Brlstow and ^Vhitaker — On the Chesil Bank. 435 



shore having been invoked in turn as best explaining tlie origin of 

 the bank. Our own theory will, we believe, suit all conditions. 



There is one point on which all must agree ; it is that the bank 

 could not have been formed without the huge natural groyne, or 

 breakwater, of the Isle of Portland, which bounds it on the east, and 

 stops the shingle in its easterly course ; but beyond this we venture 

 to differ from the explanations that have been given to account for 

 the presence of the shingle in so anomalous a position. 



The above theories rest on the supposition that the form of the 

 neighbouring land, at the time of the formation of the bank, was 

 much the same as now ; and although the theory of Sir H. De la 

 Beche would seem to allow that the beach might have been formed 

 against land, and separated merely by the sinking of the land (in 

 this case the shingle ought surely to have been driven back as the 

 land sunk), yet the other theories imply that the bank was originally 

 formed as a detached mass, separated from the land as now by a 

 narrow channel of water, unlike other long tracts of shingle, which 

 are formed against the land, and which, travel as they may, touch 

 the land.^ On the other hand, the theory that we suggest needs no 

 such supposition, but starts with the reasonable assumption that the 

 Chesil Bank maj"- have been formed at first in the same way as the 

 ordinary shingle-beaches of our coast, and that what was once an 

 ordinary beach, banked up against the land, has been since separated, 

 as a bank or bar, by the denudation of the land behind it, such 

 denudation having taken place in a way that would hinder the back- 

 ward motion of the shingle, and would leave a narrow channel (the 

 present Fleet) between the bank and the land. 



In order to make our theory more easily understood, it will be 

 well to give a short description of the Chesil Bank. In doing this, 

 we shall avail ourselves of Mr. Coode's account, which has made 

 needless any measurements on our part ; at the same time we ought 

 to state that both of us can speak from personal knowledge of the 

 coast and of the bank, the first named of us having done the 

 Geological Survey mapping of that district, while the other spent 

 great part of a summer holiday in an examination of the Dorsetshire 

 coast. 



The Chesil Bank (including under that name the whole of the 

 continuous strip of shingle from Burton Bradstock to Portland) is 

 the largest accumulation of shingle in this country, and more than 

 fifteen miles long. On the N.W., for five or six miles, it touches the 

 shore, but on the S.E., from Abbotsbury, it is divided from the main 



1 "We are aware that at the mouths of many rivers bars of shingle stretch a long 

 way across from one side, sometimes indeed to such an extent as to turn the rivers 

 along the shore (between the land and the shingle), in the direction of the prevailing 

 set of the currents, for some distance. But these are not really analogous to the 

 Chesil Bank, where the shingle-beach is far longer, and where there is no river 

 emptying into the sea, but only a succession of very small streams. There are also 

 cases of shingle-banks completely damming up streams, and with a marsh or expanse 

 of fresh-water on the land side, as at Siapton Sands, South Devon, and Cuckmere, ia 

 Sussex. 



