32 



THE WONDERS OF GEOLOGY- Lect. I. 



these subterraneous lakes of molten rock are probably 

 isolated ; others may communicate with each other by 

 channels more or less pervious ; and the extensive distri- 

 bution of such sources of heat is supposed to account for 

 the phenomena of earthquakes and volcanoes, and for the 

 constant increase of temperature beneath the surface of the 

 earth, in proportion to the depth that is reached.* 



Lign. 1.— The supposed appf.arance of the earth as seen from the moon. 

 (From Sir H. Be la Beche's Theoretical Geolojy.) 



The earth's surface is computed at 190 millions of square 

 miles; of which three-fifths are covered by seas, and another 

 large proportion by vast bodies of fresh water, by polar ice 

 and eternal snows; so that, taking into consideration sterile 

 tracts, morasses, &c, scarcely more than one-fifth of the 



* See the profound investigations " On the state of the interior of 

 the Earth/' by William Hopkins, Esq. Pltilos. Trans, for 1S39 and 

 1342. 



