PEOCEEDINGS OF GEOLOGICAL SOCIETIES. 
147 
J ura to the Old Red Sandstone, tliere is a conformable series of strata, which, 
although closely linked together, may be classed into three distinct groups, 
namely, 1st, a set of lower grits (or quartz-rock), many thousand feet thick ; 
2ndly, a great mass of thin-bedded slates, two thousand feet or more thick ; 
and 3rdly, a set of upper grits, with intercalated seams of slate of equal thick- 
ness. Beds of limestone occur here and there sparingly in all the three 
divisions ; the thickest being deep down in the lower grits. All the lioiestones 
are thickest 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 south- 
west to north-east strike, sometimes in Bute approaching to due north and 
south. 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 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 undulation, with an 
anticlinal axis extending from the north of Cantyre through Cowal by the head 
of Loch Bidun on to Loch Eck (and probably by the head of Locli 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 tbe hiU 
called Bcn-y-happel, near the Tighnabruich quay in the Kyles of Bute. South- 
ward of this ridge, which is composed of the lower grits or quartzite, the thin- 
bedded greenish slates and the upper grits succeed conformably ; and the latter 
are separated by a trap-dyke from the Old Red Sandstone of Botlisay. This 
section the author described in detail ; also the corresponding section to the 
north of the anticlinal axis, towards Loch Eyne, and along the west shore of 
Loch Tyne. The lower grits extend as far as Loch Gilp, and are then suc- 
ceeded 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 Loch Pyne to Jura Sound) the grits and 
slates are intimately mixed, with numerous intercalated beds of greenstone, 
some being of great thickness. Mr. Jamieson pointed out that this feature 
of the district has hitherto in great part been misunderstood, and that Mac- 
ciiUoch was in error when he denominated these rocks " chloritc-schist." 
The probable relationship of the rocks of the Islands of Shuna, Luing, and 
Scarba to those of Jura and Bute were then dwelt upon ; the greenstones of 
Knapdale, &c., and their relation to the sedimentary rocks, were described in 
detail ; and the limestones of the district briefly noticed. As no fossils have 
hitherto been found; pala;ontological evidence of the age of these rocks is 
wanting ; but the author, regarding their general resemblance to the quartz- 
rocks, limestones, and mica-schists of Sutherlandshire, thinks them to be of the 
same date as those rocks of the north-west Highlands. 
2. "On the position of the beds of the Old Bed Sandstone in the Counties 
of Forfar and Kincardine, Scotland." By the Rev. Hugh Mitchell. Com- 
municated by the Secretary. 
In Forfar- and Kincardine-shire, south of the Grampians, the Old Red Sand- 
stone is developed in the following series, with local modifications : — 1st (at 
top) conglomerate ; 2nd, grey flagstone with intercalated sandstone (about 
forty feet deep at Cauterland I)en, one hundred and twenty feet at Carmylie) ; 
3rd, gritty ferruginous sandstone, with occasional thin layers of purplisli flag- 
stone. Of the last, one hundred and twenty feet are seen at Cauterland Den ; 
