﻿Vol. 64.1 ME. H. BtTEY ON THE EIVEE WET. 333 



The Caker Stream. — It will be remembered that the Caker 

 Stream flows for some distance at the junction of the Chalk and 

 the Upper Greensand. These junction-beds are sandy/ and there is 

 abundant evidence all along the foot of the western Downs that 

 they constitute a line oi special weakness. The Lower Chalk also, 

 as we have seen, is non-resistant, and here, as elsewhere, forms 

 large areas of nearly level ground. The MalmEock (Upper Green- 

 sand), on the other hand, is very hard, and has been but little 

 removed from the hills to the east of this valley. 



There is hardly any room for doubt that the present conditions 

 have been brought about by the simple removal of the Chalk 

 from part of a river-system originally established in the Chalk 

 alone, and that this result has been greatly facilitated by the 

 presence of the weak junction-beds ; but the details of the original 

 valle3''-system are rather obscure. The wall of Chalk separating 

 this valley from the nearly parallel Tisted Yalley is broken through 

 in three places by wide and flat passes, and the drainage in all 

 three gaps is mainly towards the Tisted Yalley. If the original 

 drainage had been along the present line of the Caker Stream, by a 

 valley comparable to, though smaller than, the Tisted Yalley, we 

 should certainly expect tributaries from this western side, as well 

 as those which, as we have already seen, flow in from the Green- 

 sand. The comparative absence of these, coupled with the size 

 and apparent age of the three branches of the Tisted Yalley, leads 

 me to think that the latter indicate the original lines of drainage, 

 which the Caker Stream, being the first to reach the soft junction- 

 beds, has succeeded in capturing one after the other. 



It is, however, unnecessary to enter into further discussion of 

 this point, because the conclusion of main interest to us is the 

 same in any case — namely, that we have here another example of 

 the conversion of a Chalk valley into a "Wealden one. In the 

 Parnham Yalley it is the lower end which has changed its character ; 

 here, by an odd combination of circumstances, it is the upper end 

 of the stream which has entered the Wealden Beds ; but the time 

 is perhaps not so very far distant when the rest of the Chalk will 

 be removed between Wilsham and Cuckoo's Corner, and then this 

 stream will be difiicult to distinguish throughout its course from one 

 of purely "Wealden origin. 



EXPLANATION OF PLATES XXXVI & XXXVII. 

 Plate XXXVI. 



Map on the scale of 2 miles to the inch, showing the six sections of the Eiver 

 Wey which lie within the Wealden area. The upper part of the River 

 Wey (consequent) and the branch of the Headley Stream which comes 

 down from Haslemere are not included. 



Plate XXXVII. 



Map of the Alton district, on the scale of 2 miles to the inch. The courses of 

 the principal valleys are marked by dotted lines, and the heavy broken 

 line marks approximately the lower outline of the Chalk. 



1 'The Cretaceous Eocks of Britain ' Mem. Geol. Surv. vol. i (lyOO) p. 113 

 & vol. ii (1903) p. 60. 



