152 THE MARQUETTE IRON-BEAKING DISTRICT. 



THE MONA SCHISTS. 



Tlie Moua scliists einhrace green and gray fibrous rocks with a well- 

 cliaracterized schistosity, dense greenish-gray ones that are not pronouncedly 

 schistose, and highly foliated dark-green ones with the aspect of hornblende- 

 schists. These are interbanded with one another, and with certain light- 

 pink, yellow, or white talcose and sericite-schists, described later under the 

 heading "acid schists." The green schists are all composed of the altered 

 constituents of diabases. They are probably all derived from the lava or 

 the tuff form of this I'ock. The-s' are referi-ed to as greenstone-schists to 

 distinguish them from tlie true amphibole-schists, which are composed 

 essentiallv of amphibole and quartz, and which are without the distinctive 

 features of nn altered erupti\'e, whatever their origin niay have been. 



DISTRIBUTION AND TOPOGRAPHY. 



Tlie Mona schists, with the associated acid schists, occupy the eastern 

 portion of the Northern Complex, extending westward from Lake Superior 

 on the east to about the west line of R. 26 W., where they are replaced 

 by the Kitchi schists. In its eastern portion the area stretches northward 

 a mile beyond the northern limit of the accompanying map (Atlas Sheet IV) 

 to a great area of gneissoid granite, which is similar in its characteristics to 

 the granites farther west. A mile west of the east line of R. 26 W. the 

 belt narrows and has a width of only IJ or 2 miles. Here it is bounded 

 on the nortli b^' a narrow belt of coarse red syenite, lying parti}' within 

 the limits of the map. On the south the schists are in contact with the 

 transgression fjuartzite of the Lower Marquette series throughout its entire 

 extent, except toward the east, where they jiass beneath the Pleistocene 

 deposits bordering the lake. 



The topography of the area is, in a minor way, rugged in the extreme. 

 Large and small hills of the schists rise with rough, jjrecipitous faces above 

 the level of the sun-ounding country, and lift their smooth, glaciated lieads 

 from 200 to 900 feet above the level of the waters of Lake Superior. When 

 the hills are low their tops onlv project as smooth, round knobs al)ove the 

 drift deposits surrounding them (PI. IV, fig. 1). The higher hills are 



