Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/64

38 38 G. H. KINAHAN ON THE CHESIL BEACH, DORSETSHIRE, till it reaches the nodal line off Swanage, a distance of 150 miles. 13. The current in the Chan- nel between Portland Bill and Cape la Hogue is about 3*5 knots an hour*. 14. In Lyme Bay there is a small bank (Skerries bank) at the S.E. of Start Bay. 15. As there are no off-shore banks across the mouth of Lyme Bay, also as the narrow between Portland Bill and Cape la Hogue tends to augment the force of the current, already progressively in- creasing, after it has passed Start Point and is approaching the Swanage nodal line, the land- ward movement of the water into Lyme Bay from the main up -channel current ought to in- crease progressively in power from Start Point to Portland Bill. 16. As the tidal wave going eastward up the English Channel proceeds much faster at the centre than on its margins (see any co- tidal map), there is necessarily an " offing tide " setting into the different bays. This ought to tend to generate " on-shore" or " countertides " at the eastern sides of the different bays. If such a countertide existed to the east of Lyme Bay, it would cause a driftage northward from the Bill of Portland toward Chesil- ton. It would also account for the Chesil beach ending at Che- silton. 17. The fifteen-, twenty-, and twenty-five-fathom lines on the reaches the nodal line off Cour- town, a distance of 150 miles. 13. The current in the Chan- nel between Cahore Point and Braichypwll is 2*5 knots an hour. 14. In Wexford Bay there are many off-shore banks, principally in a line between Greenore and Cahore Points. 15. On account of the off- shore banks in Wexford Bay the landward movement from the main up-channel current can- not increase progressively in strength. There are also "cross tides" generated by the efflux from the Wexford-Harbour la- goon that modify considerably the effects of the landward move- ment from the main current. 16. At Cahore Point there is a " countertide " running on shore towards the S.S.W. for the last three hours of the " flow." This tide is due to the on-shore set of the " offing tide" generated by the tidal wave running much quicker up the centre of the Irish Sea than at its margins. This countertide has stopped the shingle beach from extending on- to Cahore Point. 17. The soundings on the Admiralty Charts would suggest of Cape la Hogue) and the line joining Beachy Head and Cape Ailly (near Dieppe) the flow of spring tides is as follows : — west part 23 knots, central part 36 knots, east part 3 knots, off Cape Barfleur 5*4 knots, and over Hurd's Deep 2*16 knots per hour.
 * Between the line joining Start Point and the Casquets (islands a little west