A brief description of the geological history of the range may not be amiss here. It will be noted by the traveller from the north that the opposing line of heights in Surrey have their steepest face (or "escarpment") on the south side, while the Sussex Downs have theirs on the north. A further peculiarity lies in the fact that the river valleys which cut across each range from north to south are opposite each other, thus pointing to the probability that the fracture which caused the clefts was formerly continuous for fifty miles through the great dome of chalk which extended over what is now the Weald. The elevation of this "dome," caused by the shrinking and crumpling of the earth's crust and consequent rise of the lower strata, was never an actual smooth rise and fall from the sea to the Thames valley; through the ages during which this thrust from below was in progress the crown of the dome would be in a state of comparatively rapid disintegration, and it is because of this that we have no isolated masses of chalk remaining between the two lines of hills. The highlands called by geologists the "Forest Ridge" are in the centre and are the lowest strata of the upheaval; they are the so-called Hastings sands which enter the sea at that town half-way between Beachy Head and Dover cliffs. North and south of this ridge is the lower greensand, forming in Sussex the low hills near Heathfield, Cuckfield and Petworth, and which reaches the sea south and north of Hastings. It was at one time supposed that the face of the Downs originally formed a white sea cliff and that an arm of the sea stretched across what we know as the Weald, but the simpler explanation is undoubtedly the correct one. [Illustration: WANNOCK.] The Downs themselves are composed of various qualities of chalk; some of such a hard, smooth and workable material that, as will be seen presently, the columns in some of the Downland churches are made from this native "rock." While the upper strata is soft and contains great quantities of flints, the middle layers are brittle and yield plenty of fossils, lower still is the marl, a greyish chalk of great value in the fertilization of the gault. This latter forms an enormous moist ditch or gutter at the foot of the escarpment, and from the farmer's point of view is essentially bad land, requiring many tons of marl to be mixed with it before this most difficult of all clays becomes fertile. Between the chalk and the gault clay is a very narrow band of upper greensand, only occasionally noticeable in the southern range, but strongly marked in the North Downs.