GEOLOGY. 647 



precipitate themselves to the bottom of an immense gulf 

 with a roar which seems to shake the surrounding rocks; 

 in other cases, as in the falls of the Zambesi, the river 

 divides into several bodies and forms a series of whirlwinds 

 of vapour, which, like Avaving columns, rise towards the 

 clouds and fall in fine rain. 



