270 Scientific Proceedings^ Royal Dublin Society. 



It is not an uncommon thing to find a beach after a gale covered 

 with fine shingle at the higher levels ; and again, after another 

 gale of apparently equal severity, to find the same area covered 

 with shingle many times larger in size. For example : — Let Oddi- 

 combe beach, during spring-tides, be visited by a heavy gale from 

 the eastward. It will be seen from the table that the sea-drift will 

 be about forty miles, and that the waves will in consequence be 

 comparatively short and powerless. The waves will only throw up 

 the smaller class of shingle ; but will throw such shingle to a high 

 level, on account of the height of the tide. A week later, at neap- 

 tides, let the same beach be visited by another gale of equal violence 

 from the south-eastward. The sea-drift will be about 150 miles. 

 The waves will be much larger ; they will consequently be able to 

 cast up larger shingle than the waves of the preceding week, and to 

 cast it further. Should the waves of the second gale overreach 

 those of the first, the work of the first will be obliterated ; should 

 they just fail to reach them, the result will be that at the higher 

 levels the small shingle will be above, or more remote from, the sea 

 than the large shingle. Reverse the order of events. Let the neap- 

 tide gale from the south-east precede the spring-tide gale from the 

 east. The relative positions of the large and small shingle will 

 now be reversed. The large will now be more remote from the sea 

 than the small. 



A somewhat analogous distribution of shingle may arise from 

 heavy waves at low- water reaching as far as smaller waves at high- 

 water. 



Mr. Kinahan has stated that on the east coast of Ireland 

 "ground-swells due to S.W. and W. winds have intervals of one, 

 two, five, or more minutes between them, and are much larger than 

 the ordinary wind waves, or the tidal waves, which may be break- 

 ing at the same time, rise much higher on the beach, and often at 

 one sweep carry away a mass of materials that it has taken a number 

 of small waves to pile up" — {Travelling of Sea-beaches^ loc. cit. p. 5.) I 

 have hitherto avoided the use of the term " ground-swell," owing to 

 the difficulty of ascertaining its precise meaning. Mr. Eussell has 

 defined a ground-swell as a wave that is the result, or consequence, 

 of the action of the wind, but which has ceased to be under the in- 

 fluence of the wind (R. 53), and speaks of "the long, low swell, the 

 residue and telegraph of some distant storm" — {Trans. Brit. Assoc, 



