or lefs thick, and is frequently feparated at
irregular didances of feven or five fathom,
tec. by a marl containing adventitious fub-
ftaoces, and in fome places only a few
inches thick, while in others the marl is
two feet.* The whole of this ftratum is
compofed of marine exuviae, which (hew
it not to be what is underfiood by primitive
limeftone. On the furface of this ftratum
is fometimes found rotten ftone, particularly
near Wardlow Mire and Aftiford, which
appears a decompofed argillaceous fubftance
containing oxyd of iron. It feels fmooth,
and is much ufed for poliftnng brafs in the
manufactories at Sheffield.
This, ftratum abounds with a variety of
(hells, entrochi, coralloids, madrepores, &c.
The vallies often contain ratchell or rubble,
* I f more notice were taken o f the divifions in the limeftone,
by the marl and adventitious matter interpofmg, probably
the formation of calcareous, earth might be better ex,-
a confuted mafs of various fubftances, of
different fizes, collected by their rolling
from the mountains at various periods.
Sometimes the hills on one fide are lime-
ftone, and on the other grit or ffiiftus. For
inftance, the limeftone, which to the fouth
weft of Caftleton is uppermoft, is 300 yards
below, under the oppofite mountains, which
are of grit, incumbent on (hale. As neither
the ftrata of (hale nor grit make their appearance
on that of limeftone, to the fouth
weft of Caftleton, nor in many other parts
of this country, it was the opinion of Mr.
Whitehurft, that fuch ftrata were diflocated
and thrown into confufion.
The limeftone forms a variety of beautiful
marbles; near Wirkfworth fome are
found in thin ftrata, of a light ftone colour,
full of marine remains, and ufed for paving,
flooring, &c. called Hopton ftone. Near Mo-
liyafti, and at Foolow, a beautiful variety is
found