18431882] INSULAR FLORAS 487 



say I incline to your theory, but I cannot accept it as an Letter 369 

 established truth or unexceptionable hypothesis. 



The " Wire bird ' being a Grallator is a curious fact 

 favourable to you. . . . How I do yearn to go out again to 

 St. Helena. 



Of course I accept the ornithological evidence as tremen- 

 dously strong, though why they should get blown westerly, 

 and not change specifically, as insects, shells, and plants have 

 done, is a mystery. 



To J. D. Hooker. Letter 370 



Down, Aug. 8th [1866]. 



It would be a very great pleasure to me if I could think 

 that my letters were of the least use to you. I must have 

 expressed myself badly for you to suppose that I look at 

 islands being stocked by occasional transport as a well-estab- 

 lished hypothesis. We both give up creation, and therefore 

 have to account for the inhabitants of islands either by con- 

 tinental extensions or by occasional transport. Now, all 

 that I maintain is that of these two alternatives, one of which 

 must be admitted, notwithstanding very many difficulties, 

 occasional transport is by far the most probable. I go thus 

 far further that I maintain, knowing what we do, that it 

 would be inexplicable if unstocked islands were not stocked 

 to a certain extent at least by these occasional means. 

 European birds are occasionally driven to America, but far 

 more rarely than in the reverse direction : they arrive via 

 Greenland (Baird) ; yet a European lark has been caught in 

 Bermuda. 



By the way, you might like to hear that European birds 

 regularly migrate via the northern islands to Greenland. 



About the erratics in the Azores see Origin, p. 393. 1 

 Hartung could hardly be mistaken about granite blocks on 

 a volcanic island. 



I do not think it a mystery that birds have not been 



1 Origin, Ed. vi., p. 328. The importance of erratic blocks on the 

 Azores is in showing the probability of ice-borne seeds having stocked 

 the islands, and thus accounting for the number of European species and 

 their unexpectedly northern character. Darwin's delight in the verifica- 

 tion of his theory is described in a letter to Sir Joseph of April 26th, 1858, 

 in the Life and Letters, II., p. 112. 



