196 . ON THE DETRITAL TIN-ORE OF CORNWALL. 
(4). The tin-ground, which consists generally of rounded 
masses of felspathic granite and of tin-ore; the latter 
being, in great measure, (wood-tin )of divergingly- fibrous 
structure ; with ore of this kind both the pyramids and 
the prisms of crystals of quartz, are now and then 
invested.* Fragments of different vein-stones, and not 
unfrequently crystals of quartz, are imbedded in the 
other ingredients ...... Biatiereiee valerieioioreke SoogcdoDaddGG |» 4 WO 9) aa. 
The granite (shelf) beneath abounds in felspar but contains little quartz 
or mica. Within short distances, however, it varies in hardness, and every- 
where its surface is uneven; in the softest parts the depressions are deepest, 
and here the ore is both richest and most plentiful. 
Between Towednack-church and Amellibrea operations in the 
lower part of Cold-harbour-moor disclose :— 
(1). Peat...... Oo0dd0.s0d0 DODO DEIdIOd0000 b00c e--- fora depth of 23 feet ; 
(2). Disintegrated, subangular, granitic matter, 
(gravel) ; unequally mixed with blue clay to 
different depths in various parts of the vale ; 
but generally unproductive........0-cccee. 
Beneath the clay a brownish-buff hue prevails, 
and small quantities of tin-ore are scattered 
through the gravel; but lower and more pro- 
ductive portions of the deposit assume a red- 
dish brown tint ; and, in these, angular and, 
more or less, rounded masses of tin-bearing 
vein-stones are numerous ...... 6000 ds0000 
9 ” 63 9 
The granite (shelf) underneath presents an undulating surface of unequal 
hardness ; from the deeper depressions in the softer parts of which moderate 
quantities of detrital tin-ore have been obtained. 
At Tregilsoe,t on the confines of Ludgvan and Saint Hilary, 
a section of the short and shallow vale which terminates in 
_Marazion-marsh, presents— 
(1). Peat ;—of which the surface—maintaining a tolerable parallelism - 
to that of the tin-grownd—declines irregularly, but the thickness 
iss) pLetiysuMitormilly,vaboubm tere cielee See eniridert Sd006c00¢ - 6feet; 
* Klaproth, Mineralogical Observations on Cornwall, p. 20. Rashleigh, 
British Minerals, i, p. 48, Pl. xxxii, Fig. 4. Carne, Cornwall Geol: Trans: 
iv, p. 100. 
‘““A remarkable mamillated variety [of wood-tin] has occurred very 
lately, in siti, at Sancreed, it is in the form of thick concretions capping 
crystals of quartz.” 
Gree and Lerrsom, Manual of Mineralogy, (1858), p. 358. 
+ Named Tregilliow in the Ordnance Geological Map of Cornwall, Sheet 
XxXxiil. 
q 
