But that the volcanic zone includes in some places more than one outflow 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 conspicuous 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 (Fig. 230). 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. [Illustration: _North Hill_ _South Hill_ Fig. 230.--Section of the volcanic series at Kellerton, Devonshire. _a_, Breccias and sandstones; _b_, lavas.] 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, near Kellerton, 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 Red Sandstone and Permian 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 Palæozoic 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.