CHAPTER VI. 

 THE REPUBLIC TROUGH. 



By Henry Lloyd Smyth. 



INTRODUCTION. 



The Republic syncline (Atlas Sheets IV, VII, X, and XI) is sharply 

 marked off from the rest of the Marquette district by the simplicity of its 

 structure and by the fact that the folding has taken place about an axis 

 which strikes northwest and southeast, or in a direction considerably inchned 

 to the general course of the great Marquette synclinoriura. The Republic 

 svncline is thus transitional to the north-and-south type of structure that 

 prevails beyond it to the west over three townships, and to the south as 

 far as the Felch Mountain trough, in T. 42 N. The Republic area proper 

 beo-ins near the south end of Lake Michigamme and continues southeast to 

 the northwest sections of T. 46 N., R. 2!) W. As thus defined, it is a simple 

 syncline in Algonkian rocks, about 7 miles in length, with nearly parallel 

 sides from one-half to 1 mile apart; on both sides and at the southeast 

 end it is inclosed by Archean rocks, while at the northwest end it rather 

 suddenly flares out into the main Marquette synclinorium. 



To the northeast it is separated from the southern boundary of tlie 

 main Marquette trough by an area of Archean granite and gneiss about 6| 

 miles broad. To the west and southwest about half this distance, over 

 similar Archean rocks, divides it from the next narrow Algonkian syncline. 

 While the general direction of the main Marquette fold is nearly east and 

 west, the fold is constricted on a section through the Champion mine, 

 where it is only 2 miles wide, and its southern boundary has a northwest- 

 ward trend, to whicli the Republic fold is very nearly parallel. 



