286 
VOLCANOES OF THE LOWER OLD RED SANDSTONE 
BOOK \' 
under the uiiconformahle overlap of the Lower Carboniferous Sandstones, while 
the top is cut off by a fault which brings down the 
Carboniferous formations against the eastern flank of 
the hills. Proliably not less voluminous is the pile of 
ejected material in the Ocliil Hills, where, though the 
base of the whole is concealed by tlie fault which throws 
down the coalfield, some 6500 feet of lavas, tuffs and 
conglomerates can be seen. There were thus, during 
the time of the Lower Old lied Sandstone, more than 
one volcano in Central Scotland which might be com- 
pared in bulk of ejected material to Vesuvius. 
That the eruptions were mainly subac^ueous is in- 
dicated, as I have sliown, by the intercalated bands of 
sandstone and conglomerate between the successive lavas, 
as these are traced away from the centres of discharge, 
and likewise, even more impressively, liy the hardened 
sand which has been washed into former fissures and 
crevices in the lava. Put that, in some cases, the vol- 
canic cones were built up above tbe surface of the lake 
may be legitimately inferred from tbe remarkable 
volcanic conglomerates which occur, more particularly 
in the great chain of the Ochil and Sidlaw Hills. 
These thick accumulations of well-rounded and water- 
worn blocks are interspersed between sheets of andesite, 
and are mainly made up of andesite fragments. Im- 
pressive sections of tlieni may be seen along the Kin- 
cardineshire coast. The conglomerates are sometimes 
so remarkably coarse, many of their blocks exceeding 
two feet in diameter, and so rudely bedded, that it is 
only by noting the position of oblong boulders that one 
can make out the general direction of the stratification. 
In their smooth rounded forms, these Idocks resemble 
the materials of storm -beaches on an exposed coast. 
The trituration of the andesite fragments has given rise 
to a certain amount of green paste, wliich firmly wraps 
round tlie stones, and retains casts of tliem after they 
have dropped out. It is furtlier deserving of remark 
that while in some districts, as in the central Ochils, the 
materials were entirely derived from tlie destruction 
of volcanic rocks, in others a large proportion of non- 
volcanic materials is mingled with the debris of the 
lavas. South of Stoneha.ven, for example, large boulders 
of quartzite form a conspicuous feature in the con- 
glomerates, of which in places they make up quite half 
of the total constituents. There can be little doubt, I 
think, that the materials of these coarse detrital acciunulations were gathered 
I 
