1858.] CONTINENTAL EXTENSION. ^^j 



sub-fossil. In the Pacific Islands there are cases of identity, 

 which I cannot at present persuade myself to account for by 

 introduction through man's agency ; although Dr. Aug. Gould 

 has conclusively shown that many land-shells have thus been 

 distributed over the Pacific by man's agency. These cases of 

 introduction are most plaguing. Have you not found it so in 

 the Malay Archipelago .'' It has seemed to me in the lists of 

 mammals of Timor and other islands, that several in all prob- 

 ability have been naturalised. . . . 



You ask whether I shall discuss " man." I think I shall 

 avoid the whole subject, as so surrounded with prejudices ; 

 though I fully admit that it is the highest and most interesting 

 problem for the naturalist. My work, on which I have now 

 been at work more or less for twenty years, will not fix or 

 settle anything; but I hope it will aid by giving a large col- 

 lection of facts, with one definite end. I get on very slowly, 

 partly from ill-health, partly from being a very slow worker. 

 I have got about half written ; but I do not suppose I shall 

 published under a couple of years. I have now been three 

 whole months on one chapter on Hybridism ! 



I am astonished to see that you expect to remain out three 

 or four years more. What a wonderful deal you will have 

 seen, and what interesting areas — the grand Malay Archi- 

 pelago and the richest parts of South America ! I infinitely 

 admire and honour your zeal and courage in the good cause 

 of Natural Science ; and you have my very sincere and cordial 

 good wishes for success of all kinds, and may all your theories 

 succeed, except that on Oceanic Islands, on which subject I 

 will do battle to the death. 



Pray believe me, my dear sir, yours very sincerely, 



C. Darwin. 



C. Darwin to W. D. Fox. 



Feb. 8th [1858]. 



... I am working very hard at my book, perhaps too 

 hard. It will be very big, and I am become most deeply 

 interested in the way facts fall into groups. I am like Croesus 



