i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 363 



bed of the sea. We do not know whether the lava was injected as 

 a thin layer or the whole body of the material under the coast slightly 

 pushed back to afford relief of the strain under the sea, but a dis- 

 placement of the latter kind seems the more probable. A sea wave 

 of considerable magnitude^ was noticed on that occasion, but it was 

 not so large as sometimes develops, and the sea bottom may have 

 subsided only very slightly. But on August 13, 1868, the whole 

 South American coast from Valdivia in Chili to Guayaquil in Ecua- 

 dor was violently shaken by a terrible earthquake, with its highest 

 intensity near Arica. A few minutes after the earthquake the ob- 

 servers were surprised and alarmed to notice the sea slowly receding 

 from the land, and very soon vessels which had been anchored in 

 seven fathoms of water were left high and dry, with no means of 

 escape. In a short time their surprise was converted into terror at 

 the sight of a mighty ocean wave fifty or sixty feet high returning 

 with terrible velocity and carrying everything before it. The vessels 

 stranded on the beach at Arica, including the U. S. S. Water ee, 

 were swept up by the gigantic wave and carried nearly a half mile 

 inland and again left stranded higher than before.^ The wave rolled 

 back and after a short interval again swept the shore ; and the 

 furious oscillation of the water thus started continued for a day 

 or two before the sea finally quieted down. This great sea w^ave was 

 propagated over the Pacific and observed almost all over the world. 

 In 1877, May 9, another great earthquake visited the same 

 region and was followed by a wave of even greater magnitude, of 

 exactly the same type, the water first slowly receding from the land, 

 and then returning as a gigantic w^ave carrpng everything before it. 

 This wave of 1877 is known as the Iquique wave. At Arica the 

 hulk of the stranded U. S. S. Wateree was again picked up and 

 carried still further inland, which would indicate that at Arica the 

 height of this wave surpassed that of 1868. The sea continued to 

 oscillate in periods of something like an hour and did not subside 

 for a couple of days. 



^ In his valuable work on " Earthquakes," chapter IX, Professor Milne 

 gives a catalogue of sea waves. Different waves present different phenomena, 

 and we here treat only of the best established types. 



' Dutton, " Earthquakes in the Light of the New Seismology," p. 281. 



