THE STORY OF THE ISLANDS. 219 



thus separated from Portugal by sea varying from 

 2000 to 2500 fathoms. Within a short distance from 

 the islands themselves, the sea is about 1000 fathoms 

 deep; within 300 miles it is 1800 fathoms, and soon 

 deepens to 2500. With the Bermudas the case is 

 similar : some 450 miles off, we reach the sea-bottom 

 at 3825 and 3875 fathoms. St. Helena has sea of 

 2860 fathoms deep between it and Africa, some I TOO 

 miles off. Contrariwise, the sea around our own 

 shores is comparatively shallow ; but, as I have 

 remarked, whenever a continental island shows, like 

 Madagascar, a deep channel between it and its main- 

 land, the story such depth tells us is one of long 

 detachment from the mother-country. 



So far, islands have shown us that, geologically, 

 their history is interesting in respect of the marked 

 variation between the two classes. Not less interest- 

 ing is the additional evidence about islands which their 

 animals and plants have to tell. Whence, let us ask, 

 have detached islands, like the Azores, obtained their 

 animals and plants ? Upraised from the sea-bed, as 

 were these islands, their living population must have 

 been derived from other and previously peopled 

 lands. This supposition is confirmed by our finding 

 that on the Azores we discover no animals or plants 

 excluding those of man's introduction which are 

 not found on the Portuguese coast. 



The rabbits, weasels, mice, and a single kind of 

 lizard, found in the Azores, are importations. The 

 birds which, of course, can fly over the intervening 

 sea, are those of Europe ; such also are the insects ; 

 and such, again, are the plants. In a word, there is 

 nothing about the animals and plants of the Azores 

 which we cannot explain by a reference to their 



