140 EARTHQUAKES. 



and left of A^ would give rise to a series of reflected waves. 

 If the lines drawn representing wave fronts are districts 

 of compression, then, where two of the lines cross each 

 other, there would be double energy in producing com- 

 pression. Similarly, districts of rarefaction might accord, 

 and, again, compression of one wave might meet with the 

 rarefaction of another and a neutralisation of effect take 

 place. A diagram illustrating concurrence and interfer- 

 ence of this description is given in Le Conte's ' Elements 

 of Geology,' p. 115. The interference which has been 

 spoken of, however, is not the greatest which would occur. 

 The greatest would probably be beneath the bluff and the 

 scarps which run down to join the level ground below. 

 This would be the case because it is a probability that 

 there might not only be cases of interference of single 

 reflected waves, but also of waves which had been not only 

 twice but perhaps thrice reflected. For example, a wave 

 like Bj (which is parallel to A^ of the first supposition), 

 advancing in a direction parallel to 6j, might be reflected 

 along the line b^ giving rise to waves like Bg, which in 

 turn might be reflected along 63 giving rise to waves like 

 B3. The number of districts where there would be con- 

 currence and interference would, in consequence of the 

 number of times waves might be reflected, be augmented. 

 Here the violence of the shock would, at certain points, be 

 considerably increased, but as a general result energy 

 must be lost, so that even if some of the reflected waves 

 found their way into the portion we have regarded as 

 being in shadow, their intensity would not be so great as 

 if they had entered it directly. 



The shaking down of loose materials from the sides of 

 hills may be partially explained on the assumption of an 

 increased disturbance due to interference. 



Earthquake bridges. — In certain parts of South 



