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Proceedings of the Royal Irish Academy. 



second order, and have no drifting power, but locally they may be waves 

 of the first order or " waves of translation ; " also, wind may pile up 

 water and form " waves of ti'anslation." Thus in a continued heavy gale 

 from the south, the wind will pile up the water in the Irish Sea, to which 

 piling is due heavy large waves that break on the east coast of Ireland. 

 In-coming tidal currents, augmented by the wind blowing in the same 

 direction, are capable of doing the maximum amount of driftage on a 

 coast line, while, if the wind blows adverse to the in-coming tidal 

 current, it modifies the coast work, or even for a time may wholly stop 

 it. Adverse wind and tidal waves pile the gravel and sand on a beach 

 in transverse sloping ridges. If the wind and tide are equal the ridge 

 will be regular ; if the tide is greatest, the top of the ridge will slope 

 in the direction the tide is flowing, while the upper end of the ridge 

 slopes with the direction of the wind if the latter is in excess. This 

 ridging of a beach may also occur under other circumstances, for the 

 waves of translation due to the piling of water by wind breaking on 

 a coast line will ridge the beach, also heavy wind blowing against an 

 outgoing tide may force it on to the beach, and piles the latter in 

 ridges. If wind and tidal action are contrary, the maximum power of 

 the wind- waves seems to be during the ebb of the tide, and especially 

 at the low-water of spring tides, when they root up portions of the 

 sea bottom (between d, and e, fig. 5), that under ordinary circum- 

 stances remains undisturbed. 



If there are contimious heavy gales blowing obliquely to the in- com- 

 ing tidal wave (in the direction of the arrow B, fig. 6), accumulations 



Fig. 6. 



of sand and gravel, due to the wind waves, will form at n and p, while 

 accumulations due to tidal action will collect at o and q. To form the 

 accumulations at n and p, continuous gales will be necessary, while a 

 good gale of forty-eight hours' duration in the direction of D will carry 

 them all away ; and even this time would not be necessary, but that 

 before the accumulation at p can be carried away, that at q must be 

 dissipated, for as long as there is any sand at q, it will be carried by 

 wind and tide to p, and so prevent the latter from decreasing in 

 size. 



