Geological Society of Londcn, 339 



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 Charles Lyell supported the same view, and mentioned a 

 case which had occurred at Salisbury some few 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- 

 vation of valleys. He also mentioned the discovery by Dr. Harris 

 of flint gravel identical with that of the present valleys beneath the 

 Basalt of Miocene date in Antrim. 



Mr. Searles V. Wood, Jun., insisted on the impossibility of even 

 an enormously increasing rainfall filling the valleys as suggested by 

 Mr. Tylor, and pointed out the influence which such an accession of 

 fresh water must have had on the animal life in the estuaries. He 

 also mentioned tidal action as an excavating agent in valleys. 



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 Yalley 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 

 ascertained. 



Prof. Eamsay made some concluding remarks (as President), ex- 

 pressing his disagreement with the views of the author as to the 

 enormous magnitude of the ancient rivers. 



co:E^<:E^:ESI=»Ols^lDEz^^cE. 



ON THE CAUSE OF CONTORTIONS, FAULTS, AND DISLOCATIONS IN 

 THE CRUST OF THE EARTH. 

 Sir, — I observe from several recent articles in the Geological 

 Magazine, as, for example, the paper of Mr. Wilson in your 

 May number (p. 205), and the letter of Mr. Maw in that for 

 this month (p. 294), that the attention of geologists is being 

 directed to the mechanical effects of upheaval or depression acting 

 on extensive portions of the rocky crust of the earth. May I be 

 allowed to ask the consideration of those who may be engaged 

 in such inquiries to certain passages relating to this subject to 

 be found in my volume on Volcanos, which may not have fallen 

 under their observation ? I refer especially to pages 46-52 (edit. 

 Longman, 1862), in which it is suggested that whether the dis- 

 turbing force be elevation or depression (arising from whatcA^er 

 cause), there must exist a centre, or central axis, of dislocation, where 

 the disturbing force will be at its maximum, and also some lateral 

 limits beyond which it does not operate ; and that the effect pro- 

 duced on the mass of rock included within these limits must be 

 similar to '' that which is known to be produced in a beam fixed at 



