EARTHQUAKES IN GEOLOGY 



determined. No doubt, some of these distant tremors 

 originate in the ocean bed ; but the seaquake can only be 

 localised when the water is put into a state of vibration 

 sufficiently energetic to rock the ship and its loose objects 

 and thus affect the senses. Vast waves are sometimes 

 rolled in on the shores of continents, and are undoubtedly 

 caused by some great disturbance beneath the ocean. 



Such waves have been known through a long period 

 of history in the Eastern Mediterranean, where they have 

 ravaged the shores of Syria and Asia Minor; and it is 

 sometimes supposed that the great deluge on which the 

 Ark of Noah floated was accompanied by a mighty sea- 

 wave, rolled in upon the lands of Chaldea from the Persian 

 Gulf. Off the Pacific coast of South America these waves 

 arise most often and most mightily. They have been 

 especially formidable in the angle where the coast of 

 Peru meets that of Chili, and the harbours of Pisco, 

 Arica, Tacna, Iquique, and Pisagua have been repeatedly 

 subjected to these destructive invasions. Usually they 

 are foreshadowed by a violent earthquake, and the in- 

 habitants, taking warning, fly to the hills. The sea- 

 wave does not, however, always follow the earthquake, 

 but it appears often enough to arouse serious fear that 

 it may come whenever the ground is strongly shaken. 

 The first sign of the coming disaster is the withdrawal 

 of the sea from the shore, leaving bare the bed of the 

 harbour. A few minutes later the sea returns in a 

 high, irresistible wave, which overflows the adjoining 

 lands. Again it withdraws and again returns, and 

 these oscillations may last for many hours, slowly 



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