166 G. H. Kinahan — Irish and Canadian Roclis, Compared. 



as Laurentians ^ greatei* or less exposures of schistose rocks ; while 

 among the Huronians, gneiss occurs. This is similar to what occurs 

 in the old country ; as always in a tract belonging to the " Gneiss 

 series," and even often in the " Gneissic Granite," subordinate 

 schistose rocks appear, while in the " Schist series," and even in 

 some places in the " Sub-Metamorphic rocks," subordinate gneiss 

 occurs. From ocular demonstration it is evident, as has been 

 already mentioned, that the Laurentians and Huronians are litho- 

 logical 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 

 Laurentians and Huronians. Those that seem most known and have 

 been more generally studied occur more or less in the neighbourhood 

 of the Canadian Pacific Railway, between Port Arthur and Winnipeg ; 

 and of these the one to which the greatest attention has been directed 

 is the section at the rapid of the outfall of the Lake of the Woods 

 near Eat Portage. This junction is stated by Sir J. W. Dawson and 

 others to be a "Fault boundary." Such a statement cannot be 

 lightly passed over, especially by an Irish geologist, when he thinks 

 ot" the intricate boundaries in S.E. Ii'eland (cos. Dublin, Wicklow, 

 and Wexford) between the Cambrians and the Cambro-Silurians, that 

 were first unravelled by Jukes ; especially those in the neighbour- 

 hood of Carrick Mountains and Glenealy, co. Wicklow, and at 

 Poulshone and Bannow, co. Wexford. As, from the light supplied 

 by Jukes, I was able to satisfy myself that such intricate uncon- 

 formities may occur, I should be rash to state that somewhat similar 

 unconformabilities did not occur in Ontario ; yet at the same time I 

 may be allowed to make suggestions, — or to say that I could not find 

 any satisfactory reasons for supposing that there is an unconform- 

 ability between the Huronians and the Laurentians. 



Here we may digress and ask what are geological — that is, petro- 

 logical divisions ? Years ago I have heard American geologists state 

 tliat the European maps are more lithological than geological ; and 

 the more the subject is studied, the more reasons appear to believe 

 they are right in this opinion ; as the major number of the divisions 

 on these maps partake more of lithological grouping than of being 

 natural petrological, that is, geological, divisions. This is especially 

 the case in reference to the Kainozoic and Mesozoic rocks ; as the 

 different groups in them are merely lithological groups ; but it is 

 not so much the case in the Palaeozoic rocks, as in the latter the 

 groups for the most part have a claim to be petrological ; but not 

 always, as the rocks between the Carboniferous and the Cambro- 

 Silurian are still in a higgledy-piggledy condition. The subdivisions, 

 however, are only lithological, as is demonstrated by a comparison 

 of the rocks of Ireland with those of England ; the sub-groups that 

 occur in regular succession in the English groups being quite mixed 

 up in the Irish ones.^ 



1 Sehvyn lias specially mentioned, that Ihe present boundaries and mapping of this 

 county is only provisional, and that hereafter there will, probably, be found in it 

 tracts of rocks belonging to the Huronians. 



2 It has been stated,— pala^ontological evidence proves these different groups; 



