172 EARTHQUAKES. 



deposition, produced by currents, had reached an angle 

 beyond the limits of repose of the material of which it 

 was formed. Mallet does not insist upon the existence 

 of these submarine landslips, but only suggests their 

 existence as a means of explaining certain abnormal sea 

 waves which do not appear to have been accompanied by 

 earthquakes. 



In the generality of cases sea waves are accompanied 

 by earthquakes, but it may often happen that the connec- 

 tion between the two is difficult to clearly establish. One 

 simple explanation for the origin of waves occurring with 

 earthquakes, is, that in consequence of the earthquake a 

 large volume of water suddenly finds its way into cavities 

 which have been opened, the disturbance produced by the 

 inrush giving rise to waves. 



A second explanation is, that the land along a shore is 

 caused by an earthquake to oscillate upwards, the water 

 running off to regain its level. A supposition like this is 

 negatived by the fact that these disturbances are felt far 

 away from the chief disturbance, on small islands. Also, it 

 may be added, that the whole disturbance appears to 

 approach the land from the sea, and not in the opposite 

 direction. Thus, in the earthquake of Oahu (February 18, 

 1871), it was remarked that the shock was first felt by 

 the ships farthest from the land.^ 



Another suggestion is that the waves are due to a 

 sudden heaving up of the bottom of the ocean. If this 

 lifting took place slowly, then the first result would be 

 that the water situated over the centres of disturbance 

 would flow away radially in all directions from above the 

 area of disturbance. 



If, however, the submarine upheaval took place with 

 great rapidity, say by the sudden evolution of a large 

 ' Aw. Jour. Sci. vol. i. p. 469. 



