PEEFACE. 



In the following pages it has been my object to give a 

 systematic account of various Earth Movements. 



These comprise Earthquakes, or the sudden violent 

 movements of the ground; Earth Tremors, or minute move- 

 ments which escape our attention by the smallness of their 

 amplitude ; Earth Pulsations, or movements which are 

 overlooked on account of the length of their period ; and 

 lastly, Earth Oscillations, or movements of long period 

 and large amplitude which attract so much attention 

 from their geological importance. 



It is difficult to separate these Earth Movements from 

 each other, because they are phenomena which only 

 differ in degree, and which are intimately associated in 

 their occurrence and in their origin. 



Because Earthquakes are phenomena which have at- 

 tracted a universal attention since the earliest times, and 

 about them so many observations have been made, they 

 are treated of at considerable length. 



As very much of what might be said about the other 

 Earth Movements is common to what is said about Earth- 



