452 THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



Above these conformable fovmations comes the unconformably placed 

 Upper Marquette series, the base of which rests now on one member, now 

 on the other, or on the Archean. 



East and south of Negaunee, and extending thence to the shore of 

 Lake Superior at Marquette, is a series of rocks which resemble lithologic- 

 ally neither the Upper nor the Lower Marquette series in the productive 

 area. It consists, in ascending order, of quartzite with basal conglomer- 

 ates, dolomite, and slates, and thus bears a close resemblance lithologically 

 and stratigraphically to the three lower members of the Menominee series. 

 This series, named by Wadsworth the Mesnard series, has been regarded 

 by him as belonging with the Upper Marquette series, or at least as over- 

 lying the Lower Marquette formations just described. Maj. T. B. Brooks 

 had earlier correlated the dolomite with the Lower Marquette quartzite, 

 and had supposed that there was a gradual passage from one into the other 

 along the strike. Mr. C. R. Van Hise has recently stated that its position is 

 below the Ajibik quartzite. 



This series is found only in the eastern part of the Marquette area, 

 between^ Goose Lake and Lake Superior, a distance of about 6 miles. 

 Elsewhere, over by far the greater part of the Marquette district, no member 

 of it has been recognized. 



The geological structure of the Marquette range presents the general 

 features of an east-west striking complex syncline or synclinorium. The 

 pre-Cambrian sedimentary rocks, with their associated intrusive and extru- 

 sive igneous rocks, occupy the trough, in which there is much local com- 

 plexity of structure. The trough is flanked on the north and south by the 

 older Archean crystallines. 



At the western end of the district the peculiar Republic^ trough 

 branches from the main synclinorium, and runs southeast into the Archean 

 rocks for 6 or 7 miles, having a nearly constant width of about one-half to 

 three-quarters of a mile. In this trough the Algonkian rocks have been so 

 closely compressed that they stand essentially on edge. The interior is 

 occupied by the ^^^ounger Upper Marquette quartzites and schists, between 

 which and the underlying Archean walls the older Lower Marquette ii-on 

 formation and quartzite here and there occur. 



The northwestern end of the Republic trough is about the western 



' Op. cit., p. 525. 



