AGRONOMY 



swamps, or perhaps it may come to the surface, forming springs. 

 In certain seasons, or in places where there is a stratum of 

 impervious subsoil, there may be saturated areas above the 

 water table that will cause tile drains to run. The real water 

 table, however, lies deeper. It varies with the rainfall, rising 

 in wet seasons and falling in dry ones. We dig our ordinary 



Photograph by II. L. Hollister Land Co. 



FIG. 22. One of the main laterals, or branches, of an irrigation canal 

 From this stream smaller channels lead to the separate fields 



wells down into it, and in dry seasons they may dry up, owing 

 to the lowering of the water table. The fluctuating water 

 level may sometimes affect the character of mineral springs 

 flowing from it, giving them an excess first of one mineral 

 and then of another as the water comes in contact with differ- 

 ent rock strata. Above ground a water surface is level, but 

 in earth the water table curves upward under hills chiefly 

 because the soil retards the downward progress of the free 



