76 EARTH FEATURES AND THEIR MEANING 



curbing are raised into broken arches, and the tracks of railways 

 are thrown into local loops and kinks which imply a very consid- 

 erable local contraction of the surface (Fig. 64). With unvarying 

 regularity railway or other bridges which cross rivers or ravines, 

 if the structures are seriously damaged, indicate that the river 

 banks have drawn nearer together at the time of the disturbance. 



In such cases, whenever 



these have 



Trffnmff either been broken or back- 



tilted as a whole in such a 

 j- 



FIG. 66. Diagrams to show how the compres- manner as to indicate an 



sion of a district and its consequent contraction a pp roac h o f the founda- 

 during an earthquake may close up the joint 



spaces within the rock basement and concen- tions which was prevented 



trate the contraction of the overlying mantle at the top by the stiffness 



where this is partially cut through and so Q ^ e p-i r d er (Fig. 65). 

 weakened in the valley sections. 



The simplest, explana- 

 tion of such an approach of the banks at the sides of the valleys 

 cut in loose surface material is to be found in a general closing up 

 of the joint spaces within the underlying rock, and an adjust- 

 ment of the mantle upon the floor mainly in the valley sections 

 (Fig. 66). 



The plan of an earthquake fault. In our consideration of earth- 

 quake faults we have thus far given our attention to the displace- 



Sea/* o I Milt 



FIG. 67. Map of the Chedrang fault which made its appearance during the Assam 

 earthquake of 1897. The figures give the amounts of the local vertical displace- 

 ment measured in feet (after R. D. Oldham). 



ment as viewed at a single locality only. Such displacements are, 

 however, continued for many miles, and sometimes for hundreds 

 of miles ; and when now we examine a map or plan of such a line 

 of faulting, new facts of large significance make their appearance. 

 This may be well illustrated by a study of the plan of the Chedrang 



