278 The Iron Bearing Rocks of Mhmesota — Wincliell. 



It is not at all unlikely that this formation may prove to be 

 of great value as an iron-producing horizon in Minnesota, since 

 many productive mines are situated in the same rocks in New 

 York and Canada. 



Next younger than the Vermilion series is the Keewatin. This 

 formation was first described under this name ( which means "north") 

 by Mr. A. C. Lawson of the Canada geological survey, who studied 

 it on Lake of the Woods. It consists of vertically-bedded green 

 schists and slates, which are in places hydro-micaceous and have 

 a soft, greasy feel. The Keewatin appears to grade insensibly into 

 the older crystalline schists, which are found between it and the 

 granite on both sides. It is largely composed of eruptive material 

 which has been re-arranged and re-deposited in water. In it are 

 found peculiar agglomerate schists in which the pebbles are of the 

 same green diabasic material as the magma which surrounds them. 



In this formation are found the wonderfully pure and exten- 

 sive deposits of specular iron ore, which have made the Lake Su- 

 perior region famous. In fact, tlie only mines that have been really 

 worked in. this state are in the Keewatin, at Tower and Ely. The 

 ore is largely hematite, but contains some magnetite in places. It 

 is very hard, as a rule, and the cost of explosives is no small item 

 in the mining expenses. At the Minnesota mine, for instance, 

 there was used in the month of July ov'er 30,000 pounds of dyna- 

 mite and powder, and 1,300 men were employed to drill, break up 

 and handle a quantity of ore not very much greater than was 

 mined by half that number of men at the Chandler mine where 

 the ore is in a crushed or brecciated condition. 



The ore beds are in vertically placed lens-shaped masses, and 

 are mingled with or accompanied by large amounts of banded 

 red, white, black and gray jasper. So intimately mixed are the 

 ore and jasper rock or "jaspilite" as it is called, that much of it is 

 worthless. But at many places there are deposits 100 feet long, 

 30 to 90 feet wide and of indefinite depth where the ore contains 

 on an average less than 2 per cent, of all impurities and that mostly 

 silica. Its particular value lies in its low content of phosphorus, 

 averaging less than one-tenth of one per cent. For this reason 

 Minnesota ore is in great demand by the manufacturers of Besse- 

 mer steel. 



While speaking of the mines in the Keewatin formation it 

 will not do to omit mention of the Chandler mine at Ely, which 



