278 EARTHQUAKES. 



in the production of oscillations, pulsations, and tremors 

 will be referred to. 



Earthquakes consequent on faulting, — In the chapter 

 on Earth Oscillations, the causes producing the phenomena 

 of elevation and depression are briefly indicated. 



By the variations in stress accompanying elevations 

 and depressions, cracks are produced. Inasmuch as com- 

 pression would crush the rocks constituting the earth's 

 crust, we must conclude with Captain Dutton that these 

 cracks are formed by tension. By elevation, the upper 

 rigid crust of the earth is stretched, and fissures are pro- 

 duced. The sudden formation of these fissures or faults 

 gives rise to earthquakes, and perhaps also to volcanic 

 vents. That earthquake and volcanic regions are situated 

 on areas where there is evidence of rapid elevation is 

 strikingly illustrated round the shores of the Pacific. 



Lasaulx considered that the earthquake of Herzogen- 

 rath was more or less intimately connected with the great 

 mountain fissure — the Feldhiss — which crosses the coal 

 region of the Wurm.* The sudden elevation or sinking 

 of large areas at the time of an earthquake may be a 

 consequence of these dislocations. 



It has already been pointed out that the earthquake 

 region of Japan is the one where we have evidence of 

 recent and rapid elevation. That certain earthquakes of 

 this region may possibly be the result of faulting we have 

 the evidence of our senses and of our instruments. The 

 sudden blows and jolts which are sometimes felt are in- 

 dicative of the sliding of one mass of rock across another. 



Should the ground be simply torn asunder, this tearing 

 would give rise to a series of waves of distortion, vibrating 

 in directions parallel to the plane of the fissure. Sup- 

 posing this motion to be propagated to a number of 

 * Von Lasaulx, Eartliq^ialies of Herzogenrath. 



