PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



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Jura to tlie Old Red Sandstone, there 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 limestones 

 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 BAdun 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. 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 Bed Sandstone of Bothsay. 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 Fyne. 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 Eyne 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- 

 culloch was in error when he denominated these rocks " chlorite-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; palseontological 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 Borfar and Kincardine, Scotland." By the Bev. Hugh Mitchell. Com- 

 municated by the Secretary. 



In Borfar- and Kincardine-shire, south of the Grampians, the Old Bed 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 Den, one hundred and twenty feet at Carmylie) ; 

 3rd, gritty ferruginous sandstone, with occasional thin layers of purplish flag- 

 stone. Of the last, one hundred and twenty feet are seen at Cauterland Den ; 



