ON THE CHESIL BEACH AND CAHORE SHINGLE BEACH. 29 



3. On the Chesil Beach, Dorsetshire, and Cahore Shingle Beach, 

 County Wexford. By G. Henry Kinahan, Esq., M.R.I. A., &c. 

 &c Communicated by Prof. Ramsay, F.R.S., V.P.G.S. (Read 

 June 21, 1876.) 



[Plate II.] 



Preliminary Remarks. 



SEA-beaches are common around our coast lines ; but none seem 

 to have attracted so much attention as the Chesil Beach on the 

 north-east margin of Lyme Bay, Dorsetshire. This is probably 

 due to the circumstance of the beach being situated on a much 

 resorted-to coast, its great length, and the peculiar assortment of the 

 fragments composing the accumulation, these being arranged as if 

 they had been passed through a series of sieves of gradually de- 

 creasing coarseness. This last particular has even attracted the 

 attention of the fishermen, who say they can tell, on the darkest 

 night, at what part of this beach they have landed, by the size 

 of the pebbles at the place. 



The latest published paper on the Chesil Beach is that of Prof. 

 Prestwich, read before the Institution of Civil Engineers, February 

 2nd, 1875 ; and from the discussion at the reading of it it is evident 

 that opinions still differ much on the subject. This has emboldened 

 the writer of this paper to come forward, more especially as no 

 previous writer seems to have taken into consideration the special 

 effects that the " flow " of the tide, which is most accelerated at 

 the nodal or hinge-line in the English Channel, must have on the 

 east shore of Lyme Bay — also because he has specially studied 

 Cahore shingle beach, co. Wexford, which in many points is analo- 

 gous to the Chesil Beach. 



Tides in the English Channel and Irish Sea. 



At Portland Bill on the English Channel, and at Cahore Point 

 on the Irish Sea, the tidal currents are considerable, and must 

 work more or less actively ; but to understand them, it is necessary 

 to give an epitome of what is known about the tides in these 

 seas. The tidal waves and currents in the seas surrounding Great 

 Britain and Ireland were but imperfectly known until after the 

 investigations carried on by the late Admiral Beechey and Lieut. 

 F. W. L. Thomas, R.N. The result of their researches in regard 

 to the English Channel and Irish Sea is given in the manual of 

 Tides and Tidal Currents by the Rev. S. Haughton, F.T.C. Dub- 

 lin ; and to it we are indebted for much of the following*. 



The tides rise and fall twice in a little more than twenty-four 

 hours t ; but the risings and fallings are not always of equal extent, 



* Galbraith and Haughton's Scientific Series. 



t This and other statements below in reference to the tides will be found 

 fully explained and proved in Haughton's book. 



