570 THE MARQUETTE lEOX-BEAEING DISTRICT. 



area which extends beyond the district. It is rather probable that the 

 eastward-projecting hind between the west and southwest arms of I.ake 

 Michio-auime marks an intermediate antichne, which, liowever, does not rise 

 high enough to bring to the surface any rocks higher than the Michigamme 

 schist. The Repubhc tongue and the Western tongue are closely com- 

 pressed synclines which branch off from this main area in southeast and 

 south directions. 



It has been seen that the main east-west syncline has superimposed 

 upon it secondary folds; upon these again are those of the third order, and 

 upon these those of a fourth order, and so on, until the plications in many 

 places are microscopic. Pumpelly's principle, that these minor folds are 

 often of the same character and usually have the same pitch as the folds 

 of the next order of which they are a part, has been of great assistance in 

 working out the stratigraphy of the district (PI. XXXV). 



From the foregoing description it is clear that the Marquette district is 

 one of complex folding. In fact, no better example is known to me of this 

 class of deformation.^ 



Where the formations are brittle the close plications have resulted in 

 their being fractured through and through, and in many places they pass 

 into reibungsbreccias (Pis. VII, VIII, IX, and XXVI, fig. 2). These phe- 

 nomena are particularly prevalent in the Negaunee iron formation and in 

 the quartzites. The miire plastic formations have yielded without major 

 fracturing, Ijut in a minor way they show everywhere the effects of deforma- 

 tion. A microscopical study shows that not a cubic inch of material has 

 escaped dynamic action. Ahnost every original grain of fair size gives 

 eA-idence of interior movement. The rocks have been kneaded thi-oughout. 

 While, as a further consequence of dj^namic action, there has been local 

 faulting at \^arious places, with two or three exceptions no important faults 

 have lieen observed in the district. 



The only fault in the district, besides that in the Republic tongue 

 (described on pp. 541-547), large enough to materially displace the forma- 

 tions, is in sec. 6, T. 47 N., R. 25 W. (Atlas Sheet XXXVII). Here, in the 



'Principles of pre-Cambriau North American geology, by C. R. Van Hise: Sixteenth Ann. 

 Kept. U. S. Geol. Survey, Part 1, 1896, pp. 626-631. 



