THE IROX BEAKING MEMBER. 261 



been certainly detenuiiiccl. Notliing will be here added to what was said 

 as to the character of the ferruginous rocks of the Marquette, Menominee, 

 and VermiUon hike disti'icts, except to state that not infrequently mingled 

 with the nonmechanical detritus are considerable quantities of mechanical 

 material. While nuich addition;vl work has been done upon them, it has 

 not gone far enough to warrant a detailed account. However, the Animikie 

 series, in its iron formation and its simple unfolded condition, is so remark- 

 ably like the Iron-bearing member of the Penokee series, that additional 

 material has been obtained and a careful study made of it in order to com- 

 pare its character and origin with those of the latter series. 



The following general description of that part the Animikie series 

 which contains in its Ijest development the iron formation is Ijy the senior 

 author.^ 



The Animikie roclcs arc exposed in four distinct areas, one of wliicli is separated 

 from the others by an overlap of the great gabbro which forms the base of the Kewee- 

 naw series. Tlie others are separated from one another, so far as known, by drift 

 covering only. The tirst of these areas is that which, with its principal development 

 in Canada, along the shores of Thunder bay, crosses into the United States in north- 

 eastern Minnesota, the national boundary line being within this formation from the 

 outlet of Gunflint lake eastward to the eastern extremity of Pigeon point. Around 

 Thumler bay the rocks of this series, which are chiefly black slates, graywackes, argil^ 

 laceous quartzite, iuterstratitied diabase, and gabbro layers, which are many in num- 

 ber and iudividuiilly often have a considerable thickness, are exposed on a large 

 scale. Immense dikes of gabbro and diabase also penetrate these layers, the gabl)ro 

 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 Animikie slates. 



In the vicinity of Thunder bay the Animikie rocks are often nearly horizontal, 

 but show a general tendency toward a southeastward inclination. As the formation 

 crosses into United States territory it shows more marked inclinations, which average 

 probably about ten degrees, though at times less than this, and sometimes rciieh as 

 much as twenty degrees. Tln^ mitional boundary line is situated within this forma- 

 tion from the month of Pigeon river to (Uinflint 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 Animikie series against an older formation of granite 

 and schists is very handsomely shown. The actual contact of the two formations is 



'R. D. Iiviiii;: On tliu Cl;issitii':iti()n "f tlir Early C'aiiiliviaii and Prc-Caiiiliiiaii Fnrniatidiis; 

 7tli Annual Rt'imrt U. S. Geol. Survey, ISSS. jip. tL'lM2'J. 



