It feemed to me to be a queftion, whether
this fubftance be not a limeftone,
ftrongly impregnated with pyrites, which
are in a decompoling ftate j the green earthy
matter irfufpeCt to be chlorite.
At Pindar and on Tidefwell Mpor, where
the lead ore is alfo faid to occur in this fubftance,
I examined another variety of it,
but found it elfentially to agree with the.
former. I therefore conceive that the con-
fufed terms of miners have milled the very
refpeCtable authors before mentioned, who
had not fufficient time nor opportunity to
inftitute a ftriCt enquiry. In truth, the
miners have applied the fame name of
toadftone, or cat dirt, to fubftances extremely
remote, and which have only a
partial refemblance in exterior appearance.
SECTION
S E C T I O N VII.
Account o f the Fluor Mine, and o f the manner
o f working that mineral
I n the fourth'feCtion of this work, I have
already explained the appearance of feveral
Derbylhire ftrata. The reader will now
forgive my proceeding to fome, in which I
am myfelf much interefted. The mountain
B, (fee plate 2.) appears an aflemblage of
vaft rocks of limeftone, without connection
or, regularity, and is full of openings or caverns
of immenfe depth, filfures, &c. In
this mountain are the two mines that produce
the beautiful compact fluor*, here
called Blue John, which is found in pipe
* This fubftance adts as a fpeedy flux to metals, owing tQ
its peculiar acid, whence the name of Jlu or.
f 3 ■ > - veins