THE EEPUBLIC TROUGH. 535 



found ill close proximity to granite, the disintegration of which would have 

 supplied all of its essential constituent minerals, certainly raise a strong 

 presumption that such actually has been its origin. 



SECTIOX III.— THE ITPER INLVRQUETTE SEKIES. 



In the Republic area proper only the lower member of the Upper Mar- 

 quette series, the Goodrich quartzite, is well exposed. This is, in the main, 

 a white quartzite, usually massive and heavily bedded near- the base and 

 passing upward into the mica-schist of the Michigamme formation. At the 

 base, conglomerate layers occur, in the pebbles of which all the underlying 

 rocks are abundantly found. The conglomerates, while usually unimpor- 

 tant, are represented in great volume at the south end of the trough, where 

 they are beautifully exposed by the extensive mining operations about 

 Republic Mountain. In these conglomerates the great majority of the 

 pebbles have a local origin, being derived from the rocks upon which 

 the conglomerates directly rest. 



Under the microscope the Goodrich quartzites and quartz-schists show 

 a decidedly less degree of metamorphism than do the Ajibik quartzites. 

 Roundish grains of feldspar, usually microcline, derived from the under- 

 lying granites, are plentiful, and the quartz areas often exhibit distinct 

 indications of original rolled nuclei. In the quartz-schist and mica-schist, 

 into which the more massive quartzite iisually passes upward, cei'tain defi- 

 nite layers of a darker color are often distinguishable, in which iron oxides, 

 usually magnetite, abundantly occur. In these layers false bedding is 

 often strongly brought out, and it is believed that the iron oxides are in 

 large part original sediments. 



The Goodrich quartzite is, on the whole, the thickest rock in the 

 Republic area, and, by reason of its volume and character, that which 

 most frequently outcrops. 



The Michigamme schist occupies the center of the tongue, and, because 

 less resistant than the inferior formations, the Michigamme River does not 

 wander far from its borders. In most respects this schist is similar to the 

 remainder of the formation elsewhere, and thei-efore will not be further 

 considered here. 



