1858.] CONTINENTAL EXTENSION. 467 



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 IV. 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 



