vi] OF EVOLUTION 59 



Catastrophist invoked, it would be wiser at present to 

 1 doubt and not dogmatise.' 



To what extent the MS. of the Principles, sent 

 to the publisher in 1827, was added to and altered 

 two years later, we have no means of knowing ; but 

 that the work was to a great extent rewritten would 

 appear from a letter sent to Murchison by Lyell, just 

 before his return to England. In it, he says : 



1 My work is in part written, and all planned. It 

 will not pretend to give even an abstract of all that 

 is known in geology, but it will endeavour to establish 

 the principle of reasoning in the science ; and all my 

 geology will come in as illustration of my views of 

 those principles, and as evidence strengthening the 

 system necessarily arising out of the admission of 

 such principles, which, as you know, are neither more 

 nor less than that no causes whatever have from the 

 earliest time to which we can look back to the present, 

 ever acted, but those that are now acting, and that 

 they never acted with different degrees of energy 

 from that which they now exert'; but in 1833, in 

 dedicating his third volume to Murchison, he refers 

 to the MS., completed in 1827, as a ' first sketch 

 only of my Principles of Geology 61 ' 



At one period, Lyell contemplated again delaying 

 publication till he had visited Iceland. In the end, 

 however, after declining to act as professor of geology 

 in the new ' University of London '(University College), 



