198 



PHYSIOGRAPHY 



shaking all the time, though shocks sufficiently violent to be de- 

 structive to life are few. 



Distribution. Earthquakes are perhaps most common in 

 volcanic regions, though not confined to them. It can hardly be 



Fig. 196. Map showing in black the principal earthquake regions of the 

 Old World. (Montessus de Ballore.) 



said that such earthquakes are caused by volcanoes, since many of 

 them do not occur at the time of volcanic eruptions. Many great 

 earthquakes have been near the edge of the continental platforms. 

 Mountain regions in general seem to be more subject to earthquakes 

 than plains, though earthquakes originating in mountain regions 

 sometimes spread to plains. Earthquakes, on the other hand, 



