FEOM START POINT TO PORTLAND. 531 



the Channel the flood is deflected to the north for one hour, and then 

 flows steadily to the east ; in the centre of the second region the 

 antagonistic forces produce a definite spell of slack water when they 

 meet, but in the eastern end near Start Point the oncoming flood is 

 deflected to the south and south-east for two hours before it is able to 

 overcome the opposing ebb current. During the same period the ebb 

 to the east of the Start is deflected first of all to the south of west, 

 then to the north, and there is no period of slack water. During the 

 last part of the ebb, therefore, the tidal current is setting directly into 

 the Great West Bay. 



It thus appears that the Great West Bay participates in the effects 

 of the conflict between the "true Channel stream," and the "inter- 

 mediate stream," and these effects are such that a definite spell of slack 

 water occurs on the last of the flood,* and that there is an inset on 

 the last of the ebb.f It is e\'ident, therefore, that these conflicting 

 currents tend on the whole to weaken the tides in the Great West 

 Bay, and the peculiar disposition of the bottom-soil there is in part 

 due to this cause. 



The strength of the tidal currents is manifested by the rate. Whilst 

 the rate outside is over two knots per hour at springs, within the Great 

 West Bay, off Berry Head, it is less than one knot. The centre of this 

 region, in fact, is almost at rest so far as the tides are concerned, and 

 farther in towards the land, off Beer Head, the currents move definitely 

 round a complete circle during the tidal period. 



At the two extreme corners the currents rush in and out with great 

 velocity. The latter phenomenon is associated with, and partly the 

 result of, the heaping up of the waters within a confined area. When 

 the flood- tide passes round the Start it has to contend against not 

 merely the rising ground, but also a sheet of water which will stand 

 compression only to a limited extent. The main stream is conse- 

 quently deflected away from the bay towards Portland. For the 

 first three hours of flood the water-level steadily rises all over the 

 area, and the trend of the current all along the shore is towards the 

 east. When high water is reached the current is still eastward out- 

 side and in the easterly portion of Lyme Bay, but as we pass in 

 towards the land of the westerly portion, the current gradually gets 

 slower, until it ceases altogether, and finally changes its direction and 

 flows to the west. The waters heaped up at the head of the bay by 

 the rising tide must find some outlet after high water, and whilst the 

 eastward current outside has still some three hours to run. As we pass, 



* Except, perhaps, to the east of the bay, near Portland. 



t The direction of the surface currents here, as elsewhere in the English Channel, 

 is greatly determined by the prevailing winds. Cf. W. Garstang, Joum. M. B. A., 

 V. p. 199. 



NEW SERIES. — A'OL. VI. XO. 4. 2 N 



