48 ' Soil-Carriers 



This dust, which is exceedingly fine, has travelled 

 thousands of miles on the wings of the wind, the greater 

 part of it having been borne across the Atlantic from 

 the banks of the Orinoco and Amazons. Its value as a 

 fertilizer is recognised by the North American farmers, 

 who use a similar deposit of ' ilint-earth ' to mix with 

 some of their heavy soils. Very fertilizing also must be 

 the volcanic dust, which, being carried high up into the 

 air, at times probably far above the cloud-region, is 

 conveyed enormous distances before it finally sinks to 

 the earth. 



The most tremendous volcanic outburst on record is 

 that of Krakatoa in 1883, when millions of tons of 

 matter were hurled into the upper air, and dust, to 

 the depth of two inches, fell a thousand miles off. 

 The vegetation of the neighbourhood was, of course, 

 utterly destroyed, being deeply buried in ashes and 

 pumice-dust; but the great farm is so extensive that 

 occasional ruin here and there is of little moment 

 compared with the benefits which follow in the long 

 run, especially when the ravages made are so quickly 

 repaired as they sometimes are. In this instance it 

 took less than five years to cover up the dismal scene 

 of desolation with a fresh growth of tropical luxuriance. 

 Just so Vesuvius is said to smother and destroy the 

 crops in its neighbourhood every eighth year ; but it is 

 this very fact which makes the soil so wondrously 

 fertile during the other seven. 



However, we are concerned just now chiefly with 



the work done by the wind, and must glance at one 



' curiously interesting sample of it which has been 



observed in the valley of the Limagne, in Auvergne. 



Here there is no active volcano to furnish dust, and 



