428 THE CRYSTAL FALLS IROISr-BEARINO DISTRICT. 



tions fall away gently to the south in a series of waves, produced by 

 several concentric minor folds transverse to the main axis. Of these minor 

 folds but one is at all distinct to the east of the general anticlinal axis, 

 while to the west of this axis at least three are well made out within the 

 Michigamme Mountain area. The much greater breadth of the Algonldan 

 formations on the west side of the dome than on the east is probably due 

 to the persistence of these minor folds toward the northwest. 



The general character and aspect of the formations of the two areas 

 and their succession is in so many respects identical with the formations of 

 the Felch Mountain range that no doubt can be entertained that they are 

 really the same formations. Nevertheless certain differences mark these 

 rocks with a distinct individuality. These differences will be considered in 

 detail in the descriptions of the several formations. In general they may 

 be summarized as involving a great reduction in thickness of the Sturgeon 

 formation, with a corresponding increase in the Randville dolomite, the 

 appearance of surface igneous rocks at the Mansfield horizon in the Fence 

 River area, and a less uniform and complete metamorphism in the whole 

 Algonkian series. 



SECTION I. THE ARCHEAlSr. 



The rocks of the Archean core are well exposed through the Avest- 

 central sections of T. 44 N., R. 31 W., while farther north in T. 45 N., R. 31 

 W., outcrops are few and scattered. Much less attention was paid to this 

 area than to the Felch Mountain Archean; our work, as a rule, stopped 

 with the location of the boundary, and, therefore, the following brief state- 

 ments as to its character embody observations along the southern and east- 

 ern margins only. 



The prevalent rock in the Archean is granite, varying from medium to 

 coarse grain, and often carrying very large porphyritic Carlsbad twins of 

 flesh-colored microcline. Banded gneisses and mica-gneisses and mica- 

 schists, such as are so abundant in the Felch Mountain Archean, are rare but 

 not entirely absent. While in many localities the granites are much crushed 

 and even sheeted along adjacent parallel fractures, tlieir originally massive 

 character is sufficiently evident. They have the composition and structure 

 of typical igneous granites. The primary minerals are entirely without 

 definite arrangement. 



