SOIL PHYSICS 471 



When a vein of water is struck, it is always found in a layer of 

 sand and gravel, or some other open, porous soil; it is always a 

 layer which allows the ground-water to percolate easily through 

 it. Figure 286 represents an ideal case. The soil above and 

 below the bed of gravel, A, is so fine in texture that water 

 passes through it slowly. Therefore neither well No. 1 nor 

 well No. 2 receives water freely from it. But the gravel bed, 

 or GRAVEL POCKET as the geologists call it, increases immensely 

 the exposed surface of the well. This pocket of gravel per- 

 forms exactly the same function for this well No. 1, as the in- 

 filtration-gallery performs for the well in Fig. 281. Well No. 2 

 would evidently have to be extended till it reached gravel bed, 

 B, before it could be supplied with water from any other source 

 than from the clay. It is evident, then, that a vein of water is 

 merely a vein of sand or gravel, porous soil, through which the 

 ground-water percolates rapidly. The trouble with a poor well 

 is that it is sunk in clay or other material through which 

 water moves but slowly. When water is removed from the 

 well the water nearest in the soil soaks into the well and it 

 too is removed. If the pumping continues long enough the 

 water table about the well is lowered as shown about well No. 

 2, Fig. 286 ; in fact, the water table may be lowered to the very 

 bottom of the well. This could not take place if the well were 

 sunk in soil which was sufficiently open and porous so that 

 water flows readily through it. 



554. Witching for Water. It has not been long since it was 

 common to find people who believed that a vein of water could 

 be located by use of a DIVINING ROD. In almost every com- 

 munity some person could be found who honestly believed that 

 he could, by using the divining rod of a favorite wood and shape, 

 actually determine the location of an adequate supply of 

 underground water. If asked to give a good, scientific reason 

 for the fact that the stick turned downward in his hands as he 

 walked over the supposed vein of water, he was invariably 

 unable to do so but insisted that experience proved it. He 

 drew his conclusion from the fact that wells sunk in accord- 



