G. H. Kinalian — Irhh and Canadian Rocks, Compared. 163 



structures peculiar to some calcareous or allied rocks ; while in the 

 typical gneissic granite or granitoid gneiss, all the original structural 

 lines are obliterated ; they or any subsequent foliation being replaced 

 by a nearly perpendicular one ; but the strata of this new foliation 

 seems to follow the strike of the original stratification. 



In some places there is a hard boundary between the gneissic 

 granite and the gneiss ; or the latter may be absent, the granite 

 being margined by schist. This seems to suggest that it is possible 

 the coarse foliation of the gneissic granite may be due to a second 

 Metapepsis of a more limited extent ; that while it affected them and 

 developed the leaves of foliation, it did not invade the adjoining 

 strata. We will now proceed to the metamorphic rocks of Canada.^ 



A feature that strikes a stranger is the massive coarseness of the 

 foliation in some of the Laurentian gneiss. This appears to me, as 

 mentioned in connection with the Irish rocks, to be due not to exces- 

 sive raetamorphism at one and the same time ; but to stages, the 

 rocks having been invaded two, three, or even many more times by 

 successive but independent periods of metamorphism ; thus develop- 

 ing but not obliterating the leaves due to the earlier metaraorphisms.^ 



This coarse foliation is very conspicuous in the previously men- 

 tioned gneissic granite called Labradorians by the Canadian geolo- 

 gists. Of it we have no exact representatives among the Irish rocks ; 

 the nearest approach in structure being the gneissic granites of 

 Carnsore, co. Wexford ; of the barony of Moycullen, co. Galway ; of 

 the Erris district, co. Mayo ; and of the Castlebar district, also in 

 Mayo. The latter being an intrusion, is in this respect more like 

 the Canadian rocks than the others, which were originally stratified 

 rocks.^ 



^ It appears remarkable that metamorphism seems to be so restricted to the older 

 rocks in Canada. Is it possible, that in the areas called Archaean, from their 

 lithological character, there may be newer rocks included? If not, why should 

 metamorphism be so confined to them, when in a little spot like Ireland we have 

 metamorphosed Cambrians, Cambro- Silurians, Devono-Silurians, Carboniferous (?) 

 and Lias. 



^ Excessive metamorphic action in a portion of an area will change rocks into 

 granite ; but if a milder metamorphism invades rocks at different successive times, it 

 ought to more and more develope the plates or leaves without obliterating them. This 

 can be seen on a small scale in different places in Ireland, the best perhaps being along 

 the before-mentioned boundary of the older, or " Slieve Croob" granite of the Mouriie 

 Mountain district. In general in Irish localities the additional metamorphism seems 

 due to Metapepsis, succeeding Paroptesis, or vice versa ; but in some places one period 

 of Metapepsis seems to have been followed by another. As the Canadian rocks are so 

 ancient, we may suppose that at least three or four times they have been covered by 

 a sufficient depth of strata to develope metamorphic action, but not sufficient to 

 convert them into typical granite. It appears to me an interesting problem, why in 

 such vast areas we should have gneiss without its being, in part, converted into 

 granite of metamorphic origin ? Unless we suppose that some of the rocks that are 

 now gneiss wei-e at one time granite, but by subsequent metanioi'i)hic action foliation 

 was developed in it, and thus by degrees it was changed into gneiss. Such a change 

 can take place; because if the "Slieve Croob granite" was covered up with a 

 sufficient depth of strata, it would be entirely converted into gneiss. 



^ Mixed up, either as strata or small intrusions, ynt\\ these rocks of "Wexford, 

 Galway, and Mayo, are eruptive rocks ; they, however, were portions of the geo- 

 logical groups (Cambrians and Cambro- Silurians) and not subsequent intrusions, 

 as was the case in respect to the Castlebar district porphyritic gneiss. 



