there
are inliers of Wenlock, Ludlow and Downtonian rocks, coming to the surface
along anticlines truncated by faults and surrounded by Old Red Sandstone
and Carboniferous strata. In the south-east of the county there is a part
of the large granite mass that stretches from Loch Doon south to Loch Dee,
giving rise to wild scenery and bounded by the high ground near the head of
the Girvan Water, boulders of which have been distributed over a wide area
during the glacial period. Along the northern margin of the uplands the
Lower Old Red Sandstone is usually faulted against the Silurian strata, but
on Hadyard Hill south of the Girvan valley they rest on the folded and
denuded members of the latter system. The three divisions of this formation
are well represented. The lower group of conglomerates and sandstones are
well displayed on Hadyard Hill and on the tract near Maybole; the middle
volcanic series on the shore south of the Heads of Ayr and from the
Stinchar valley along the Old Red belt towards Dalmellington and New
Cumnock; while the upper group, comprising conglomerates and sandstones,
form a well-marked synclinal ford at Corsancone north-east of New Cumnock.
The Upper Old Red Sandstone appears as a fringe round the south-west margin
of the Carboniferous rocks of the county, and it rises from beneath them on
the shore of the Firth of Clyde south of Wemyss Bay. The Carboniferous
strata of the central low ground form a great basin traversed by faults,
all the subdivisions of the system being represented save the Millstone
Grit. Round the north and north-east margin there is a great development of
volcanic rocks--lavas, tuffs and agglomerates--belonging to the Calciferous
Sandstone series, and passing upwards into the Carboniferous Limestone. The
lower limestones of the latter division are typically represented near
Dalry and Beith, where in one instance they reach a thickness of over 100
ft. They are followed by the coal-bearing group (Edge coals of Midlothian)
which have been wrought in the Dalry and Patna districts and at Dailly. The
position of the Millstone Grit is occupied by lavas and tuffs, extending
almost continually as a narrow fringe round the northern margin of the Coal
Measures from Saltcoats by Kilmaurs to the Crawfordland Water. The workable
coals of the true Coal Measures have a wide distribution from Kilwinning by
Kilmarnock to Galston and again in the districts of Coylton, Dalmellington,
Lugar and Cumnoc