38 The Great World's Farm 



in the Atlantic at certain seasons of the year, and is 

 carried to Europe as far inland as the Tyrol. This dust, 

 which is exceedingly fine, has traveled 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 recog- 

 nized by the North American farmers, who use a similar 

 deposit of "flint-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 prob- 

 ably 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 milhons 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 neighborhood w^as, of course, utterly destroyed, but 

 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 neighborhood 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 yet the fields seem to 

 get it — and that, too, without the drawback of being 

 suffocated every few years. Where does it come from.? 



The wind blows chiefly from the west and southwest,, 

 across the mountain-chain of the Domes. The air on the 



