202 THE RIVER VALLEYS OF 



break, such a movement naturally taking place along 

 a soft, .weak bed. Thus, if the chalk in the Weald was 

 broken, but fixed at one side, the greensand would 

 be pushed out from under it along the gault ; and the 

 Hastings beds might be pushed out from under all, 

 along one of the Weald clays. Such a movement in 

 the Weald, although the average angle of dip be only 

 one degree, 1 would form terraces between the outcrops 

 of the chalk and greensand, and the greensand and 

 the Hastings beds in the north and south parts of 

 the valley respectively, 15 feet and 10 feet wide. 



As soon as this movement was complete, or even 

 while it was yet in progress, denudation would be 

 at work marine denudation if the movement was 

 submarine, meteoric abrasion if it was subeerial. Thus 

 either denudant, if it had time enough, might possibly 

 have accomplished the work that has since been done ; 

 but it appears much more natural to suppose that 

 neither of these agents did all the work, but that 

 their efforts were combined; each accomplishing its 

 allotted portion. Le Conte has shown that it is pro- 

 bable that all elevations and crumbling up of the 

 earth's crust commence beneath the sea, and all 

 rocks thus raised must necessarily be exposed to the 

 full force of the sea prior to being raised above its 

 influences. In the case of the Weald, the sea would 



1 The average angle is higher ; this is the lowest mean angle of dip 

 that can well be assigned. 



