﻿686 MR. H. BURY ON THE DENUDATION OF [Nov. I9IO, 



nature, by their relative immaturity. So long as we persist in 

 regarding this portion of the river-system as having originated 

 with the Arun, this immaturity calls for, without receiving, an ex- 

 planation. But, if we suppose that the original drainage-system 

 belonged to the Wey, this difficulty vanishes ; for the Arun, as 

 we have seen, lies at a much lower level than the Wey, and while 

 grading the bottom of the valleys stolen from the latter, has not yet 

 had time to adjust the sides. We also, in this way, overcome the 

 further difficulty of understanding how a southern river can have 

 extended as far north as Leith Hill. The view, then, which I take 

 of the early course of this river can be gathered from fig. 8 (p, 684). 

 The original watershed ran (roughly speaking) through Itching-field 

 and Plaistow, and the Horsham Kiver curved round into the Wey 

 at or near Loxwood. When the Lower Greensand escarpment 

 retreated, the longitudinal river did not follow it (perhaps because 

 the dip is so slight), but kept up connection by means of obsequent 

 streams which are now more than 6 miles long. Owing to the 

 softness of the Weald Clay, and the greater proximity of the Arun 

 to the sea, this river was able, at a comparatively late stage, and 

 after a large area of the Clay had been adjusted to the Wey, to 

 cross the original watershed and behead the Horsham branch of the 

 latter river. This, of course, at once transferred to it all the tribu- 

 taries lying above the point of capture ; but the Dunsfold region 

 continued to be drained by the Wey, and was only annexed by the 

 slow process of obsequent growth. It is entirely in accordance with 

 this view that the adjustment of the North ltiver to its surround- 

 ings, though far from complete, is yet more advanced than that of 

 the Dunsfold streams. 



If we had been unable to trace the history of these northern 

 extensions of the Arun — if its presence close to the Greensand 

 escarpment on both sides of the Wey had appeared to be of long 

 standing — we might have been tempted to assume that we were 

 here in the presence of an earlier river-system, developed on the old 

 Wealden island postulated by Prestwich. But we see now that no 

 such assumption is necessary ; on the contrary, we have strong- 

 reason for believing that these northward excursions are all of 

 recent date, and have resulted largely from the softness of the 

 Weald Clay, which can hardly have been exposed on such an island. 

 The same is true of the other northward extension of the Arun, 

 past Petersfield : this, too, is a secondary, not a primary feature, 

 and has only been rendered possible by the exposure of soft beds 

 in comparatively recent times. 



(F) River Adur. 



This river is so complex that it is not easy at first sight to 

 determine which part of it should be regarded as the main conse- 

 quent trunk : I believe, however, that the stream which runs past 

 Cowfold, at right angles to the outcrop of the Hastings Beds, merits 

 this description. It receives on its eastern side three subsequent 



