jR. D. Irving — Is there a Huronian Group f 261 



from each other, so far as known,, by drift covering only. The 

 first of these areas is that which, with its principal develop- 

 ment in Canada, along the shores of Thunder Bay, crosses into 

 the United States in northeastern Minnesota, the national 

 boundary line being within this formation from the outlet of 

 Grunflint Lake eastward to the eastern extremity of Pigeon 

 Point. Around Thunder Bay the rocks of this series, which 

 are chiefly black slates, grey wackes, and argillaceous quartzites, 

 with interstratified diabase and gabbro layers, are exposed on 

 a large scale. Immense dikes of gabbro and diabase also 

 penetrate these layers, the gabbro dikes, which are at times 

 several hundred feet in thickness, being noticeably much closer 

 in character to the great gabbro at the base of the Keweenaw 

 series than to those gabbros which are interleaved with the 

 Animike' slates. 



In the vicinity of Thunder Bay the Animike rocks are 

 often nearly horizontal, but show a general tendency toward 

 a south-eastward inclination. As the formation crosses into 

 United States territory it shows more marked inclinations, 

 whose amounts average probably about ten degrees, though at 

 times less than this, and again reaching as much as twenty 

 degrees. As already said, the national boundary line is situ- 

 ated within this formation from the mouth of Pigeon River to 

 Gunflint Lake, but on the north side of the latter lake, and 

 again to the north of the next lake to the east, called North 

 Lake, the unconformable abutment of the Animike series 

 against an older formation of granite and schists is very hand- 

 somely shown. The actual contact of the two formations is 

 not seen, but the exposures approach to within a few feet of 

 each other, and their relative attitudes are such as to leave no 

 question whatever with regard to the unconformity. Not only 

 is this shown by the vertical position of the schists as con- 

 trasted with the flat inclinations of the slaty series, but also by 



Olivine, Gdbiro 



\ J^oonZ.aXe Qun,Tlirtt JLiake 



A7iirni7c^ Series > Sc7ttH qrcmrte 



Fig. 9. — Section across Gunflint and Loon Lakes, on the national boundary 

 line. Scale 1-J miles to the inch. Designed to show the relation of the Animike 

 series to the older schists and granite, and to the newer Keweenawan gabbro. 

 Scale 1 mile to the inch. The black bed at the base of the Animike is the 

 ferruginous horizon. The remainder of the Animike in the section is composed 

 of slates and slaty quartzites with interstratified greenstones. 



the way in which the latter beds, to the north of the two lakes 

 mentioned, fit into the sinuosities of outline of the older for- 

 mation. The entire contrast as to lithological characters be- 

 tween the two sets of rocks furnishes further proof. A north 



