214 THE LURE OF THE LAND 



age, and which, by reason of the slope or contour of the 

 land, run off over the surface, carrying along particles 

 of sand and clay. When this water accumulates in a 

 depression in the field the force of the torrent may be 

 sufficient to cut out a great gully in a short space of 

 time. 



" The extent of washing to which the soil is exposed 

 depends upon the quantity of rainfall in a given time, 

 the slope or contour of the surface, the texture of the 

 soil, the vegetative covering of the surface, and the kind 

 and condition of cultivation. A soil composed chiefly 

 of moderately coarse grains of sand, and having good 

 underdrainage, will absorb the heaviest rainfall without 

 much danger of surface erosion. A sandy-clay soil, 

 on the other hand, into which the water can not perco- 

 late with anything like the rapidity of the precipita- 

 tion, will be washed and gullied by the torrent of water 

 which must flow over the surface. 



CHEMICAL RELATIONS OF THE SOIL TO SURFACE WASHING. 



" It has been repeatedly shown by experiments and 

 by the experiences of farmers that a soil, as a rule, 

 absorbs water more readily as the content of organic 

 matter and of humus increases. Surface erosion can,, 

 therefore, be largely prevented by such a system of 

 cultivation and cropping as will introduce as large a 

 quantity of organic matter into the soil as possible. A 

 very old method of recovering washed and gullied lands 

 is to place straw in the furrows while plowing, the 

 straw not only acting mechanically to hold the soil in 

 place and prevent surface erosion, but also in a very 

 efficient way to increase the quantity of humus, thus 

 making the soil hold large quantities of water which 

 otherwise would have passed off over the surface. In 



