524 C. K. LEITH 



and Logan's Original Huronian, based on lithological character and 

 relations to the intrusives. 



Dr. Coleman's conception of the Laurentian is the same as that 

 attributed to the Canadian geologists in general in the comments on 

 p. 440. 



Mclnnes 1 describes the geology of the Seine River and Lake She- 

 bandowan map-sheets, which cover an area extending west and north- 

 west of Port Arthur, Ontario. Laurentian granites and gneisses With 

 many variations occupy three fourths of the area. The relations to 

 the overlying Keewatin and Coutchiching rocks, wherever they have 

 been found in contact, have been those of intrusion. 



The Huronian is represented by Coutchiching and Keewatin rocks. 



Coutchiching mica-schists and fine-grained gneisses, a continuation 

 of Lawson's Coutchiching in the Rainy River district to the west, enter 

 the area of the Seine River sheet on the west side. However, toward 

 the east these rocks become associated with large quantities of gneisses, 

 and for the eastern two thirds of the Seine River sheet and for the entire 

 Lake Shebandowan sheet the gneisses are predominant and the belt is 

 mapped as Laurentian. In other parts of the district the Keewatin 

 schists, near their contact with the Laurentian gneisses, assume a char- 

 acter exactly similar to the Coutchiching schists and associated gneisses, 

 and could not be lithologically distinguished. Indeed, the Coutchich- 

 ing seems to be an extremely altered phase of the Keewatin. 



In long bands infolded with the Laurentian and conforming in 

 strike with the foliation of the gneiss are bands of Keewatin rocks 

 varying greatly in width. They vary in composition from extremely 

 basic igneous masses, and their derived products, to acid quartz-por- 

 phyries, and their derived products, and include also quartzites, con- 

 glomerates, and slates. The basic rocks form the largest volume of 

 the rocks of the series. The series is separated lithologically in map- 

 ping into three divisions. There can be no doubt that the Keewatin 

 here includes rocks which are of widely differing age. 



Overlying unconformably the Keewatin rocks is the Steep Rock Lake 

 series, so named from its occurrence in the neighborhood of this lake. 

 The series is mapped as an upper division of the Keewatin series. As 



1 " The Geology of the Area Covered by the Seine River and Lake Shebandowan 

 Map-Sheets, comprising Portions of Rainy River and Thunder Bay Districts, Ontario," 

 by Wm. McInnes : Ann. Rept. Geol. Surv. of Canada, Vol. X, Pt. H, 1899, pp. 13-51. 

 With geological map. 



