Field meeting at Lewes, Berwick, and Newhaven: Saturday, 16th July, 1949

Abstract

THE party, consisting of eleven members and friends, met outside Lewes Station at 11 a.m., and went on foot to the Castle, climbing the steep side of the valley of the Lewes Winterbourne, a typical perennial stream, then dry. From the roof of the Castle Keep the Director pointed out the main geomorphological features and drew comparisons between this and corresponding views across the Weald from its northern side. The absence of any prominent escarpment of the Lower Greensand was particularly striking, and, as a result, the hills of the Forest Ridge, twelve to fifteen miles away, were unobscured. The town of Lewes stands on a chalk spur projecting eastwards into the Ouse valley, which is thereby restricted in width to a few hundred yards. The precipitous hillside opposing the end of this ridge, represents a river-cliff whose profile appears to plunge under the alluvium, and is presumably graded to a buried channel of the river. The Cliffe, as it is termed, is breached by The Coombe, a straight dry valley ending in a double bifurcation when followed .. upstream for half a mile. The origin of this valley has been the subject of controversy for over a century; once thought the product of a strike-fault [1*], or a steep flexure [2], it is now considered by Gaster [3] to have been formed independently of any structure. Attention was aroused by the fact that the Ouse flows through a narrow valley at Lewes, whereas a little downstream the much wider subsequent valley of Glynde Reach carries only a narrow brook, seemingly a misfit. It was asked whether the course of the Ouse through Lewes was the result of backward cutting by a resequent stream until a hypothetical detour of the main consequent flow through Glynde Reach was short-circuited, so producing the outlier of chalk downland comprising Cliffe Hill and Mount Caburn. These variations in valley width can, however, be explained on structural grounds; because the Glynde Reach valley is anticlinal and eroded along the strike of the Upper Greensand and Gault, its greater width would thus result. In the same way may be explained the narrowness of the Ouse valley at Lewes, where it passes entirely through Chalk folded down in the complementary Mount Caburn syncline. Other land-forms of interest were seen in fragments of the