412 THE DISTRIBUTION OF ANIMALS AND PLANTS 



tion during all the vast lapse of time between the middle 

 Tertiary and the present period. This is a fact which gives 

 to the oceanic islands the greatest geological interest, and 

 induces us to look into their actual fauna and flora for the 

 representatives of species known on the mainland only as 

 fossils. It is thus that we look to the marsupials of Australia 

 as the nearest analogues of those of the Jurassic of Europe, 

 and that we find in the strange Barramunda (ceratodus) of its 

 rivers the only survivor of a group of fishes once widely distri- 

 buted, but which has long since perished elsewhere. 



Perhaps one of the most interesting examples of this is 

 furnished by the Galapagos Islands, an example the more re- 

 markable that no one who has read in Darwin's fascinating 

 " Journal " the description of these islands, can have failed to 

 perceive that the peculiarities of this strange Archipelago must 

 have been prominent among the facts which first planted in 

 his mind the germ of that theory of the origin of species which 

 has since grown to such gigantic dimensions. It is curious 

 also to reflect that had the bearing of geological history on the 

 facts of distribution been as well known forty years ago as it is 

 now, the reasoning of the great naturalist on this and similar 

 cases might have taken an entirely different direction. 



The Galapagos are placed exactly on the equator, and there- 

 fore out of reach of even the suspicion of having been visited 

 by the glacial cold, though from their isolation in the ocean, 

 and the effects of the currents flowing along the American 

 coast, their climate is not extremely hot. They are 600 miles 

 west of South America, and the separating ocean is in some 

 parts 3,000 fathoms deep. The largest of the islands is 75 

 miles in length, and some of the hills attain an elevation of 

 about 4,000 feet, so that there are considerable varieties of 

 station and climate. So far as is known they are wholly vol- 

 canic, and they may be regarded as the summits of submerged 

 mountains not unlike in structure to the Andes of the main- 



