10 GEOLOGICAL SURVEY, CANADA. 



the latter being a large part of the basement upon wliioh the Steep- 

 rock series was unconformably deposited. 



I approached Steeprock lake from the west, coming up the 

 Seine river from Eainy lake. In doing so I traced out nearly con- 

 tinuously the geological boundary between the Keewatin of Eainy 

 lake and a series of quartzites and slates which for convenient 

 reference I shall here call the Seine series. The Seine series lies 

 to the south of the Keewatin, and is post-Keewatin in age. The 

 contact between the two series is marked not only by the striking 

 contrast in the general character and physical appearance of the 

 rocks, but also by the occurrence of several lenses of conglomerate, 

 of which the most important is that of Shoal lake. To the south of 

 the quartzites and slates are the mica schists of the Coutchiching 

 series. The relations of the Seine and Coutchiching series will not 

 here he discussed. 



It was my expectation in following the basal conglomerates of 

 the Seine series eastward, that they would prove to be the same as 

 one of the conglomerates described by Smyth on Steeprock lake. 

 This expectation was, however, not realized. The boundary line 

 between the Keewatin and the Seine series was followed with a 

 steady E.-W. strike along the Atikokan river as far as the iron mines 

 east of Sabawe lake. The east and west strike of the base of the 

 Seine series is transverse to the more nearly N.W.-S.E. folds, which 

 have involved the Steeprock series in vertical attitudes a little to 

 the north of the Atikokan river. This stratigraphic and structural 

 relationship indicates that the folding which involved the Steep- 

 rock series as a sharp trough sunk down into the older Archaean 

 had taken place anterior to the deposition of the Seine series ; since 

 no such folding affects the even trend of the strike of the latter. 

 It is, therefore, inferred tentatively that the Steeprock series is 

 older than the Seine series, an inference which should be confirmed 

 by a careful search in the conglomerates of the Atikokan river for 

 pebbles of the Steeprock series. To the south of Sabawe lake the 

 Seine series is cut by the granite gneiss which forms so large a 

 j'eature of the geology of the Seine River and Shebandowan sheets. 

 "^he phenomena of intrusion and the metamorphism of the Seine 

 series consequent upon the intrusion are splendidly exemplified. 

 No one who is at all familiar with the geology of the Thunder Bay 

 district will question the unconformable superposition of the 

 Animikie upon the complex of which this granite gneiss forms a 



