30 THE story of 1111: EARTH. 



mir. ridotite, to t 1 



in which if onstituent. Th 



tion 



s of the basalt family sometii 



s -sid< o ilumns, 

 miliar in the island of Staffa, and 

 ay in the north of I A 



lava ti« i • imes d 'ii its floor and a 



: and two independent - 

 olumns of different sizes may thei 

 tned, separated by a crystalline part in the 

 midd 



h of these kinds of lava may a 



ted by fragmental rocks, having tl I of 



dust. In past periods of 

 time, beds of vol< anic agglomerate, of ashes, and 



mmon in association with 



compact lava-. In North Wales, among the 



the ashes are enormously thick in 



I • :• B, A: an Mouddwv and Arenig inoun- 

 little doubt that tin- ash 



tnic throats aeai D< g< 



In • Its near 



at Po< • mbc ai e m 

 by the n ind. And , i -mbc the lava flow 



is highl th the filled with 



•ion 



w in these old h 



< c bet v 



] i 1 1 1 1 o 1 1 i i 

 . whit h 



