354 Scientific Proceedings, Royal Dublin Society. 



Laurentians there are intrusive masses of coarse gneissic granite 

 Labradorians or Norians of the Canadian geologist. 



From the published writings in connexion with the oligoclasic gra- 

 nite and associated metamorphic rocks of the county Donegal, it is 

 evident that the sequences are very similar to those in the counties 

 Gal way and Wexford, there being a mass of granite that graduates 

 in some directions through coarse oligoclasic gneiss into schists; 

 while in other places, similar to those on the south of the Gralway 

 mass, it is margined by fine orthoolasic gneissic granites. At the 

 same time, however, as a general rule, the boundary between the 

 more intensely altered rocks and the sub-metamorphic rocks seems 

 to be more marked than usual. This, however, from the peculiar 

 faults and dislocations of the rocks, should be expected. 



It is unnecessary now to dwell longer on the Irish localities, 

 more especially as hereafter some of them will have to be men- 

 tioned in detail ; but I would again call attention to certain traits 

 in metamorphism. Years ago I pointed out that in the West 

 Gralway and Mayo district, the planes of foliation of rocks in the 

 second stage of metamorphism^ followed the planes of the more 

 conspicuous structures in the original rocks, whether these be due 

 to lamination, cleavage, oblique lamination, spheroidal structure, 

 concretionary structure, or any of the peculiar structures found in 

 calcareous rocks ; while in the typical granitoid gneiss all the ori- 

 ginal structures, except the planes of stratification, are nearly 

 always obliterated, the new foliation being vertical, or nearly so. 

 As in many places there is a hard boundary to the granitoid gneiss, 

 it may be suggested that it is possible that its coarse foliation is 

 due to a newer and subsequent metapepsis, which extended only to 

 certain limits, intensifying the foliation inside these, while it did 

 not affect the rocks outside them. We may now proceed to the 

 metamorphic rocks of Canada. 



Why is metamorphism in Canada so much restricted to the 

 older or Archsean rocks, when, in our little island, we have meta- 

 morphosed Cambrian, Cambro-Silurians, Devono-Silurians and 

 Lias ? 



A striking feature of the Canadian Laurentians is the massive 

 coarseness of the foliation in some of the gneiss. This, as just 



^ See " Geology of Ireland," chapter x. 



