358 8cienUfiG Proceedings, Royal Dublin Society. 



the Devonio-Silurians of Gralway and Mayo, and the Cambro- 

 Silurians and Cambrians of Donegal, Sligo, Mayo, Gralway, Water- 

 ford, Wexford, and Wicklow, calcareous rooks which are more 

 or less intimately connected with basic eruptive rocks, and which 

 appear to me to be in some way the result of vulcanicity (" Geol. 

 of Ireland," chap, xii., p. 194). In the township of Buckingham, 

 and elsewhere in Ottawa county, there are apatites that make 

 very like the above-mentioned Irish Cambro- Silurian and Cam- 

 brian limestones, they being associated and entangled with basic 

 eruptive rocks — and, perhaps, it may be allowable to suggest, that 

 in some way not as yet explained the carbonate is replaced by 

 the phosphate of lime by methylosism — a somewhat allied case 

 being the change of pyroxene into amphibole by some unknown 

 paramorphosic action. 



The rocks which par excellence are called Laurentians belong 

 to the lithological groups for which I have suggested the names 

 " Gneissic Granite" or " Granitoid Gneiss" and " Gneiss Series" ; 

 while the Huronian rocks par excellence belong to the groups called 

 " Schist Series" and " Submetamorphic rocks. ''^ 



To these general classifications, however, there are exceptions ; 

 because, as in the Ottawa country, there are found in the districts, 

 at the present time mapped as Laurentian," more or less extensive 

 tracts of schistose rocks ; while, on the other hand, in the Huronian 

 tracts there are some gneiss. This is similar to what occurs in the 

 Old Country, as rarely will you find rocks of the " Gneiss Series," 

 or even of the " Gneissic Granite," in which subordinate schistose 

 rocks do not occur ; while in the "Schist Series" there are always 

 in places gneissoid rocks, and even in places among the " submeta- 

 morphic rocks." As already mentioned, the Laurentians and 

 Huronians are undoubtedly lithological groups ; but are they also 

 petrological, that is, geological groups? This we have now to 

 consider. 



In the province of Ontario there are numerous junctions of the 



^ These different groups are fully explained in chapter x., page 177, of the " Geo- 

 logy of Ireland." 



^ Selwyu specially mentions that the present boundaries and mapping are only pro- 

 visional, and that hereafter many tracts of Huronian rocks will probably be found in the 

 areas at present mapped as Laurentian. 



