IO 0 NATURAL HISTORY 
th z ground dove-coloured transparent quartz, the grain from one-fixth 
of an inch diameter downwards : there is a cryftalline, farinaceous, 
fmall fand, inclofed betwixt the grains, with a vaft quantity of Sil- 
very talc interfperfed ; at the diftance of two inches, generally more, 
is a Spot of black cockle, half inch or under in diameter ; when the 
{pots are larger, they are more diftant. It is commonly called the 
Silver Stone ; and indeed is of great luftre in the microfcope, every 
other granite placed by its fide looking flat and tame. It is much 
coveted for walling in afhler-work, being tough, keeping a good 
edge, and working eafy. One Specimen weighed to water as 
2 - - to 1 1 the fecond, of a more yellow ground , weighed more, 
viz. as 2 — - jo to i. It imbibes water ftrongly, makes no effer- 
vefcence with acids, gives fire with fleel j being calcined, the black 
{pots go off', even in a fmall fire ; the talc will perpetually keep its 
colour, though the other parts grow brown with age ; perhaps it 
might do very well for Silvering grounds for paper-hangings, and all 
the ules of talc. 
Yellow gra- Of yellow granite there is a great quantity ; the ground brown- 
yellow, Speckled throughout with black foliaceous talc of the fourth 
of an inch diameter and under ; the charge dark, cloudy, many 
grains of cockle from the fourth of an inch and under in diameter, 
intermixed with large, toothy, whitifh, opake prifms of quartz, 
from an inch and half long by an inch wide and under. The 
ground of this ffone being fo porous, and the charges fo frequent, large 
and hard, make it one of the moft fhattery granites we have, fit 
only for rough works, where neither Squares, {harp edges, nor 
moldings are required. It weighs to water as 2 - - ** to 1 : it im- 
bibes water ftrongly, and difeharges it as fuddenly ; fo that walls 
of it muff be very damp. 
Much better is the yellow granite of Tregonin. Its ground is 
yellow, and being fomewhat earthy, not more firm than the former ; 
but then the grains of its charge are but from the Sixth of an inch 
diameter downwards, and its black Specks of talc from the eighth 
of an inch diameter and under, Seeded fo thick, as to be feldom 
more than the eighth of an inch diftant. This is a very beautiful 
ftone, works as well as the white Tregonin before-mentioned, and 
is therefore reckoned among our heft granites ; although I muft 
oblerve, that the ground is fo very earthy and tender in both, that 
it can never bear a high polifti. It weighs to water nearly as the 
white of this place, viz. as 2 - - to 1 : imbibes moifture ftrongly, 
but evaporates it flowly, and is therefore much dryer for walling 
than the foregoing. 
Red gramte. On the lands of Treaflo, in the parifh of Ludgvan, there is a 
granite of a red ground , quartz laminated with oblong, lucid, 
rhomboidal 
