AXD CAIIORK SHINGLE BEACH, CO, WEXFORD. 33 



one. Such beaches, however, do not travel, but gradually add to 

 the surface of the land. 



The following facts may also be appealed to in favour of the 

 greater power of tidal currents: — a ship at anchor always rides with 

 the tide, except in excessive wind ; and then it is the wind, not the 

 wind-wave, that veers round the ship. Fishermen's nets that break 

 loose during a storm always float with the tidal current ; so also do 

 wrecks, timber, and the like : these being below or only a little 

 above the surface of the water, cannot be driven by the wind ; but 

 if the wind-waves are more effective than the tidal currents, they 

 ought to go with the former, not with the latter*. We also find 

 that off-shore banks and shoals always lie with the course of the 

 flow-tide currents, irrespective of the direction of the most prevailing 

 or most effective windsf. 



It will be found that if the effective winds come in a contrary 

 direction to the flow tide, all permanent sand and gravel banks, di- 

 verting the " invers " or mouths of rivers and streams, are due to the 

 currents of the flow tide. Continued winds in a contrary direction 

 may often temporarily pile up a bank ; but as soon as they cease, 

 the bank is rapidly carried away and disappears J. Many interesting 

 facts may be learned from the study of wrecks on sea-beaches. If 

 a ship is cast broadside on, and the wind and tidal currents are in 

 the same direction, the beach inside the wreck is scooped out. If, 

 however, the current and wind-waves are contrary, a bank is cast 

 up behind the wreck, the greater accumulation of the sand being to 



* Instructive experiments may be made with bottles so filled that they 

 will float at, but not above, the surface of the water, also with corks. These 

 will go with the flow of tide (though not with its ebb) across a whole gale of 

 wind. 



\ In some places on the east coast of Ireland both the flow and ebb tide, as 

 marked on the Admiralty charts, run obliquely across the off-shore banks. In 

 such places, however, they are only surface currents, as there are undercurrents 

 along the banks. It may be stated that the latter currents are caused by the 

 banks; but if so, what originally formed the banks ? As the banks are parallel 

 to the flow-tide current in the channel of the Irish Sea, does it not appear pro- 

 bable that these undercurrents may be tbe edge of the mid-channel current ? 



The most prevailing and most effective winds are not necessarily the same. 

 In the south of Ireland the most prevailing wind is from the S.W. ; this wind 

 sweeps across the lowlying S.E. portion, and on the S.E. coast is an off-shore 

 wind that has little effect, the most effective winds coming from the S.E. 

 and N.E. 



\ In the East Bay (Portland) there are two drifts, one northward from Port- 

 land towards Weymouth, and the other westward from Lul worth towards Wey- 

 mouth. It has been suggested that these driftages are due to the bay being open 

 to the full force of the wind from the S.E. If, however, we examine the tidal 

 currents, we find that an offset incoming stream runs from Portland northward 

 while the offing tide forms an on-shore tide in the eastern portion of the bay, 

 which flows from east to west. The set of the offing tide on shore here mu3t be 

 very considerable on account of the long loop each hour's tide makes up the 

 channel (see any co tidal map), the VII. -o'clock wave (Full and Change of moon) 

 touching the shores at Portland Bill and Cape la Hogue at the same time that 

 the end of the loop is further up than Portsmouth ; while the loop of the VIII.- 

 o'clock wave is still further out of proportion. 



O.J. G. S. No. 129. d 



