THE RErUBLIO TROUGH. 547 



reason such movement could take place more readily along any one surface, 

 the neighboring surfaces would be relieved and one of maximum movement 

 would result. It is conceivable that in the same way one local maximum 

 might relieve several neighboring maxima, and so a large amount of move- 

 ment might be accumulated along a single surface. A maximum movement 

 starting in the specular jasper would, on account of the slight upward con- 

 vergence of dip, necessarily tend to cut across the quartzite at the contact. 

 The quartzite might be traversed until a surface of maximum movement in 

 it was reached, which would then be followed and a fault would result, 

 which in the direction of the strike might easily pass from one rock to the 

 other more than once. It is evident that a break formed under such condi- 

 tions, accompanied by considerable displacement, would result in the surface 

 relations that may now be observed on Republic Mountain. 



THE ORE DEPOSITS. 

 POSITION OF ORE DEPOSITS. 



The iron ores of the Republic area all belong to the hard-ore class, 

 and are both magnetite and specular hematite, the specular slate ores being 

 the more abundant. They occur in bodies of very irregular shape and 

 sometimes of great size. The rule that has generally guided exploration 

 in the Marquette district, that the hard-ore bodies occur immediately at or 

 not far beneath the base of the upper quartzite, holds good in the Republic 

 area. It is a significant fact that while this rule of occurrence beneath the 

 upper quartzite has few or no exceptions, the position of the ore bodies 

 with reference to the base of the lower series is exceedingly variable. At 

 Republic Mountain and at the Michigamme mine the ore bodies lie at least 

 1,500 feet above the granites. At Champion and at the Riverside mine the 

 distance is not more than 400 feet. The hard-ore bodies are therefore not 

 confined to any one horizon in the iron-bearing member, but occur at the 

 particular honzon to which it happened to be eroded at the time the 

 upper quartzite was deposited. The contact deposits of the Republic area 

 have relationships with both the lower and upper series. Some are appar- 

 ently entirely within the upper series; others are certainly entirely within 



