448 EEACTION OF THE INTERIOR OF THE EARTH. 



frameworks, but from a network of fissures on the 

 earth's surface, from which they have poured forth, 

 often forming, as it were, strata covering an extent of 

 many square leagues. We are probably to include 

 among these phenomena the old masses of trap of the 

 lower Silurian formation of the south-west of England, 

 by whose exact chronometric determination my illus- 

 trious friend Sir Roderick Murchison has so greatly 

 enlarged the scope and heightened the character of our 

 knowledge of the geological construction of the globe, 



