86 



FARM DEVELOPMENT 



neath level tracts, there serving as natural sub-irrigat- 

 ing waters to be drawn upward by capillarity, or to be 

 reached direct by the roots of plants. Porous earth, as 

 at D, Figure 35, allows part of the rainfall to sink deeply. 

 This upon reaching a porous layer, as gravel, B, lying 

 upon impervious clay or rock, seeps sidewise, reaching 

 the surface at a lower level, K. Here it may flow out 

 as a spring, or simply seep slowly out, and result in keep- 

 ing the hillside moist, or it may flow down through the 

 open soil in the valley and keep that moist, or it may 

 flow into an open water-bearing stratum with impervious 

 clay or rock both above and below, and lie there with very 

 little movement. In such cases this water is often sub- 

 jected to great pressure, because the head of water above, 



as at B, Figure 36, t \ 



is high. A well sunk 

 into such a vein of 

 water under pressure, 

 makes an opening 

 through which artesian 

 water rises to, or 

 above, the surface of 

 the earth, or oftener 

 only a short distance 

 in the well. 



In regions where the 

 rainfall is not ample, 

 the furrow-slice should 

 be kept as mellow as 

 practicable so as to give easy access to rain water, that 

 none may be lost by flowing off over the surface. An 

 open, loose furrow-slice, four or more inches thick, in a 

 climate with too little rainfall and with dry, hot atmos- 

 phere and drying winds, does much to retard the loss 

 of moisture from the soil by evaporation. The moisture 

 line, under such conditions, rises only to the bottom of 



Figure 36. Shows how water confined between 

 impervious strata, as in A between B and C, is 

 subjected to pressure, making it possible to secure 

 flowing wells, as at D. The water of rains, sinking 

 in the pervious earth to the right of A, flows be- 

 tween the impervious layers. The pressure at any 

 point is sufficient to force the water to rise to a 

 height somewhat less than the height of the water 

 in the region where it enters the soil. 



