GEOGRAPHICAL DISTRIBUTION 14i) 



y.tlantic must have been recently connected with Europe 

 or Africa, and Europe likewise with America. Other au- 

 thors have thus hypothetically bridged over every ocean, 

 and united almost every island with 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 Gordian knot of the dispersal of the 

 same species to the most distant points, and removes 

 many a difficulty; but to the best of my judgment we 

 are not authorized in admitting such enormous geograph- 

 ical changes within the period of existing species. It 

 seems to me that we have abundant evidence of great 

 oscillations in the level of the land or sea; but not of 

 such vast changes in the position and extension of our 

 continents, 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. Whenever it is fully 

 admitted, as it will some day be, that each species has 

 proceeded from a single birthplace, and when in the 

 course of time we know something definite about the 

 means of distribution, we shall be enabled to speculate 

 with security on the former extension of the land. But 

 I do not believe that it will ever be proved that within 

 the recent period most of our continents which now stand 

 quite separate have been continuously, or almost contin- 

 uously, united with each other and with the many exist- 



