﻿Vol. 66.] DENUDATION OF THE WESTERN END OF THE WEALD. 685 



to us now, might be sufficient to guide an early stream ; but we 

 have no right to assume such a fold except under very strong com- 

 pulsion from collateral arguments. 



On the other haud, this river is most difficult to account for as a 

 subsequent outgrowth from the Aran. It passes close by the head 

 of the Adur, which at Christ's Hospital is only separated from it 

 by a narrow belt of flat ground; so that it must, on this hypothesis, 

 have captured some territory from the latter river. This, however, 

 is most improbable : the Arun and the Adur have equally good 

 access to the sea, and there is nothing elsewhere to suggest that 

 the former had any advantage ; on the contrary, its failure to 

 expand eastwards in the Weald Clay farther south indicates that 

 there at any rate the Adur occupied the more favourable position. 

 This objection, then, seems to me a serious one, so long as we 

 attribute the subsequent river (if such it be) to the Arun, but it 

 disappears if we suppose that the river was originally a branch of 

 the Wey ; and that proposition I shall now endeavour to prove. 



Prom about Horsham westwards the river runs in Weald Clay 

 (with occasional beds of Horsham Stone), and the hills bounding its 

 valley on the north rise with an abruptness which is most unusual 

 in these soft strata. On the well-known relief map of the Weald 

 the ridge to the north of Rudgwick is absurdly exaggerated, and 

 made to appear almost equally steep on both faces : in reality it 

 slopes very gradually to the Wey on its northern side, and is only 

 steep towards the south, where we find a rise near Rowhook of 

 200 feet in about a mile, and the hillside is scored with valleys of 

 the narrow and abrupt type which we are accustomed to associate 

 with obsequent streams. 



In this region the sharp gradients of the valley may be attributed 

 in part to the river having recently swung over towards its northern 

 boundary; but farther east, near Warnham, there is again a steep 

 hillside (gradient=120 feet in a mile), although the river does not 

 run within 2 miles of the spot. Two important obsequent streams 

 enter the Horsham River from the north, one being known as the 

 North River, while the other may be referred to as the Warnham 

 Brook, and we find on each side of these streams gradients almost 

 as steep as those of the main valley. 



Disregarding the North River for the moment, and fastening our 

 attention on the ridges of higher ground bounding it, we observe 

 that the Weald Clay, which covers all this district, stretches up 

 the slopes of Leith Hill and its neighbours almost to the 700-foot 

 contour ; but, as we pass southwards, the ground falls away to 

 300 feet O.D. in little more than a mile, and then for upwards 

 of 4 miles there is scarcely any variation in level until we plunge 

 down, as already described, into the Horsham Valley. The North 

 River and Warnham Brook cut through this upland plain of clay with 

 gradients which are far more sudden than we should expect from 

 the nature of the soil. In fact, if we compare these valleys with 

 those of other parts of the Weald Clay area, we can hardly fail to 

 be impressed, even after making due allowance for their obsequent 



