Geological Structure of the South-west Highlands of Scotland. 235 
December 19, 1860.—L. Horner, Esq., President, in the Chair. 
The following communications were read :— 
1. “ On the Geological Structure of the South-west Highlands of 
Scotland.” By T. F. Jamieson, Esq. Communicated by Sir R. I. 
Murchison, V.P.G.S. 
In this paper the author attempts to throw light on the relations 
of those rocks which figure in geological maps as the mica-schist, 
clay-slate, the chlorite-slates, and the quartz-rock of the South-west- 
ern Highlands, which range N.E. through the middle of Scotland, 
forming an important feature in the geology of that country. An 
examination of these rocks, as displayed in Bute and Argyleshire, 
has led Mr. Jamieson to believe that, from the quartz-rock of Jura 
to the border of the Old Red Sandstone, there is a conformable series 
of strata, which, although closely linked together, may be classed 
into three distinct groups, namely, Ist, a set of lower grits (or 
quartz-rock), many thousand feet thick; 2ndly, a great mass of 
thin-bedded slates, 2000 feet or more thick; and 3rdly, a set of 
upper grits, with intercalated seams of slate of equal thickness. 
Beds of limestone occur here and there sparingly in all the three 
divisions ; the thickest being deep down in the lower grits. All the 
limestones are thiclfest towards the west. The siliceous grits also 
appear to be freer from an admixture of green materials towards the 
west. All the members of the series (namely, the upper grits, slates, 
and lower grits) have a persistent S.W.—N.E. strike, sometimes in 
Bute approaching to due N. and 8. They are conformable, and 
graduate one into another in such a way as to show that they belong 
to one continuous succession of deposits. The materials of which they 
have been formed seem to have been derived from very similar sources. 
The upper and the lower grits are very similar in composition, being 
made up of water-worn grains of quartz, many of which are of a 
peculiar semitransparent bluish tint. 
The rocks of the district have been thrown into a great undula- 
tion, with an anticlinal axis extending from the north of Cantyre 
through Cowal by the head of Loch Ridun on to Loch Eck (and: 
probably by the head of Loch Lomond on to the valley of the Tay, 
at Aberfeldy), and with a synclinal trough lying near the parallel 
of Loch Swen. The anticlinal fold is well seen in the hill called 
Ben-y-happel, near the Tighnabruich quay in the Kyles of Bute. 
Southward of this ridge, which is composed of the lower grits or 
quartzite, the thin-bedded greenish slates and the upper grits suc- 
ceed conformably ; and the latter are separated by a trap-dyke from 
the Old Red Sandstone of Rothsay. ‘This section the author de- 
scribed in detail; also the corresponding section to the north of the 
anticlinal axis, towards Loch Fyne, and along the west shore of Loch 
Fyne. ‘The lower grits extend as far as Loch Gilp, and are then 
succeeded by the green slates and the upper grits, which falling in the 
synclinal trough are repeated through Knapdale towards Jura Sound, 
where the green slates again form the surface along the eastern coast 
of Jura, lying on the quartzite or grits of that island. Throughout 
the synclinal trough and the neighbouring district (that is, from 
