KiNAHAN — On Canadian Arc/man, and Pre- Cambrian Bocks. 359 



Huronian and Laurentian rocks, those that have been most studied 

 being in the neighbourhood of the Canadian Pacific Railway, be- 

 tween Port Arthur, on Lake Superior, and Winnipeg. Of these, 

 that to which greatest attention has been directed is the junction 

 at the rapids from the Lake of the Wood close to the settlement 

 of the Rat Portage. This junction is very well exposed at the 

 rapids, and in other places, and is stated by Sir W. J. Dawson and 

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

 lightly passed over, especially by an Irish geologist, when he re- 

 members the boundary between the Cambrians and Cambro-Si- 

 lurians in south-east Ireland. These boundaries are so intricate in 

 diiferent places in the county Wicklow, especially in the neighbour- 

 hood of the Carrick Mountain and G-lenealy, and in the county 

 Wexford, at Poulshone and Barrow, that it required a man of special 

 powers of observation, such as Jukes, to be able to point out the 

 unconformability of the two groups. As, from the light supplied 

 by him, I have been able to satisfy myself that such intricate un- 

 conformabilities may occur, I would be rash in stating that very 

 similar unconformabilities may not occur in Ontario ; yet, at the 

 same time, I may be allowed to make suggestions, or, in the pre- 

 sent case, to state that I see no reasons for supposing that there 

 is necessarily an unconformability between the Laurentians and 

 Huronians. First, in no place that I could hear of, in Ontario or 

 Quebec, are the Huronian rocks found resting on the upturned 

 edges of the Laurentians, while all the junctions seem to be such 

 as what we should naturally expect to find at the meeting of two 

 distinct lithological groups. This question, however, has got into 

 a tangle, as it must be allowed that in Europe, at the present time^ 

 our geological maps should more properly be called lithological, 

 as the major portions of the divisions marked on them are litholo- 

 gical and not geological divisions. This is specially the case with 

 the Cainozoic and Mesozoic, as the different groups in them are 

 merely lithological groups ; but it is not so much the case in the 

 older (Palaeozoic), as in it the " formations" seem in a great mea- 

 sure to be geological groups; but the sub-divisions are not so. 

 Take, for instance, the sub-divisions of the English Devonio- Silu- 

 rians and those of the Cambro-Silurians, and look for them in the 

 same order in either Ireland or Scotland, and the result will be 

 that they are found to be mixed up confusedly. The undue pro- 



