32 ENGINEERING FOR LAND DRAINAGE. 



drained soil thaws earlier in the spring. The warm 

 surface air enters, and the soil becomes fitted for culti- 

 vation several days earlier than one which contains too 

 much water. 



Heaving of Soils. 



One great benefit derived from proper drainage is 

 that soils do not heave to such an extent as to injure 

 plants. When soils which are saturated with water 

 freeze, the water expands about one eighth in volume, 

 and as a result the surface of the soil is raised, carrying 

 with it plant-roots which are not anchored below the 

 frost line. A thaw melts the ice, and the soil under 

 ordinary conditions settles back to its original position, 

 but plants with shallow rooting remain in their raised 

 position. Alternate freezing and thawing, which take 

 place in some localities several times during the winter, 

 not infrequently leave the roots of clover, wheat, and 

 rye partially or wholly out of the ground. Fields of 

 clover and wheat have been ruined in this way, and 

 meadows of timothy and orchard-grass have been 

 greatly injured during one winter. If the soil is not sat- 

 urated, that is, if there is air space in it and the moist- 

 ure has sufficient space for expansion when it freezes 

 without materially disarranging the soil grains, no such 

 injurious effects as have been named will follow. The 

 heaving effect of frost upon soils may be demonstrated 

 in an interesting way by the following experiment. 

 Before the ground freezes in the fall drive pegs of about 

 one inch section and six inches long flush with the sur- 

 face of the ground, some in soils well drained, and 



