File:The Quarterly journal of the Geological Society of London (12645713935).jpg

182 PROCEEDINGS OF THE GEOLOGICAL SOCIETY.
3. Clay-slate Formation of Bute. — The first formation I shall
notice is the clay-slate. This, as shown by Dr. Macculloch and in
my own map, forms a narrow band along the southern flank of the
Grampians, from Arran to Stonehaven, everywhere presenting very
similar and unmistakeable characters. These it is unnecessary to
repeat, and some local peculiarities will be noted in the special sec-
tions. I shall also pass over its relations in Arran, only remarking,
that the granite appears to have risen up nearly in the line of junc-
tion between the clay-slate and the mica-slate. In Bute the clay-
slate dips to the S.E. at angles ranging from 20° to 60°, and appears
to rest on the mica-slate, also dipping in the same direction. Some
sections near Rothsay have led me to suspect that in this island
there are two formations of the clay-slate, as intimated by Mr. D.
Sharpe, the upper green or light-grey slates appearing to rest un-
conformably on the lower blue slates.
4. Loch Long and Gareloch. — On the mainland a similar S.E. dip
prevails along the Eirth of Clyde, though in some plaees, as near
Dunoon, the outer range of clay- si ate can scarcely be said to occur.
On the Gareloch a better section of the clay-slate in its relation to
the mica-slate is seen, though still in some places concealed by de-
tritus. This section is represented in fig. 1, beginning on the north
Eig. 1. — Section on Gareloch.
N.W. S.E.
Loch Gareloch Rose- Firth of
Long. Head. neath. Clyde.
Mica-slate. Clay-slate.
side of Loch Long, near Castle Carrick, and extending to the Clyde,
near Roseneath.
On the north side of Loch Long the mica-slate, rising up into the
gnarled and rugged mountain -group known as Argyll's Bowling
Green, forms an anticlinal axis, apparently oblique to the direction
of the loch. On both sides of Loch Long the mica-slate is so twisted
and contorted that the dip is almost undeterminable. Occasionally
the beds are horizontal, then they dip to the north or south at angles
ranging from 15° to 80°, or, again, are, as it were, twisted in both
directions in the most complex manner. The average direction is,
however, N.E. by E. (or N. 55° E.), and thus nearly parallel to the
general range of the strata. Several dykes or veins of greenstone
intersect the strata, but do not produce much change either on their
direction or character,.
The strata, generally a distinct lustrous mica-slate, intersected by
quartz-veins, continue to dip S. 35° E. from Loch Long to Gareloch
Head. Near the latter place the beds become more regular, with