The ridge of the Scuir, presenting as it does so strong a topographical contrast to the green terraced slopes of the plateau-basalts on which it rests, consists of some very distinct bands of black and grey lava, long known as "pitchstone-porphyry." To the nature and history of these rocks I shall return after we have considered a remarkable bed of conglomerate which lies below them. On the lower or southern side of the ridge the bottom of the pitchstone, dipping into the hill, is exposed on the roof of a small cave where the ends of its columns form a polygonal reticulation. It is there seen to repose upon a bed of breccia or conglomerate, having a pale-yellow or grey felspathic matrix like the more decomposing parts of the grey devitrified parts of the pitchstone. Through this deposit are dispersed great numbers of angular and subangular pieces of pitchstone, some of which have a striped texture. Fragments of basalt, red (Torridon) sandstone, and other rocks are rare; and the bed suggests the idea that it is a kind of brecciated base or floor of the main pitchstone mass. A similar rock is found along the bottom of the pitchstone on both sides of the ridge (_c_, in Fig. 279). Here and there where this breccia is only a yard or two in thickness, it consists of subangular fragments of the various dolerites and basalts of the neighbourhood, together with pieces of red sandstone, quartzite, clay-slate, etc. The matrix is in some places a mass of hard basalt debris; in others it becomes more calcareous, passing into a sandstone or grit in which chips and angular or irregular-shaped pieces of coniferous wood are abundant.[253] A little further east, beyond the base of the Scuir, a patch of similar breccia is seen, but with the stones much more rounded and smoothed. This outlier rests against the denuded ends of the basalt-beds forming the side of the hill. Its interest arises from the evidence it affords of the prolongation of the deposit eastward, and consequently of the former extension of the precipice of the Scuir considerably beyond its present front.