In general it is rare to find veins in this
fécond ftratum, but there are fome inftances
of lead ore being found in it.
No. 3, The ftratum of {hale or fhiftus
is not ftratified ; it fpmetimes is 120 yards
in thicknefs ; and is the uppermoft ftratum
in many of the valleys, where the moun-
tains on one fide are grit, and on the other
limeftone : the fhale betwixt the two enterring
the edge of the limeftone, and pafling
under the grit. The hot waters of Buxton
are found in this fubftance.
It is of a dark brown or blackifti colour,
bituminous, and appears much like an in-,
durated clay : it does not contain vegetable
impreflions, though fometimes impreffions,
of marine fubftances are found in it much
impregnated with pyrites. It is not gene-
nerally confidered as a ftratum fertile in
veins of lead ore, though fometimes that
fubftance is found in it, for being incum-
v 1 ' bent
bent on limeftone, the veins ftrike from it
into the {hale, and carry lead ore with them
to fome diftaiice. In its fparry veins are
frequently cavities, called lochs by the miners,
which are incrufted with fine and rare
cryftallizations of calcareous fpar in great
variety.
By expofure to the atmofphere, this {hale
decompofes in lamip-tz; its fradture is dull:
it abforbs moifture : contains fulphur burning
with a blue flame, and becoming of a
redifti brown colour: frequently refills
acids, but fometimes effervefces {lowly:
contains nodules and thin beds of pyrites.
The waters palling through it are chalybeate,
and frequently warm. It is incumbent
on limeftone, and is feparated from it
by a thin bed of clay.' When it approaches
the limeftone, it of courfe effervefces with
acids; in fome cafes even containing a
large