268 Scientific Proceedings, Royal Dublin Society. 



sionally be present whether the beach be coarse sand or shingle ; 

 without absorption there can be none. 



In the cases we have been considering, the beach-material has 

 been treated as though homogeneous as to size, form, and specific 

 gravity, a state of things that can never obtain in the case of shingle 

 beaches, whose component pebbles usually vary much in size and 

 character. 



It will be at once apparent, that the conditions prevailing above 

 and below the margin of repose will differently affect stones that 

 differ in size, form, and weight. The stone that can climb to the foot 

 of the slope that rises so rapidly above the margin of repose may 

 fail in getting higher, whereas a smaller stone, retained in the 

 grasp of the water, on the lesser slope below, may be light enough 

 to mount the steeper incline, and remain there when assisted to 

 do so by the diminution in strength of the backward current by 

 absorption. As a matter of fact, it is not uncommon to find the 

 pebbles composing the steep bank above the high- water margin of 

 repose for the day smaller than those on the strand below. I have 

 already mentioned one instance of this at Oddicombe during neap 

 tides, on the 20th October, 1882; and I find, on reference to my 

 note-book, that the bank of shingle, formed, or re-formed, by the 

 spring tide of October 14th, at Babbicombe, consisted of finer 

 shingle than that on the strand immediately below it. Similar 

 instances could be multiplied. On the other hand, it would be 

 easy to find cases in which, from exceptional causes, the shingle 

 below a bank was smaller than that composing the bank. 



The form and specific gravity of shingle affects its distribution 

 by the waves. To take them separately : — It is evident that were 

 the waves to wash a number of pence and bullets up a smooth rock 

 slope, on which the pence could rest and the bullets could not, in 

 course of time all the pence would be found high up on the slope, 

 whilst all the bullets would be collected at the bottom. In the 

 case of beaches where the shingle is partly derived from slate- 

 ^ rock and partly from limestone it is a common thing to find the flat 

 shingle at higher levels than the more spherical. Similarly, on 

 sandy beaches, slate shingle will work its way up the strand by 

 virtue of its superior powers of anchoring itself on the turn of the 

 current. 



Sir John Coode has noticed this fact in connexion with the 



