156 THE CRYSTAL FALLS lUON-BEAEING DISTltlCT. 



slates, whicli are iuterbedded A\'iTh mucli smaller quantities of graywackes 

 and chert. The slates are eroded much more readily than the associated 

 harder beds, and therefore, except along valleys, we rarely find the soft 

 slates exposed. The graywackes and cherty rocks are the ones which form 

 the striking topographical features of the landscape, the slates forming 

 softly-rounded hills. The drift is also an important factor in the scarcity 

 of outcrops. In the northern and western parts of the districts especially 

 the drift is very heavy. In this portion the youthfulness of the topography 

 is emphasized by numerous swamps, lakes, and generally imperfect di'ain- 

 age. In the southern and southwestern parts of the district, owing to the 

 presence of larger streams, and consequently more advanced erosion, the 

 drift has been removed to a greater or less extent, so that the topographical 

 forms approach much nearer to those of an imglaciated region. For 

 instance, the general strike of the graywacke and cherty ferruginous slate 

 beds in the southern portion of the area, T. 42 N., Rs. 32 and 33 W., can 

 be closely followed by the north-south to northwest-southeast ridges which 

 they form, the intervening valleys being in all probability imderlain by the 

 softer carbonaceous clay slates. Also in this Ancinity, from the Chicago 

 and Northwestern Railway eastward to the Michigamme River, exposures 

 of intrusives with some sedimentaries stand out from the sand plains as 

 rounded knobs. 



MAGNETIC LINES. 



A considerable amount of detail magnetic work has been done in 

 the vicinity of the ore-bearing areas, in the hope that with the assistance 

 afforded by the magnetic needle the iron belts might be better traced than 

 they could be by means of the very scanty outcrops. I shall here describe 

 those lines of magnetic disturbance which have been traced for considerable 

 distances. They are indicated on the map, PL III, by solid blue lines. 



Magnetic line D. — Tlils lluc of iTiaximum magnetic disturbance was traced 

 northwest from near the southeast corner of T. 46 N., R. 32 W., around 

 Bone Lake, then southwest and south tlu'ough T. 46 N., R. 33 W., luitil 

 finally lost near the south side of sec. 34 of the same township. The 

 tracing of this line was begun where outcrojjs were wanting, and it was 

 not possible to connect it directly with any magnetic formation until sec. 

 34, T. 46 N., R. 33 W., was reached. Here it was connected with outcrops 

 of magnetitic slate and graywacke which overlie the Hendock formation, 



