WATER-BEARING FORMATIONS 39 



An anticline is the arched part of a rock fold. 



A syncline is the trough of a rock fold. 



A fault is a rock fracture the sides of which have been dis- 

 placed from their original position with reference to one another. 



The dip of a bed is the angle by which it deviates from the 

 horizontal plane. 



Strike is the compass direction of the intersection of an in- 

 clined bed with a horizontal surface. 



A joint is a plane of fracture or crack in a rock the sides of 

 which have not been materially displaced with reference to one 

 another. 



Cleavage planes are minor planes traversing a rock, as a rule 

 in one direction, and in many rocks are simply lines along which 

 the rock tends to split rather than actual fractures. They are 

 commonly due to the action of pressure on compact rocks. 



Foliation and schistosity are planes of easy splitting, due to 

 the arrangement of the minerals of the rock with their elongated 

 directions parallel with one another. 



