On the Sculptures of the Chalk Downs in Kent, Surrey, and Sussex

Abstract

The Author classifies the various forms of sculpture of the Chalk Downs under three heads, namely, (1) dry valleys of simple form, (2) dry valleys of complex form, and (3) wet valleys. He draws attention to the relatively small catchment-areas of the dry valleys, and to the large number of tributary valleys found in some districts, two points which he considers have not hitherto received entirely satisfactory explanation. While accepting the view that frozen conditions in former times altered the drainage-system of the Chalk, he argues that the most potent excavating force was the frost itself, acting on Chalk saturated or highly charged with water. He points out the following peculiarities of dry Chalk valleys:—(1) the great size and breadth of the valleys in relation to their catchment-basins; (2) the ramifications of some of the valley-systems; and (3) the termination of many dry valleys just short of the crest of the Chalk Downs. In order to account for these phenomena, the Author propounds the following theories:— (1)The chief part of the valley, during and after periods of low temperature, being occupied by a mass of ice, erosion of the Chalk would naturally be more active at the sides than in the bottom of the valley: lateral development and sometimes elaborate ramification being the result. (2)The diminution of the catchment-area, due to the cuttingback of the valley towards the highest level, would have the effect of removing one of the chief agents in the breaking-up of the Chalk, with the result that the valley would die out just short of the crest of the Chalk Downs.