9 8 
THE PERMIAN VOLCANOES 
BOOK VII 
singularly uneven. Prominent hills of Culm grit, several hundred feet 
high, rose above the basins in which the earliest Permian sediments were 
deposited, and these eminences were gradually submerged and buried under 
the detritus. 
But that the volcanic zone includes in some places more than one out- 
flow of lava with layers of sandstone, breccia and tuff between the successive 
sheets may be proved in different parts of the district. Thus the two con- 
spicuous hills at Kellerton are composed of several sheets of highly slaggy 
lava, separated by breccia, and a third much thinner sheet lies above these, 
intercalated in a mass of breccia, sandstone and sandy tuff (dig. 230). 
XorthHlll Southtfill 
Fig. 230. — Section of the volcanic series at Kellerton, Devonshire, 
a, Breccias and sandstones ; 6, lavas. 
Again, at Budlake the sandstones and fine breccias include a thin band of 
vesicular lava, while farther to the east they are interrupted by a higher 
and thicker zone of similar material. 
These igneous sheets can be shown by many interesting sections to have 
been poured out contemporaneously with the deposit of the sedimentary 
material among which they occur. At Crabtree, for instance, neai Keller- 
ton, the uppermost lava is a thin sheet of highly slaggy texture, which rests 
immediately on the gravelly red sandstone and catches up parts of it, while 
the pebbles include fragments of some of the andesites below. The dark 
lavas are occasionally traversed by veins of fine hard sandstone, which 
descending from above, like those in the Old Bed Sandstone and 1 ermian 
lavas of Scotland, have been produced by the silting or drifting of fine sand 
into cracks in the lava, before the igneous material was entirely buried. 
These features are well exposed in the high ridge of the Belvedere near 
Exeter (Fig. 228), where, over a thin and inconstant band of red breccia 
and marl which rests on the upturned ends of the Culm-measures, a band of 
dull-red andesite may be seen. This rock, partly compact and partly highly 
amygdaloidal, is in some portions full of irregular fissures and cavities filled 
with sandstone. 
Nowhere among the Paheozoic volcanic rocks of Britain are more 
remarkable examples of the slaggy structure to be found than in these 
Devonshire lavas of probably Permian age. I would especially cite the 
rock of Knowle Farm, a few miles to the west of Crediton, as in part a mere 
spongy pumice, blocks of which would originally have floated in water. 
One of the best sections in the district for the exemplification of the 
internal structures of these lavas is that in the large quarry at the top of 
Posbury Hill. On the west side of this quarry the rock is tolerably com- 
