160 O. H. Kinahan — Irish and Canadian Rocks, Compared. 



The south-east of Ireland is very instructive, as on both si<les of 

 the rib of granite of the Leinster range there are bands of Paroptesis 

 rocks; but while those to westward of the rib, with some peculiar 

 exceptions hereafter mentioned, retain their Paroptesis form, those 

 in the band to the eastward of the rib have been changed into gneiss 

 and schist by the Metapepsis that subsequently invaded those por- 

 tions of the counties of Dublin, Wicklow and Wexford. Therefore 

 we have as a general rule to the westward of the granite rib a band 

 of "baked rocks" (due to Paroptesis), while eastward of the rib 

 there is a band of gneiss and schist (due to Paroptesis and subse- 

 quent Metapepsis), outside of which are sub-metamorphic rocks. The 

 metapeptic action that invaded the latter area seems to have been 

 most intense in lines running about E.N.E. and W.S.W., so that if 

 we traverse the county from south to north, we cross over zones of 

 " submetamorphic rocks" and of rocks belonging to the "Schist 

 Series ; " ^ that is, if we ignore other metamorphic actions now to be 

 mentioned. 



In this region, besides the intrusion of the normal Leinster granite 

 (Haughton's type), which is supposed to have taken place in Post 

 Cambro-Silurian time, there were also newer intrusions that may 

 have occurred in Devono-Silurian^ times; and as the latter were 

 accompanied by Paroptesis, the rocks in connection with them are 

 additionally altered ; the " baked rocks " to the westwai'd of the rib 

 being changed into schists, while to the eastward of the rib they 

 have had the metamorphism intensified. There is also to be con- 

 sidered what may have been the effect of the granitic roots (the 

 laccoliths of Gilbert) of the eruptive rocks contemporaneous witli 

 the Cambro- Silurians, as these also seem to have had Paroptesis in 

 connection with them, and this necessarily was prior to the Metapepsis 

 of the district. Although the effect of this Paroptesis is not now 

 very conspicuous, yet it should be mentioned, as it sliows how many 

 different times the same rocks may be subjected to metamorphic 

 action of some kind or another. 



There is also in this area a peculiarity in the metamorphism. 

 Years ago Jukes pointed out that the younger or Cambro-Silurian 

 rocks were more altered than the older Cambrians ; and suggested 

 that it might be more apparent than real, as none of the Cambrians 

 in contact with the granite were exposed. But down in the south- 

 east of the Co. Wexford, away from the granite rib, the same thing 

 occurs ; as nearly invariably along the boundary between the 

 Cambrians and the Cambro-Silurians the last are more altered than 

 the first.^ To the north-west and westward of Eathdrum, Co. 



^ Ibid, Chapter x. page 175. 



^ In the old world the terms Lower Silurian, Upper Silurian, Devonian and Lower 

 Old Red Sandstone are used so indiscriminately that it is hard to know exactly what 

 rocks are meant. In this paper Selwyn will be followed and to indicate Lower 

 Silurians Phillips's term Cambio-Silurian will be used, while all the others will be 

 included under the term Bevono- Silurian. 



3 In connection with this metamorphism of adjoining rocks, it may be mentioned 

 that in the Belvoir section (Cambro-Silurian), Co. Clare, there are some beds in the 

 fossiliferous strata altered apparently for no particular reason. 



