and an the Origin of the Valleys of Auvergne, 203 



Such a notion, indeed, would be quite at variance with the 

 general tenor of my work on Volcanos, the express object of 

 which was to shew, that the same causes which produce volcanic 

 phenomena at the present moment, operating at some former 

 period on a greater scale, but always agreeably to the same sys- 

 tem, have had an important share in preparing the earth's sur- 

 face for the abode of the existing races of animals *. 



It is, however, true, that certain writers, whose opinions I 

 have quoted rather than adopted at the commencement of the 

 work in question, embarrassed by the difficulties they encoun- 

 tered in their attempts to explain the phenomena alluded to by 

 the operation of present agents, and perhaps not sufficiently 

 considering the still greater objections to the supposition of a 

 change having taken place in the course of nature, may have 

 laid themselves open to Mr Ly ell's criticisms, by adopting the 

 opinions of earlier naturalists with respect to a want of con- 

 formity in the physical constitution of the earth during ancient 

 and modern times. . 



Hence, in order to enable others to form a candid estimate of 

 the comparative merits of the views of Mr Lyell with respect to 

 the excavation of valleys, and those of the Diluvianists, it seems 

 important that we should do away with the prejudice that would 

 operate against the latter, from associating them with this hypo- 

 thesis ; and it may therefore be worth while to shew that no ne- 

 cessary connexion exists between the two, but that all the postu- 

 lates of the diluvial theory may be resolved into the operation of 

 known agents, acting according to laws at present recognised -j*. 



It will doubtless be considered as so far favourable to this 

 system, if it can be proved, that it supposes no other catastro- 

 phes or revolutions to have taken place, than such as would na- 



• Similar, too, have been the conclusions to which I have since been led 

 by my researches on the presence of iodine and bromine in the salt-springs 

 of this country, as it appears from the results I have obtained, that the con- 

 stituents of the earliest seas, such for instance as existed at the time of the 

 transition formation, were precisely the same as those of the present day, 

 and, consequently, that the laws of nature in this respect have continued from 

 the first unchanged. — See Phil. Trans, for 1830. 



f Having written the greater part of this letter whilst on the continent, I 

 was not aware that Mr Conybeare had already entered a protest, in the An- 

 nals of Philosophy for October last, against the notion, that in the diluvial 

 theory the operation of a different system of causes is necessarily implied. 



o2 



