﻿Yol. 64.] ME. H. BUEY OIS^ THE RIVEK WET. 321 



to the rarnhain Eiver at Bourne Mill. About a mile to the north 

 of this stream, and roughly parallel to it, another brook descends 

 from Hungry Hill, and forms the present head of the Blackwater ; 

 it continues on an east-south-easterly course till it comes opposite 

 the end of the Hog's Back, and then turns sharply northwards. 



The valley to the east of the above-mentioned Chalk mound 

 deserves especial attention. A subsequent valley runs down past 

 Scale at the foot of the Hog's Back, and at present only produces a 

 mere trickle of water ; but there is a suggestion that it may once 

 have extended nearly to Puttenham, before being beheaded by an 

 obsequent tributary of the Godalming Eiver. At first sight it looks 

 as if this tiny stream flowed to the south of the Chalk mound to join 

 the Farnham River, but more careful observation reveals the fact that 

 it turns northwards near llunfold and flows out over the Chalk 

 to join the Blackwater. This very interesting fact — that a stream 

 does still flow out from the Wealden to the Tertiary area at this 

 point — was, I find, noted by George Long in 1839, ■■ but was after- 

 wards entirely overlooked. Topley,^ indeed, asserts that there is no 

 stream flowing through this pass, although the alluvium deposited 

 by it is marked on the Geological-Survey map. 



It has long been known that pebbles derived from the Hythe 

 Beds of the Lower Greensand, which must have come at least as 

 far as from Hindhead, are to be found in the gravels to the north 

 of the Chalk in this region. They occur ver}^ sparingly in the 

 * Southern Drift' ^ to the north of Parnham, 600 feet above O.D. ; 

 much more frequently in the lower, and probably later gravels 

 bounding the Blackwater Valley (Fox Hills, Chobham Eidges, 

 Hartford-Bridge Flats, etc.) * ; and in moderate quantities in 

 gravels lying on the Chalk itself in the gap already described 

 (Water Lane, see 6-inch Ordnance-Survey map). All this showed 

 to earlier writers that there must have been some Wealden river 

 flowing northwards in this region ; but, until the principles of river- 

 capture had been fully expounded by many writers on both sides 

 of the Atlantic, its connection with the recent river-system could 

 not be clearly understood. W^ith our present knowledge, we may 

 safely assume that at no very distant date there was a consequent 

 river coming down from Hindhead and flowing through this gap, 

 after being joined by the Tilford and Farnham Eivers on the west, 

 and the Scale stream on the east. But it is a curious fact that this 

 consequent river is hard to identify among the many streams from 

 Hindhead, and it is possible that during the present cycle of 

 erosion it never attained to any great size " ; while many of the 

 Lower Greensand pebbles were doubtless supplied by the other 

 streams which are now collected by the subsequent Tilford Eiver. 

 It is doubtful whether there was ever a stream of importance 



1 Proc. Geol. Soc. vol. iii (1838-42) p. 101. 

 = ' Geology of the Weald ' Mem. Geol. Surv. 1875, p. 279. 

 3 J. Prestwich, Quart. Journ. Geol. Soc. vol. xhi (1890) p. 161. 

 ^ H. W. Monckton, ibid. vol. xlviii (1892) pp. 29 et seqq. 

 ^ The Darent is another Wealden river which has no well-marked con- 

 sequent head. 



t2 



