SOIL WATER 85 



Near the surface it seeps down slowly, but as it 

 goes deeper it gathers volume and power. If the 

 soil is shallow, it soon strikes hardpan and over- 

 flows as surface drainage. If the soil is deep, it 

 may sink down many hundreds of feet until it 

 comes to some kind of a check or channel; per- 

 haps a stratum of rock, perhaps a layer of coarse 

 gravel. Down this it passes, joining forces with 

 other underground currents, as the rill joins the 

 brook and the brook joins the creek. This channel 

 may lead it many miles away to where the stratum of 

 rock or gravel comes to the surface. Then it 

 gushes forth as a spring near the base of some hill, 

 or on the bottom of some lake. Or it may not come 

 to the surface but seek a lower level and there 

 seep upward through the soil because of the pres- 

 sure of other water behind it. Just as surface water 

 flows down hillsides and collects in valleys, so 

 underground water may sink through the soil of the 

 mountain, hill, knoll or ridge, until it reaches the 

 levels, where it may be pushed up towards the 

 surface again by the pressure of water behind 

 it. Many thousands of acres of farm lands are 

 thus sub-irrigated, or watered from below, by 

 water that has seeped down from higher land, 

 perhaps many miles away. When drained, these 

 soils become very productive, not only because 

 of the equable supply of water that they 

 receive from below, but also because this 

 water, having perhaps travelled a long dis- 

 tance in seeking its level, has dissolved much 

 plant food from the soil through which it has 

 passed. 



Loss of Plant Food in Seepage Water. This 

 latter phase of the seepage of soil water has a very 

 important bearing upon the fertility of the land. 



