(_a_) Lavas without Tuffs.--Examples occur of sheets of toadstone which consist entirely of contemporaneously ejected diabase, basalt or dolerite. This rock is then dull green or brown in colour, more or less earthy in texture, and irregularly amygdaloidal. The vesicles are extremely varied in size, form and distribution, sometimes expanding until the rock becomes a slaggy mass. A central more solid portion between a scoriaceous bottom and top may sometimes be observed, as at the Great Rocks Quarry, Peak Forest Limeworks (Fig. 181). In this, as in other examples, a remarkably hummocky and uneven surface of limestone lies below the igneous band, the calcareous rock presenting knobs and ridges, separated by cauldron-shaped cavities and clefts, some of which are several yards deep. These inequalities are filled in and covered over with a soft yellow and brown clay, varying up to three or four feet thickness, and passing upwards into the more solid toadstone. There can hardly be any doubt that this singularly uneven limestone surface is due to the solvent action of water lying between the limestone and the somewhat impervious toadstone above, and that the clay represents partly the insoluble residue of the calcareous rock, but chiefly the result of the action of the infiltrating water on the bottom of the igneous band.[40] [Footnote 40: _Geological Survey Memoir on North Derbyshire_, p. 20 and footnote.] [Illustration: Fig. 181.--Section of vesicular and amygdaloidal diabase resting on Carboniferous limestone, Peak Forest Limeworks, Great Rocks Quarry. 1. Limestone with a surface dissolved into cauldron-like hollows; 2. Rotten yellow and brown clay resulting from decomposition of toadstone and white clay from the solution of the limestone--sometimes three or four feet thick; 3. Toadstone, a diabase with highly slaggy base. ] [Illustration: Fig. 182.--View of the superposition of Carboniferous limestone upon toadstone, Raven's Tor, Millersdale (length about 100 feet). 1. Toadstone; 2. Limestone; _f_, Fault.] Junctions of the upper surfaces of the lava-sheets with the overlying limestone show that the igneous material sometimes assumed hummocky forms, which the calcareous deposits gradually overspread and covered.[41] A good example of this kind may be observed by the roadside at the foot of Raven's Tor, Millersdale. As shown in the subjoined figure, the limestone has here been worn into a cave, the floor of which is formed by the toadstone. The latter rock, of the usual dull green, slaggy and amygdaloidal character, is covered immediately by the limestone, but I did not observe any fragments of the toadstone, nor any trace of ashy materials in the overlying calcareous strata. This section shows that after the outflow of the lava, the sedimentation of the limestone was quietly resumed, and the igneous interruption was entirely buried.