EROSION SURFACES IN THE FOREST OF BOWLAND

Abstract

Summary Geomorphological studies, including field work and cartographic analysis, indicate both a relation between geological structure and topography, and the presence of former erosion surfaces, these two characteristics being super-imposed on each other. The alternations of Namurian sandstones and shales, together with a dominance of gentle dips is conducive to the formation of dip slopes, anti-clinal hills and synclinal valleys with resulting similarity between structure contour and topographic maps. In contrast, field mapping and new methods of cartographic analysis indicate two major and one minor erosion surfaces, which cut across structural features. It is concluded that a polycyclic landscape has evolved, with inclined and undulating erosion surfaces largely of subaerial origin, which have become locally adjusted to geological structure both during their formation and subsequent to uplift. The highest surface (the Bowland Surface) ranges from 1200 to 1700 feet O.D. and at the time of formation consisted of undulating hills. Below this is the Wyresdale Surface which rises from 420 to about 1000 feet O.D. and, it is thought, formerly comprised a series of shallow valleys incised into the Bowland Surface. This surface is itself strongly dissected, with recent valleys incised into it so that it essentially forms the higher relatively gentle slopes of valley-in-valley systems. A third, still lower surface descending to about 250 feet O.D. has been recognized (the Lower Wyresdale Surface), similar in form and origin to the Wyresdale Surface. Although the greater part of these surfaces is considered to be of subaerial origin there is some suggestion that the lower two were affected by marine erosion in the extreme west, where they are at their lowest.