PEEFACE. 9 



to allude to subjects on which there is much diversity 

 of opinion ; to some that are usually approached with 

 uneasy tenderness, as coming in conflict with prevalent 

 beliefs ; and to others on which the united labours of 

 Geologists, during the last fifty years, have thrown but 

 little reliable light or information. In either case he 

 has expressed his opinions freely, but without dogma- 

 tism ; firmly, but solely under the warrant of Geology ; 

 and always with a frank admission of the many defi- 

 ciencies and imperfections of that science. As there 

 is nothing to be gained by offending a prejudice where 

 we cannot establish a conviction, he has contented 

 himself by stating what Geology affirms, without allud- 

 ing to what it appears to contradict ; and as the estab- 

 lishment of truth does not always follow the overturn- 

 ing of error, the expounder of science may surely be 

 permitted to attempt the one without hazarding an 

 endeavour to accomplish the other. In approaching 

 our subject, therefore, a subject too often treated as 

 if it lay beyond the pale of natural law, let it be 

 clearly understood that we are dealing with Life solely 

 in its geological aspects. We appeal unto Caesar ; 

 let us be judged by Ctesar's laws. 



GILMORE PLACE, EDINBURGH, 

 February 1861. 



