File:The Quarterly journal of the Geological Society of London (12736136875).jpg

THE BORROWDALE SERIES AND THE CONISTON FLAGS.
465
hard grey or bluish grey, cleaved, and often highly calcareous
shales, containing numerous nodules or thin but distinct bands of
limestone. In some places the beds of limestone are the most
largely developed ; and in other places the shales predominate ; but
the two elements of the group are usually intermixed, and alternate
with one another indefinitely. At some localities, again, as at Ash
Gill, near Torver, and at the head of Appletreeworth Beck, the shales
are largely developed at the expense of the limestone, and are suffi-
ciently thick to have been extensively worked for slates. At Keisley,
near Dufton, again, the series is almost calcareous, and the shales
appear to be entirely confined to its upper portion. Finally, at
Beck and Waterblain, near Millom, the group consists of an upper
series of cleaved fossiliferous shales, in the lower part of which a
great thickness of limestone is developed, dis continuously, in the
form of great lenticular masses of a purely calcareous nature.
In its intimate characters the limestone of the Coniston Limestone
group differs greatly in different localities. Usually it presents
itself as a hard, compact, greyish blue, grey, or nearly black lime-
stone, which, in thin sections prepared for the microscope, exhibits
a subgranular matrix in. which fragments of Crinoids, Corals, or
Brachiopods are imbedded at intervals. At Keisley (fig. 2), where
we have most carefully examined it, three principal varieties may be
distinguished : — (1) a hard, compact, greyish blue limestone with the
microscopic characters and general aspect of the ordinary variety of
the limestone just alluded to ; (2) a reddish or pink compact marble
with numerous patches of white calcite, both portions of the mass
appearing, in microscopic sections, to be crowded with minute organ-
isms and fragments of larger fossils ; (3) a light- coloured, whitish
blue or white, coarsely crystalline limestone, which is seen, in thin
sections, to be composed of innumerable fragmentary organic remains
and microzoa ; imbedded in transparent calcite, and having large
crystals of calc-spar with their characteristic cleavage-lines shooting
through the mass in various directions.
Fig. 2. — Sketch Section of the Coniston Limestone at Keisley, near
Dufton. (Length rather more than one third of a mile.)
Fault.
Jsi'.N.W.
Keisley.
High-Cup- Pennine
Gill Beck. Fault.
S.S.B
a. Borrowdale series. b. Coniston Limestone.
c. Barren ground, occupied in whole or in part by the Graptolitic
mudstones.