682 THE JOURNAL OF GEOLOGY. 



In column III. I have made two divisions of the ferruginous 

 rocks. These are sharply separated in aspect, and in the 

 western part of the Marquette district at least, each has its own 

 place in the stratigraphical column. The specular jasper when 

 present, always overlies the magnetite-actinolite-schists. No 

 theory of difference in origin is implied, and the distinction is 

 entirely one of convenience. 



Dr. Wadsworth has not, I believe, published a detailed 

 section of the rocks at Republic. 



III. 



All the rocks of the Upper and Lower Marquette series have 

 been closely folded in the Republic area into a syncline, about 

 seven miles long, the axis of which runs about northwest and 

 southeast. The present fold for most of its length is sunk 

 deeply into the Archean, the axis being practically horizontal. 

 South of Smith's Bay, however, the axis rises with a pitch of 

 nearly 45 °, the several formations swing around successively in 

 horseshoe form through an angle of 180 , from the northeastern 

 to the southwestern side, and the fold, so far as it affects the 

 bedded rocks, abruptly terminates. Through the greater part of 

 the length of the trough the rocks on the two sides of the axial 

 plane have been squeezed nearly into parallelism. On the 

 eastern side, few of the many surface observations show in the 

 upper quartzite a dip less than 8o°, which is the average to a 

 depth of more than 900 feet in No. 8 shaft. On the western 

 side the dips are somewhat lower, but will average nearly 8o°. 



The formations in the unconformably underlying Lower 

 Marquette series on the eastern side of the trough dip at 

 uniformly higher angles, and stand either vertical, or show a 

 slightly overturned dip towards the east. There is then a pretty 

 constant upward convergence of the two series along the contact, 

 averaging perhaps 15 . 



The distance in which the turn is made at the southeast end 

 of the trough, or at the bottom as it really is, is relatively very 

 short. The radius of the generalized curve into which the 



