ORE DEPOSITS IN MANSFIELD SLATE. 73 



EXPLORATION. 



Exploration has developed no other deposits along the Mansfield slate 

 belt.-^ If other deposits exist, it is highly probable that they extend to the 

 rocJi surface — that is, are covered by the di-ift mantle alone. 



The intervals between possible ore bodies along the strike of the slates 

 ar^ probably occupied by mixed chert and ore or ferruginous chert. Explora- 

 tions should extend from the impervious slate below the iron-bearing forma- 

 tion to the impervious rock above the iron-bearing formation. In order to 

 explore the belt thoroughly, rows of pits cross-sectioning the formation oiight 

 to be made at intervals not greater than 100 feet, and even with such inter- 

 vals an important deposit might be missed, for it frequently happens that at 

 the surface of the rock an ore deposit is smaller than it is at a moderate 



depth. 



SECTION III.— THE HEMLOCK FORMATION. 



This formation, the most interesting petrographically in the Crystal 

 Falls district, consists almost exclusively of typical volcanic rocks, both 

 basic and acid, with crystalline schists derived from them. Sedimentary 

 rocks play a very unimportant role. With one exception they have been 

 formed directly from the volcanics, and occur interbedded with them. 

 Cutting through the volcanics are intrusive rocks, which likewise- include 

 both basic and acid kinds. Chemically the intrusive and extrusive rocks 

 show very close relationships. The name Hemlock has been given to this 

 volcanic formation because the river of that name flows through it for a 

 number of miles, and in places aff'ords excellent exposures. 



DISTRIBUTIOSr, EXPOSURES, AND TOPOGRAPHY. 



Beginning in sec. 36, T. 46 N., R. 32 W., the place where the Hemlock 

 formation enters the part of the district studied by me, the formation has a 

 width of one-half of a mile. From this place the formation has a north- 

 western course for about 5 miles, gradually widening. It then bends to the 

 west, and after a short distance to the south, which course it follows for 

 about 9 miles. In township 45 N., Rs. 32 and 33 W., the belt has a maxi- 

 mum width of 5 miles. At the end of the southern course the formation 



' Since the above Tvas written I liave been informed that Mr. George J. Maas, of Kegaunee, has, 

 with a diamond drill, located a body of bessemer ore 30 feet thick ou lot 6, sec. 20, T. 43 N., R. 31 W., 

 1 mile south of the Mansfield mine. 



