54 THE CRYSTAL FALLS lEON-BEAEING DISTRICT, 



SECTION II.— THE MANSFIELD SLATE. 



The fonnatiou of the Lower Huroniau, which is next higher than the 

 Raudville dolomite, is composed of sedimentary beds, in which a slate pre- 

 dominates. 



This formation is found in its most typical development in a narrow 

 vallev thi'ongh which the Michigamme River flows, and in which the village 

 of Mansfield and a mine of the same name are situated. The valley and the 

 slates are well known in the Crystal Falls district on account of their eco- 

 nomic importance. For this reason the name "Mansfield slate" is here 

 applied to this formation. 



DISTRIBUTIONS, EXPOSURES, AND TOPOGRAPHY. 



The part of the valley occupied by the Mansfield slates begins at the 

 northern section line of sees. 17 and 18, T. 43. N., R. 31 "VV., and extends due 

 south for 3 miles to the southern section line of sec. 29 of the same township. 

 The slate belt is widest at the north, being over one-fourth mile wide on 

 the westren side of section 17. To the south it gradually diminishes in 

 width, until it finally disappears in sec. 29. The strike of the sedimentary 

 rocks is almost due north-south, except in a few places where the rocks 

 have been gently flexed and the strike varies a few degrees. The dip is 

 high to the west, ranging from 65° to 80°. 



The influence of the Mansfield slate belt upon the topography is 

 strikingly shown by the depression in which the slates are found, and 

 which contains the Michigamme River. The slates are surrounded on 

 all sides by igneous rocks wliich form fairly high hills, those to the west 

 being composed of rocks of volcanic origin, those to the north, east, and 

 south being intiaisive, and later than either the sedimentaries or the vol- 

 canics. The Michigamme River flows south thi-ough sec. 1, T. 43 N., R. 

 32 W., and meets the east and west ridge of intrusives in the northeastern 

 pai't of sec. 12 of the same township and range. It cuts tln-ough this at an 

 oblique angle, changing its course to the southeast In sec. 7, T. 43 N., 

 R. 31 W., it leaves the intrusives and penetrates a short distance into the 

 volcanic rocks, their contact not being able to cause a change in the course 

 of the river, owing to the slight difference in resisting power between the 

 intnisives and the volcanics. Still flowing to the southeast, it finds at 



