The Origin of Soil 



decomposition of vegetable substances. To 

 give you an idea of the causes which from 

 the remotest times have fertilised the dust of 

 the rock, we will limit ourselves to the 

 following example. 



Geography has taught you something about 

 a volcano. It is a mountain, the summit of 

 which is hollowed out into an immense 

 excavation forming a funnel. At times in the 

 vicinity of a volcano the earth quakes ; 

 formidable noises, like the rolling of thunder, 

 or the reports of cannon, resound in the 

 depth of the mountain. The crater throws 

 up to the sky a tall column of smoke — dark 

 in the daylight, fiery red at night. Suddenly 

 the mountain is rent open, and from its 

 crevices a river of fire, a flow of molten rocks, 

 pours out. After a time the volcano quiets 

 down and the source of the terrible stream 

 dries up. The lava itself is arrested and leaves 

 off flowing, and after a period which may last 

 for years, is completely cooled. Now what will 

 become of this enormous bed of black cavern- 

 ous stone, like the hearth of a blacksmith's 

 forge ? What will this sheet of lava produce, 

 covering a surface of several square miles ? 



This desolate, accursed surface seems des- 

 tined never to be clothed in green. But that 



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