Ordnance gazetteer of Scotland > Volume 6

STIRLINGSHIRE
conglomeratic than those occupying the same geological
horizon situated several miles to the S. The con-
glomerate bands close to the great fault are composed
chiefly of porphyrite pebbles, but as we ascend in the
geological succession the porphyrite pebbles disappear,
and the blocks consist wholly of various metamorphic
rocks of the Highlands. The strata occupying the
centre of the syncline, which are the highest members
of this formation in the county, are composed of grey
sandstones which yielded to Mr E. L. Jack numerous
plant remains, regarded by Mr Kidston as specimens of
Arthrostigma (Dawson). These grey sandstones underlie
the great conglomerates of Uamh Var in Perthshire,
which are hardly, if at all, represented in this county.
Resting on the denuded edges of the Lower Old Red
Sandstone strata comes a succession of red sandstones
and conglomeratic marls, forming the base of the Car-
boniferous system. Along the line of junction the
Lower Old Red strata are inclined to the NW, while
the members of the overlying group are inclined to the
SE. It is evident, therefore, that in this area there is
additional proof of the extensive denudation which
intervened between the Lower Old Red Sandstone and
the deposition of the red sandstone series at the base of
the Carboniferous system. The unconformable junction
between the two formations is not traceable, however,
across the county, for between Eippen and Balfron they
are brought into contact with each other by a fault
trending ENE and WSW. This fault is a continuation
of the great dislocation throwing down the Clackmannan
coalfield against the Old Red volcanic rocks of the
Oehils. Near the top of the group there is a concre-
tionary cornstone which has been worked for lime at
intervals between Balfron and Gargunnock. The red
sandstones just described are succeeded by blue, grey,
green, and red clays, with numerous thin bands and
nodules of impure cement-stone, and occasional beds of
sandstone, forming the base of the Cement-stone group.
They skirt the N escarpment of the Campsie Fells, and
are likewise seen in some of the glens on the S side of
the range near Clachan of Campsie and on the hills above
Kilsyth. One of the finest sections of these beds occurs
in the Ballagan Burn near Strathblane. Along the base
of the escarpment on the N and W sides of the range
they are overlaid by white sandstones, which at intervals
are associated with fine volcanic tuffs. These tuffs are
specially observable to the E of Fintry, and also to the
N of Kilsyth, where they alternate with sheets of
porphyrite. To these succeed a grand development of
contemporaneous volcanic rocks consisting almost wholly
of sheets of diabase porphyrite, with few or no inter-
calations of tuffs. Occupying the same horizon as the
volcanic rocks of the Kilpatrick and Renfrewshire hills
(see article on geology of Renfrewshire, Ord. Gaz.,
vol. vi.), they reach a thickness in the present area of
nearly 1000 feet. The successive lava flows are
admirably displayed on the S side of the chain, forming
a series of parallel beds recognisable even from a
distance. Skirting the escarpment on the S side, a
great fault is traceable from Strathblane E to near the
Carron Water, which brings the overlying Carboniferous
Limestone series into conjunction with the cement-
stones and the porphyrites at the base of the volcanic
series. At the E end of the range, however, from a
point W of Stirling S towards the Carron Water, the
upper limit of the volcanic rocks is well defined. In
that direction the lavas are gradually thinning out, but
eventually they pass underneath blue shales with
cement-stone bands forming the top of the Cement-
stone group. It is apparent, therefore, that in Stir-
lingshire this group is mainly represented by volcanic
rocks. It is interesting to observe, however, that not
far to the E of Bridge of Allan, at Causewayhead, this
volcanic series is not represented at all ; and where the
horizon emerges in the Cleish Hills from beneath the
Clackmannan Coalfield it is represented merely by some
bands of tuff. The roots of some of the old volcanoes
which discharged the lavas of the Campsie Hills are
still to be found in different parts of the county,
STIRLINGSHIRE
especially on both sides of the Blane Valley W of
Strathblane. Dumgoyne Hill is perhaps one of the
best examples in that region. They also occur on both
sides of the Endrick at Fintry, where they pierce the
sedimentary beds underlying the volcanic series and
the porphyrites and tuffs at the base. Meikle Bin, the
highest peak in the Camnsie range, marks the site of
another of these ancient volcanoes.
As indicated in the table of geological formations the
triple classification of the Carboniferous Limestone
series obtains in this county. Beginning at the W
limit of this important division we find the limestones
of the lower group lying at low angles against the
volcanic rocks. From the researches of the Geological
Survey it would appear that on descending the hill
slope the observer crosses the Hosie Limestone and the
Hurlet Limestone with the underlying coal, until, in
the bed of the valley, he finds the white sandstone
underlying the limestones. On the South Hill of
Campsie the same beds reappear, and the Hurlet lime-
stone and coal can be traced more or less continuously
round the slope. Passing E to the neighbourhood of
Kilsyth, there is a great development of the middle
coal-bearing group, forming indeed one of the most
valuable mineral fields in Scotland on account of the
various seams of coal and ironstone. From Cairnbog E
by Kilsyth to Banton the beds are thrown into a series
of small arches and troughs, the most conspicuous being
the anticlinal fold at Kilsyth, locally known as ' The
Riggin.' Again, in the tract between Denny and Stir-
ling, the various subdivisions of the Carboniferous
Limestone series dip towards the E, and there is a
general ascending series from the Hosie Limestone
through the coals and ironstones of the middle group
to the Index, Calmy, and Castlecary Limestones of the
upper group.
Along the E margin of the county the strata just
described are followed by the Millstone Grit, consisting
of alternations of thick sandstones and fireclays, with
irregular seams of coal and clayband ironstone. To
these succeed the true Coal-measures, which are well
developed between Stenhousemuir and Grangemouth,
and again at Falkirk. At the former locality the pro-
minent seams are the Coxroad, the Splint, and the
Craw Coals, the highest being the Virtuewell seam.
Between Dennyloanhead and Coneypark there is a small
outlier of Coal-measures thrown down by two parallel
faults running E and W. On the N side the outlier is
brought into contact with the Carboniferous Limestone,
and on the S side against the Millstone Grit and the
Carboniferous Limestone.
There are numerous intrusive sheets of basalt rock as-
sociated with the Carboniferous strata, of which, perhaps,
the most conspicuous extends from Abbey Craig through
Stirling to Denny, where its outcrop is shifted further
W by a fault. It is perhaps connected with the sheet
so often repeated in the neighbourhood of Kilsyth,
though here it occupies a higher horizon among the coal-
bearing series of the Carboniferous Limestone, while at
Denny the sheet is intruded in the lower limestones.
A glance at the Geological Survey maps will show the
number of Tertiary basalt dykes traversing the county.
During the glacial period the direction of the ice
flow between Loch Lomond and Loch Katrine was
nearly N and S. On reaching the plain between Dry-
men and Stirling, the movement was gradually deflected
towards the SE, and eventually as the ice crossed the
range of the Campsie Hills, the direction became nearly
E, parallel with the escarpment on the S side of the
range. There is an extensive deposit of boulder clay
throughout the county, which varies in character with
the underlying strata. An interesting feature con-
nected with it is the occurrence of shells at certain
localities in the Endrick Valley. Near Drymen station,
a section was exposed showing on the surface about 12
feet of boulder clay resting on 7 feet of laminated blue
clay, which yielded marine shells and the antler of a
reindeer. Mr R. L. Jack believes that the shell
fragments found in the boulder clay in the basin of the
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