428 Correspondence — P. Lake. 



THE EIVERS OF WALES. 



Sir, — May I be permitted to assure Mr. Strahan that it is not his 

 eritioisms to which I object, even though he still finds the second 

 part of my paper too great a tax upon his credulity. What really 

 concerns me, as a worker in the Principality, is, that the Quarterly 

 Journal of the Geological Society should be open to speculation 

 about the rivers of South Wales and closed to speculation about 

 those of North Wales, Philip Lake. 



August 8, 1902. 



LITTOEAL DRIFT. 



Sir, — My friend Mr. W. H. Wheeler's new book on the Sea-Coast 

 has been reviewed with such universal commendation that it may 

 seem invidious to offer any word of criticism. But, as my own work 

 in the same direction was reviewed in the Geological Magazink. 

 some years ago. and as if Mr. Wheeler is right I am most un- 

 doubtedly wrong, it may be as well to point out briefly my reasons 

 for divergence, leaving it to experts to decide the questions at issue. 



Mr. Wheeler's conclusions are based, explicitly or implicitly, on 

 some six hypotheses, viz. : — 



(1) That the tidal wave is a wave of translation. 



(2) That the flood -tide current generally, as a current, is- 

 a stronger current than the ebb-tide current. 



(3) That the flood -tide current generates tidal wavelets of 

 translation. 



(4) That sea waves on approaching the shore become waves of 

 translation. 



(5) That sea waves approaching the shore raise the mean level 

 of the water, with the eiJect of adding temporarily to the volume of 

 water above mean level, as compared with the volume below 

 that level. 



(6) That the proportion of height to length of wave may be as 

 much as 1 to 3. 



Mr. Wheeler incidentally discusses a wave with the assumed 

 proportions of 30 feet long and 10 feet high. 



It would be scarcely possible to discuss the evidence, mathematical, 

 observational, and experimental, on these six points, under some two 

 or three hundred pages. 



In this as in many other cases controversialists do not use the 

 same terms with the same meanings, so that the nomenclature must 

 first be cleared, e.g. : — 



(1) The tidal wave, due to the attraction of moon and sun, gives 

 rise to two currents, an ebb and a flood ; but, when the flood runs 

 up a channel such as the Severn, and creates a ' bore,' observers are 

 apt to speak of such bore as the tidal wave itself, instead of as 

 a subsidiary wave due to the retardation of the tidal flow-current 

 in the river. 



(2) As the flood-tide current at sea runs, as a rule, three or more 

 hours after high-water, the term ' flood tide ' is ambiguous. 



