TREVELYAN ON FRACTURED BOULDERS. 147 



2. On the Geology of North Wales. By Daniel Sharpe, 



Esq., F.G.S. 



[The notice of this memoir is postponed.] 



March 20. 1844. 



William Pole, Esq., A.C.E., Professor of Engineering at 

 Elphinstone College, Bombay, and Frederic Joseph Sloane, Esq., 

 of Florence, were elected Fellows of this Society. 



The following communications were read : — 



l o 



1. On Fractured Boulders found at Auchmithie near Ar- 

 broath. By W. C. Trevelyan, Esq., F. Gr. S. 



In a visit paid to the coast of Forfarshire in the summer of 

 1840, I observed, for the first time, at Auchmithie, near Arbroath, 

 at the foot of a cliff consisting of old red conglomerate, some 

 pebbles and boulders which had fallen from the rock above, and 

 which, from their remarkable fractures and contortions, attracted 

 my attention, and being in the same neighbourhood in the autumn 

 of 1843, I found in the same spot many more specimens of the 

 pebbles, some lying at the foot of the cliff and others remaining in 

 their matrix. 



Subsequently, in the picturesque conglomerate rocks at Dunottar 

 Castle, near Stonehaven, I discovered similar appearances ; but, 

 in this instance, the pebbles were much larger, and the fractured 

 ones even more abundant than in Forfarshire. 



At Auchmithie, the pebbles which predominate in the con- 

 glomerate consist of granite, porphyry, gneiss, jasper, and reddish 

 quartz — those of the quartz being chiefly abundant. Of most 

 of these different kinds of pebbles, fractured specimens may be 

 found. 



The conglomerate is traversed by veins of carbonate of lime and 

 sulphate of barytes ; and it is in the neighbourhood, or in the 

 actual course of these veins, that the -fractured pebbles in many 

 instances occur. Sometimes the parts of a pebble traversed by 

 one of these fissures are faulted by it, and have their levels dis- 

 placed to the distance of several inches. Thus it appears that the 

 formation of the fissures and the fracturing of the pebbles have' 

 been contemporaneous. 



It is to the bent appearance of some of these pebbles, and the 

 appearance of their having been softened and the broken parts 

 re-united as if by pressure, that I am desirous more especially to 



t 2 



