40G THE GEOLOGY OF 



great syncline a representative of the volcanic series is found near Aberfoyle 

 close to the great Highland fault. Here a band of andesite appears, overlaid 

 by massive conglomerates and sandstones which are highly inclined or 

 vertical. Southwards the angle of inclination decreases, and the strata have 

 a gentle dip on both sides of the synclinal axis, where they consist of grey 

 sandstones, which yielded to Mr. R. L. Jack plant-remains, regarded by 

 Mr. Kidston as specimens of Arthrostigma (Dawson). 



Representatives of the Lower Old Red Sandstone likewise occur in Arran 

 to the east and south of the granite area. In the latter district Mr. Gunn 

 recently detected the volcanic zone in association with the sandstones. The 

 Lower division is largely developed in the extreme southeast of Kintyre 

 between Campbeltown and Southend, where the sandstones are accompanied 

 by trappean conglomerates and pierced by necks of volcanic agglomerate. 



Upper Division. At the close of the Lower Old fled Sandstone period 

 important geographical changes again ensued, for everywhere there is a 

 marked unconforniability between the upper division of this system and 

 older formations. The vast accumulation of deposits, both sedimentary and 

 volcanic, of the lower division was elevated, folded, and subjected to pro- 

 longed denudation. Indeed, in some instances, the old Silurian tableland 

 was trenched by narrow valleys, as in the far northeast in the Lammer- 

 muirs. Subsidence again ensued, but as vet the marine fauna of the 



O ' v 



Carboniferous period was excluded from the area of sedimentation. Though 

 the Upper Old Red Sandstone rests everywhere unconformably on older 

 formations, it graduates upwards into the Carboniferous rocks. Indeed it 

 was at one time regarded as forming a lower subdivision of the Calciferous 

 Sandstone. Lithologically the red sandstones of the upper division resemble 

 those of the lower, and they likewise yield land-plants and fishes. The fish- 

 fauna, however, is wholly different from that met with in the Caledonian or 

 lower division, one of the most characteristic forms being Holoptychius 

 nobilissvmus. 



In Upper Clydesdale the Upper Old Red Sandstone extends from Hynd- 

 ford Bridge on the Clyde, east by Carnwath, to Dunsyre Hill, being a 

 continuation of the Cairn Hill sandstones of the Pentland chain. In Ayr- 

 shire it is traceable from the shore at the Heads of Ayr, in a southeasterly 

 direction, lapping round the Lower Old Red volcanic rocks, and underlying 

 red sandstones, to Blairquhan in the Girvan Valley. There the cornstone 

 near the top of this division is well seen in the Lannielane quarries, south 

 of Kilkerran Castle. Again to the north of the Campsie and Kilpatrick 

 Hills a narrow belt of these red sandstones can be traced from Kippen, by 

 Killearn, to the Firth of Clyde near Cardross. Here there is additional 

 evidence of the marked unconformability between the two divisions of the 

 system, for the upper red sandstones dip to the southeast, and the lower 

 are inclined to the northwest. The cornstone near the top of this series 

 has been traced at intervals along the north side of the Campsie Fells, and 

 has been worked for lime between Balfron and Gargunnock. On the shores 

 of the Firth of Clyde the Upper Old Red Sandstone is traceable from 

 Wemyss Bay, southwards by Largs and Fairlie, to Ardrossan. On the pro- 

 montory at Rosneath, at Toward Point, and again in the island of Bute, it is 

 faulted against the crystalline schists of the Highlands. These red sand- 

 stones likewise occur in Arran, both to the east and south of the main 

 granite mass, and likewise in Kintyre to the southwest of Campbeltown, 

 and on the west coast near Cleongart. 



The Carboniferous formation is largely developed in the West of Scotland 

 where it occupies the greater part of the Central Lowlands, extending west- 

 wards to the shores of the Clyde, and southwards to Dalmellington in the 

 County of Ayr. There is sufficient evidence for maintaining, however, that 

 originally it must have covered a much wider area, for though the Silurian 



