202 Proceedings of the Royal Irish Academy. 



Ground swells — continued. 



With E. winds, sometimes seem to assist in filling the beaches, 

 but with N.E. winds they " cut out." 



With the "counter-tides," "cut out" the beaches. 



With the "half counter-tides," sometimes " fill in " the 

 beaches. 

 The cutting out due to "ground swells" and contrary winds is 

 different from that due to the S.E. winds ; as the latter carry the 

 beach forward, while the other suck out the beach into deep water. 

 "Ground swells" due to S. winds break on the shore line nearly as 

 quickly as ordinary wind waves ; but the waves of the other " ground 

 swells " have intervals of one, two, five, or more minutes between 

 them ; the latter are much larger than the wind or tidal waves, which 

 may be breaking at the same time, rise much higher on the beach, and 

 often at one sweep carry away a mass of material that it has taken 

 a number of the small waves to pile up. Some of the big waves, or 

 "rollers," that visit the coast on rare occasions, are due to earth- 

 quakes. 



III. The Carriage of large Stones in Beep Water. 



On the coast of Gahvay, in many of the small bays or strands, are 

 beaches composed of very large, roundish shingle, many of the blocks 

 weighing two or three cwt. and a few over a quarter of a ton. These 

 beaches were found to be fuller after storms than at other times ; 

 many of the blocks were derived from rocks situated more or less to 

 the southward of the beaches, and those blocks, in order to reach the 

 positions in which they were, must have travelled through water fif- 

 teen or more fathoms deep. As, after storms, laminaria and other deep- 

 water seaweeds were observed to be attached to the blocks most re- 

 cently brought in, a series of observations were made during the calms. 

 It was ascertained that, in places both in the bays and in the open sea, 

 in water from twenty fathoms deep to low water of spring tides, 

 there are variously- sized blocks scattered about irregularly on sandy 

 bottoms ; and on these seaweeds grow rapidly, some having leaves 

 whose measured lengths were over twenty feet. It was also found that, 

 when the leaves were full grown, the weeds made the stones buoyant ; 

 in some cases so much so that they were, during each " flow-tide," 

 drifted from their places towards the shore. By other observations it 

 was found that places which had been dotted over with stones, with 

 sea weeds attached, were after storms free from them. This was 

 ascertained by marking favourable spots on the chart, and visiting 

 them as soon as possible, during low water, after a storm. Some of 

 these stations were four miles from the coast line. 



Mr. J. Chaloner Smith, M. Inst. C.E., pointed out to me a .sandy 

 strand, below the south end of the Bray shingle beach, which was 

 supposed to be always free from blocks. Circumstances prevented me 

 from making observations here, therefore I turned my attention to 



