456 PEOCEEDINGS OP THE aEOLOGICAL SOCIETY. April 22, 



Discussion. 



Mr. Prestwich dissented from the view of the author, that the 

 valleys had been excavated to their present depth before the gravels 

 were deposited ; and, with reference to a former paper, explained 

 that Mr. Tylor and himself had taken different points of observation 

 near Montiers, and that his own views as to the separation which 

 in some cases may be shown to exist between the high- and low- 

 level gravels were correct. 



Mr. Evans also combated Mr. Tylor's views, and pointed out the 

 difficulty of accounting for deposits of gravel such as are at present 

 found in valleys already excavated to their present depth. 



Mr. W. Boyd Dawkins objected to calling in hypothetical causes 

 to account for effects when existing causes are sufficient, and cited 

 the sudden melting of snow as a sufficient cause, as had already 

 been suggested by Mr. Prestwich. 



Sir Chables Lyell supported the same view, and mentioned a 

 case which had occurred at Salisbury some 30 years ago as an in- 

 stance of the effects of such floods. He also cited the existence of 

 flint implements in the gravels on either side of Southampton Water 

 as evidence of the existence of man during a long period of excava- 

 tion of valleys. He also mentioned the discovery by Dr. Harris, 

 Bishop of Gribraltar, of flint gravel identical with that of the present 

 vaUeys beneath the Basalt of Miocene date in Antrim. 



Mr. Searles Y. Wood, jun., insisted on the difficulty of increased 

 rainfall filling even the old river-channels of Mr. Prestwich, far less 

 entire valleys, as suggested by Mr. Tylor ; and pointed out that such 

 increase would so freshen the estuaries, that the valleys might have 

 been excavated by tidal action, and yet yield freshwater remains. 



Prof. Ansted showed, by calculation, that even a vast increase in 

 the rainfall would not suffice to fill the valleys so as to deposit the 

 gravels as at present found. 



Mr. Whitaker quoted the existence of distinct terraces of gravel 

 one above the other in the Thames valley as proving the gradual 

 excavation of the valley. 



Prof. Morris doubted as to the precise character and age of the 

 deposits in the valleys in South Wales having been accurately ascer- 

 tained. 



Mr. Tylor briefly replied. 



Prof. Ramsay made some concluding remarks, expressing his dis- 

 agreement with the views of the author as to the enormous magni- 

 tude of the ancient rivers. 



