126 IGNEOUS AGENCIES, 



open sea they create no current, and are not even perceived ; but, 

 when they touch bottom near shore, they rush forward as great 

 breakers fifty or sixty feet high, sweeping away everything in their 

 course. 



Being waves of gravity, their velocity, though very great on ac- 

 count of their size, is far less than that of the earth-waves, and they 

 reach the neighboring shore, therefore, some time later, and often 

 complete the destruction commenced by the earth-waves. 



Examples of the Sea-Wave. — In the great earthquake which de- 

 stroyed Lisbon in 1755, the epicentrum was on the sea-bed fifty or more 

 miles off the coast of Portugal. From this point the surface earth- 

 waves spread along the sea-bottom until they reached shore. It was 

 the arrival of these waves which destroyed Lisbon. About a half -hour 

 later, when all had become quiet, several great sea-waves, one of them 

 sixty feet high, came rushing in, deluging the whole coast and com- 

 pleting the destruction commenced by the earth-waves. This wave was 

 thirty feet high at Cadiz, eighteen feet at Madeira, and five feet on the 

 coast of Ireland. It was sensible on the coast of Norway, and even on 

 the coast of the West Indies, after having crossed the whole breadth 

 of the Atlantic, 



In 1854 a great earthquake shook the coast of Japan. Its focus was 

 evidently beneath the sea-bed some distance off the coast, for, in about 

 a half -hour, a series of water-waves thirty feet high rushed upon shore 

 and completely swept away the town of Simoda. From the same cen- 

 ter the waves, of course, spread in the contrary direction, traversed the 

 whole breadth of the Pacific, and in about twelve and a quarter hours 

 struck on the coast of California at San Francisco, and swept down the 

 coast to San Diego. These waves were thirty feet high at Simoda, fif- 

 teen feet high at Peel's Island, about 1,000 miles off the coast of Japan, 

 0-65 feet, or eight inches, high at San Francisco, and six inches at San 

 Diego.* 



On the 13th of August, 1868, a great earthquake desolated the coast 

 of Peru. Its focus was evidently but a little way off shore, for in less 

 than a half -hour a series of water-waves fifty or sixty feet high rushed 

 in and greatly increased the devastation commenced by the earth- waves. 

 These waves reached Coquimbo, 800 miles distant, in three hours; 

 Honolulu, Sandwich Islands, 5,580 miles, in twelve hours ; the Japan 

 coast, over 10,000 miles, the next day. They were also observed on 

 the coast of California, Oregon, and Alaska, over 6,000 miles in one 

 direction, and on the Australian coast, nearly 8,000 miles in another 

 direction. This series of waves was distinctly sensible at a distance of 

 nearly half the circumference of the earth. Had it not been for the 



* Report of Coast Survey for 1862. 



