34 



ELEMENTARY SCIENCE 



the water flows naturally, without pumping. This is be- 

 cause the bottom of the well is in a porous layer that receives 

 water at some place that is higher than the top of the well. 

 The receiving place may be many miles away from the 

 well. Suppose the top of the well is five hundred feet 



FIG. 13. Photograph of an artesian well. 



above sea-level, and the well is two hundred feet deep. It 

 goes down through layers of clay and rock through which 

 the water cannot escape upward. At last it enters a 

 porous layer that is full of water. Now this porous layer 

 extends for many miles in every direction, but everywhere 

 it is covered by rock and clay except in some hills that are 

 fifty miles away. These hills are formed by the turning 

 up of the underground layers of rock and clay. Here the 

 porous layer comes to the surface, and here it receives 



