File:The Quarterly journal of the Geological Society of London (13860395994).jpg

PROF. C. LAPWORTH ON THE GIRVAN SUCCESSION.
585
S.E.
Fig. 14. — Typical Section near Balclatchie Bridge.
N.W.
Ba. Ardwell Graptolitic Shales and Flags.
a 1 . Dark carbonaceous and iron-stained shales, with Graptolites.
(n) Basal zone of calcareous and carbonaceous shales, with Climacograptus
Scharenbergi, Lasiograptus HarJcnessi, and Cryptograptits tricornis.
Ad 2 . Balclatchie Grits and Conglomerate.
d 2 '". Ashy gritstones and flaggy beds, fossiliferous.
d 2 ". Calcareous boulder conglomerate, with Lingula canadensis.
d 2 '. Green flaggy gritstones, calcareous, fossiliferous.
Ad 1 . Balclatchie Shales.
Grey and green calcareous and nodular mi idstones, highly fossiliferous —
with Barrandia, Remopleurides laterispinifer , Ampyx Hornei, Asapkus
gigas, Siphonotreta micula, Bicranograptus tardwscidus, &c.
Ac. Benan Conglomerate.
Coarse conglomerate and interbedded sandstones, with boulders of quartz
and felsite.

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Basaltic dykes.
teristic features. Boulders of quartz, granite and felstone, often of
large size, are confusedly huddled together in a greenish matrix
composod of a sandy or more or less ashy material, which weathers
on the surface to a dull orange tint. Its highest beds are well ex-
posed in some small cliffs that overhang the roadway to the north
of the bridge, where they exhibit distinct evidence of their bedded
nature in the visible arrangement of the rounded balls of white
quartz and grey porphyrite in regularly parallel lines, and in the
distinct alternation of coarse conglomeratic bands with others of a
sandier texture. These all dip steadily to the northward, at an
angle of from 50 to 60 degrees, and distinctly follow each other in
unbroken sequence.
The highest beds of the conglomerate proper can be studied foot
by foot in these cliffs. Towards their termination they become
somewhat looser in texture, and the matrix of the rock grows more
sandy. At their summit, where they are pierced by three small
basaltic dykes of a most interesting character, they pass up con-
formably into an overlying group (the Balclatchie Beds, Ad) of
calcareous shales and mudstones and flaggy grits, highly fossiliferous.
The unbroken continuity of the sequence at this locality is easily
demonstrated. The pebble-beds characteristic of the Benan Con-
glomerate below, and the shaly beds characteristic of the Balclatchie
zone above, distinctly alternate with each other in a curious group
Q.J.G.S. No. 152.