The Pre-Glacial Valleys of Arran and Snowdon

Abstract

THE history of the British Isles in the Pliocene has an important bearing on their glacial geology and on the origin of their existing geographical features. Physiographic evidence indicates that the Lower Pliocene was in Britain an epoch of depression, during which the sea covered parts of South-Eastern England, whereas the Middle and Upper Pliocene were marked by an uplift which excluded the sea from the British Isles, except in East Anglia and Western Cornwall. It is generally agreed that this uplift raised the low-lying plains that had been formed during the Lower Pliocene into plateaus from 500 to 1,400 feet above sea-level. The uplift lasted through a long period of time; and such a slowly rising land would naturally be greatly denuded by rivers. Plateaus and platforms due to the Pliocene uplift have been described by Dr. Mort for Arran and by Professor W. M. Davis for Snowdon; yet in their discussion of the present topography of those districts they attribute a very slight influence to stream erosion during the long pre-Glacial elevation.