408 



INSULAR FLORAS AND FAUNAS WITH 



[Ch. XLI. 



4 - 



from 



Miocene 



Made 



seen^ is near the line C D^ which, expresses a depth of 10 000 

 feet, and the same may be said of the eastern portion of the 

 Canarian archipelago. On the western side of this last the 

 ocean has a depth of several thousand feet^ dividinc^ Fnerta- 

 Ventura and Lanzerote from the mainland. The general 

 abruptness of the cliffs of all the Atlantic islands^ coupled 

 with the rapid deepening of the sea outside the 100 fathom 

 line, are characters which favour the opinion that each island 

 was formed separately by igneous eruptions in a sea of great 

 depth. JSTo geologist can doubt that the beds of lava and 

 volcanic ash originally sloped down gradually towards the 

 shore, and that the abrupt precipices now so general and often 

 from 1,000 to 2^000 feet in perpendicular height facing the 



underminin 



t? 



waves. 



/ 



From 



modern 



basin of the Atlantic, we can be at no loss to conceive tlie 

 manner in wliicli sucli groups as the Azores or Canaries 



originated . 



I have already mentioned that the foundations 

 of a future archipelago seem now in the act of being laid 

 midway between St. Helena and Ascension, which are about 

 600 miles distant from each other.^ Here in mid-ocean no 



m 



ubmarine 



eruptions are occasionally wit- 

 nessed. On this spot, so far out of sight of land, we may 

 expect on some future day that a cone and crater will be 

 built up as was Sabrina in 1811, in the sea off St. Michael's, 



1831t 



Medite 



rose up in a deep part of the 

 from the nearest land, the south coast of Sicily. Although 

 both these islands were gradually swept away by the waves, 

 they have left reefs of solid rock in that part of the sea from 

 which, on some future occasion, a new volcanic cone may 



arise. 



^ See abovcj p. 04. 



t See above, p. 60. 



