492 Whitaker — On Subaerial Denudation. 



out of tlie question) : more too must have been worn away than 

 was deposited afterwai-ds by the rivers, for much would be carried 

 out to sea to form a marine deposit. Of course freshwater beds are 

 both less common and thinner than marine beds, but so also, as 

 aforesaid, the comparatively trifling denudation that has formed our 

 hills and valleys is of far less amount than that which has planed 

 down vast tracts of country and carried off therefrom a great thick- 

 ness of rock. Perhaps, indeed, the proportion that the effects of 

 marine denudation bear to those of subaerial denudation is not far 

 from the same as that which marine deposits bear to freshwater 

 deposits. 



To those who say that subaerial agents are too small and too weak 

 for the work which has been put to their credit, it may be answered 

 that unlimited time would get over that difficulty ; and it should be 

 borne in mind that good evidence has been brought forward that in 

 late geological times our climate was far more severe than now, and 

 that there may have been a far more rainy period before the present 

 order of things was established ; or in other words, that the agents 

 in question were far more powerful than they now are in these 

 islands. Great change indeed has taken place in historic times : the 

 felling of forests, the draining of land, the embanking and canaliza- 

 tion of rivers, the reclaiming of marshes, and the like human handi- 

 works having had their effect in lessening rainfall and floods, and 

 therefore also the wearing action of surface water. 



As astronomy has proved the existence of almost boundless space, 

 so geology needs almost boundless time. The former science gives 

 us our liveliest picture of infinity, and the latter our best idea of 

 eternity. When astronomers talk without any opposition of im- 

 measurable space, surely geologists should be allowed immeasurable 

 time. The last Wollaston Medallist has eloquently said, " The lead- 

 ing idea which is present in all our researches, and which accom- 

 panies every fresh observation, the sound which to the ear of the 

 student of nature seems continually echoed from every part of her 

 works is Time ! Time ! Time ! " ^ 



Lastly, it seems to me that the discussion on the question of 

 denudation has been argued on a wrong foundation. Surely, if we 

 can explain the facts and appearances we see by actions and oper- 

 ations that can be seen going on at the spot now, we are bound to 

 take such explanation until it can be disproved, or until a better one 

 can be given, and we have no right to call in the aid of other and 

 distant operations, without there is some good sign of their having 

 been once present (thus for instance with regard to many rock- 

 basins now far from glaciers, there are unmistakeable signs of their 

 once having contained ice). As a simple matter of reasoning there- 

 fore, apart from all scientific truth, we are bound to accept the 

 theory of subaerial denudation until it can be put aside. Geologists 

 should not call on those who hold it, and who show its agreement 

 with things seen, to disprove other theories ; but rather should 

 expect its adversaries to disprove it, and to show firstly, that rain, 

 1 Scrope, "The Geology, etc., of Central France," Ed. 2 (1858), p. 208. 



