CHAP. V. AND DENUDATION. 23 



south of France. In China, as Bichthofcn 

 maintains, beds appearing like fine sediment, 

 several hundred feet in thickness and extend- 

 ing over an enormous area, owe their origin 

 to dust blown from the high lands of central 

 Asia.* In humid countries like Great 

 Britain, as long as the land remains in its 

 natural state clothed with vegetation, the 

 mould in any one place can hardly be much 

 increased by dust ; but in its present con- 

 dition, the fields near high roads, where there 

 is much traffic, must receive a considerable 

 amount of dust, and when fields are harrowed 

 during dry and windy weather, clouds of dust 

 may be seen to be blown away. But in all 

 these cases the surface-soil is merely trans- 

 ported from one place to another. The dust 

 which falls so thickly within our houses con- 



* For La Plata, see my ' Journal of Researches,' during the 

 voyage of the Beagle, 1845, p. 133. Elie de Beaumont has 

 given (' Lecons de Geolog. pratique,' torn. 1. 1845, p. 183) an 

 excellent account of the enormous quantity of dust which is 

 transported in some countries. I cannot but think that Mr. 

 Proctor has somewhat exaggerated (' Pleasant Ways in Science,' 

 1879, p. 379) the agency of dust in a humid country like Great 

 Britain. James Geikie has given (' Prehistoric Europe,' 1880, 

 p. 165) a full abstract of Richthofen's views, which, however, 

 he disputes, 



