THE CHILDHOOD OF THE EARTH 



lava reproduce for us, like models in miniature, the great 

 outbreaks of the past. On the largest possible scale 

 similar effects may be seen on the great lava plains of the 

 Moon, where the giant craters that we can see through 

 telescopes are not the mouths of extinct volcanoes, but the 

 banked-up edges and shores of lava outflows. 



On a much smaller scale than this, but still on a 

 gigantic scale, the same thing took place in Western 

 North America, where there are vast tracts of land which 

 are best to be explained by supposing that there were 

 once great outbreaks and overflows. The area which has 

 there been flooded with lava has been estimated to be 

 larger than that of France and Great Britain put to- 

 gether, and the depth of the total mass erupted reaches 

 in some places as much as 3700 feet. Some rivers have 

 cut gorges in this plain of lava, laying bare its com- 

 ponent rocks to a depth of 700 feet or more. Along 

 the walls of these ravines we see that the lava is arranged 

 in parallel beds or sheets often not more than ten or 

 twenty feet thick, each of which, of course, represents a 

 separate outpouring of molten rock. 



These are comparatively modern lava plains, although, 

 of course, the outpourings in North America occurred ages 

 before historic time, or, indeed, before there are any 

 traces of man^s existence on the earth. Such lava out- 

 flows can only occasionally be examined as in the 

 instance just quoted when rivers have cut deep into them. 

 Consequently we have to speculate on the connection 

 between the dykes and fissures and the lava flood itself. 

 But in various parts of the world lava plains of much 



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