Page:The Formation of Vegetable Mould through the Action of Worms (1881).djvu/251

 south of France. In China, as Richthofen maintains, beds appearing like fine sediment, several hundred feet in thickness and extending 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 condition, 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 transported from one place to another. The dust which falls so thickly within our houses