EARTHQUAKES IN GEOLOGY 



One of them is the St. Paul's Rocks district, of which 

 mention has already been made. Another district from 

 which seaquakes have been reported with exceptional 

 frequency is the North Atlantic in the neighbourhood 

 of the Azores. Between these islands and the coast of 

 Portugal it may be remembered that the great quake 

 originated which, on November 1st, 1775, destroyed Lisbon. 

 The West Indian Deep, that profound basin of the 

 Atlantic lying north of the Lesser Antilles and east of 

 the Bahamas, where the Atlantic has its greatest depths 

 and where its bottom has its greatest inequalities, is 

 another district from which an unusual number of sea- 

 quakes have been reported. The usual explanation of 

 their origin is that in these neighbourhoods, owing to the 

 great pressure of water above them, there are continual 

 slips and fractures of the sea bottom, like landslips on 

 land, and that into the great cavities thus produced the 

 water rushes, and thus sets up disturbances which show 

 themselves on the surface like waves, very much in the 

 same way that the water rushing through the escape of 

 a bath produces small disturbances on the surface of the 

 water in the bath. To satisfy the requirements of such 

 a wave as rolled in upon the South American coast at 

 Arica in 1868 would require the sudden drop of many 

 hundred square miles of sea bottom perhaps of several 

 thousand square miles. 



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