384 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
perhaps accompanying, the volcanic outbursts. In the case of the Clyde 
plateau, for example, if we examine its base in the neighbourhood of Fintry, 
we find that it lies upon some 500 feet of Carboniferous white sandstone, 
red and green marls and cement-stones, which rest on the Upper Old 
Bed Sandstone. Yet only eight miles to the eastward, this considerable 
mass of strata disappears, and the bottom of the lavas comes down upon 
the red sandstones. Five miles still further in the same direction the 
volcanic masses likewise die out, and then the Carboniferous Limestone 
series is found at Abbey Craig to lie, with scarcely any representative of the 
Cement-stone group, on the Upper Old Bed Sandstone (Fig. 114). Again, to 
the south-west of Fintry, the zone of cement-stones below the volcanic series 
continues to vary considerably in thickness and sometimes almost to disappear, 
while in Ayrshire the lavas lie immediately on the red sandstones. 
These irregularities, not improbably indicative of inequalities of sub- 
Fig. 114. — Vertical sections of the escarpment of the Clyde plateau from north-east to south-west. 
I. Section at the east enl of the Campsie Ilills, four miles west from Stirling. II. Section above Glins, six miles 
west from No. I. III. Section at Stratliblaiie Hill, eight miles further south-west. IV. Section at Lang 
Craig, east from Dumbarton, eight miles south-west from No. 111. V. Section above Fort Matilda, Greenock, 
eleven miles from tlio previous section and ou the south side of the Clyde. 
1. Lower Old Red Sandstone; 2. Upper Old Red Sandstone; 3. Carboniferous shales, sandstones and cement- 
stones, (the “Ballagau beds”); 4. Thick wliite sandstone which comes in above the Ballagan beds; 5. 
Andesite lava-sheets ; 0. Interstratified tulFs. The dotted lines connect the base of the volcanic serie.s. 
sidence and of deposition, may have been connected with the subterranean 
disturbances which culminated in the abundant outbreak of volcanic action. 
But though the volcanic rocks of the plateaux' may be traced overlapping the 
underlying strata, no evidence has anywhere been detected of an unconform- 
ability between them and the Lower Carboniferous or Upper Old Bed 
Sandstone series. 
1. BEDDED LAVAS AND TUFFS 
The successive sheets of lava in a plateau usually form thin and wide- 
spread beds which are only occasionally separated by intercalations of tuff 
