156 Mackintosh — The Sea v. Rivers. 



But if these terraces have resisted the action of rain to so great an 

 extent during the immense period required by the river to deepen 

 its bed 300 feet, is it consistent to attribute to rains the power of 

 eating out " the G-ault valley," in the neighbourhood, to a depth of 

 120 feet, and breadth of 1^ mile ? Dr. Foster and Mr. Topley dis- 

 pose of the marine theory in a very summary manner. But I cannot 

 see the force of their objections. (1) The want of corresponding 

 level, all round the Weald, of the foot of the Chalk escarpment, can 

 be explained by unequal elevation, especially if several upheavals 

 are admitted ; and the fact of rivers flowing in the lowest parts is 

 quite reconcileable with the idea of these parts having been scooped 

 out by the sea, and does not necessarily imply that they were mainly 

 excavated by rivers. (2) With regard to the assertion that the 

 escarpments follow the strike, of the beds, changing their direction as 

 the strike changes, this remark cannot apply to the smaller bays and 

 combes of the South Downs, the side-cliffs of which often run at 

 right angles to the strike. That the British Isles do not furnish an 

 example of long lines of cliff following the general direction of the 

 strike is no more remarkable than it is that they do not supply an 

 instance of the sea denuding the fractured summit of a series of for- 

 mations anticlinaUy arranged like those of the Weald district of 

 Sussex and Kent. (3) The absence of shingle or ordinary marine 

 deposits • at the foot of the escarpments can be satisfactorily ex- 

 plained, by supposing that they were removed soon after they were 

 formed, as the land rose above the sea ; or washed away during a 

 second submergence, if not by the ordinary action of the sea, at 

 least by a debacle, or series of debacles, occasioned by violent 

 upheavals or depressions. The Woolhope valley of elevation in 

 Herefordshire has been denuded without leaving any trace of the 

 denuding agent, and very few would ventiire to assert that its con- 

 centric system of valleys, with only one effective outlet, could ever 

 have been worn do'WTi and swept out by rains and brooks^ (4) As 

 it is quite certain that many changes of level have occurred in the 

 Wealden area since the process of denudation commenced at the 

 summit of the Chalk ranges, if not at a greater altitude, any objec- 

 tions to the marine theory founded on the present relative levels of 

 different parts, cannot be regarded as possessed of much force, more 

 especially when they come from subaerialists, whose theory of 

 river-action involves a succession of local elevations. 



Denudation of the Malvern Hills. — The Malvern Hills form per- 

 haps the driest mountain ridge in England ; and yet this ridge is 

 much indented on its eastern side by valleys and hollows of denu- 

 dation. Some account of these may perhaps prepare us for forming 



' Have any geologists yet particularly noticed what the sea is now doing under the 

 chalk cliffs of the Isle of Wight ? From some statements in Mr. Whitaker's paper 

 (Quar. Jour. Geul. Soc, vol. xxi, Nov., 1865) I should infer that in many places no 

 deposit is allowed to accumulate under the cliffs, and that the " hard Chalk-marl and 

 harder Upper Green-sand stretch out as a foreshore for some way westward of their 

 outcrop in the cliff," so free from detritus, as to allow their even bedding to be 

 clearly perceived. 



