360 THE WORK OF RUNNING WATER 



pores and openings in the soil and rock. The spaces between 

 sand and gravel particles are so large that considerable water 

 runs quickly through them. The spaces in clay, which is 

 dense and compact, are so small that little water runs through 

 them. The larger and more numerous the openings in the 

 soil, the greater is the quantity and speed of the water which 

 flows down through it. Beneath the loose soil there is rock, 

 through which the water must flow or seep. The farther 

 below the surface these rocks are, the more pressed and com- 

 pact are they, and the smaller are their pores and cracks. 

 Water seeps so slowly through the deep underground rocks 

 that it accumulates around them and saturates them with 

 water. When the downward flow is stopped, much of the 



water backs up and fills 

 the ground. The level 

 below which the ground 

 is saturated with water 

 is called the level of 



FiG. 226. Diagram showing the relation of the ground water Or the 

 level of ground water (the broken line) to the wafer fa U| p Wpll nnlr 

 surface of the ground and to a lake and river. WH1 >le ' W CJ 



to this depth always yield 



water. The water table or the level below which the ground 

 is saturated with water varies from time to time. In rainy 

 seasons the water table is high ; in dry seasons it is low. The 

 wise farmer digs a well which is deep enough to be below water 

 level at all times. The water level varies from place to place ; 

 in regions of abundant rainfall it is higher than in regions of 

 scanty rainfall; in valleys it is nearer the surface than in 

 mountains; in some areas it is so far below the surface that 

 wells must be sunk thousands of feet to reach it. In other 

 areas it is so near the surface that it forms marshes; and it 

 may even come to the surface and form lakes and ponds. A 

 lake is shown in Figure 226, formed by a high water level. 



