MANSFIELD SCHISTS IN FBLCH MOUNTAIN RANGE. 411 



strong. Accordingly, a close agreement in the sequence and in the charac- 

 ter of the principal events thus indicated in the history of the two rocks 

 may be recognized. These considerations make it quite certain that the 

 recrystallization of the two formations was essentially' contemporaneous. 

 From the character of the accessory minerals in the dolomite it is probable 

 that the crystallization was not accompanied by the inti'oduction of foreign 

 material from outside, in notable quantities, but consisted in a mineralog- 

 ical rearrangement of the elements present in the rock from the beginning. 



SECTION VI. THE IMANSFIEED SCHISTS. 



Above the Randville dolomite comes a formation composed chiefly of 

 fine- to medium-grained mica-schists. Owing to their exceedingly soft 

 character and small thickness, these rocks are exposed naturally in only a 

 few localities in the Felch Mountain area. A series of phyllites less meta- 

 morphic but otherwise similar, and occupying the same stratigraphical 

 position, immediately above the dolomite, outcrop characteristically at the 

 Mansfield mine, and especially north of it, near the Michigamme River, in 

 T. 43 N., R. 31 W. For these reasons it is convenient to name the forma- 

 tion for the Mansfield locality. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The existence of the Mansfield formation in the Felch Mountain area 

 is known mainly from test pits and the records of diamond-drill borings 

 and eai'ly explorations. Fortunately, these are so widely distributed that 

 the persistence of the formation is well proved. Many drill holes have 

 passed through it into the dolomite. Immediately above it comes the mag- 

 netic Groveland formation, which even when covered betrays its presence to 

 the compass needle. With the upper and lower limits thus determined, and 

 with the large body of data supplied by the test pits and records, there is 

 no difficulty in indicating its approximate boundaries for the greater part of 

 the map. 



On the west, mica-schists belonging to the Mansfield formation have 

 been proved by diamond drilling to occur between the dolomite and Orove- 

 land formations in the south half of sec. 34, T. 42 N., R. 30 W. Farther 

 east there is a line of outcrops in the eastern portion of section 35, and the 



