270 TOILERS IN THE SEA. 



them as crowning the submerged summits of extinct 

 volcanoes. The lagoon in the centre corresponded 

 to the crater of the volcano, and the belt of land 

 encircling the lagoon was the rim of the crater. 

 This theory was rendered the more probable from 

 the volcanic nature of the region in which the best 

 known atolls had been found. This was the only 

 theory which held any position in the world when 

 Darwin announced his hypothesis. The objections to 

 the volcanic theory have been summarised by Dana : 



(1) The volcanic cones must either have been sub- 

 aerial, and then have afterward sunk beneath the 

 waters, or else they were submarine from the first. 

 In the former case the crater would have been de- 

 stroyed, with rare exceptions, during the subsidence ; 

 and in the latter there is reason to believe that a 

 distinct crater would seldom, if ever, be formed. 



(2) The hypothesis moreover requires that the 

 ocean's bed should have been thickly planted with 

 craters, seventy in a single archipelago, and that 

 they should have been of nearly the same elevation, 

 for, if more than twenty fathoms below the surface, 

 corals could not grow upon them. But no records 

 warrant the supposition that such a volcanic area 

 ever existed. The volcanoes of the Andes differ 

 from 1 ,000 feet to 10,000 feet in altitude, and scarcely 

 two cones throughout the world are as. nearly of 

 the same height as here supposed. Mount Loa and 



