OBSERVATIONS, 33 
fcraped by a knife like foap ; but in the 
fire it acquires a considerable degree of 
hardnefs. It is made ufe of in the ma¬ 
nufacture of porcelain, and for this pur- 
pofe is collected by the managers of the 
Porcelain manufactory at Worcefter, who 
pay 20 pounds iterling for a tun of twen¬ 
ty hundred weight, becaufe the digging 
of it, on account of the great brittlenefs 
of the Serpentine rock, is very dangerous. 
The analyfis of this fpecies is given. 
No. 7. 
There is alfo found a lefs fine fort with 
fpots of iron ochre, and likewife a variety 
©f a reddifh brown colour, mixed with 
green. That of Ruan minor is of a grey- 
ilh white, and light date blue colour. 
There is found alfo a whitifh fieatites 
grown through with calcareous fpar, 
which gives to the former a Smooth Alin¬ 
ing fraCture. 
White Porcelain earth: this is produced 
by the decompofed feldfpat of a decayed 
granite which fills the valleys in Corn- 
P wall. 
