EARTHQUAKE WAVES. 81 



Earthquakes are always accompanied, on the 

 coasts, by movements of the sea more or less con- 

 siderable, and it is this part of the phenomenon which 

 has caused the greatest disasters. To the movement 

 of the sea, again, is added a temponiry or permanent 

 change of its level. 



During the earthquake of 1820 the level of the 

 sea at Acapulco remained during two hours at about 

 30 feet below the points of the coast which corre- 

 sponded with its ordinary level. A part of the road- 

 stead was left dry. After two hours the sea returned, 

 and rose from four to five yards above its ordinary 

 level — that is to say, from 40 to 45 feet above the 

 point to which it had receded : it then oscillated 

 about its ordinary position, and finally resumed its 

 old relative level. There can be no doubt that the 

 soil of Acapulco was itself raised during this two 

 hours to the height mentioned, and afterwards settled 

 down again as described. The effect of the raz de 

 maree was terrible. The sea, resuming possession of 

 its bed, advanced upon the land like a wall with ex- 

 treme rapidity; and then, overleaping its ancient 

 limits by the impetus of its return, ovei-threw what- 

 ever opposed its progress, and destroyed a part of 

 the city. 



Similar movements of the sea accompanied the 

 earthquake which destroyed Talcaguana, on the coast 



G 



