454 dr. f. b. white on the [May 7, 



arctic character of the fauna ; and, 2, the road by which it came ; 

 but these will be most conveniently treated of together. 



St. Helena is, as has been already said, a small island of ancient 

 volcanic origin, very distant from any continent, and surrounded by 

 very deep sea. The nearest land is Ascension Island, 698 miles 

 north-west of St. Helena ; and nearly double that distance uorth of 

 Ascension lie the Cape-Verd Islands. Improbable as it may 

 seem to many, this is the route by which, I think, the aboriginal 

 fauna reached St. Helena. 



But it is not necessary to believe that the colonists crossed such 

 wide stretches of ocean. "Stepping-stones," in the shape of other 

 islands, doubtless existed ; and, in fact, we can trace the remains of 

 some of them. For, deep as is the ocean round St. Helena, a some- 

 what shallower sea (still, however, very deep) extends between it 

 and Ascension, and is continued north to the equator, where a yet 

 shallower place is to be found, not more than 700 or 800 miles from 

 the Cape-Verd Islands. It seems not only possible but extremely 

 probable that in this equatorial shoal we have the wreck of an island ; 

 and as the line indicated coincides with an area of depression as well 

 as of volcanic action (extending more or less from Iceland to Trinidad 

 and Tristan d'Acunha), there is no reason why other islands should 

 not have existed, of which (as Mr. Darwin says) " not a wreck now 

 remains." 



It may be argued against this theory that, if it were probable, then 

 Ascension should have a larger native fauna than it at present pos- 

 sesses ; but, as far as I can learn, the present Ascension is of com- 

 paratively recent origin, and supplies an argument in favour of my 

 view that volcanic action has made great alterations in the sup- 

 posed line of route. If (as seems probable) the present Ascension 

 is comparatively recent, it by no means follows that an older island 

 did not once occupy its place and possess a larger fauna than its suc- 

 cessor, which has been possibly colonized from St. Helena. (I may 

 here call attention to Mr. Melliss's remarks 1 , that Sterna fuliginosa 

 does not remain all the year at St. Helena, but probably migrates to 

 Ascension, returning to St. Helena at the end of the year. If there is 

 any thing in Mr. Wallace's theory that the lines of migration of birds 

 often coincide with ancient land-connexion 2 — which, however, Colonel 

 Drummond Hay has shown 3 to be by no means invariably the case — 

 then this would seem to point at some closer connexion in former 

 times between St. Helena and Ascension.) 



But even assuming that the supposed requisite intermediate islands 

 existed, it is necessary to find some means by which the tide of emi- 

 gration was induced to flow towards St. Helena. 



At the present time both the ocean-currents and the prevailing 

 winds would tend to lessen, if not, as seems more probable, to 

 entirely prevent, emigration in that direction, even if the " stepping- 

 stone " islands still existed. The S.E. trade is the prevailing wind ; 

 and the great Agulhas current sweeps past St. Helena from the 



1 L.c. p. 98. 2 Geographical Distribution of Animals, i. p. 22. 



» Scottish Naturalist, 1877-78. 



