IG TRELIMINARY INQUIRIES. 



colonizntion occurs in many (probablj^ In all) I am ready to admit ; and from instances to be afterwards 

 noticed, I am disposed to reckon the proportions of such intermixtures in the flora, in the most 

 favourable circumstances, at not more than two per cent. In the fauna I think it must be much 

 less. 



As the question is a most important one in relation to geographical distribution, and Mr. 

 Darwin's view strikes at the root of a great portion of the propositions which I shall have to submit 

 to the reader in this work, I must consider his arguments in some detail. 



" Edward Forbes (saj's he) insisted that all the islands in the Atlantic must recently have been 

 connected vnth Europe or Africa, and Europe likewise with America. Other authors have thus hj'po- 

 thetically bridged over everj^ ocean, and have miited almost everj' island to some mainland. If, 

 indeed, the arguments used by Forbes are to be trusted, it must be admitted that scarcely a single 

 island exists which has not recently been united to some continent. This view cuts the Gordiau Icnot 

 of the dispersal of the same species to the most distant points, and removes manj^ a difRcidty. But to 

 the best of my judgment we are not authorized in admitting such enormous geogra^jhical changes 

 within the j)eriod of existing species. It seems to me that we have abundant evidence of great oscil- 

 lations of level in our continents, but not of such vast changes in their position and extension as to 

 have united them within the recent period to each other, and to the several intervening Oceanic 

 Islands. I freely admit the former existence of many islands now buried beneath the sea, which may 

 have served as halting-places for plants, and for many animals during their migration. In the coral- 

 producing oceans such sunken islands are now marked by rings of coral or atolls standing over them. 

 A^Hienever it is full}' admitted, as I believe it ivill some daj^ be, that each species has proceeded from 

 a single birth-place, and when, in the coui-se of time, we know something definite about the means of 

 distribution, we shall be enabled to speculate with secm-itj' on the former extension of the land. But I 

 do not believe tliat it will ever be proved that within the recent period continents which are now quite 

 separate have been continuously, or almost continuously, united with each other, and with the manj^ 

 existing Oceanic Islands. Several facts in distribution — such as the great difference in the marine 

 Faunas on the opposite side of almost every continent — the close relation of the tertiary inhabitants 

 of several lands, and even seas, to their present inhabitants — a certain degree of relation (as we shall 

 hereafter see) between the distribution of mammals and the depth of the sea — these, and other such 

 facts, seem to me opposed to the admission of such prodigious geological revolutions within the recent 

 period as are necessitated on the view advanced by Forbes, and admitted by his many followers. The 

 nature and relative proportions of the inhabitants of Oceanic Islands like-^-ise seem to me opposed to the 

 belief of their former continuity with continents." And in another place he thus siuns up : " All the 

 foregoing remarks on the inhabitants of Oceanic Islands — namely, the scarcity of kinds, — the richness 

 in endemic forms in particular classes, or sections of classes, — the absence of whole groups, as of batra- 

 chians and of terrestrial mammals, notwithstanding the presence of aerial bats, — the singular proportions 

 of certain orders of plants, herbaceous forms ha\ing been developed into trees, &c. — seem to me to 

 accord better with the view of occasional means of transport having been largely efficient in the long 

 course of time, than with the view of all oiu- Oceanic Islands having been formerly connected by con- 

 tinuous land with the nearest continent : for, on this latter \aew, the migration would probably have 

 been more C(jmplete : and if modification bo admitted, all the forms of life woidd have been more equally 

 modified, in accordance with the jiaramount importance of the relation of organism to organism."* 



* Darwin, op. cit. p. 427. 



