224 THE VERMILION IRON-BEARING DISTRICT. 



down iu synclines upon the basement greenstone, and hence to belong to 

 the same class of deposits as do those occumng at Ely. The one mined 

 from the old pit known as the North Lee mine is presumed also to have 

 been a deposit in an analogous position. 



DEPOSITS OCCURRING WITHIN THE IRON FORMATION. 



The deposits within the iron formation may be of two modes of 

 occurrence: (ci) They may have jasper both as a foot and hanging wall, 

 and hence may lie within it and grade in all directions into it (these 

 deposits are of small size); or (5) they may have paint rock (soapstone, or 

 soap rock, as it is indifferently called by the miners) as foot wall, below 

 which is again jasper, with similar paint rock or jasper as the hanging wall. 

 Of this latter character, with an occasional pocket of ore lying wholly 

 within the jasper, are the deposits worked at Soudan. The ore deposits 

 showing the different modes of occurrence just mentioned are of very 

 irregular shape and vary greatly in size. Masses of greenstone project 

 from them into the jasper as a result of the irregularities of the foot wall, 

 due chiefly to folding; or the plane of separation between the ore and the 

 jasper is very irregular and projections of jasper extend down into the ore, 

 and the ore' extends into the jasper, such irregularities rendering the mining 

 very uncertain and expensive. Occasionally great horses of jasper occur 

 in the midst of an ore deposit. 



The deposits occurring within the iron formation are far less likely to 

 be as large and as continuous as those which lie at the bottom of the forma- 

 tion and rest upon an impervious basement, for the reason that the deposits 

 occurring within the iron formation owe their existence to the introduction of 

 igneous rocks in the form of sills or dikes, or to the peculiar conditions of 

 fracture. Where the dikes are numerous there may be a number of rela- 

 tively small deposits separated from one another by intervening walls 

 (subordinate dikes) of soap rock or paint rock of varying thickness. This 

 condition is well illustrated in the case of the ore deposits on Soudan Hill, 

 which are being mined by the Minnesota Iron Company. 



In structure Soudan Hill is a large anticline trending a little north of 

 east and pitching steeply to the west. The summit of this anticline is 

 occupied by a syncline having the same strike and pitch as the anticline, 



