420 MY LIFE [Chap. 



rapid, which may, indeed, have been so, but which we have 

 no evidence yet to prove. I conceive, therefore, that the 

 immensity of time, measured in years, does not affect the 

 argument. My paper was written too hastily and too briefly 

 to explain the subject fully and clearly, but I hope these 

 few remarks may give my ideas on the point you have 

 especially referred to." 



In 1867, when a new edition of the " Principles of Geology " 

 was in progress, I had much correspondence and many talks 

 with Sir Charles, chiefly on questions relating to distribution 

 and dispersal, in which he, like myself, was greatly interested. 

 He was by nature so exceedingly cautious and conservative, 

 and always gave such great weight to difficulties that occurred 

 to himself or that were put forth by others, that it was not 

 easy to satisfy him on any novel view upon which two opinions 

 existed or were possible. We used often to discuss these 

 various points, but in any case that seemed to him important 

 he usually preferred to write to me, stating his objections, 

 sometimes at great length, and asking me to give my views. 

 In reply to some such inquiries I sent him my paper on the 

 birds of the Lombok to Timor groups, and wrote to him at 

 the same time more fully explaining its bearing, as afterwards 

 given in my " Malay Archipelago." I also wrote him on the 

 curious facts as to the distribution of pigs in the whole 

 archipelago, as illustrated by facts he had himself given 

 showing the remarkable power of swimming possessed by 

 these animals. Another fact he wanted explained was the 

 presence of a few non-marsupial mammals in Australia, and 

 why there were not more of them, and why none were 

 found in the caves. On these points I wrote to him as 

 follows : — 



"My dear Sir Charles, 



" I think the fact that the only placental land 

 mammals in Australia (truly indigenous) are the smallest of 

 all mammals is a very suggestive fact as to how they got 

 there. Mice would not only be carried by canoes, but they 



