Geological Society of London. 519 



that at which the Eskdale granite consolidated, was yet itself finally 

 consolidated at a much less depth, the mass having eaten its way 

 upwards at a certain point, and perhaps representing an unsuccessful 

 effort towards the formation of a volcanic centre. 



The examination showed that the mean of the pressures under which 

 the Lake-district granites probably consolidated was nearly the same 

 as the mean which Mr. Sorby arrived at for those of Cornwall. In 

 conclusion the author stated that he wished these results to be con- 

 sidered as preliminary only, since the complete investigation would 

 necessarily occupy far more time than was at his disposal ; at the same 

 time he ventured to hope that general accuracy was insured, while 

 pointing to the many little-known causes which might affect the 

 conclusions. 



Pakt II. On the Eskdale and Shap Granites, with their associated 

 lletamorphic Rocks. 



The author brought forward evidence in this Paper to prove the 

 possibility of the formation of granite by the extreme metamorphism 

 of volcanic rocks. The passage is shown in the field, and may be 

 observed in a complete series of hand specimens. Frequently, indeed, 

 the actual junction is well marked, but in other cases the transition is 

 gradual ; and there occur at some little distance from the main mass, 

 inlying patches of what may be called Bastard granite. The micro- 

 scopic examination proves the passage from a distinctly fragmentary 

 (ash) to a distinctly crystalline rock, and to granite itself. Also the 

 chemical composition of the altered rocks agrees very closely with that 

 of the granite. 



Both Eskdale and Shap granite were believed to have been formed 

 mainly from the rocks of the volcanic series by metamorphism at con- 

 siderable depths ; but the granite of Shap was thought to be in great 

 measure intrusive amongst those particular beds which are now seen 

 around it. A decided increase in the proportion of phosphoric acid 

 was noted in the volcanic rocks on approaching the granite, and a 

 decrease in carbonic acid. 



12. "On the Correlation of the Deposits in Cefn and Pontnewydd 

 Caves, with the Drifts of the neighbourhood." By D. Mackintosh, 

 Esq., F.G.S. 



Believing that the time has arrived for making some attempt to 

 correlate cavern-deposits with glacial and interglacial drifts, the author 

 ventures to bring forward the results of a personal examination of the 

 remnants of the deposits in Cefn and Pontnewydd caves, compared 

 with old accounts given by Mr. Joshua Trimmer and others. He has 

 been led to regard the following as the sequence of deposits before the 

 caves were nearly cleared out (order ascending) : — 1. Loam with bones 

 and smoothly rounded pebbles, nearly all local (cemented into conglom- 

 erate in Pontnewydd cave). As a few foreign pebbles of felstone have 

 been found in this bed, it could not have been deposited by the adjacent 

 river Elwy before the great glacial submergence ; and the author gives 

 reasons for believing that it was not introduced by a freshwater stream 

 from the boulder-clay above in Postglacial times, but that it may 

 possibly represent the middle drift of the plains, and may have been 



