VOLCANOES AND 



will at length become easier towards the ocean by the 

 forcing up of ridges or volcanoes along the other margin 

 of the trough. Ridges with peaks in them will usually 

 result, and this is the beginning of a new range of 

 mountains in the sea, which are destined to rise slowly 

 from it parallel to the great range of mountains on 

 the shore. There may thus be two parallel ridges, 

 perhaps hundreds of miles apart, with a valley between 

 them. This valley may be drained in the course of 

 ages, or filled in by the processes of erosion which we 

 have described in the earliest chapters of this volume. 



It will be of interest to quote at this point what 

 Pliny nearly two thousand years ago said in his Natural 

 History (Book II) on islands which have been uplifted 

 from the Mediterranean, evidently as the result of 

 volcanic causes : 



"Land is sometimes formed in a different manner, 

 rising suddenly out of the sea, as if nature was com- 

 pensating the earth for its losses, restoring in one place 

 what she had swallowed up in another. Delos and 

 Rhodes, islands which have now been long famous, are 

 recorded to have risen up in this way. More lately 

 there have been some smaller islands formed : Anapha, 

 which is beyond Melos ; Nea, between Lemnos and the 

 Hellespont; Halone, between Lebedos and Teos; Thera 

 and Therasia, among the Cyclades, in the fourth year 

 of the 135th Olympiad. And among the same islands, 

 130 years afterwards, Hiera, also called Automate, made 

 its appearance ; also Thia, at the distance of two stadia 

 from the former, 110 years afterwards, in our own times, 



192 



