286 Correspondence — T. M. Beade. 



Greenwood and Mr. Kinaiian with regard to the transportation of 

 the pebbles which form this beach : Colonel Greenwood, if I under- 

 stand him rightly, considers the pebbles to travel along the beach, 

 being moved onwards by waves under the influence of the wind, and 

 consequently^ on the average travelling in the direction of the prevail- 

 ing wind. I have, I am afraid to say how long ago, noticed this action 

 on the Chesil Beach. 1 have seen the waves rolling in from the Atlantic 

 (for we are not here in the presence of narrow seas, as Mr. Kinahan 

 appears to think) take up the pebbles from one spot, and dash them 

 down again some little distance to the leeward. They no doubt 

 travel along the Beach under this action. But does it follow that 

 that is how they came there ? I say, no. If it were, how could the 

 larger stones be at the end most distant from the main land ? 



Some of the most violent storms on this coast come somewhat 

 from the south of south-west, so that their action is, I suspect, rather 

 to carry the pebbles by wave-action towards the north-west end of 

 the Beach, and probably their attrition, as they move onwards, partly 

 accounts for their gradual decrease in size as we follow them in that 

 direction. 



Among the pebbles are a few, chiefly at the southern end, from 

 Portland ; but the larger proportion consists of Chert from the Upper 

 Greensand of the west of Dorset and of Devon, and of other pebbles, 

 which appear to be derived from the Trias of the same district. This 

 shows that they have come across the west bay. Sir Charles Lyell 

 explains the case thus : ^ " The force of the sea increases southwards, 

 and as the direction of the bank is from north-west to south-east, the 

 size of the masses coming from the westward, and thrown ashore, 

 must always be largest where the motion of the waves and currents 

 is most violent." It seems then that the currents must store up an 

 accumulation of pebbles beneath the bay, within reach of the shore, 

 which, on occasions of unusual wave-action, are cast up in masses 

 upon the beach. 



0. Fisher. 



WHY ARE THE LARGEST STONES FOUND AT THE EAST END OF 

 THE CHESIL BANK? 

 SiK, — -It has puzzled many observers to find that, contrary to 

 expectation, the largest shingle is at the east end of the Chesil Bank, 

 though it is well ascertained that the whole mass of pebbles have 

 travelled from the westward — the usual inference being that the 

 further the pebbles have travelled the smaller they become. 



As bearing on the mechanical problems involved in this striking 

 phenomenon of nature — which, seen in its whole extent from an 

 elevation, resembles nothing so much as a large railway embank- 

 ment — the fact is extremely interesting, and admits to my mind of 

 a very simple explanation ; for the individual stones merely follow 

 the law applying to the whole bank, which increases in height and 



1 Principles, vol. i. p. 539. 1872. 



