232 Correspondence. 



was delivered, before the above Society by Dr. P. P. Carpenter (late 

 of Warrington, near Manchester), " On the Cuttle-fishes and their 

 allies." Dr. Carpenter included in his interesting lecture descriptions 

 of both fossil as well as recent forms, and exhibited illustrations of 

 the several genera. The President (Dr. Smallwood) on behalf of 

 the Society returned thanks to Dr. Philip Carpenter for his valuable 

 and instructive lecture. — Montreal Gazette, February 13, 1866. 



ATMOSrHERIC V. MARINE DENUDATION. 

 To the Editor of the GtEOlogical Magazine. 



Sir, — Having publicly advocated atmospheric action as the power 

 by which the present " form of the ground " has been produced, I 

 would wish to say a word or two on the clever articles you are pub- 

 lishing by Mr. D. Mackintosh, in which the sea is treated as the chief 

 agent. 



I am glad to see that Mr. Mackintosh does not allude to the action 

 of internal force as having any direct effect on the external features 

 of the ground. So long as we were hoodwinked by the hocus-pocus 

 of " grand convulsions," and believed it possible for mountain chains 

 to jump out of the interior of the earth like so many "jacks in the 

 box," no advance in real knowledge was possible. 



It may be taken for granted, then, that all the external features of 

 the ground (except of course volcanic cones and craters) are the 

 direct result of external agencies (Presidential Address to Section C. 

 British Association, Cambridge, 1862). It may also be taken for 

 granted that as all lands have risen out of the ocean, marine denuda- 

 tion has done something towards the production of their present 

 form, and that during the time they have stood as dry land atmos- 

 pheric agencies have also done something towards it. The problem 

 is to apportion to the marine and atmospheric agencies the amount 

 of work each has performed. 



In reading Mr. Mackintosh's articles I recognise ideas which a 

 few years ago I held as stoutly as he does now, and I believe there- 

 fore that he is following the same path which I did towards a fuller 

 appreciation of the j)recise operation of these natural agencies. I 

 think I was hardly aware of the change which had taken place in my 

 o^va convictions, as the result of constant observation in the field, 

 till I hit upon the solution of a problem that had long puzzled me, 

 namely, the precise mode of production of the river valleys of the 

 South of Ireland. (See Quart. Jour. Geol. Soc, London, vol. xviii.) 



This solution requires that the rivers should never have ceased to 

 i-un through the ravines, by which they traverse isolated hills be- 

 tween their sources and the sea, during the denudation of the plains 

 by which those hUls are surrounded. Had the sea ever marched 

 across the country, and worn it down to form those plains, it must 



