102 
NATURAL HISTORY 
Reel, weighs to water as 2 - - * to 1. The fpecimen weighed in 
air fifteen penny-weights ten grains ; and after being immerfed three 
minutes, and carefully wiped, it weighed fifteen penny-weights ten 
grains and half, by which it appears, tnat this marble admitted no 
water at all into its pores. It burns to a whiter colour, but makes 
no fign of fermenting afterwards, when fprinkled with common 
water? Much better is the marble about a mile north of Padftow, 
at a place called Pormiffen, where there are in the cliff great quan- 
tities of marble, the Jlvata one foot and halt thick at a medium, 
intermixed with fhelfy flat ; the marble is fometimes cut into chimney- 
pieces and tables, makes flabs for hearths, and fmall fquares for inlert- 
ing between the angles of free-ftone pavements ; the ground of it 
fomewhat blacker than the foregoing, and the veins wider ; as to the 
ground , grit, texture, finer and clofer ; the fermentations with acids 
the fame q : it takes a very high polifh, but fo hard withal, that 
perhaps Italian marble is full as cheap * Among the Cornifh mar- 
bles, according to Linnaeus’s Syftem, (fee page 156) we mu ft reckon 
a fine gypfum or plaifter of Paris, difcovered lately in the parifh of 
St. Clare, near Lifkerd, equal to any thing of that kind round abroad. 
sect ix It may not be here unfeafonable to add a remark or two 
Oftheweight upon the weight and dampnefs of ftones in general, and of the 
of aS™ 6 foregoing in particular. As by weighing them in water 
we difcovered their fpecific gravity nearly, with regard to one 
another and to the common ftandard- water ; fo by weighing them 
carefully wiped after their immerfion, we may perceive what quan- 
tity of water has entered their pores, and in what time, which may 
lead us to fome ufeful obfervations ; and, among the reft, to efti- 
mate the dampnefs of each fort of ftone in walls and pavements ; 
for according to the quantity of water imbibed in any given time, 
and its flownefs or readinefs to remit and evaporate that moifture, 
fo will be the dampnefs of any wall built of that ftone with like 
and equal cement. If it retains as well as imbibes, then it mu ft 
be faturated with water before it can occafion any damp ; and tnere- 
fore the free-ftone of Carantok, and any other of like nature r , im- 
bibing freely, and retaining greedily, will fuck entirely into its body 
all the common moifture of the air and cement, and keep it there 
without imparting any perceivable quantity to the infide or the wall 
or room. If it imbibes water fuddenly and as readily parts with it, as 
fome of our granites do, it will infallibly occafion damps within and 
without; it will difperfe it’s dampnefs inwards, yielding it to the 
•1 Dr. Woodward takes notice of marble nodules alfo in the parifh of Kilkhampton : it cuts into neat 
variegated with brown, red, and white, from the moldings, and bears carving : it will not ferment 
fhores of the Land’s End. Cat. Ax, b 7. with acids. 
* There is a blue-black ftone of a marble tex- r Portland, Bath, and Oxford, 
ture found on Gunhilly downs; I have noted it 
attra&ion 
