Mr. Ussher informs me that in the quarry the visible exposure of the acid rock is surrounded an covered by mica-porphyrite, probably andesite.] The geographical conditions in which the red rocks of Devonshire accumulated were those so characteristic of the Permian and Trias formations throughout Britain. The red sandstones and sandy marls gathered in inland basins, where the water seems to have become too saline and bitter to support animal life. The strata are consequently singularly devoid of organic remains. The climate was probably arid, and the absence or scarcity of traces of terrestrial vegetation indicates that the land around the water-basins stretched in wide sandy and rocky wastes. In the dry atmosphere and under the influence of rapid radiation the cliffs and crags of Culm-measures would disintegrate into angular rubbish, and this material, slipping into the lakes or washed down by occasional rain-storms, forms now the breccias that constitute so typical a feature in the Permian system. [Illustration: Fig. 228.--Section at Belvedere, S.W. of Exeter. _a_, Culm-measures; _b_, breccia and marls; _c_, lavas; _d_, red pebbly sandstones.] [Illustration: Fig. 229.--Diagram to show the unconformability and overlap of the Permian rocks in the Crediton Valley. _a_, Culm-measures; _b_, breccias and sandstones; _c_, lava-group; _d_, breccias with fragments of lava passing up into sandstones and marls (_e_).] It was while this geographical type continued in the South-west of England that the volcanic eruptions took place which we are now considering. De la Beche correctly referred these eruptions to the early part of the red sandstone series. A brief examination of the ground suffices to show that although, as he pointed out, the volcanic rocks lie towards the base of that series, as shown in Fig. 228, they do not all occupy the same platform. That in some cases the lavas lie directly on the Culm-measures, while in others they are separated from these strata by 100 feet or more of red sandstones and breccias (Fig. 229), would not in itself be proof of any difference of age or stratigraphical position in the igneous rocks, for the floor on which the Permian formations were here laid down can be shown to have been 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.