SOUDAN FORMATION. 183 



the jaspei's. The secoudary nature of the oxide that fills the cracks is 

 indisputably shown by this occurrence, and is strongly indicative of the 

 secondary origin of that in the bands, the two probably being' of contem- 

 porary formation. In studying the formation it was noted that two series of 

 cracks had been formed in the jaspers, the older having been filled with 

 vein quartz and the younger with hematite. 



THE IRON ORES. 



The upper part of the Soudan formation is in a strict sense the ore- 

 bearing portion. Indeed, this is the iron-bearing formation which has given 

 to the Vermilion district its great economic importance, since from this have 

 been derived great quantities of the high-grade ore which has assisted 

 materially in making .the Lake Superior region the greatest single factor in 

 the development of the iron industry of the United States and of the world. 

 The ores of the Vermilion district comprise several varieties — massive, 

 granular hematite, specular hematite, and insignificant amounts of mag- 

 netite and limonite. There are, of course, also all kinds of mixtures of 

 these, showing- gradational phases from one variety to the other. 



The predominant ore is an exceedingly hard, massive, granular, steel- ' 

 blue hematite. The specular ore occurs locally in small masses. The 

 magnetite is obtained only in small quantities, and is intimately associated 

 with the hematite. Occasionally small bodies of magnetite ore are found, 

 not large enough to be of special value, or to Avan-ant an attempt to obtain 

 a grade of magnetite ore. Such occurrences are very exceptional. The 

 limonite is very subordinate, occurring only associated with the hematite. 

 There seems to be a general misapprehension as to the character of the ore 

 in tile Chandler mine at Ely, the greatest producer of the district. It is 

 very commonly spoken of as a soft ore. This is, however, purely a relative 

 term, in this case depending upon the brecciated condition of the ore, which 

 enables it to be won with less drilling and with much less expenditure 

 of high explosives than is required, for instance, in the Minnesota Iron 

 Company's mine at Tower. The ore is found in an extremely brecciated 

 condition by the miners, and this brecciation is taken advantage of and 

 really increased by the method of mining employed. As a result of this 

 more or less finely brecciated condition the ore is obtained to a great 



