found under, and in a variety of ftrata in
other parts of Europe, yet in this county it
has been hitherto confined to the argillaceous.
No. 2. Siliceous grit,, forming a ftratum
of unequal thicknefs, fometimes exceeding
120 yards.
No. 3. -Shale or fhiftus* appearing like
an indurated clay, of various thicknefs,
fometimes equal to No. 2.
No, 4. Limeftone of various thicknefs,
from four fathoms to more than 200, and
not cut through.
No. 5. Toadftone, which frequently divides
the limeftone.
No. 6. Limeftone, beyond which no
mine in Derbylhire has penetrated.
Each ftratum is feparated by a fmall feam
of clay, or marl, differing in thicknefs from
two or three inches to two feet; and of
various colours, from the ochre yellow to
t.ho
the brown, and afh green. It is worthy of
notice that whatever ftratum appears the
uppermoft, this reprefentation will fhew the
fubfequent arrangement; a circumftance de-
ferving attention in mining countries: for
by the knowledge of the upper ftratum the
_ fkilful miner is enabled to form an idea of
what mav be found underneath, whether
coal, iron, &c. &c.
The furface of the valley of Caftleton is
rubble, compofed of broken fragments of
various fubftances, fome as fmall as coarfe
gravel, reaching to the depth of a few fathoms,
as reprefented.in the plate.
I fhall now proceed to examine the fubftances
thatcompofe each ftratum, and thus
endeavour to point out the ufe of minera-
logical knowledge, as many gentlemen for
want of receiving fome information on that
interefting fcience, have been expofed to
the arts of their agents, and have fuffered
" * Ogreat
/r