IXTERESTING LOCALITIES OF ^'EGAUNEE FORMATION. 385 



bands between the finei'-gniined ones distinctly sliow the clastic character 

 of the quartz grains. 



Humboldt area. — Wcst of scc. 20 tlicrc are no exposures foi' a mile or more, 

 but in sec. 18 appears the southeastern end of the Mount Humljoldt ridge 

 (Atlas Sheets XVI and XIX). This is of minor iin])ortance in sec. 18, but 

 in sees. 11 and 12, T. 47 N., R. 21) W., soutli nt' lluiiiboldt, becomes an 

 important bluff, with steep-faced sides and an uneven top. Everywhere 

 lapon the ridge are large and luimerous exposures of the Negaunee forma- 

 tion. P^xcept upon the north and west l)orders, tlic i-ocks of tlie Negaunee 

 formation are all dense, fine-grained, but distinctly banded griinerite- 

 magnetite-schists. The strike generally con-esponds with the trend of the 

 formation. In the ledges in sec 18, southeast of the road, tlie scliistosity is 

 nearly east and west, while the true bedding, as shown liy the minor folds, 

 is southeast and northwest. The axes of these minor folds ])lunge to the 

 southeast. On the north and west faces of the bluff the strikes x-cwv with its 

 form, being parallel to its face — that is, in })assing from the north face of the 

 bluff toward the west the strikes gradually change to the southwest, then 

 to the south, and in the southwestern ])art even to the southeast. The dips 

 are ver}" generally to the north or northeast, but in the southwestern ])art 

 of the area there are, for shoi't distances, reverse or southern dij)s. Between 

 the ledges having a north and those having a south dip there is a little 

 valley, which is thei-efore on the crown of the anticline. This strongly 

 suggests for this part of the area a quaquaversal or dome structure, although 

 it is thought that the anticline spoken of is of a second order, being a sub- 

 ordinate bend in the general northward-dipping beds. The secondary fold 

 shows superimposed folds of the third order, and these again those of the 

 foiu'th order, and so on, until microscopic plications are reached. Where 

 the change of strike is the most rapid — that is, at the northwest and south- 

 west corners of the bluff — the plications are closest, and in some places the 

 rocks are brecciated. Throughout the central part of the bluff the expo- 

 sures of greenstone are almost as abundant and numerous as those of the 

 griinerite-magnetite-schist (PI. XXXIII). The very considerable width of 

 the belt of griinerite-magnetite-schist in sees. 11 and 12, as compared with its 

 breadth to the southeast, may be in part due to the large amount of intrusive 



MON XXVIII 25 



