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XXI. 



PKELIMINARY OBSERVATIONS ON THE GRANITES OF 

 WICKLOW AND DOWN. By W. J. SOLLAS, M.A., L.L.D., 

 Professor of Geology, &c, Trinity College, Dublin. 



[Head May 1G, 1888.] 



Grakite, wherever it occurs in Leinster and Ulster, is a truly 

 igneous rock, separated in every case by a clear line of demarcation 

 from the schists which surround it. 



The following statements are true of the main granitic masses 

 of Wicklow and Newry : — 



1. For some distance inwards from its boundary the granite is 

 in many places foliated so as to assume a gneissose character. 

 Good instances oocur at the Scalp, and about the head of Glenda- 

 lough, Co. Wicklow, and near Castlewellan, Co. Down. Mr. Traill 

 lias previously called attention to the instance near Castlewellan, 

 and I have to thank my friend Mr. Teall for the suggestion that 

 I should look for " crushed granite " in Wicklow. 



2. The planes of foliation in the granite are parallel to those of 

 the adjoining schists. The explanation of the erroneous opinion 

 that in some cases the granite might result from metamorphosis 

 (*. e. the melting up of sedimentary material) is to be found in this 

 fact. 



3. The foliation of the granite, in the case of the Leinster 

 granite, is shown by microscopical investigation to be the result of 

 pressure, acting on the previously consolidated rock. 



4. Hence it follows that the phenomena of contact metamor- 

 phosis preceded in order of time the production of foliation. This is 

 independently proved by the fact that the garnets developed by 

 contact metamorphosis in the surrounding schists are traversed by 

 cracks which are directed chiefly at right angles to the planes of 

 foliation. These last are diverted on each side of the garnets. 



5. The foliation of the granite and surrounding schists was 

 simultaneously produced by great earth movements which took 



