SOUDAN FORMATION. 173 



occurs just north of the boundary in Ontario, and is known to continue 

 northeastward for manj^ miles within Canadian territory. 



The Soudan formation has its greatest development in the western part 

 of the district, the most prominent areas extending from Tower, on Ver- 

 milion Lake, in T. 62 N., R. 15 W., on the west, to Fall and Garden lakes, 

 in T. 63 N., R. 11 W., just a few miles east of the well-known town of Ely, 

 on the east. 



The formation is most notably exposed in areas lying about midway 

 between the north and south limits of the district. At Tower and Soudan 

 it underlies broad areas and forms the prominent topographic features 

 known as Tower, Lee, and Soudan hills, and Chester, or Jaspei-, Peak. 

 Other fairly large areas occur in a belt just north and east of Ely, in sec. 

 25, T. 63 N., R. 12 W., and in sec. 30, T. 63 N., R. 11 W. North and south 

 of and between the areas mentioned, the formation underlies rather narrow 

 belts trending east-northeast to west-southwest. Each of these belts is made 

 up of a series of narrow bands of the iron formation, interbedded in some 

 cases with small quantities of fi^agmental rocks and intimately associated 

 with the Ely greenstone and the late intrusives, which cut through both, 

 the Ely greenstone and the Soudan formation. As shown on the maps 

 in the accompanying atlas, some of these belts, especially those near the 

 center of the western part of the district, can be followed for a number of 

 miles east and west; one was traced for 16 miles. Others are very much 

 shorter, having been traced for only a few miles, and these small areas 

 grade down to those which are mere patches, a few inches or feet across 

 and a few feet or paces in extent — that is, along the strike. However, it is 

 believed that all of these, from the largest to the smallest, with the excep- 

 tion possibly of certain small vein-like masses which will be mentioned 

 later, are parts of one general formation, now separated from one another 

 by folding and erosion. 



A glance at the maps will show that the areal distribution of the 

 Soudan formation is closely connected with that of the Ely greenstone. 



EXPOSURES. 



One would ))e inclined to think, judging from the resistant nature of 

 the rocks constituting the iron formation, that it would be well exposed 

 throughout the district. Such is, however, very far from the case. Except 

 in a few places, notably at Tower, Lee, and Soudan hills and Jasper Peak; 



