574 



MR. PALMER ON THE MOTIONS OF SHINGLE BEACHES. 



likely to be again disturbed, because many days may intervene before another tide 

 may reach them; and they thus become united to the surface on which they rest, and 

 gradually contribute to its height. 



The greatest motion of the pebbles being where they are exposed to the action of 

 the greatest number of waves, we must look to the lower levels of these flats to trace 

 the further course of the greater portion of the shingle. But even the slope of the 

 surface of the lower levels is so very gradual, that the undulating motion of the 

 water is proportionally diminished ; the action of the water then becomes greatest in 

 the direction of the land. While, then, we bear in mind the nature of the soil over 

 which it acts, we find an almost insurmountable impediment to the further progress 

 of the shingle, and are enabled to account for the rapid extension of the Sandwich 

 Flats towards the sea, which, in fact, is only the continuation of that process which 

 has been for ages in operation, and which has formed a large portion of those exten- 

 sive marshes between the Isle of Thanet and the main land of Kent. 



Section 6. 



Having described those chief principles which regulate the motion of the shingles 

 on this coast, and having traced their progress to a final destiny, I shall now proceed 

 with some further general remarks referring to the application of the foregoing ob- 

 servations. 



So much effect has been attributed to the motion of the tidal currents, that vast 

 sums have been expended in attempts to divert the motion of the shingles to a distance 

 from the general line of the shore, from whence, by the increased depth and velocity 

 of the current, it has been expected they would be carried past a particular spot, 

 through which a permanently open channel has been required. Such attempts have 

 been made at various periods during upwards of two centuries at Dover, and more 

 recently at Folkstone in the same neighbourhood. It is hardly necessary to observe, 

 that such attempts have not been successful, and from the principles which I have 

 laid down, their failure may be easily accounted for. 



If a wall or pier be extended from the shore into the sea, it is evident that such 

 erection will in the first instance impede and prevent the progressive motion. It is 

 also evident, that the progressive is not necessarily combined with the accumula- 

 tive action, but, on the contrary, where the former is impeded the latter is assisted. 

 The accumulative action, therefore, continues until the angle formed by the pier and 

 the line of the shore is occupied, and the pier being no longer an impediment to the 

 progressive motion, that motion is again restored, and the general mass proceeds as 

 if no impediment had existed. 



The most perspicuous evidence of these results is exemplified at the harbour of 

 Folkestone. (See Plate XXVII.) 



Previously to the commencement of this exclusively artificial work, the beach tra- 

 velled along the line of cliffy in the ordinary way. 



