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Lower. \ 



THE CLYDE TERRITORY. 405 



jy f Band of cornstone near the top. 



pper. ^jj e( j s an( Jstones and conglomerates. 



Unconformability. 



3. Sandstones, grits, and conglomerates with pebbles of 



andesite. 

 2. Contemporaneous volcanic rocks (andesites and tuffs) with 



thin intercalations of sandstones and conglomerates near 



the top. 

 1, Chocolate-coloured sandstones w r ith Cephalaspis Lyelli and 



conglomeratic bands, with greywacke-conglomerate at 



the base. 



Lower Division. On the south side of the great midland valley, and along 

 the margin of the Silurian tableland there is an important development of 

 the lower division of the Old Red Sandstone. On the south side of the 

 Girvan valley, the members of group 1 rest unconformably on an eroded 

 platform of Silurian rocks, and on the north side of the same valley they 

 reappear, and are largely developed near Maybole and Kirkoswald, passing 

 northwards underneath the overlying volcanic series (group 2 in table) which 

 extends north by Dunure Castle to near the Heads of Ayr. In Lanarkshire 

 the Lower Old Red Sandstone is let down against the Silurian strata by the 

 great fault w T hich skirts the tableland. The red sandstones and con- 

 glomerates (group 1 in the table) are well seen in the gorge of the 

 River Clyde at Lanark, whence they stretch westwards by Lesmahagow to 

 near Darvel in Ayrshire, where they pass underneath the overlying volcanic 

 series (group 2). The volcanic group is also exposed on the slopes 

 of Tinto, and can be traced westwards to near Douglas, reappearing in the 

 Duneaton Water to the west of the Douglas coalfield. Along their south- 

 east margin the lavas and tuffs pass upwards into the members of the over- 

 lying beds (group 3). Indeed between the Duneaton Water and the Clyde at 

 Lamington the beds forming the highest division of the Lower Old Red 

 Sandstone lie in a synclinal fold of the volcanic series (group 2). Grits and 

 yellow sandstones occurring at the base pass upwards into massive con- 

 glomerates, and these are overlaid in turn by chocolate-coloured sandstones. 

 These beds furnish evidence of the cessation of volcanic activity, for the 

 sandstones are largely composed of volcanic detritus, and the pebbles in the 

 massive conglomerates consist mainly of andesite. 



The Lower Old Red Sandstone strata in Lanarkshire and Ayrshire are 

 traversed by various basic and acid eruptive rocks. Near the head- waters of 

 the Avon, southeast of Darvel in Ayrshire, a small mass of granite occurs, 

 containing petrological types, which, according to Dr. Flett, resemble those 

 met with in the Loch Doon granite, both masses being presumably of the 

 same age. Numerous sills of acid material have been injected, mainly along 

 the lines of bedding of the lower red sandstones, of which the massive 

 sheet of quartz-felsite on the crest of Tinto are a conspicuous example. 



On the north side of the midland valley the members of the Lower Old 

 Red Sandstone can be traced from the Forth above Stirling, west by Dry men, 

 to a point on the Firth of Clyde, near Cardross. In the eastern part of this 

 area the strata are arranged in a great synclinal fold, the central axis of 

 which coincides with a line drawn from Flanders Moss, in the valley of the 

 Forth, to near Drymen. The strata forming this syncline belong to the 

 highest division of the Lower Old Red Sandstone (group 3), for on the 

 southeast side the volcanic series (group 2) rises from underneath these 

 sandstones in the Ochil Hills, where the lavas, tuffs, and agglomerates 

 reach their greatest development in Scotland. On the north side of this 



