40 tf. H. KINAHAN ON THE CHESIE BEACH, DORSETSHIRE, 



as also the stream out of Wexford Harbour, which is ebbing for 

 some hours after the tide is flowing in the Bay, must more or 

 less prevent the offshoots from the up-channel current increasing 

 progressively in strength. Consequently the results on the Cahore 

 beach are not so regular or so marked as on the Chesil beach 5 

 but notwithstanding all these adverse circumstances, the tendency 

 on the Cahore beach is for the largest fragments to be carried 

 furthest and thrown up highest. 



Another point to be considered is the great size of Lyme Bay 

 compared with that of Wexford Bay. Lyme Bay, as just mentioned, 

 is open, and the Chesil beach exposed to the full force not only of the 

 tidal current but also of the most prevailing and effective winds. 

 The current also is progressively increasing in velocity as it goes 

 eastward*, and therefore carries large fragments with it, to be driven 

 on shore and accumulated in a high and massive beach when the 

 current has its maximum power during excessive winds f . As the 

 currents branching in shore from the main up-channel stream are 

 continually increasing in velocity from west to east, each carries 

 different-sized fragments, which, when stranded, cause the shore- 

 accumulation to have its peculiar arrangement. 



The site of the Cahore lagoon, prior to its being a lagoon, and 

 when the sea was at least 30 feet lower than at present, was a 

 peat-bog, the land then stretching considerably to seaward, as the 

 bog is found off shore at the four-fathom line. Since then there 

 have been different oscillations in the level of the sea, during one 

 of which a gravel and shingle beach, which eventually grew into an 

 iEolian drift bank, was formed, joining Cahore with the land to the 

 south, and enclosing to the west of it a lagoon. As on this portion 

 of the coast the more prevailing on-shore winds are from the north- 

 eastward, they often, while they last, pile up large quantities of sand 

 in Pollduff, the small bay on the north of Cahore. These accumu- 

 lations, however, are carried away in an incredibly short time if the 

 tidal current going northward is augmented by one or two heavy 

 gales from the south-east. On account of this periodical nlling-up of 

 Pollduff, the drainage of the Cahore lagoon was at first accomplished 

 by a canal cut through the middle of the iEolian-drift ridge. This 

 canal, however, was always filling up by the tidal and wind driftages, 

 and eventually, about twenty years ago, was abandoned ; now, and 

 for seme years past, all traces of it are obliterated. At present 

 the tract is drained by works that open into Pollduff. 



Conclusion. 



From the facts now stated, it seems reasonable to conclude that the 

 Chesil and Cahore beaches are due to nearly the same natural causes, 



* See note, p. '68. 



t On the west coast of the Aran Islands, Galway Bay, the storm-waves when, 

 aided by the tidal current have great power, and hurl up and toss about huge 

 blocks, fornung a rampart, called by Prof. King, D.Sc, "the Block Beach." 

 This beach in one place on the Middle Island caps a cliff 170 feet in perpen- 

 dicular height ; but usually the cliffs on which it occurs are much lower. 



