CHAP, xri OCEANIC ISLANDS 247 



temperate zone, and they differ less than six degrees 

 in latitude, yet the vegetation of the one is wholly 

 temperate, while that of the other is almost tropical. 

 The productions of the one are related to Europe, as those 

 of the other are to America, but they present instructive 

 differences ; and both afford evidence of the highest value 

 as to the means of dispersal of various groups of organisms 

 across a Avide expanse of ocean. 



THE AZORES, OR WESTERN ISLANDS. 



These islands, nine in number, form a widely scattered 

 group, situated between S?'' and 39° 40' N. Lat. and 

 stretching in a south-east and north-west direction over a 

 distance of nearly 400 miles. The largest of the islands, 

 San Miguel, is about forty miles long, and is one of the 

 nearest to Europe, being rather under 900 miles from the 

 coast of Portugal, from which it is separated by an ocean 

 2,500 fathoms deep. The depth between the islands does 

 not seem to be known, but the 1,000 fathom line encloses 

 the whole group pretty closely, while a depth of about 

 1,800 fathoms is reached within WO miles in all directions. 

 These great depths render it in the highest degree improb- 

 able that the Azores have ever been united with the 

 European continent ; while their being wholly volcanic is 

 equally opposed to the view of their having formed part of 

 an extensive Atlantis including Madeira and the Canaries. 

 The only exception to their volcanic structure is the 

 occurrence in one small island only (Santa Maria) of some 

 marine deposits of Upper Miocene age — a fact which 

 proves some alterations of level, and perhaps a greater 

 extension of this island at some former period, but in no 

 way indicates a former union of the islands, or any greater 

 extension of the whole group. It proves, however, that 

 the group is of considerable antiquity, since it must date 

 back to Miocene times ; and this fact may be of im- 

 portance in considering the origin and peculiar features of 

 the fauna and flora. It thus appears that in all physical 

 features the Azores correspond strictly with our physical 

 definition of " oceanic islands/' while their great distance 



