The existence of a ‘wind gap’ or ‘pass’ at the head of a dry dip valley clearly points to the former extension of that valley beyond the present escarpment; and the depth of the gap is a measure of the size of the valley before being beheaded by the recession of the escarpment. Thus the gap at Merstham is about 300 feet deep, and the valley would probably have continued south some miles on to the Wealden uplands; the floor of this valley falls regularly north, and presents all the features due to a stream flowing in that direction previous to the formation of the Gault strike valley. As an instance of a less developed beheaded valley, the Maplescombe valley, which joins the Darent valley on the right bank at Farningham, may be instanced. The Maplescombe valley has a ‘wind gap’ of possibly 100 feet deep, and so its former southward extension would not have continued into the Wealden area as far as the Merstham valley; moreover, the floor does not slope regularly to the Darent, but is steepest at the head, the distance between each contour-line increasing as one descends the valley, viz.—

The present valley floor, particularly the upper part, is evidently not the one down which a stream from the Weald would have flowed, for at the above noted rate of increased slope the valley would ‘run out’ (or become extinct) at a very few hundred yards south of the present Chalk escarpment, and this short length is not compatible with the excavation of a valley 100 feet deep, such as the present wind gap.