6 4 NATURAL HISTORY 
pepper-corn, and plainly a congeries of fmaller cryftals cemented 
together into a lump : their angles were fomewhat^ blunted, but the 
fmaller gravels or hands were quite angular ; mixed with dm gravel, 
was a good deal of leafy talc, which, in the microscope, ap- 
peared as fo many lammce of cryftal. The three eighths fuf- 
pended in the water, and left to fettle, depofited an exceeding white 
clay ; it whitens the fingers, flicks to the tongue, is extremely 
fmooth to the touch, taftlefs, a little gritty between the teeth, 
owing to the fmaller grains of talc, which never deferted the Clay 
during the depuration. Being of fo fair a colour, I ground fome of 
it with nut oil, but it loft its whitenefs, and became fat, and of a 
dove colour : with linfeed oil it grew much more yellow, fo that 
it will not, as a colour, be fit for painters ; with aqua fortis it 
makes not the leaft effervefcence, but refolves into a pafte ; put into 
a fierce fire, and kept there four hours and forty minutes, it nei- 
ther vitrified nor altered its colour, and acquired no more hardnefs 
than is neceffary for paftils for drawing. As this Clay feparates fo 
eafily from its fand, has much talc, (and therefore will not vitrify) 
and the pureft colour, it may poftibly, both without as well as 
with its fand, upon different occafions, be a very ufeful ingiedient 
for making porcelain ; at prefent, in its natural ftate, it ferves only 
to make bricks for fmelting-houfes, enduring the moft intenfe fire 
of the furnace better than any other within equal reach of the 
workmen. By its diffolving fo readily in water, it may be a kind 
of marie, and ufeful as a manure. 
sect. ix. There is a Jlratum of clay not very different from the foregoing 
Trewren m the tenement of Trewren, in the parifh of Madern : it lefifts the 
< " !a - ' fire well, and is ufed by the melters for the fame puipofe as that 
above, but is not near fo white, fmooth, and foft j by burning a 
fmall quantity of it, it appears more tenacious, and fitter for ftone 
and potters ware, being reduced into a very hard dome by my ftudy 
fire. There are many other whitifh Clays m in Cornwall of much 
the fame nature as thole already mentioned. I have only to remark, 
that in the heart of the bed of clay found at Amelebreh, there are 
fome fcattered ftony glebes of red earth, like the Rubrica of Pliny, 
and the Miltos of the Greeks. I immerfed this ruddle in water, 
but it would not diffolve : upon grinding it, the ftony part was 
hard and gravelly, but being well ground down with clarified 
linfeed oil, it made a very good red, and mixed kindly with 
white, making a good flefh colour, and though laid on thick on 
the canvas, would not ftart, nor alter its colour ; fo that a better 
m As at Tregonin Hill in Breag, at Treaffo in Ludgvan, in the parifh of St. Enodor, and near the 
town of Loflwythyel, &c. 
red 
