154 THE MARQUETTE IKON-BEARING DISTRICT. 



Others are squeezed basic lavas. A sliarp line of demarcation between 

 these rocks and the tuftaceous greenstones of the Kitchi formation to the 

 west is therefore not to be expected, for the former are probably only much 

 metamorphosed phases of rocks like the latter. 



From the Algonkian beds to the south the schists are separated by 

 conglomerates and great unconformities. In the conglomerates large 

 bowlders of the schists are often found; consequently there can be no 

 cpiestion but that the latter rocks were consolidated and had been made 

 schistose l)efore the basement beds of the overlying clastic series were laid 

 down upon them. 



The ]\[ona schists are therefore pre-Algonkian. They are older than 

 the granites of the Basement Complex, and are of about the same age 

 as the rocks of the Kitchi formation, which are probably their western 

 equivalents. 



I'ETKOGRAPHICAL CHARACTER. 



The structure of tlie schists varies within wide limits. In some places 

 the rocks are very fine grained and as fissile as slates; at others they are 

 coarser-grained, fibrous, and distinctly foliated; again they may be very 

 coarse grained and fibrous but possessed of only indistinct foliation; and, 

 finally, they may be dense and apparently quite massive. In the latter 

 case they always yield to fracture much more readily in one direction 

 than in others, and in thin section inider the microscope they are seen to 

 have a schistose structure. The schistosity of all the well-foliated varieties 

 dips at high angles, and strikes nearly east and west, approximately parallel 

 to the trend of the Marquette trough. 



Dr. AVilliams, who has studied the rocks of this area in detail, 

 divides the eastern portion of the area into a northern and a southern 

 half, in the former of which banded schists prevail; in the latter, apha- 

 iiitic varieties. In neither half, however, are the rocks of either variety 

 excluded by those of the other. Farther west the dense and the banded 

 fibrous schists are associated in the most intimate manner. 



bask; schists. 



The dense varieties. — Tlic aphauitic scliists as a rule have a light-green 

 color, sometimes shading to grayish or pinkish green, and a uniformly fine 



