152 EAKTHQUAKES. 



strata, which, before the earthquake, by their continuity 

 prevented the rising of subterranean water under hydro- 

 static pressure.^ 



Kiuge explains the coming up of the waters as being 

 due to the same causes which he considers may be the 

 origin of disturbances in the sea. 



The most reasonable explanations of the eruption of 

 water, mud, sand, and gas through fissures are those given 

 by Oldham and Mallet in their account of the Cachar 

 earthquake. 



In the case of a horizontal shock passing through a 

 bed of ooze or water-bearing strata, the elastic wave will 

 tend to pack up the water during the forward motion to 

 such an extent that it will flow or spout up through any 

 aperture communicating with the surface. By the re- 

 petition of these movements causing ejections, sand or 

 mud cones, like those produced by a volcanic eruption, 

 may be formed, and by a similar action water may be shot 

 violently up out of wells, as was the case in Jamaica in 

 1692. 



If an emergent wave acts through a water-bearing 

 bed upon a superincumbent layer of impervious material, 

 this upper layer is, during the upward motion, by its inertia 

 suddenly pressed down upon the latter. 



This pressure is equal to that which would raise the 

 upper layer to a height equal to the amplitude of the 

 motion of an earth particle, and with a velocity at least 

 equal to the mean velocity of the earth particle resolved 

 in the vertical direction. 



For a moment the water bearing strata receive an 

 enormous squeeze, and the water or mud starts up 

 through any crevice which may be formed leading to the 

 surface. 



' Jahrl.f. Min. 1840, p. 173. 



