ON ROCK REMAINS IN THE BED OF THE ENGLISH CHANNEL. Ill 



northward and north-eastward, and it is only when the Dover ebb has 

 slackened, some time afterwards, that the direct np-Channel flood can 

 be resumed. On the turn to the ebb the case is different. The two 

 streams simply flow away from one another, and there is very little 

 or no appreciable deflection through the south. While there cannot 

 perhaps be much doubt as to the existence of this north-easterly gain, 

 nearly as far, at least, as mid-Channel, the existing data available are 

 too incomplete to admit of its being definitely estimated with confi- 

 dence as to the result. I have made reference to the surface current 

 measurements as shown in the English and Irish Channel Tidal 

 Streams, compiled for the Admiralty by Commander Simpson, R.N., 

 and in order to form some estimate on this basis the measurements 

 of the mean current between neaps and springs for each hour were 

 combined, and a mean resultant worked out for one complete tide at 

 10-mile intervals S. 23° W. from the Eddystone. The values thus 

 obtained are as follows : — 



Eddystone N. 23° E., 10 miles . . N. 24° E., 2-2 miles 

 20 „ . . N. 21° E., 1-3 „ 



30 „ . . N. 26°E., M „ 

 40 „ . . N. 39° E., 1-2 ,. 



These results must, of course, be treated with reserve. In the first 

 place, they are derived from measurements in which, admittedly, too 

 great reliance must not be placed on detail ; and in the second place, 

 they are surface measurements, and, however accurate as such, do not 

 necessarily represent the condition of things at the bottom. But they 

 show a remarkable degree of regularity in the general result, which 

 seems to justify their being given here. The most doubtful point is 

 that at 50 miles, where different conditions arise with the commencing 

 approach to the French coast, and there is more southerly drift than 

 at the other points. Owing to the difficulty of estimating closely 

 from the tidal charts the force and direction of the current here at 

 some intervals of the tide, the position has been left out of considera- 

 tion. Close to this point, Mr. D. J. Matthews has made, from time 

 to time, a number of measurements with the Ekman-Nansen current 

 meter. In August, 1905,* he was able to carry these observations 

 through one complete tide at different depths. From his 22 measure- 

 ments at the surface on this occasion I have derived a resultant of 

 S. 4° W., 0'96 mile. At 70 metres, however, his 18 measurements give 

 a resultant of S. 21° E., 0-40 mile. The gain at this point would there- 

 fore seem to be a southerly to easterly one. The most important 



* Conseil Perm. Inter nat, pour VExpI. de la Mcr. Bulletin Trimcstr. August, 1905. 

 Part B. , p. 25. 



