DISTUKBANCES IN THE OCEAN. 171 



that a vessel entering the harbour was alternately afloat 

 and aground. 



In 1761, on July 17, a similar phenomena was observed 

 at the same place. 



A like occurrence took place at Kilmore, in the county 

 of Wexford, on September 16, 1864, when the water ebbed 

 and flowed seven times in the course of two hours and a 

 half. These tides, which appear to have taken about five 

 minutes to rise and five minutes to fall, were seen by an 

 observer approaching from the west as six distinct ridges 

 of water. The general character of the phenomena appears 

 to have been very similar to that which was produced at 

 the same place by the Lisbon earthquake of 1755; and 

 the opinion of those who saw and wrote about their 

 occurrence was that it was due to an earthquake disturb- 

 ance. Such phenomena are not uncommon on the Wexford 

 coast, where they are popularly known as ' death waves,' 

 probably" in consequence of the lives which have been lost 

 by these sudden inundations. 



They have also been observed in other parts of Ireland, 

 the north-east coast of England, and in many parts of the 

 globe. They will be again referred to under the head of 

 earth pulsations. 



Cause of sea ivaves. — Mallet, who in his report to the 

 British Association in 1858, writes upon this last -mentioned 

 occurrence at considerable length, whilst admitting that 

 many may have originated from earthquakes, he thinks it 

 scarcely probable that an earthquake blow, sufficiently 

 powerful to have produced waves like those observed at 

 Kilmore, should not have been felt generally throughout 

 the south of Ireland. He, therefore, suggests that some- 

 times waves like the above might be produced by an 

 underwater slippage of the material forming the face of a 

 submarine bank, the slope of which by degradation and 



