C 504 ] 



L.— LISBELLAW CONGLOMEEATE, CO. FERMANAGH, AND* 

 CHESIL BANK, DORSETSHIRE. By G. H. KINAHAN, 

 M.R.I. A., Etc. (Plate XII.) 



[Eead, March 23, 1887.] 



It would appear that the process of formation, and the agents at 

 work during the accumulation of the " Lisbellaw Conglomerate," 

 have been a puzzle to those who have examined it, or rather to 

 those who have published the results of their examination. 



It ought not, however, to be so hard to understand, as similar 

 accumulations are due, not only to the artificial groynes erected on 

 beach-lines, but also to natural groynes, as they occur on the south- 

 east coast of Ireland. As the accumulations due to groynes, arti- 

 ficial or natural, seem not to have been studied by those observers, 

 it may possibly be allowable to give an epitome of the effects due 

 to them, and their general characters. 



In general, artificial groynes are placed as near together as to 

 form a continuous permanent shingle beach ; and if they are ju- 

 diciously erected, that is, raised plank by plank as they fill, much 

 in connexion with the present inquiry cannot be learned from 

 them. 



But in many places on coast-lines more or less isolated groynes 

 have been put down to project individual portions of a coast-line, 

 as is the case in places along the coast of Waterford. From such 

 individual groynes we learn, if we follow the " flow-tide " stream 

 towards the groyne, that the accumulations gradually become wider, 

 and, in general, the materials coarser, till at the groyne there is a 

 massive shingle accumulation. This seems to be invariably the 

 case on the coast of Waterford, and also in various places on the- 

 English coast ; but in other places, as presently mentioned, where 

 the tidal-drift is solely a fine sand, the accumulation, although it 

 will increase in bulk, yet the sizes of the materials will not do so. 

 On the down-stream side of a groyne, like those on the beaches of 

 Waterford, the accumulations will be small in dimension, and the 

 material composing them much finer than those on the up-stream 

 side. 



