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Page 147:-
Of these divisions, the FIRST, or Clayslate, being lowest in the
series, forms Skiddaw, Saddleback, Grasmoor, and Grisedale Pike,
with the mountains of Thornthwaite and Newlands; it extends
across Crummock Lake, and by the foot of Ennerdale as far as Dent
Hill; and after being lost for several miles, it is brought to
light again in Black Comb.
If we regard the granite of Skiddaw as a nucleus upon which these
rocks are deposited in mantle-shaped strata, the first has been
commonly called gneiss; but being rather more slaty, and less
granular, than the gneiss of some other countries, it is
sometimes called mica slate. Higher in the series the mica is
diminished, and the slate is marked with darker-coloured spots:
it is then provincially called Whintin, and is quarried for
flooring-flags and other useful purposes. This again is succeeded
by a slate of a softer kind, in which crystals of chiastolite are
plentifully imbedded: as we approach the summit of Skiddaw, these
crystals gradually disappear, and it there becomes a more
homogeneous clay-slate.
These rocks are of a blackish colour, and divide by natural
partings into slates of various thickness, which are sometimes
curiously bent and waved: when these partings are very numerous,
though indistinct at first, they open by exposure to the weather,
and in time it becomes shivered into thin flakes, which lessens
its value as a roofing slate. In some places, the thin laminae
alternate with others of a few inches in thickness; which are
harder, and of a lighter colour, containing more siliceous
matter; and, from the sonorous quality of some of those slates, a
set reduced to a musical scale has been for more than half a
century exhibited at Crosthwaite's
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