ANNIVERSARY ADDRESS OF THE PRESIDENT. li 



racters where the beach was shmgly, or by the ledge or terrace alone, 

 hi the absence of shingle. In what cases then would this terrace-like 

 feature be obliterated ? In the first place, if the rise of the land 

 were absolutely continuous for a great length of time, and therefore 

 extremely slow, there would be no general cause for the formation of 

 a terrace at all, for a terrace could only result generally from the 

 land remaining a long time at the same level, and then being suddenly 

 raised to another level. If the rise of the land were of sufficient 

 magnitude to place the raised beach above high-water mark, the 

 terrace might still be destroyed by the action of the sea, provided the 

 land remained at the new level long enough for that action to wear 

 away the new beach sufficiently to undermine the old one, and thus 

 form, to a certain height, a new face to the cliif or higher land front- 

 ing the sea. The smaller the rise of the land, the sooner, of course, 

 would the obliteration take place. 



This mode, however, of obliterating raised beaches would evidently 

 be much less effective in those cases in which the inclination of the 

 surface of the land at the sea-margin should be small, than in those 

 in which it should be comparatively large, and the same observation 

 would also apply to the action of terrestrial and atmospheric causes. It 

 would be difficult, for instance, to account, by means of the causes alone, 

 now mentioned, for the absence of all indications of former beaches 

 on many of the sloping surfaces of the Wealden, unless we suppose 

 the land, during its last emergence, to have risen much more con- 

 tinuously than it appears to have done along the southern coast ; and 

 even in that case the entire non-existence of rounded pebbles in the 

 district would still, as Sir R. Murchison has contended, present a 

 great difficulty, unless we can assign some more efficient cause for 

 their removal. Their formation would, I conceive, in many places 

 within the Wealden be the necessary result of coast-action. 



The cause which I consider as adequate both for the removal of 

 all rounded pebbles and for the obliteration of terraces, is that dilu- 

 vial action to which our author refers the distribution of the small 

 angular detritus of the district. This action I conceive to be that of 

 waves of translation (as Sir Roderick also supposes) produced by 

 earthquake movements frequently repeated, while the lower parts of 

 the district were immersed at different depths beneath the surface of 

 the ocean. These movements, however, were quite distinct from those 

 which gave its geological configuration to this region, being probably 

 referable, as already stated, to the same period as the smaller faults 

 described by Mr. Austen in the neighbourhood of Peasemarsh, the 

 latest period at which the district was under water. The magnitude 

 of these movements need not alarm the most timid geologist. Assu- 

 ming them to have been frequently repeated, it is certainly not essen- 

 tially necessary to suppose them of much greater intensity than that 

 of many earthquakes of modern times. It is necessary, however, to 

 suppose this to have been the last aqueous agency effectively exercised;; 

 in this district. It can not, according to this view, have been followed, 

 by any long-continued diurnal action of the sea. And this, I have 

 f eason to believe, is essentially what Sir R. Murchison contends for, 



d2 



