164 O. H. Kinnhan — Irish and Canadian Hods, Compared. 



Some of the varieties of granite are also remarkable for the 

 massive character of their crystallization, more especially the peg- 

 matites. This, among others, is very conspicuous in the white mica 

 pegmatite of the Vale of the Du Leivre, the felspar being in con- 

 siderable masses, while the plates of the white mica are in places 

 over nine inches across. 



These pegmatites belong to Sterry Hunt's " Endogenous rocks"; 

 he suggesting that the minerals crystallized out of solution. Such 

 a supposition can be easily understood when pegmatite is found 

 in small masses or in lenticular veins ; but it is not so easily con- 

 ceived when we have to treat with large masses.^ Still, however, 

 it is possible, if not probable, that Sterry Plunt may be right ; as in 

 great thicknesses of rocks there is no reason why there should not 

 be vast vugs filled with mineral solutions ; and when the minerals 

 crystallized out, they would fill such cavities, thus forming masses 

 of pegmatite or other rocks that had a similar genesis. In the 

 Aughowle district, co. Wicklow, there is a pegmatite locally called 

 " Bastard Granite," a variety of which is the " Plumose Granite " 

 of Jukes. This rock occupies a considerable area, and is somewhat 

 like the Canadian pegmatite, although not as coai'sely crystalline. 

 Fi'ora it I would suggest, that it is probable the coarse crystallization 

 of pegmatite may be original structure and not due to subsequent 

 metamorphism ; the mass of this Wicklow pegmatite is newer than 

 the normal Leinster Granite (Haugh ton's type), and consequently 

 ought to be younger than the time of the Eegional Metamorphism ; 

 as there is no newer metamorphism recorded in its vicinity that 

 might have affected it. At the same time, the Canadian rocks are so 

 much older, it is quite possible that their crystallization may have 

 been augmented by metamorphism. 



In the Province of Ontario and the neighbouring portion of the 

 Province of Quebec, the Archsean rocks are divided up into Huro- 

 nians and Laureutians. Selwyn has pointed out, that these divisions, 

 although lithological, have not been proved to be petrological ; while 

 as far as I can learn, Logan has not stated that he had found any 

 proofs of their being petrological groups. On the other hand, how- 

 ever, Dawson (Sir J. W.), Sterry Hunt, and others seem to insist 

 that they are not only lithological, but also petrological groups. 



A rock that appears to be considered a typical Ontario Laurentian 

 is a pinkish or flesh-coloured fine-grained gneiss. Hand-specimens 

 of this gneiss are undistinguishable from some of the rocks of the 

 Cambrians of the Saltees and Forlorn, S.E. "Wexford, of the Cambro- 

 Silurians, counties Wexford and Wicklow, of the Cambro-Silurians, 

 CO. Galway, of the Cambrian (?) of Erris, co. Mayo, and of the 

 Cambro-Silurians and Cambrians (?) of the co. Donegal. Some of 

 these metamorphic rocks, as for instance those at Forlorn, were 

 evidently originally felspathic and probably tuffose stratified rocks ; 

 this probably was also the case in many places where similar gneiss 

 occurs in the counties Galway, Mayo, and Donegal ; but there are 

 also in those places, aiid in the co. Wicklow, similar gneisses that 

 evidently were originally intrusions of felstone or felsite. In the 

 high ground called Chelsea Mountains, Ottawa county, there is a 



