CRUSTAL MOVEMENTS 



199 



are not confined to mountains. As in the case of the Charleston 

 earthquake, they sometimes originate beneath plains. 



Causes of earthquakes. Earthquakes are probably due to vari- 

 ous causes. Some small ones are perhaps due to the falling 



Fig. 197. Map showing the principal earthquake regions of the New World. 

 (Montessus de Ballore.) i 



in of the roofs of underground caves. If the roof of Mammoth Cave, 

 for example, were to fall in, there would be a slight earthquake in 

 the vicinity. Earthquakes accompany violent volcanic eruptions, 

 and in these cases the explosions which cause the eruption are 

 doubtless the cause of the earthquakes. Great landslides and 

 avalanches may cause slight earthquakes, and it is probable that 



