624 Extracts from the Minute Book of the Geological Society • 
found in any quantity. I have observed spots of pyrites in frag- 
ments of limestone taken out of a well behind the houses on the 
south side of Union street, Stonehouse ; and among the fragments 
of rock raised from the solid ground in a new well on the north 
side of the same street, I have found specimens of limestone and 
slate containing animal remains and pyrites blended together. 
Quartz occurs mixed with the limestone in some large fragments 
near the wall at the western end of Mount-wise, and also in some 
of the rocks forming the cliffs to the eastward of the Devil’s point ; 
but these instances are rare, and the quartz is small in quantity. 
The caves which occur in the limestone of Plymouth afford 
stalactitical concretions in great variety of form, and in considerable 
abundance. Numerous forms of crystallized calcareous spar are also 
to be met with in our district, among which may be enumerated 
the primitive and inverse rhomboids, and an acute rhomboid, the 
hexagonal prism, and an acute dodecahedron in the greatest perfec- 
tion. Some fragments of crystals, which I possess, are beautifully 
transparent, and of unusual size ; but such specimens are not com- 
mon, and are now difficult to be procured. 
1821, March 2. 
A letter from James Vine, Esq. Treas. g. s. was read, containing 
a notice on a method of hardening gypsum, lately discovered. 
It appears that if gypseous alabaster be heated considerably, and 
then immerged in water, it acquires a degree of hardness so great 
as to admit of a polish like marble, and may then be used for 
making slabs, and for other oeconomical purposes. 
