FOLDING OF THE NEGAUNEE FOIIMATION. 333 



with tlie uuderlyiuo- Sinmo slate and the overlying Goodrich quartzite. 

 By studying these lines it is seen that the formation is in a number of east- 

 west secondary folds, which produce several large reentrants and salients, 

 each of which is composed of smaller reentrants and salients, due to folds 

 of the third order (PI. XV). 'The eastern swings of the contact lines mark 

 synclines, and the western swings anticlines. Putting it in another way, 

 in going west the iron formation first appears above the Siamo slate in 

 several fingers, each being a syncline. These to the west unite to form the 

 broad area. Farther to the west the Goodrich quartzite appears, and hides 

 the iron formation in a manner exactly similar. The secondary folds are 

 still further modified and complicated by the intrusion of the igneous 

 masses, about which the iron formation in some ])laces has a quaquaversal 

 dip. At other places the dip is but little modified by the intrusives (fig. 17). 

 The western arms of the iron formation also have minor overfolds, which 

 are more easily discernible when infolded with the Goodrich fiuartzite, 

 but for the most part the belts are not sufficiently well exposed to indicate 

 the minor folding. 



A few localities in which such subordinate folds appear may, however, 

 be mentioned. East of Palmer the general syncline of the iron formation 

 has near its center a subordinate anticline, which causes the belt of Good- 

 rich quartzite at Volunteer to split just south of Palmer into two arms 

 (Atlas Sheet XXXII). As a result of this anticline the lower members of 

 the formation are exposed near the railroad track east of Palmer, in the 

 center of the iron belt. At Humboldt the griinerite-magnetite-schist has a 

 subordinate anticline, which causes the Goodrich qiiartzite to be distributed 

 about the great mass of griinerite-magnetite-schist in a quaquaversal 

 fashion. 



Upon the secondary folds are superimposed those of the third order 

 (Pis. XV and XVI and figs. 18 and 19), and on these those of a still higher 

 order, and so on to microscopic plications. 



RELATIONS TO rNDERLYING AND OVERLYING FORMATIONS. 



The iron-bearing formation rests conformably upon the Siamo slate or 

 the Ajibik quartzite, and grades downward into one or tlie other of these 



