338 \V. II. ('. SMITH — ARCHEAN ROCKS WEST OF LAKE SUPERIOR. 



of the contact between them, as justly observed by Barlow.* These 

 features have been so clearly and precisely described by Lawson in his 

 official reports that it is unnecessary to repeal them here; suffice it to 

 say that 1 have found his description to apply to all the contacts that I 

 have observed in the portions of Rainy River district nol reported on by 

 him. While it is true that some of these features, such as the intimate 

 interbanding of the gneisses or foliated granites and the schists, may be 

 regarded as analogous to the intimate interbanding frequently observed 

 in sedimentary strata : and while it is also true that some other features, 

 such as the angular fragments of one rock embedded in the other may, 

 where these brecciated zones are narrow, he due to the shattering of the 

 rocks along a line of fault, still there are many contact features which 



cannot be accounted for on any tl -y which holds to the sedimentary 



origin of the granite gneisses; such features are the apophyses of granite 

 which can be traced directly into the main mass, and which sometimes 

 are parallel to the planes of schistosity of the rocks which they invade 

 and sometimes cut across these planes. It must not be forgotten that 

 the phenomena that have been described by Lawson are not isolated 

 instances of peculiar occurrences extending in the aggregate over but a 

 small proportion of the contact line, but are typical examples every- 

 where characteristic of the contact, and the absence of which is rare. 



Character of the Contact. — A comprehensive and careful study of the 

 contact of the Laurentian and Ontarian rocks of Rainy River district 

 forces us to the conclusion that it is eruptive or irruptive in character. 



Origin of the Laurentian Rocks. — Either, then, the so-called Laurentian 

 rocks of this district have been irrupted in the form of a plastic magma 

 into the overlying rocks after these had become consolidated (the attrac- 

 tive theory of Dr Lawson) or else a remarkably continuous series of 

 later eruptions have been extruded in the planes of contact between 

 the Laurentian and Ontarian rock, presumably the line of weakness. 



Laurentian Roch the younger. — This latter theory is open to so many 

 and serious objections that it has i'vw adherents. If the former theory 

 is correct, the granite gneisses, with regard to all the relations of which 

 we have any certain knowledge, are younger than the rocks which they 

 invade, and, as they pierce both the Contchiching and Keewatin. their 

 present condition is of post-Keewatin origin. 



Selection of the Term Laurentian based mi imperfect Knowledge. — The 

 earlier descriptions of the Laurentian rocks of eastern Canada must be 

 regarded as imperfect, and the contact features have not been described. 

 They are therein spoken of as metamorphic sediment interior to the 



* The Contact of the Laurentian and Hnronian Rocks North of Lake Huron, by A. E. Barlow, 

 Am. Geologist, vol. vi, no. 1, ]>. L9, Also ante, pp. 313-332. 



