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Proceedings oj the Royal Irish Academy. 



the bay, and not round its margin ; being sorted in their carriage, the- 

 largest going furthest, and fonning a shingle beach at the back of the 

 second headland (h). 



Banks off a coast line are connected Tvith counter-currents, but 

 whether such currents have induced the banks or the banks the cur- 

 rents, it is hard to determine. Off a head will be found the end of a 

 shoal, or shoals, and farther up the coast, at a second headland, often 

 very slight, Tve find that a counter-current has been generated, which 

 flows back along the coast to the first headland, where meeting 

 the CTin'ent in the opposite dii-ection, both flow seaward, forming a 

 "race," till they meet the "tail" of the shoals. Such races seem 

 seldom, if ever, to form bars or half -tide banks, although they sensibly 

 affect the soundings. The genesis of the "counter-tides" is yery 

 obscui'e, as also the manner in which they finally join into the main 

 tide. 



It is not unusual for rocky islands off a coast line to affect the mn 

 of the tides. Such islands usually lie off a headland, being a portion 

 of the rocks of the headland, disconnected from it by denudation. 

 Under some circumstances, such an island will split the tidal cur- 

 rent, causing a portion on the up-stream side to form a counter-tide 

 that will flow backwards along the coast line ; while from the main- 

 land, toward the island, a half-tide ridge often forms. If there 

 are many islands off a headland, the cuiTcnts may be much more 

 complicated. 



Off the inver or mouth of a large river a bank often forms,, 

 owing to the diiftage of the tide being partially stopped by the 

 water flowing out of the river ; let (5) fig. 3 represent such a bank. 



Fig. 3. 



In this case, if the bank is only covered during very high tides, when: 

 the tide begins to flow into the estuary («) there will be a current run- 

 ning between the bank and the shore, in the direction of (^d) ; but after 

 half or three-quarters of the tide has come in, there will be a " coun- 

 ter-tide " in the direction of (c) ; while, after the tide has turned, and 

 the tidal cun-ent is running in the direction of the arrow (C), there 

 will be a cun-ent into the estuary between the bank and the shore, 

 in the direction of the arrow {e) ; and this latter current will contiaue ^ 



