244 



DISLOCATIONS OF STRATA 



nature of the fault. The friction of the rocks grinding against 

 each other in the fault frequently smooths and polishes them, 

 which gives the characteristic appearance known as slickensides. 



The movements of the beds along the fault plane are usually 

 simple, and in only one direction, but there are several different 

 kinds of measurements to be taken, which express important 

 facts. The amount of vertical displacement between the two 



FIG. ioi. — Section through faulted beds, b' c, throw; b c, heave; b b' , strati- 

 graphic throw, which in this case is measured along the fault plane, because the 

 latter happens to be at right angles to the bedding planes. The angle b b' c is the 

 angle of hade ; b' b c, the angle of dip. Foot wall to the right of the fault, and 

 hanging wall to the left. 



fractured ends of a given stratum is called the throw {b { c, 

 Fig. ioi), and the heave, or horizontal throw, is the horizontal 

 distance through which one end of a fractured stratum has been 

 carried past the corresponding end on the other side of the fault 

 plane (b c, Fig. ioi). The heave of a fault increases in propor- 

 tion to the throw, as the hade increases. In a vertical fault, which 

 has no hade, there is no heave, however great the throw ; for in 

 that case the fractured ends of the strata are not carried past each 

 other horizontally, and the throw of the fault is measured along 

 the fault plane. With the amount of throw remaining constant, 



