70 THE OCEAN 



in doing so it carried away nearly all her 

 deck-houses, cabins and upper works. 



As a rule, however, the largest ocean waves 

 are not particularly dangerous to a well-built, 

 sea-worthy ship unless they curl or break, for 

 by heading into the waves and either steam- 

 ing slowly or "lying to" the ship will rise 

 and fall, but will safely ride out the seas. It 

 is the breaking seas that sailors fear and mari- 

 ners often hang bags of oil over the ships' bows 

 and then the oil, spreading upon the surface 

 of the sea, prevents the weaves from breaking. 



Although wind is the commonest cause of 

 waves yet there are certain waves which are 

 produced by other causes. An earthquake at 

 sea, or even on land; a subterranean volcanic 

 eruption, — or even the sudden eruption of a 

 volcano on shore, — may start a wave, or a 

 series of waves, on its travels. Such waves 

 are known as "tidal waves" for like the tides 

 they travel across immense areas of the ocean. 

 Although, at sea, such a wave may be only a 

 few feet in height and would hardly be no- 

 ticeable, yet it may be of enormous area and 

 may affect the water for a great depth. When 



