280 Correspondence. 



ation. of roots of trees with the waters of a streamlet, in -under- 

 mining and removing the banks. If you examine almost any one of 

 the little tumbling rills among the mountains of the Upper Carboni- 

 ferous formation, you will find it buried in trees. The fibres of the 

 roots insert themselves in the smallest crack, and push themselves 

 between the layers of rocks ; and by degrees they thicken and grow 

 strong, and lift huge masses of stone, with a seemingly irresistible 

 force, loosening the earth at the same time above and below and 

 around. The action of the rain easily washes away the earth, the little 

 tree becomes a great tree, and, either because it is undermined be- 

 neath, or because the weight above becomes too much for its hold, 

 it is sure to come down with a crash into the brook, carrying with it 

 a large portion of the bank in its fall. The next flood removes all 

 trace of the ruin. The sand and soil and the small stones are swept 

 away, while the larger stones keep their places peaceably in the 

 channel where they fell, to make fantastic waterfalls and still hol- 

 lows for the minnows. Yours, etc., 



T. Ashe. 

 Leamington College, May 7th, 1866. 



DENUDATION.— REPLY TO Mr. G. POULETT SCROPE AND 

 Me. J. B. JUKES. 



To the Editor of the GtEological Magazine. 



Sir, — The appearance in your Magazine of two communications 

 on Denudation renders it necessary that I should again trouble you 

 with a few remarks before the completion of the series of observa- 

 tions on which I am now engaged. 



Not having visited the localities described in your last number by 

 the eminent author, Mr. G. Poulett Scrope, I can ofier no opinion 

 relative to the conclusions at which he has arrived, I should not 

 think of underrating the power of temporary as well as permanent 

 torrents, to excavate channels in the gravels of the Tyrol, Cumber- 

 land, Wales, or any country subject to waterspouts and heavy falls 

 of rain ; and I could agree with all that Mr. Scrope has advanced 

 concerning the denudation of Auverg-ne, without requiring to recant 

 any opinions I have advocated. The facts on which Mr. Scrope's 

 reasonings are based, namely, the resistance offered to the atmosphere 

 by the basaltic cappings of the mountains of Auvergne during an 

 immense period of time which can scarcely be exaggerated, furnishes, 

 perhaps, the most convincing proof which can possibly be adduced, of the 

 impotence of rain as a denuding agent on hard rochs,^ and ought to 

 prepare our minds for believing that many of the inland sea-clifis 

 and rocks of England and Wales have retained their wave-worn 

 shapes since the Glacial submergence, if not since a much more 



1 The phrase " impotence of rain," I have applied only to the action of mere rain 

 on compact rocks and grass-coyered land, and not to torrents, charged with solid 

 abrading matter, and acting on exposed gravel, loose stones, or soft materials. When' 

 using the phrase, I was not alluding to volcanic or alpine districts where conditions 

 are, or have been, exceptiotially favourable to atmospheric denudation. 



