204 FIRST BOOK OF FORESTRY 



If we cover the table with a four-inch layer of garden 

 earth, and repeat our sprinkling, care being taken not to 

 sprinkle too hard, we observe a very interesting and 

 important fact. 



There is at first hardly any water on top of the soil 

 it soaks in ; but after a time there arise little rivulets on 

 top, and by gathering they grow larger and we have 

 exactly what we see in our settled plowed districts, an 

 ordinary surface run-off. But, in addition, we note after 

 a little time that there is also a run-off along the face 

 of the table just as before, except that the water runs 

 slowly ; it has to seep along. This is our underground 

 drainage, such as occurs everywhere, and it is this under- 

 ground water which feeds our springs, streams, and lakes 

 when there is no rain ; and it is underground water that 

 we reach in digging our wells. Thus, when the rain falls 

 on a bare rocky area some of the water evaporates, most 

 of it runs off as fast as it falls, and when the rain is over 

 the rocky surface is dry. On the earth or soil-covered 

 area, on the other hand, part of the rain water runs off at 

 the surface, but much of it soaks into the ground and 

 stays there until there is enough to form slow under- 

 ground streams. Thus, the soil acts as a water storage 

 for plant and stream. If we stop sprinkling, the surface 

 run-off soon stops, but the underground drain keeps on 

 moving for many hours. This is what happens all over 

 the land. 



