132 THE VERMILION IRON-BEARING DISTRICT. 



14 W., covers almost the entire central portion of the district and has there 

 an approximate width of 10 miles. This great width of the El^^ green- 

 stone continues to the east very nearly as far as Pine Lake, in R. 10 W. 

 Within this area its continuity is interrupted in a number of places b}^ nar- 

 row belts of sediments of later age trending- approximately east to east- 

 northeast. These, although of minor importance so far as areal distribu- 

 tion is concerned, are of great economic importance, as within the area 

 just described they consist for the most part of the iron-bearing formation. 

 About 7 miles west of Ely, in sec. 4, T. 62 N., R. 13 W., begins a series 

 of sedimentary rocks which splits the Ely greenstone approximately in 

 the center. This belt of sedimentary rocks continues on to the east with 

 approximately uniform width beyond the end of Fall Lake, in sec. 31, 

 T. 64 N., R. 10 W., where it ends. Just about three-quarters of a mile 

 beyond this there begins another belt of sediments which continues 

 eastward, widening very rapidly, and corresponding to this widening 

 there is a rapid reduction in the width of the greenstone areas lying 

 north and south of it. The northern belt of greenstone narrows more 

 rapidly and disappears north of Moose Lake, in sec. 16, T. 64 N., R. 9 W., 

 where it is covered by overlapping sediments. The continuation of this 

 belt is wanting' for a distance of about a mile. It then begins again in sec. 

 10, T. 64 N., R. 9 W., and continues thence northeast to the international 

 boundary. 



From here on to the northeast the extension of the Ely greenstone 

 has been traced into Canada as the result of a reconnaissance survey. The 

 boundaries of the formation in Canada, as given upon the accompanying- 

 maps, can not, therefore, be regarded as nearly so correct as those given 

 within the United States. They have been found in most places as a result 

 •of the stud}^ of exposures along the lakes and of a few traverses inland. 

 This reconnaissance shows us that the width of the Ely greenstone, as it 

 continues to the northeast, varies greatly as a result of the folding to which 

 it has been subjected. As a result of this, also, its continuity is interrupted 

 by the infolding of the younger rocks whose areas have been delimited. 

 Upon the map it appears to cover a larger area than it does in reality, for 

 the reason that the important iron-bearing formation has not been delimited, 

 although its presence within the greenstone area is known from its having 

 been observed at a great number of places. 



