ON THE DETRITAL TIN-ORE OF CORNWALL. 219 
common in the neighbourhood, has been laid open, for, perhaps 
an acre in extent and to a depth of twenty feet or more. In the 
_ deepest parts several (levels) drifts have penetrated the detritus ; 
but, for some time, operations have been discontinued. 
West of the ridge which divides the southern from the northern 
drainage* both banks of a brook which rises in Tregurthy Moor,* 
south west of Castle-an-Dinas, and falls into the Bristol Channel 
at Porth in Saint Columb-minor, exhibit traces of ancient stream- 
works ; but, within memory, one spot only has been wrought in 
the lower part of its course. 
Some forty-five years ago many of my relativest lived within a 
mile of the ancient entrenchment on Trevelgué-island ;t and— 
whilst visiting them—I had frequent opportunity for examining the 
stream-work, then under active operation at Treloy$ in the imme- 
diate neighbourhood. Where—beneath the soil 
(1). Successive layers of sand and gravel alternate, to a depth of 8 or 10 feet ;— 
(2). Vegetable remains ............ succeed rs 2 or 6 inches ;—and 
(3). The Tin-grownd, which.. varies in thickness from 6 inches to 2 feet. 
As every part of this deposit, wrought during memory of the generation 
now passing away, was beyond high-water-mark at Porth and even above 
level of the raised-beach at Fistral near Newquay,|| it contained neither shell 
nor other substance of marine origin,{ but frequently afforded granules of 
old.** 
The Shelf is of light blue and pale-buff-coloured, fissile, clay-slate. 
+ Ante, p. 216. 
: * From this spot the earliest specimens of wood-tin-ore were obtained. 
Pariiirs, Mineralogy, (3rd edition), p. 253. Micnenn, Manual of Mineralogy, 
p. 72. 
+ Lysons, Cornwall, p. 66. Hitchens and Drew, History of Cornwall, 
ii, p. 173. Parochial History of Cornwall, i, p. 242. 
~ + Henwood, Journal of the Royai Institution of Cornwall, iii, (1869), p. x. 
§ Henwood, Cornwall Geol: Trans : iv, p. 65. De la Beche, Report, p. 405. 
|| ‘‘ North of the signal-station at Newquay is a bed of shelly sandstone 
“«....and the same occurs in the cliffs around Fistral Bay, forming an exten- 
‘sive horizontal bed which rests on the edges of the slate... The sandstone 
‘of Fistral does not contain so large a portion of shells as that of Newquay; 
“and the lower part consists almost entirely of pebbles forming a kind of 
“conglomerate....These beds of pebbles and sand are situated just above 
“high-water-mark.” Boast, Cornwall Geol: Trans: iv, p. 259. 
Paris, [bid, i, p. 6. Pattison, Ibid, vii, p. 50. Tweedy, [bid, p. 55. De la 
Beche, Report, p- 405. Sedgwick and Murchison, Geol: Trans: v, (N.S. ) p. 284. 
The Ordnance Geological Map (Sheet XXxx,) indicates the remains of a 
Submarine forest near the outlet at Porth. 
{| De la Beche, Report, p. 405. 
«© «The stream-tin obtained at Treloy was feuueutly mixed with grains 
“of gold; mostly about the size of wheat, but sometimes as large as pease.” 
Mr. JouHn NicHouus, Proprietor of Treloy, MS, 
D 
