ANNIVERSARY ADDRESS OF THE PRESIDENT. 10/ 



Another fact, to which also I have already alluded as partially 

 recognizable in the records of Old Red Sandstone vulcanism, now 

 becomes increasingly evident — the tendency of volcanic vents to be 

 opened along lines of valley rather than over tracts of hill. The 

 vents that supplied the materials of the largest of the Carboniferous 

 volcanic plateaux broke forth along the broad Midland Valley of 

 Scotland, between the ridge of the Highlands on the north and that 

 of the Southern Uplands on the south. Others appeared on the 

 southern side of these uplands, in the hollow bounded to the south- 

 west by the hills of the Lake District. It is not a question of the 

 rise of volcanic vents merely along lines of fault, but on broad tracts 

 of low ground rather than on the surrounding or neighbouring 

 heights. It can easily be shown that this distribution is not the 

 result of better preservation in the valleys and greater denudation. 

 from the higher grounds, but that it points to the influence of 

 marked topographical features upon the original position of volcanic 

 vents. The following summary of the position and extent of the 

 Plateaux will afford some idea of their general characters : — 



(1) The chief plateau rises into one of the most conspicuous 

 features in the scenery of Central Scotland. Beginning at Stirling, 

 it forms the marked table-land of the Pintry, Kilsyth, and Campsie 

 Hills, stretching westwards to the Clyde near Dumbarton, whence, 

 sweeping southwards beyond that river into the hilly moorlands 

 which range from Greenock to Ardrossan, it spreads eastwards 

 along the high watershed between Renfrewshire, Ayrshire, and 

 Lanarkshire to Galston and Strathavon. But it is not confined to 

 the mainland, for its prolongation can be traced by the islands of 

 Cumbrae to the southern end of Bute, and thence by the south of 

 Arran to Campbeltown in Can tire. Its visible remnants thus 

 extend for more than 100 miles from north-east to south-west, with 

 a width of some 35 miles in the broadest part. AVe shall probably 

 not exaggerate if we estimate the original extent of this great 

 volcanic area as not less than between 2000 and 3000 square miles. 

 It is in this tract that the phenomena of the Plateaux are most 

 admirably displayed. Ranges of lofty escarpments reveal the 

 succession of the several eruptions, and the lower ground in front 

 of these escarpments presents to us, as the result of stupendous 

 denudation, many of the vents from which the materials of the 

 plateau were ejected, while in the western portion of the area 

 admirable coast-sections lay bare to view the minutest details of 

 structure. 



