66 
ziums, and are somewhat undulated, the same, with some 
variations, as the figure beneath, which comes from Oxford- 
shire, and is commonly called prismatic from its long 
columnar appearance; this is evidently mixed with clay, as 
the lower figure of tab. 67. 
This sort of Gypsum is said to be found in masses of 
different sizes, but seldom larger than three or four feet 
in thickness; they are generally rugged, and broader than 
they are thick. 
The antients are said sometimes to have used the transpa- 
rent Gypsum in the place of glass in windows ; whence it 
has been confounded with Mica and Talc—see tab. 180, 
181, &c., which substances are still often confounded, 
although so distinct, as I presume this work now clearly 
explains. 
The temple of Fortune at Seia was built of this stone, and 
without windows. The semi-transparency of the Gypsum 
admitted the light, and Pliny said that the temple appeared 
as if lighted from within*, 
Some specimens of the crystallized kind have lately been 
found at Alstone Moor on blende, &c., and by some means 
got the title of Asbestos. They are sold in moderate pieces 
for a guinea each, or perhaps more, as the dealers may be 
more or less acquainted with the subject. 
* Haiiy 3.290. In Warwickshire, Iam told that Gypsum has been used 
for building the outside of houses; where it is burned with wood for that 
purpose, and the whole mixed up together, giving it a greyish cast. It is 
said to be extremely durable, and is carefully saved when a house is on any 
occasion pulled down, asit is still more durable even if it has lasted centuries 
in the first instance. 
