I.— Drainage in the Southern Uplands: Clyde, Nith, Annan

Abstract

I. Epigenetic Heritage It has long been recognized that most of the principal rivers of the Southern Uplands bear little relation to the geological structures over which they flow. West of the Tweed their courses run southwards or slightly east of south, across the caledonoid grain of both Lower Palaeozoic and Upper Palaeozoic rocks (Fig. 1). The Tweed itself, running eastwards out to sea at Berwick, also crosses the main stratigraphical outcrops obliquely, and is no less discordant than the western rivers. Such incongruence between drainage pattern and structure is characteristic of superimposition or epigenesis, and in Scotland as in many other areas in Britain the rivers must be regarded as having cut their valleys into a surface inherited from an earlier cycle of erosion. It is not yet certainly known when and by what process that surface was moulded. Manifestly the rivers must be long post-Triassic in origin; for although there is obvious relationship between their courses and the residual outliers of New Red Sandstone in the Nith and Annan valleys — a relationship that has its bearing on the evolution of the drainage pattern — the main Permian and Triassic outcrops are transgressed with the Carboniferous on the north flank of the Carlisle basin. New Red Sandstone is also folded and faulted with the Carboniferous rocks in the Sanquhar and Thornhill basins, and in the Mauchline basin north of the Southern Uplands Fault. There can be no doubt that posthumous Armorican movements continued beyond early Mesozoic times, producing This 250-word extract was created in the absence of an abstract