where elfe to be met with; and produce
the greateft variety of fluors in the world.
In this limeftone ftratum are frequently
found openings or caverns, which are commonly
called Jhakes, or Jwallows. They
are large fifth res, the depth and communications
of which cannot be afcertained, but
they are of great fervice in feveral mines,
as receptacles for the deads, or rubbifti, and
as aqueducts to carry off the water.
I now come to a ftratum which has excited
great attention among geologifts and
mineralogifts, foreign and domeftic. No. 5.
reprefents 'Toadjlone, by which name various
fubftances have been denominated, fome
having the appearance of bafalt, with equal
hardnefs; while others are of various colours,
full of holes and quite foft. When
a fubftance is met with, intervening the
limeftone ftratum, but different in colour
and texture from the generality of limeftone
j
ftone 5 it is here generally called cat dint,
channel, or toadjlone. How far they may
prove to be what is generally underftood
by the name of toadftone, the reader will
determine.
This ftratum is very irregular in its appearance,
thicknefs, and direction. In the
neighbourhood of Wormhill, Afhover, Buxton,
Caftleton, and various other places, it
appears at the furface, being the uppermoft
ftratum. It is generally of a dark brown
colour, with a greenilh tinge, fuperficially
full of holes; but at a greater depth it is
more compaft, and the holes feem to have
been filled with calcareous fpar, and foine-
times with green globules. Fracture irregular
eafily fcraped with a knife ; but this
foft variety appears to me to be in a ftate
of decompofition.
The harder variety is found in an irregu-
D 4 x lar