356 Scientific Proceedings, Royal Dublin Society, 



Donegal some rocks in the Grlen Lough district nearly allied to 

 those just mentioned, but not, however, as coarsely foliated. As 

 these Canadian rocks occur as intrusions, the rocks of the Castlebar 

 district are more allied to them than the others.^ 



It may also be pointed out that some of the varieties of granite 

 are remarkable for their massive crystallization, m.ore especially the 

 pegmatites. This, among others, is very conspicuous in the white 

 mica pegmatic of the Yale of the Du Lievre, the felspar usually 

 being in considerable masses, while the white mica can be got in 

 plates over nine inches square. The granites of the pegmatic 

 group are called Endogenous by Sterry Hunt, and he suggests 

 that the minerals crystallize out of solution. Such a supposition 

 can easily be understood when pegmatite is found in small masses 

 or lenticular veins ; but it is not so easily conceived when we have 

 to treat of considerable tracts. At the same time it is perfectly 

 possible that in a great thickness of rocks there may have been 

 vast vugs filled with mineral solutions, out of which the minerals 

 of the pegmatites crystallized. From what I have seen in Ireland, 

 I would suggest that this massive crystallization may not be due to 

 subsequent metamorphio action. In the Aughowle district, county 

 Wicklow, there is a pegmatite locally called " Bastard granite," 

 while a variety of it is the " Plumose granite" of Jukes: this is 

 somewhat like the Canadian pegmatites, although not as coarsely 

 crystalline : it is evidently newer than the normal granite of the 

 Leinster 'type, and, consequently, ought to be younger than the 

 time of the Regional metamorphism. If this is the case, the pre- 

 sent structure is probably the original one, from which we may 

 suggest that the Canadian rocks are also in their original form ; 

 but, at the same time, as they are so much older they may have 

 been further developed by metamorphic action. 



In the province of Ontario and the neighbouring portion of the 

 province of Quebec, the Archsean rocks are divided into Huronians 

 and Laurentians. Selwyn has pointed out that such divisions seem 

 to be more lithological than geological ; while, as far as I can learn, 

 Logan has hot stated that he had found any proofs of their being 

 geological groups. On the other hand, however, Dawson (Sir J. 



' Mixed up wlili the other Aveve oruptiou loeks, L,it ihu latter wore poitions uf the 

 'afferent groups. 



