BEACHES, ETC., OF THE SOUTH OF ElfGLANB. 341 



the successive layers of rubble forming the Head. At the same 

 time it is manifest that the rise was not uniform, but consisted of a 

 series of uplifts with intervals of slow movement or temporary lulls. 



There is another point for consideration in connexion with an 

 emergence of the land. As the bed of the Channel is swept by 

 currents which drift the sand and shingle on to particular portions 

 of its bed, and leave other portions denuded and bare, so in like 

 manner, whilst the effect of the eflluent currents on the emerging 

 land has been to sweep the loose detrital matter (the E,ubble-drift) 

 down to the lower levels of the surface, it has necessarily left other 

 portions denuded and free of all drift. 



The K,ev. 0. Pisher, approaching the subject from another point 

 of view — that of the denudation of certain areas — has remarked ^ 

 that he did not see any other way of accounting for such a form 

 of surface as obtains in many of the valleys of the soft clay and 

 Chalk districts in the South of England than by a superincumbent 

 mass of water draining off from a flat or slightly dome-shaped area. 

 He infers " that the land must have been elevated by a sudden 

 movement sufficient to have caused a rush of water from the raised 

 portions to seek a lower level, — either the land being raised high 

 and dry at once, or the sea-bottom raised, though still remaining 

 beneath water. Such an elevation might be repeated again and again 

 with intervals of submergence." Allusion is made also to the 

 effects of the uplifts, which agree with several named in this paper. 

 This agreement in conclusions arrived at independently — in the one 

 case on purely geological evidence, and in the other upon the 

 abstract physical problem — cannot be regarded otherwise than as 

 confirmatory of the truth of the hypothesis. 



As illustrations of surfaces denuded in this manner I would in- 

 stance amongst other places the South Downs. There patches of 

 Tertiary and Plateau-drift beds occupy the high summits, and in the 

 valleys and low ground lies thePubble-drift derived from those beds, 

 and from the Chalk of the intermediate tracts that now remain de- 

 nuded and bare. It is the same, in a less degree, with the North 

 Downs, the debris of the Tertiary strata and of the Eed Clay-with- 

 flints of the higher summits, together with that of the bared Chalk, 

 commingling to form the rubble in the main valley at their base. 

 So likewise with the Wiltshire Downs and the Cotteswold Hills, 

 which are fringed, the one with Tertiary and Chalk debris, and the 

 other with Oolitic rubble, leaving the sides and slopes of the hills 

 bare. Again, in the Wealden area the debris has been shed from 

 off the central high dome, which is left bare, with a fringe of 

 detritus derived from Chalk and Tertiary strata along its encircling 

 valley ; whatever Eubble-drift there may be in the valleys of the 

 central area is hardly to be distinguished from the soft sandy and 

 argillaceous beds from which it is derived. 



1 ' On the Denudation of Soft Strata,' Quart. Journ. G-eol. Soc. vol. xvii. 

 (1861) p. 1. [I was not aware, when writing the preceding pages, of this paper 

 of Mr. Fisher's.] 



