158 DYNAMICAL GEOLOGY. 



event, this area is still called the sunken country. In all 

 these cases, probably, and in the last two certainly, there 

 was a great fissure of the earth-crust, and a slipping of 

 one side on the other. 



Now, these facts suggest another and, we believe, a 

 more probable cause of earthquakes. It is well known 

 that there are operating within the earth forces elevating 

 or depressing or crushing together portions of the crust. 

 We will discuss the nature of these forces in Part II. 

 Suffice it to say now that it is in this way that continents 

 are elevated and mountain-ranges are formed. Now, 

 suppose such forces operating to raise or depress large 

 areas of the crust e. g., the southern end of South 

 America it is evident that, the interior forces lifting and 

 the stiff crust resisting, there would come a time when 

 the crust would break i. e., form a great fissure. Such 

 a sudden break would produce an earth- jar which would 

 propagate itself from the fissure as focus in all directions 

 as an earthquake. Or, again, after such a fissure is formed, 

 the two walls may at any time slip on each other and pro- 

 duce an earth-jar. Now, this is not mere speculation. 

 We find such great fissures intersecting the earth in many 

 places ; they break through miles of thickness of rock, 

 and in many cases the two walls are slipped on each other 

 several thousand feet vertically. It is almost certain that 

 earthquakes are produced by the formation or the slipping 

 of such fissures. In 1873 there was ^a severe earthquake 

 in Inyo County, California, just at the eastern base of the 

 Sierra. Now, there is on that side of the range a great 

 fissure and a slip of several thousand feet. It is almost 

 certain that the earthquake was produced by a slight 

 readjustment of the position of the walls of this fissure. 

 Moreover, the thorough investigations very recently of 

 several earthquakes have seemed to establish the fact that 

 they originated in the formation or the readjustment of a 

 fissure. 



