78 



EARTH FEATURES AND THEIR MEANING 



Such points of abrupt change in the degree or in the direction of 

 the displacement may be, when looked at from above, abrupt 



turning points in the direction 

 of extension of the fault, whose 

 course upon the map appears as 

 a zigzag line made up of straight 

 sections connected by sharp 

 elbows (Fig. 70). 



Such a grouping of surface 

 faults as are represented upon 

 the map is evidence that the 

 area of the earth's shell, which 

 is included, has at the time of 

 the earthquake been subject to 

 adjustments as a series of sepa- 

 rate units or blocks, certain of 

 the boundaries of which are the 

 fault lines represented. The 

 changes in displacement meas- 

 ured upon the larger faults 

 make it clear that the observed 

 faults can represent but a frac- 

 tion of the total number of 

 lines of displacement, the others 

 being masked by variations in 

 the compactness of the loose 

 mantling deposits. Could we 

 but have this mantle removed, 

 we should doubtless find a rock 

 floor separated into parts like 

 an ancient Pompeiian pavement, 

 the individual blocks in which 

 have been thrown, some upward 



FIG. 70. Map of the faults within an area an( J SO me downward, by Vary- 



of the Owens valley, California, formed { amoimts . Less than a 



in part during the earthquake of 1872, 



and in part due to early disturbances, hundred miles away to the east- 



In the western portions the displace- wa rd from the Owens Valley, a 



ments cut across firm rock and alluvial . f ^ p&veme ^ has 



^ ^ 



deposits alike without deviation of di- 



rection (after .a map by w. D. Johnson), 



m 



been uncovered in the extensive 



