46 Soil-Carriers 



labours. As is well known, the beaver is in the habit 

 of building dams ; and these are often so solid and 

 extensive as to stop up the streams and rivers in 

 which they are constructed, causing them to over- 

 flow and form shallow lakes. 



But local floods were only the first result of its 

 work; for the streams brought down with them the 

 usual sediment, which was spread over the inun- 

 dated surface, gradually raising its level, until the lake 

 became a marsh covered with marsh-plants. Then, 

 as the sediment still accumulated, the marsh-plants 

 by degrees found the situation too dry for them, and 

 died off; their places were then taken by grasses, and 

 the lakes were thus converted into meadow land, 

 fertile, as river-formed soils usually are, and enriched 

 by the decay of the marsh plants. 



The value of river-mud is abundantly seen in Egypt ; 

 and in Hungary the br^ d river Theisz is left uncon- 

 trolled by dikes in its upper part, because the yearly 

 spring-floods which lay the whole neighbourhood under 

 water, though inconvenient, are found to be of such 

 great benefit to the soil. 



Rivers, then, must be reckoned among the most 

 important makers and carriers of soil. But the wind, 

 too, does much good service, though also occasional 

 damage, from man's point of view, as nature's labourers 

 are apt to do, in these disorganized days. 



On the Lincolnshire Wolds, for instance, and on the 

 coast of Norfolk, where the soils are light and sandy, 

 the whole of the finer portion, as well as the seed sown, 

 is sometimes altogether blown away by the equinoctial 

 gales. One field near Cromer was sown three times in 

 the course of a single spring, and was finally left to 



