220 //. L. Smyth — Lower Menominee and 



contains actinolite, magnetite and dark chert. This is the por- 

 tion of the formation that most disturbs the needle. While 

 thin sections of this rock have not yet been examined, the 

 constituent minerals are evidently not so distinctly segregated 

 as is usual in the Marquette actinolite schists. Otherwise the 

 rocks bear considerable resemblance to each other. 



The lower iron-bearing rocks of the western Marquette dis- 

 trict have beeu traced southward from the northwestern end 

 of the Republic tongue, for a long distance. Coinciding with 

 the lower portion of the iron-bearing member, or the magnetite 

 actinolite schist, is a very strong and continuous line of mag- 

 netic attraction which was first followed for part of the dis- 

 tance by Major Brooks over 20 years ago. This line of attrac- 

 tion is proved to coincide with the magnetite actinolite schist 

 member by occasional outcrops and by explorations at con- 

 siderable intervals. East of it is a granite area, and between 

 the two, the lower quartzite outcrops near the northern end of 

 the Republic tongue. Farther south the quartzite is pre- 

 sumably present, but no outcrops have been found in the 

 heavily drift-covered country. This line of attraction may be 

 called the A line. Less than half a mile west of the A line a 

 second line of magnetic attraction runs parallel to it for a con- 

 siderable distance, which may be called the B line. This B 

 line has been traced completely round an oval area in which 

 granite and gneisses have been discovered in three sections. 

 These gneisses lie east of the axis of the enclosed oval, and 

 strike parallel to the B line and dip towards the east. Through- 

 out the 20 miles or more through which the B line has been 

 followed no outcrops of any kind have been found upon it. 

 That it does, however, represent a belt of magnetic rock entirely 

 enclosing an Archaean area admits of no possible doubt. Ex- 

 plorations along the A line have established the fact that the 

 geological succession in going from east to west across it is 

 from older to younger formations. That is, the dip is towards 

 the west. The gneisses in the oval enclosed by the B line dip 

 toward the east on the east side of the axis of the oval. This, 

 coupled with the fact that both the A and B lines, in the one 

 case partially, in the other completely, encircle domes of 

 Archaean rocks, makes it certain that the rocks which they 

 represent dip towards each other. In other words, in that 

 part of their course in which they run parallel they occur on 

 opposite limbs of a synclinal fold. Moreover the space be- 

 tween them is known by exposures and exploration to contain, 

 upper Marquette quartzite and mica- schists. 



This occurrence of the A line on one side, and of the B 

 line on the other, of a long and very narrow synclinal fold, 

 together with the entirely similar general relations of each to 



