54 THEORY OF THE EARTH. 



while the less fluid portion stops at the edge of 

 the opening, raises it all round, and forms a cone 

 terminated by a crater. Thus volcanoes accumu- 

 late substances on the surface that were formerly 

 buried deep in the bowels of the earth, after having 

 changed or modified their nature or appearances, 

 and raise them into mountains. By these means, 

 they have formerly covered some parts of the con- 

 tinents, and have suddenly produced mountains in 

 the middle of the sea. But these mountains and 

 islands have always been composed of lava, and 

 the whole of their materials have undergone the 

 action of fire. Volcanoes have never raised up 

 nor overturned the strata through which their aper- 

 tures pass, and have in no degree contributed to 

 the elevation of the great mountains which are not 

 volcanic. 



Thus we shall seek in vain among the various 

 forces which still operate on the surface of our 

 earth, for causes competent to the production of 

 those revolutions and catastrophes of which its ex- 

 ternal crust exhibits so many traces : And if we 

 have recourse to the constant external causes with 

 which we have been hitherto acquainted, we shall 

 have no greater success. 



