80 G. H. Kinahan — Tide Heights and Raised Beaches. 



In column iii. it is shown that the height of high spring-tide is 

 very irregular when compared with that of mean water at the 

 respective places : and either column iv. or v. shows the variation 

 in height of the vertically undulating line formed by the margin of 

 the mean high spring-tide. The last two columns, although interest- 

 ing in themselves, are not both necessary for the subject of this paper ; 

 column v., however, gives data that can -be easily understood: and 

 as column iv. was necessary for the calculation of the height of mean 

 spring-tide at Courtown, both are given. In column v., as previously 

 mentioned, Courtown (the rise thereat of spring-tide being the least) 

 is taken as zero; from thence proceediug northward the line of 

 mean high spring-tide rises to 4*5 feet at Kingstown harbour, Dublin 

 Bay; to 6 feet at Clogher Head, co. Louth; and to Q'5 feet at Ard- 

 glass, CO. Down. North of Ardglass it begins to fall gradually to 

 5 feet at Donaghadee, co. Down ; but afterwards more rapidly, being 

 only 3 feet at Glenarm, co. Antrim, and 1 foot at Ballycastle, op- 

 posite the Mull of Cantire ; ^ while westward of Ballycastle it rises to 

 2 feet at Portrush. 



Between Portrush and the mouth of the Shannon, round the N.W. 

 of Ireland, we can calculate the heights of the following places above 

 the zero at Courtown from the Ordnance Table : Mullaghmore 

 (Station 20, Table IV.), Donegal Bay, 6 feet; Old Head (Station 6, 

 Tab. I.), Clew Bay, 5-o feet; Cashla (Station 18, Tab. lY.), Galway 

 Bay, 6 feet ; but none of them are in the open sea. We therefore 

 take the following open sea places from the Admiralty Charts : ^ at 

 Culduff Bay, N.E. coast of Donegal, the spring- tide rises to 6-5 feet ; 

 at Mulroy Bar, on the North coast of Donegal, to 11 "75 ; at Aran 

 Islands, co. Donegal, 11 feet; at Clare Island, at the mouth of Clew 

 Bay, 12-25 feet; at the West coast of Mayo, north of Killary Bay, 

 12 -25 feet ; at Bofin, an island six miles off the N.W. point of co. 

 Galway, 9*5 feet; and at Slyne Head, the point north of the mouth 

 of Galway Bay, 13 "25 feet. These different rises of the spring- tide 

 will give approximately the following as the heights above the zero 

 at Courtown : Culduff Bay 3 feet ; Mulroy Bar, 4*5 feet ; Aran, 

 4*25 feet ; Clare Island, 4*75 feet ; West coast of Mayo, north of 

 Killary Bay, 4'75 feet; Bofin, 3*5 feet; and Slyne Head, 5-25 feet. 

 These seem to indicate a gradual rise from Portrush, round the N.W. 

 coast, to Slyne Head ; the height of the tide off the coast being less, 

 as shown by the difference (1-25 feet) between the height on the 

 West coast of Mayo and that at Bonn, although not more than 12 

 miles apart. 



Prom Slyne Head to Kilbaha, on the north of the mouth of the 

 Shannon, there is a fall, the line of the latter place being 3 feet high, 



1 The reason for the rise of tide respectively at Courtown and Ballycastle being 

 less than elsewhere is explained by Haughton in his pamphlet " On tlie Tides and 

 Tidal Currents in the Irish Sea and English Channel." 



2 For an inquiry of the nature of this paper, the Admiralty heights are not very 

 satisfactory, they not being as trustworthy as those given by the Ordnance, their 

 sounding having been referred to beach marks at diflFerent harbours, They, how- 

 ever, give a general idea of the var)ang heights of the spring-tide at the different 

 places mentioned. 



