436 THE MAKQUETTE IRON-BE AEIXG DISTRICT. 



The different j)liases include black garnetiferous niiea-slates and coarse- 

 <>frained chlorite-slate.s and biotite-slates. The finer-grained varieties are 

 strongh' garnetit'erous and andalusitic. The garnet contains few inclu- 

 sions, but the andalusite, as usual, is full of the other minerals of the rock. 

 The griiueritic rocks differ from the biotite-slates only in that in place of 

 part of the mica griinerite has developed. Garnet is also abundant. 



Lake Michigamme area, — Wcst of Cliampion, soutli of tlic ccuter of scc. 36, 

 and at several places near the water's edge on the south arm of Lake Michi- 

 gamme, occur griiueritic schists (Atlas Sheets VI, VIII, and IX). In seC 36 

 the rocks are nearly pure griinerite-magnetite-schists, very closely resem- 

 bling those of the Bijiki formation at Michigamme. At the remaining places 

 to the southeast the schists are biotitic or are interlaminated with bands 

 of biotite-schist. In thin section the nearly pure griineritic schists do not 

 difter from those of Michigamme. The quartzose background is finely 

 crvstalline, but in it are seen occasional larger fragmental grains of quartz. 

 With the griinerite is a certain amount of pleochroic aniphibole, and the 

 iTsual intergrowths of the two occur. In certain slides the chloritic 

 decomposition of the griinerite is seen. The rocks are usually garnetif- 

 erous. As the rocks become less pure, biotite is found with the grunerite 

 between the particles of quartz. In an intermediate variety the biotite and 

 grunerite are about equally abundant. By a lessening of the amount of gru- 

 nerite and an increase of the chlorite and biotite the rocks pass into the 

 ordinary mica-slates and mica-schists of the Michigamme formation. 



Republic area. — At tlie soutli end of the Republic trough there are numer- 

 ous large e.\posui-es of the Ishpeming formation (Atlas Sheet XI). The 

 predominant variety is white quartzite. This passes downward into a con- 

 glomerate at the base of the formation, and it grades upward into the mica- 

 schist of the Michigamme formation. Beginning with the basal members 

 of the formation at the southwest angle of tbe Republic horseshoe, there is 

 the usual recomposed specular and magnetic ore, often " micaceous," which 

 bears clastic grains of quartz and complex fragments from the Negauuee 

 formation. At the same horizon or above this are magnificent exposures 

 of conglomerate. The predonnuant pebbles and bowlders are from the 

 Negaiuiee formation, l)ut with these are found bowlders of quartz as large 



