324 THE VERMILION IRON-BEARING DISTRICT. 



Huroniau time this area was, occu^^ied by a comparatively protected sea, 

 in which wave and current action was not very strong, and in which the 

 slates were deposited with very subordinate masses of conglomerate. 



On the south slope of the great greenstone anticline lying south of 

 West GruU Lake and Gull Lake contact between the greenstone and the 

 conglomerate derived from it can be found almost anywhere if one follows 

 the boundary line closely. The conglomerate is in most places, however, 

 so coarse that sedimentary banding is comparatively rare, and this may 

 account for Grant's error in considering it a volcanic tuff." The 

 conglomerate here is exposed over an area about If miles wide, and this 

 great width, as well as the coarseness of the conglomerate is evidence of its 

 great thickness at this place. Moreover, where bedding is shown, for 

 instance, on the hiir725 paces north of the northeast bay of Paul Lake, 

 the beds are found to dip very steeply to the north. Clearly this greenstone 

 was the shore of a great headland Avhicli was exposed to violent wave 

 action, for otherwise such a coarse and thick conglomerate would not have 

 been formed. The same statement is true for the great conglomerate which 

 occurs to the north of this headland, and which consists to a great extent 

 of granite derived from the granite of Saganaga Lake, although here the 

 conglomerate is not so thick as that south of the headland. 



THE AGAWA FORMATION (IRON-BEARING). 

 DISTRIBUTION AND EXPOSURES. 



At several places in the eastern part of the Vermilion district there is 

 found a carbonate-bearing and jaspery iron-bearing formation which is very 

 intimately associated with the Knife Lake slates and is really but a phase of 

 these. This formation occurs in widely separated areas, and in each instance 

 it is exposed in comparatively small masses ; consequently it is not possible 

 to assert with perfect confidence that all of these ferruginous rocks belong 

 to exactly the same horizon, although we are sure that they are very nearly 

 contemporaneous. The areas in which it occurs in the United States are so 

 small that we can state confidently that it will never be of economic impor- 

 tance. The formation is, however, very much more extensively developed 

 in portions of Ontario adjacent to the Vermilion district of Minnesota, and 



« Geology of the eastern end of the Mesabi iron range in Minnesota, by U. S. Grant: Engineers' 

 Yearbook, University of Minnesota, 1898, p. 54. 



