.':!28 THE BOTTOM OF TUB SEA. 



ejected ; during the second, basalts. If a volcano which 

 vomits lava is in repose, we may always expect a 

 new eruption. When, however, the lava is succeeded 

 by basalt, we may be equally sure the volcano is on 

 the eve of extinction. We must, therefore, be careful 

 not to pronounce too absolutely as to the marine 

 origin of volcanic products from their nature and 

 aspect. 



8. Bottom of the Sea brought to light in consequence of the Eruptiou 

 of "feubmarine Volcanoes. 



If a mountain belching fire is lifted above the 

 level of the sea by the action of some subterranean 

 fire, it carries with it the marine formations to which 

 it had served as a support. The same expansive force 

 acting upon a larger scale, and not limiting its effects 

 to the elevation of tlie mountain, will raise to the light 

 of day a more extende 1 region of the submarine world, 

 with all the layers of debris, sometimes of very ancient 

 formation, which cover it. 



This is what we observe to have happened in 

 Mauritius and two neighbouring islands. The con- 

 figuration of the northern part of Mauritius is that of 

 a level plane, formed of a recent calcareous rock, com- 

 posed of polypi analogous to the coral. It covers the 

 volcanic rocks which elsewhere form the summits of 

 the island. The superposition of madrepores and 



