The drainage systems of Wales and the adjacent regions

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Abstract
Summary: The streams of Wales have been incised in a surface of considerable relief. From the summit-levels shown on the one-inch Ordnance Survey map their means and standard deviations were calculated for each 10 kilometres square of the National Grid. From these data the main physiographic elements can be picked out, such as the mountain area, the high plateau and two major surfaces at lower levels. The numerical distribution of summits on each of these surfaces appears to be wholly random. Strahan's hypothesis of superposition from a Cretaceous cover is adopted with some modifications, but certain difficulties in accepting it are discussed. WALES and the adjacent regions are drained by many streams belonging to several systems; a map of these streams, based upon those shown on the quarter-inch map of the Ordnance Survey, is given as Pl. XII; it has the appearance of a complicated mosaic. A large part of the surface of the region consists of an extensive tableland in which the streams are deeply incised. Ramsay (1876, p. 223) gave a graphic description of the great extent of this tableland, “ all intersected by unnumbered valleys,” and recognized that its relief was due to “ fluviatile erosions that have scooped out the valleys ”.

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