DOMESTIC WATER SUPPLIES FOR THE FARM 



FlG. 26. Map showing position of water-table by contours (continuous lines), lines 

 of motion of ground water (arrows) and surface streams. (Slichter.) 



nature of the water-bearing passages, are far more irregular than 

 those in porous materials, in which motion is possible in any 

 direction. In granites, the water is found mainly in joints and 

 can move only in the direction in which the joint planes extend. 

 In shales, it is the cleavage planes that furnish the chief passages 

 for water, and, as these all extend in one direction, the water can 

 commonly move only in one way. In sandstones, water may 

 move in any direction that the bed extends. In limestones, solu- 

 tion channels carry practically the whole of the available water, 

 and, notwithstanding their great irregularity, they commonly 

 have fairly definite trends from the highlands towards the 

 valleys. 



Although the specific direction of movement of the rock 

 waters is controlled by the structural features of the rocks the 

 general movement of the shallower supplies, or those lying above 

 the level of the drainage in the valleys, is very similar to that of 

 the ordinary ground water, the flow trending towards the adjacent 

 valleys in almost every case. It is at such points that supplies 

 will be most easily reached by wells. 



