Account o f the. Strata in Derbyjhire.
H a VING thus given a curfory idea of
fomé interefting objects on the furface of
Derbyshire, let me next be permitted to
accompany the reader under ground, and
to explain the general formation of the
ftrata, fuppofing a mountain to be vertically
divided. This appearance will belt be un-
derftood by referring to the annexed plate,
which I Shall proceed to iliuftrate, after
obferving that the ftrata, in Derbyshire are
Singularly curious, and perhaps unlike any
thing to be found on the continent, being
confidered by foreign mineralogifts as often
prefenting exceptions from the general rules
obfervable in continental mines.
No.
No. i. reprefents the Summit of a hill,
A is argillaceous grit : a Shews irregular
beds of argillaceous and Sulphureous iron
ores attendant on coal : b is coal lying in
laminæ under the argillaceous grit. The
depth of thefe ftrata is as follows.
Although argillaceous grit is generally
above coal in this county, it is not to be un-
derftood that it is invariable So ; for a variety
of fubftances which frequently appear in
great confufion Sometimes are Super incumbent
: as vegetable earth, gravel or rubble,
compofed o f quartzofe pebbles, clay, and
pieces of argillaceous fandftone. Indurated
clay ; a Species of ftiiftus fand ftone in laminæ,
blue clay; Semi-indurated black
earth or fmut j argillaceous iron ore ; and
thin beds of prites and Shiftus. Thefe fubftances
have frequently various names, as
metal, bind, ratehel, clunch, &c. They at
all times indicate coal ; and though coal is
founds