﻿Vol. 66.] THE WESTERN END OF THE "WEALD. 687 



tributaries, which need no special description. On its western 

 side, what Martin (11) calls the ' Bines Hirer ' is also to be 

 regarded as a subsequent stream, although different in direction 

 from those on the east, since Martin's map shows that above W est 

 Grinstead it runs parallel, for some distance, with the outcrop of a 

 sandy seam, and it is also parallel to the Wisborough Green branch 

 of the Arun. It receives numerous consequent and obsequent 

 tributaries which I cannot attempt to follow out in detail, a good 

 deal of complication having been introduced by the great develop- 

 ment in this region of the Greenhurst anticline, and the syncline to 

 the south of it. 



It will be found generally that rivers which occupy a large area 

 of Weald Clay do not allow us to reconstruct the original conse- 

 quent system as easily as we could in the case of the Blackwater ; 

 but there is no reason, on this account, to ascribe to them an earlier 

 origin. The Weald Clay is soft, and, being impervious, every drop 

 of water which falls on its surface runs off in superficial channels. 

 The consequence is, not only that the rivers themselves are quickly 

 base-levelled (none of the rocks in the Wealden area offer much 

 resistance in this respect), but that the spaces intervening between 

 the streams are speedily lowered, and wide marshy plains formed. 

 On such plains the smaller streams are easily diverted even by 

 trifling obstructions, and so in time are introduced a large number 

 of divergences from the primitive rectilinear arrangement, more 

 especially as the Clay is, on the whole, remarkably homogeneous, 

 and free from alternations of hard and soft beds. I have already 

 alluded to this influence of soil in discussing the development of 

 the northern S3"stems, but in the case of the southern rivers yet 

 another factor is present — namely, the marked changes in relative 

 level of land and sea which are known to have occurred along the 

 south coast in recent times. Such oscillations cannot fail to have 

 produced alternate excavation and aggradation of the river-beds, 

 and these in turn would affect the river-junctions. In these various 

 ways I believe that most of the irregularities of the Adur and its 

 tributaries can be explained as due, either directly to structure 

 (such as the change of strike), or to the influence of the Weald 

 Clay ; and since, on the marine hypothesis, the greater part of the 

 exposure of the Weald Clay is subsequent to the plain, no argu- 

 ment against this hypothesis can be drawn from the river-system. 



The Arun and Adur both pass through transverse synclines (26, 

 p. 278), but the former has gained a further advantage by coin- 

 ciding with the region in which the Greenhurst anticline attains its 

 greatest development (12, pp. 134 & 190) ; and this coincidence I 

 consider, as in the ease of the Wey, to be connected with marine 

 planation. Here, as there, the intensity of the disturbance has led 

 to an easterly, as well as a westerly dip, thus enabling this river, 

 like the Wey, to expand in both directions. The Arun, on the 

 other hand, by the time the exposure of the Weald Clay spread 

 westwards to it, found that formation already fully occupied by the 

 Adur, and so has had to content itself, like the Blackwater, with a 

 unilateral development. 



