ON THE LAKE SUPERIOR REGION 103 



Below the Keweenawan is the Huronian system, which in our 

 opinion should include the following series: In the Marquette dis- 

 trict, the Huronian should include the Upper and Lower Marquette 

 series, as defined in the monographs of the United States Geological 

 Survey, or the Upper, Middle, and Lower Marquette series, as given 

 in the previous paragraphs. In the Penokee- Gogebic district, the 

 Huronian should include the series which have been called the Peno- 

 kee- Gogebic series proper, and the limestone and quartzite which 

 have local development, and which we visited east of the Presque Isle 

 River. In the Mesabi district, the Huronian should include the 

 Mesabi series proper, and the slate-graywacke-conglomerate series, 

 unconformably below the Mesabi series. In the Vermilion district, 

 the Huronian should include the Knife slates and the Ogishke con- 

 glomerates. In the Rainy Lake district, the Huronian should include 

 that part of the Couchiching of the south part of Rainy Lake which 

 is limited below by basal conglomerate as shown at Shoal Lake. In 

 the Thunder Bay district, the Huronian should include the Animikie 

 and the graywacke series in the Loon Lake area. In the original 

 Huronian area, the Huronian should include the area mapped by 

 Logan and Murray as Huronian, except that the Thessalon green- 

 stones should probably be excluded. 



Unconformably below the Huronian is the Keewatin. The 

 Keewatin includes the rocks so defined for the Lake of the Woods 

 area and their equivalents. We believe the Kitchi and Mona schists 

 of the Marquette district, the green schist (Mareniscan) of the Peno- 

 kee-Gogebic district, the greenstone series of the Mesabi district, 

 the Ely greenstones and Soudan formation of the Vermilion district, 

 the part of the area mapped as Keewatin by Lawson in the Rainy 

 Lake district not belonging structurally with the Couchiching, and 

 probably the Thessalon greenstone series on the north shore of Lake 

 Huron, to be equivalent to the Keewatin of the Lake of the Woods, 

 and, so far as this is true, they should be called Keewatin. 



For the granites and gneissoid granites which antedate, or pro- 

 trude through, the Keewatin, and which are pre-Huronian, the term 

 "Laurentian" is adopted. In certain cases this term may also be 

 employed, preferably with an explanatory phrase, for associated 

 granites of large extent which cut the Huronian, or whose relations 

 to the Huronian cannot be determined. 



