G. H. Kinahan — Ii-kh and Canadian Rocka, Compared. 161 



Wiclvlow, there are rocks that Wj^ley considered to be meta- 

 morphosed Cambrian, but Jukes put them in the Cambro-Silurians. 

 As has been mentioned in my description of the Irish rocks, I believe 

 Wjdey was right, and that Jukes was mistaken by supposing that no- 

 where in the county were Cambrian rocks so much altered. This 

 confusion due to different kinds and times of metamorphism, will be 

 referred to hereafter when speaking of the Canadian rooks. 



The Cambrians of the Carnsore district (S.E. Wexford) illustrate 

 some peculiar phases in metamorphism. If you follow the rocks 

 northward from Carnsore by Carne to Greenore, there are ; first, 

 oligoclasic porphja-itic granite, then oligoclasic porphyritic granitoid 

 .gneiss or gneissic granite, that graduates through gneiss into schists. 

 Gro, however, a short distance westward, and on the Saltees Island 

 are found orthoclasic gneissic granites, usually fine-grained, in 

 which are a few subordinate hornblendites (hornblende-schist), while 

 on the mainland at Forlone Point (Kilmore Pier) there are at the 

 south hornblendites, that by an alternation of beds graduates into a 

 considerable thickness of orthoclasic fine granitoid gneiss ; the last, 

 to the north, has a hard boundary, outside of which are horn- 

 blendites and other schists. This sudden change in lithological 

 characters is important. 



In the Mourn Mountain district, Co. Down, there are two distinct 

 intrusions of granite, the first, "Slieve Croob granite," probably at the 

 close of the Cambro-Silurian period, and the second at the close of 

 the Carboniferous period. The Cambro-Silurian rocks of the country 

 are altered (sub-metamorphic) by Metapepsis, probably an adjunct 

 of the genesis of the older granite ; but subsequently a new meta- 

 morphio action invaded the rocks in the vicinity of the boundary 

 between the granite and sub-metamorphic rocks, changing the latter 

 into gneiss and developing a foliation in the granite, the roclcs now 

 occurring: in the followina: order : — 



/-, • . -Li The original granite intrusion, 



(ineissio granite ) o & 



1. Granite 



2 



3. Hard boundary. 



5* Schists ( "^^^ original submetamorphic rocks. 



The newer granite (Post-Carboniferous ?) has not to any great 

 extent altered the adjoining strata ; but at the same time more or 

 less signs of Paroptesis are apparent. 



In the Counties Galway and Mayo different phases of metamor- 

 phism can also be studied. At first the metamorphism may appear to 

 follow general rules, but when details are entered into, here as 

 elsewhere, jDeculiarities hard to be explained are found. 



If a traverse is made northward from Furbogh, west of Galway 

 town, to Oughterard across the strike of the rocks, you start from a 

 tract of porphyritic oligoclasic granite that merges into porphyritic 

 oligoclasic gneissic granite, while the latter graduates through gneiss 

 into schists; still further north in the Co. Mayo these schists merge 

 into unaltered Cambro-Silurian rocks. Although across the strike 



DECADE III. — VOL. II. — NO. IV. H 



