AKCHEAiSr m FELCH MOUNTAm DISTRICT. 385 



its areal relations is very incompletely known. It includes mica-schists, 

 ferruginous schists, and thin interbedded ferruginous quartzites. These 

 rocks, which from our imperfect knowledge must for the present be grouped 

 as a single formation, are believed to have been deposited contempora- 

 neously with the somewhat similar rocks that occur in the Menominee 

 area, at Iron Mountain, but are most extensively exposed west of the 

 Menominee River, and especially in the Commonwealth and Florence 

 district in Wisconsin. 



SECTION III. THE ARCHEAK. 



The Archean occurs in the Felch Mountain district in two belts, which 

 limit the Algonkian rocks on the north and on the south. The north- 

 ern belt for the most part does not fall within the limits of the detail map 

 (PI. XLIX). It occupies a triangular corner in sees. 34 and 35, T. 42 N., 

 R. 30 W., at the extreme western end of the area sm-veyed, and even in 

 these it has not been directly observed, but its presence is inferred from 

 outcrops in the adjoining sections west and north and from the observed 

 strikes in the overlying Algonkian formations. For the next 1 1 miles east 

 its southern boundary lies in the tier of sections next north of those mapped 

 in detail and probably always less than a mile away. This boundary is 

 therefore not very accurately drawn, as only enough outcrops were visited 

 to permit its position to be fixed in a general way. Our work first touches 

 the southern area of the Archean, which is much better known on the west 

 in sees. 3 and 2, T. 41 N., R. 30 W., a short distance south of the township 

 line. Thence for 3 miles eastward the boundary follows the township line, 

 and in sec. 31, T. 42 N., R. 29 W., crosses it with a trend somewhat north of 

 east. From the west line of sec. 31 to the east line of sec. 36, T. 42 N., 

 R. 29 W., the Archean occupies the southern third of the south tier of sec- 

 tions. Thence ' for a mile and a half it bends northeast, and in sec. 32, 

 T. 42 N., R. 28 W., reaches its farthest north in the center of the section. 

 From this point the boundary runs southeast, with a sinuous embayment to 

 the south, and passes outside the limits of the map a little north of the 

 southeast comer of section 33. 



Throughout the Felch Mountain range the southern Archean is much 

 better exposed than any of the other terranes. In the western portion of 

 the "range, where hardly more than the contact zone falls within our limits, 



MON XXXVI 25 



