ARTESIAN WELLS 



53 



rock, if this rock outcrops at a sufficiently higher level in a region 

 of adequate rainfall, and is covered by a layer or bed of relatively 

 imprrvious rock. This statement involves four conditions, all of 

 which are illustrated by Fig. 34, where a is the bed of porous rock. 

 It is not necessary that the beds of rock form a basin, nor is it nece's- 



Fig. 32. Deposit from a hot spring in Yellowstone Lake. (Fairbanks.) 



'g- 33- Hot springs and geysers. Norris Geyser Basin, Yellowstone Park. 



