KiNAHAN — On Canadian Archcean, and Pre-Camhrum Bocks. 355 



mentioned, appears to me to be due, not to excessive metamor- 

 phism at one and the same time, but to the rocks having under- 

 gone two, three, or even more, successive, but independent invasions 

 of metamorphism, which developed instead of obliterating the la- 

 minse due to the earlier metamorphisms. Excessive metamorphic 

 action in a portion of an area will change the rocks into granite 

 (" Greologj of Ireland/' chap, x., p. 175), but if a milder metamor- 

 phism invades rocks at different successive times, the plates or 

 laminee should be more and more developed. This can be seen on 

 a small scale in various places in Ireland, the best, perhaps, being 

 the gneiss developed adjoining the already-mentioned " Slieve 

 Croab granite," county Down, Mourne Mountain district (" Greol. 

 of Ireland," chap, xi., p. 192). In general, in the Irish localities, 

 the metamorphism seems to be due to metapepsis succeeding parop- 

 tesis, or in other places to paroptesis coming after metapepsis ; 

 while in some places one period of metapeptic action appears to 

 have followed a former one ; and we can well imagine that very 

 old rocks may have been subjected at various times to metapepsis, 

 with, in more limited areas, paroptesis. In the west of county 

 Gralway (Connemara), to the north-westward of the tract of meta- 

 morphic granite, there are the previously-mentioned outliers, in 

 part granite and in part granitoid gneiss. These, I would suggest, 

 may probably be patches which at first were altered by paroptesis, 

 while subsequently, when metapepsis invaded the country, they 

 became granitoid- gneiss, while the adjoining rocks were changed 

 into rocks of the " schist series." Such a supposition would account 

 for there not being the ordinary gradation from the granitoid 

 gneiss through the " gneiss series" into the " schist series." 



The coarse foliation can be well seen and studied in the gneis- 

 sie granite called Labradorians by the Canadian geologists, and 

 marked "La" on Selwyn's new map. This rock has no exact 

 representative among the Irish rocks. The rocks nearest in struc- 

 ture are, perhaps, the gneissic granite ones of the barony of Moy- 

 ouUen, county Gralway, which are evidently of metamorphic origin, 

 and probably of Cambro-Silurian age ; the gneissic-granite pro- 

 trusions and courses in the Castlebar district, county Mayo, which 

 evidently came up originally as intrusions through the associated 

 Cambro-Silurian rocks ; and the metamorphic gneissic granite of the 

 Erris district, also in the county Mayo. There are also in the county 



