334 Correspondence. 



THE DEXUDATIOJT CONTROVERSY. 



To the Editor of the Geological Magazine. 



Sir, — Believing that an amicably-conducted controversy creates a 

 desire to re-examine old, and pursue new lines of investigation, I am 

 glad that my articles on " Denudation " have excited interest among 

 eminent men of science.^ I should be grateful to Mr. Aveline if, to 

 his avowal of opinion, expressed in your last nmnber, he would add 

 his reasons for supposing that the Longmynd valleys have been ex- 

 cavated by streams. I have just read Professor Jukes' testimony 

 to marine denudation in his " Student's Manual of Gealogy," pub- 

 lished in the same year (1862) in which his paper on the River- 

 Valleys of the South of Ireland was read before the Geological 

 Society. The following is a brief extract : — " The passes leading 

 across the crests of great mountain-chains could have been produced 

 by no other cause than by the eroding action of tides and currents, 



as the mountains rose through the sea Isolated crags and 



precipices, or long lines of cliff, and of steep slopes, looking down 

 upon broad plains, must have in like manner been formed by the 

 sweeping power of the sea. Broad open valleys . attest a similar 

 origin, and speaking generally, the principal features in the form of 

 the ground in all lauds have been produced by this wide-spread' 



action The results of this erosive action are exhibited to us 



often in the most striking manner in the gorges and ravines of 

 mountain slopes " (page 101). The great reason why Professor Jukes 

 so suddenly modified the above declaration of belief, would appear to 

 have been the "revelation" that, during the denudation, oiu- lands 

 have not been a sufficiently long time submerged to enable the sea 

 to accomplish it. I hope soon to be able to prove that the drift 

 deposits of Siluria furnish undeniable indications of long, if not 

 repeated, submergences, during comparatively recent periods. 



Yours truly, 



D. Mackintosh. 



DISCOVERY OF FLINT IMPLEMENTS IN KENT. 



To the Editor of the Geological Magazine. 



Dear Sir, — It may be of interest to record the fact, that a number 

 of flint implements have been found by Mr. J. Brent, jun., of Canter- 

 bury, between the Old Haven Gap and Eeculvers. These imple- 

 ments, seventeen in number, are mostly of large size, of the Amiens 

 type, very perfect. They were found strewn on the beach. One is a 

 very interesting specimen, being extremely flat and sharp, of the figure 

 represented in Sir Charles Lyell's " Antiquity of Man," page 114, 

 fig. 8, and about the same size. It is remarkably weathered, and of 

 an opaque white colour. The other specimens showed little or no 



1 In the last number at page 281, line 21, read are the result instead of "are not 

 the result." 



