CHAPTER XXIV 
CARBONIFEROUS VOLCANIC PLATEAUX OF SCOTLAND 
I. The Plateau-type restricted to Scotland — i. Distribution in the Different Areas of 
Eruption — ii. Nature of the Materials erupted. 
In the division of the Plateaux I group all the more copious erujitions 
during the Carboniferous period, when the fragmentary materials generally 
formed hut a small part of the discharges, hut when the lavas were poured 
out so abundantly and frequently as to form lava-fields sometimes more than 
2000 square miles in area, and to build' up piles of volcanic material some- 
times upwards of 3000 feet in thickness. As already remarked, this phase 
of volcanic action, especially characteristic of the earlier part of the Carbon- 
iferous period across the south of Scotland, but not found elsewhere in the 
same system in P>ritain, preceded the type of the Puys. Its eruptions ex- 
tended from alwjut the close of the Old Red Sandstone period through that 
section of Carboniferous time which was marked by the deposition of the 
Calciferous Sandstones, but they entirely ceased before the accumulation of the 
Main or Ilurlet Limestone, at the base of the Carboniferous Limestone Series 
of Scotland. Its stratigraphical limits, however, are not everywhere the same. 
In the eastern part of the region, the lavas appear to be intercalated with, and 
certainly lie directly upon, the Upper Old Red Sandstone containing scales 
of Bothriolepis and other characteristic fishes, and they are covered by the 
Cement-stone group of the Calciferous Sandstones. In tlie western district 
a considerable thickness of Carboniferous strata sometimes underlies the 
volcanic sheets. On the other hand, tlie type of the Puys, although it 
appeared in Pife, Linlithgowshire and Midlothian during the time of the 
Calciferous Sandstones, attained its chief development during that of the 
Carboniferous Limestone, and did not finally die out in Ayrshire until the 
beginning of the deposition of the Coal-measures. 
i. DISTRIBUTION OF THE PLATEAUX 
Notwithstanding the effects of many powerful faults and extensive de- 
nudation, the general position of the Plateaux and their independence of eaeli 
