should have been accumulated showing so little variety in character, and without the occurrence of any large boulders or beds of conglomerate. Perhaps it may be explained by supposing it to have been accumulated in the depths of the sea, off the mouth of a great river like the Amazon, which may have been continually pouring in sediment, but with a current not sufficient to carry large pebbles. The slate, or fine argillaceous sediment, between the two great masses of arenaceous strata may be accounted for by a subsidence of the area of deposit into deeper and stiller water, where little except the finer sediment would be floated.
The Red (Cambrian) Sandstone and Conglomerate of the Northwest Highlands, which stretches for a hundred miles from S.W. to N.E., with a comparatively narrow breadth in the opposite direction, looks as if it had been accumulated along a shore-line which was probably the coast of an ancient continent of the Laurentian gneiss. This Cambrian Sandstone is overlapped on its eastern border by the Lower Silurian schists and quartz -rocks of the Highlands, which we may therefore suppose to have been accumulated at a somewhat later period, but which, in all likelihood, consist of the sediment poured into the sea by the rivers draining the same Laurentian region to the north-west. After a great thickness of sediment had been accumulated, a glow of heat from beneath seems to have approached it, and by the expansion thereby occasioned wrinkled the mass into huge folds running from S.W. to N.E. The reason why the wrinkles run in that direction, I imagine, must be that expansion in the transverse direction was more difficult, owing perhaps to the opposing mass of the Cambrian and Laurentian land preventing extension towards the north-west side.
DISCUSSION.
Prof. Ramsay observed that the general section wonderfully corresponded with that given many years ago by Sir Roderick Murchison of the Silurian and Laurentian rocks at Cape Wrath, and it seemed to him that the large views originally propounded by Sir Roderick were confirmed by the author. He was glad that the metamorphic origin of granite was supported by Mr. Jamieson, as he had held that view for many years ; and he was pleased to find that opinions which had formerly met with so many opponents were constantly gaining acceptance. The fusion of these sedimentary rocks by metamorphic action was not identical with the fusion of lava ; but their fluidity might be the same ; and if that were the case, there could be no difficulty in accepting the possibility of the injection of such fused rocks into crevices and fissures. The crumpling of the beds, however, was due to more extensive causes than those contemplated by the author. The proportion of igneous rock injected into contorted rocks, like those of North Wales, was comparatively small, and the crumpling could hardly be due to mere local causes.
Prof. Ansted referred to what he had observed in the north-west part of Corsica, where about 40 feet of granite was distinctly inter-
