KiNAHAN — On Canadian, Archcean, and Pre-Cambrian Rocks. 351 



(Devonio-Silurian^), whicli were accompanied by Paroptesis; so 

 that in connexion with them we find the rocks more altered, the 

 " baked " rocks in the band to the westward of the ridge having 

 been changed into schists ; while in places to the eastward the 

 metamorphism has been intensified. 



A fact which seems to be important is, that in connexion with 

 the interstratified igneous Cambro-Silurian rocks there are the 

 granitic roots {laccoliths of Gilbert), and in connexion with these, 

 from the appearance of the adjacent rocks, there seems to have 

 been Paroptesis; this, however, can only be conjectured, as the 

 more recent Metapepsis has more or less obliterated it. Still, how- 

 ever, it should be kept in mind, as it shows how many stages of 

 metamorphism rocks may have gone through. 



There is also in this region a peculiarity still to be mentioned 

 in the metamorphism. Years ago, in reference to the rocks of 

 Dublin and Wicklow, Jukes pointed out that the younger, or 

 Cambro-Silurian rocks were more altered than the older, or Cam- 

 brians. This, if I remember rightly, he suggested, was more 

 apparent than real, as only the Cambro-Silurian in contact are 

 exposed. But down S. E,, in the county of Wexford, away from 

 the granite ridge, the same thing occurs ; as, nearly always, along 

 the boundary between the Cambrians and Cambro-Silurians the 

 latter are more altered than the former.^ In the county Wicklow, 

 to the north-west and westward of Eathdrum, there are rocks that 

 Jukes put in the altered Cambro-Silurians, while Wyley would 

 put them in the Cambrians, as has been mentioned elsewhere. I 

 believe Wyley is right, they being intensely altered Cambrians, 

 Jukes including them among the Cambro-Silurians on account of 

 his having proved elsewhere that the latter were much more 

 altered than the former. This confusion of the Cambro-Silurian 

 and Cambrian will be referred to again. 



^ In the Old "World the terms Lower Silurian, Upper Silurian, Devonian, and 

 Lower Old Eed Sandstone, are very much connected together. Selwyn, however, in 

 his writings, seems to have adopted for the older rocks Phillips' term, Camhro- Silurian; 

 and for the newer, Devonio- Silurian : as these are very expressive they will be used 

 in this Paper. 



- In connexion with this phenomenon it may he mentioned that, in the Belvoir 

 section (Cambro-Silurian), county Clare, there are fossiliferous and jasperized rocks 

 alternating. The reason of the difFerent degrees of action in the county Wexford 

 rocks I have attempted to explain in the "Geological Survey Memoirs." 



