10 Dover Neutral Zone. 



the chalk at Margate, London clay at Sheppej and Leigh, and 

 old river gravels, &c., elsewhere, give variety to the marine life 

 and fish-food. (See Sect. V., Fishing Grounds.) 



3. Tides and Winds. The unusual states of the tides at the 

 Straits of Dover are troublesome both to fishermen and 

 mariners, as, unfortunately, is too well known to them. Now the 

 explanation of the apparent erratic tide movements there has 

 to be sought for in the physiography of the District and its 

 antecedent derivation as given above. The rationale seems to 

 be that the area of the sea-bottom of the ancient land, with its 

 declivity northwards, still exerts an influence on current and 

 tidal phenomena. Thus, from our southernmost station, Dunge- 

 ness, a line drawn thence to Cape Gris-nez, or say Boulogne, 

 and another from the North Foreland towards Dunkerque, 

 enclose what may be termed a neutral zone. Within this, 

 besides a see-saw direction of the northerly (North Sea) and 

 southerly (English Channel) streams, the tides are rotary, with 

 scarcely an interval of slack water (Pilot's Handbook). There 

 is a heaping up of the water in the Strait, which temporarily 

 swerves any excess of North Sea flood- wave into the Thames 

 Estuary. About high tide the Channel stream has pressed 

 towards Dover or even somewhat beyond ; as ebb begins it 

 retires in favour of the North Sea stream, which follows to 

 about opposite Beachy Head. Here commences a sharp part- 

 ing ; one stream continues its westerly course, the other runs 

 back into the North Sea. 



"Whence blows the wind ! has a further effect on the 

 Thames Estuary. If it blows from the S.W., veers to the W., 

 and quickly changes to strong N.W. gales, extraordinary high 

 tides prevail in the river as happened on the memorable 29th 

 November, 1897. 



On that occasion the flood reached the ancient high-water 

 level at Leigh, and there was sad destruction on the North 

 Kent shores. The phenomena of these excessive tides, then, is 

 accounted for by the wind first driving the stream up the 



