72 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Juiie 1 3 



whole years, may not acquire any fresh spoil, yet there are very few 

 hours when its waters are unemployed, in abrading and fashioning 

 the materials already acquired. The zone of depth along which this 

 process takes place is comparatively narrow ; much of the gravel and 

 shingle seems to travel up and down from the exposed beach to shght 

 depths below ; accumulation of sand may go on for a time, but a 

 heavier sea soon disturbs this arrangement. The materials of long 

 lines of beach may also be entirely swept away, and carried down 

 into deeper water ; in this way I have seen, at one time or another, 

 nearly every portion of our south coast in the condition of bare rock 

 without sand or shingle : the sea-bed has no permanent character 

 over the first few fathoms of its depth. Bars, sand- and shingle- 

 banks, belong to this zone, and these are likewise all subject to 

 change of form and to removal, but they speedily collect again ; and 

 it is worthy of notice, as bearing on conditions to be observed at 

 greater depths, that every part of this zone preserves its distinct cha- 

 racter — the banks which form again after a sweeping of the marginal 

 zone are always of the same description as were collected there before. 

 The materials composing shingle beaches clearly show that the 

 ordinary action of the sea is at right angles to the coast-line, as they 

 will I think invariably be found to have been derived from the con- 

 tiguous cliffs. The line of flint shingle along the French coast, at 

 the eastern end of the Channel, is exactly conterminous with the 

 chalk cliffs, and like facts may be seen carried out in the minutest 

 detail along our own western shores, at places where limestone, trap, 

 or granitic rocks occur. In this case the action is simply that of the 

 tide. With this, however, there is an occasional tendency for the 

 shingle to travel onwards in a given direction. This movement has 

 nothing whatever to do with the action of the tide ; for as this in 

 every channel makes in the offing before it does in-shore, its force, 

 even if it was equal to such a process, is exerted at right angles, and 

 not parallel with the coast. Along our own southern coasts the 

 movement of the shingle is from west to east, and on the opposite 

 coast of France it is the same. Wherever the direction of the wind 

 coincides with the line of coast, an onward movement is imparted to 

 the marginal line of water, and this moves the shingle along with it ; 

 thus the flint shingle from the chalk cliffs of the department of the 

 Somme travels south, towards the mouth of the Seine, under the in- 

 fluence of north and north-east winds. The easterly movement of 

 the shingle along our own coast may be easily observed ; and in 

 order to show that the assumed cause is a sufficient one, it is only 

 necessary to establish the fact, that along the Channel there is preva- 

 lence of winds setting in the requisite direction. From the position 

 of the Channel, any winds between north and south passing through 

 the west, will act obliquely on the coast on one side or the other ; 

 and these up-channel winds are known greatly to preponderate 

 over those which pass from north to south through the east. There 

 is a peculiarity which has been observed with respect to the winds 

 west of south, that they blow with most violence at the times 

 of high tides, and particularly that they come in at the first of the 



