THICKNESS OF MANSFIELD SLATE. 



65 



The average dip of the beds is 80°, and this gives a maximum thickness 

 of 1,900 feet. Toward the south the belt rapidly narrows, until it is cut 

 out by the intruding dolerites. A thickness of 1,500 feet is probably not 

 far from the average. 



To the east of the Mansfield slates is a belt, varying in width up to 

 about 1,200 feet, in which are found large masses of metamorphosed slates, 

 surrounded by intrusive dolerite. In this belt the slate masses still show 

 a general north-south strike, with slight variations to the east or west, and a 

 westward dip. One might, perhaps, consider this a slate area which has 

 been completely saturated with intrusives. If it should be so considered, 

 this thickness should be added to the estimated thickness of the slates as 

 above given, but as intrusives predominate in it, the slate being, as it were, 

 merely incidental, I have preferred not to include it in the belt with the slate. 



ORE BEPOSITS. 



Although a great deal of exploring for iron ore has been done in the 



Mansfield slates, only one large body of ore has thus far been discovered, in 



which is the Mansfield mine. This mine 



is situated on the west bank of the Michi- 



gamme River, in sees. 17 and 20, T. 43 



N., R. 31 W. The mine was apparently 



prospering when, on the night of SejDtem- 



ber 28, 1893, a cave-in occurred, letting 



in the waters of the Michigamme River 



and drowning 28 miners. 



For two hours after the caving occurred, 

 the bed of the river below the miue was bare, 

 the water flowing into the miue workings. 

 The accompanying figure, fig. G, prepared by J. 

 Parke Chauniug, October 8, 1893, shows the 

 relative position of the shaft and the river, aud 

 the conceutric cracks caused by the caving of 

 the mine. (Plan copied from address of presi- 

 dent: Proc. Lake Superior Inst. Min. Bug., 



Vol. Ill, 1895, plate opposite p. 42.) The timber shaft is near the center of these 

 cracks. 



After the caving the mine remained idle until recently. At the present 

 writing the DeSoto Mining Company has obtained control of the mine and, 

 I understand, have freed it from water. 



MON XXXVI 5 



Dcentric cracks formed by the caving 

 of the Mansfield mine. 



