File:The Quarterly journal of the Geological Society of London (13860046263).jpg

582
PKOE. C. LAPWOKTH ON THE GIKVAN SUCCESSION.
s.w.
Crazqhead MM-
Fig. 13. — Section of Craighead Quarries.
N.E.
' West Quarry.
£ojC Quarry
Stinchar Limestone Group.
Ab 4 . Didymograp.tus-z.me.

—
(c) Shivery shales with Encrinurus, Ampyx, Leptana, &c.
(b) Blue calcareous and slightly carbonaceous shales with Climacograptus
bicornis, Diplogr. rugosas, &c.
(a) Nodular and highly calcareous shales crowded with fossils.
Ab 3 . Compact Limestones, fossils rare.
Ab 2 . Impure flaggy and nodular limestones, greatly shattered and folded, with
rare Maclurea Logani and abundant corals.
Ab. Sandy and flaggy limestones with Orthis, Leptcsna, &c.
Kirkland Conglomerate.
Aa. Basal brecciated and calcareous conglomerate and grit.
x. Igneous and altered rocks of Craighead Hill.
Car. Lower Carboniferous sandstones of the Girvan valley.
//. Faults.
The floor of the quarry itself and the little cliff supporting the
roadway to the south is composed of the purer and more compact
limestones which give the quarry its economic value. They are
here greatly hardened and have a pale greyish-white tint when
freshly broken. They contain a larger proportion of carbonate
of lime than elsewhere, and seem to have been quarried in thick
and heavy masses. A few of. the same fossils are procurable from
them as those found in the muddier beds below, but they are much
more difficult of extraction.
The terminal beds of these compact limestones are seen at the
foot of a boss of unexcavated rock which at present divides the two
quarries from each other. This boss owes its existence to the cir-
cumstance that the strata of which it is formed contain too little
lime to be available for burning

and they have been allowed to
remain, while the surrounding limestones have been quarried away.
The strata seen in this boss are, however, of great value to the
stratigraphist, as they enable him to complete the entire section of
the calcareous series visible at this locality.
In the western cliff of this mound the Compact Limestones are
seen to be overlain by about 10 feet of grey and black Graptolitic
shales, identical in mineralogical character with the Didymograptus-
shales ( Ab 4 ) of the Auchensoul band. They contain a few Graptolites
and shells. Of the former, Mrs. Gray has here collected Crypto -
graptus tricornis, Carr., sp., and Diplograptus foliaceus, Murch.
In the grass-grown, flank of the boss on its south-west aspect
these Graptolitic shales pass upwards into an equal thickness of