is usually most 
productive. 
The works are drained by aid of a water-wheel four feet in 
diameter. 
The Tregoss moors approach the granite of Castle an Dinas 
and of Belovely Beacon on the mann, and that of the great 
eastern-central range on the south, without actually touching 
either.*—They are bounded towards the north-north-west and 
north-north-east by slight elevations—scarcely to be called ridges 
—of slate, which direct their drainage to the Fal. The entire 
tract is within the slate-series; but in many spots the rock is so 
soft that it bears scarcely a trace of schistose structure, and much 
of it is, in fact, mere laminated clay.t The slate is traversed by 
several (LHivan-courses){ porphyritic dykes composed, in great 
part, of felspar and quartz; one of which is slightly sprinkled 
with tin-ore at its outcrop.§ Lodes have been wrought in several 
parts of the neighbourhood ; but, hitherto, with little success.|| 
Some forty or fifty years ago the Tregoss Moors exhibited an 
almost countless succession of low, stony, hillocks, and deep, 
weedy, pools, the abandoned scenes of earlier operations.** Amongst 
* Boase, Cornwall Geol: Trans: iv, p. 248. Dela Beche, Report, p. 86. 
+ Boase, Cornwall Geol: Trans: iv, p. 248. 
+ De la Beche, Report, p. 180. 
§ Postea, p. 217. 
|| Boase, Cornwall Geol: Trans: iv, p. 250. Henwood, Ibid, p. 235. 
q I am indebted to the kindness of Mr. Whitley, C.H., F.M.S., for a copy 
of his instructive Geological Map of the Tregoss-moors; and to Mr. H. Michell 
Whitley, C.E., for a tracing from a survey made, some forty years ago, by the 
late Mr. Richard Thomas, C.H. 
«x At some distance from both their cottages and their work the Tin 
streamers build little turfen shelters for the nests of their store-geese. As 
soon as they are hatched, therefore, the goslings find suitable food in neigh- 
bouring pools, marshes, rills, and scattered patches of grass. As harvest 
approaches some two or three thousand young geese are sold off the moors 
to farmers, who fatten them on the stubbles of several adjoining parishes, 
