276 THE VERMILION IRON-BEARING DISTRICT. 



perhaps, the conclusion that the conglomerate is the predominant clastic, 

 but it is believed the slates make up the greater part of the sediments. 



Included within the Lower Huronian there is a, horizon of iron-bearing 

 carbonates. These carry a considerable quantity of iron as carbonate in 

 addition to the calcium-magnesium carbonates. There is also developed at 

 a few localities an iron-bearing formation consisting of banded jasper, 

 cherts, and iron ore. This iron formation is present in very small 

 quantity, and certainly will never be of any importance on the United 

 States side of the international boundary. These two kinds of rock are 

 presumed to correspond to each other — that is, they belong to the same 

 horizon. On the scale on which the map is published, it would be impossible 

 to represent all of the different bauds of conglomerates, grits, slates, etc. 

 Consequently no attempt has been made to discriminate between these kinds 

 of the fragmental rocks further than to show the areal distribution of the 

 extremes. 



We are enabled to divide the Lower Huronian sediments into three 

 parts — (1) a lower division, which is predominantly conglomeratic and 

 which is most typically developed near Ogishke Muncie Lake, and is called 

 the Ogishke conglomerate; (2) a division represented only in the eastern 

 portion of the district, consisting of iron-bearing rocks and known as the 

 Agawa formation; and (3) a division which is predominantly a slate 

 formation and which we shall denominate the Knife Lake slates, since 

 these slates are well developed and splendidly exposed on and near 

 Knife Lake. Mention has already been made of the fact that the Lower 

 Huronian sediments occur in two separate areas within this district. In 

 each ai'ea both the conglomerate and slate are well developed. There are, 

 however, certain local differences in the rocks that underlie the Lower 

 Huronian, and as a consequence the sediments in the two areas are 

 slightly different. For this reason, and also as it simplities exposition, it 

 is considered best to describe the rocks of the two areas separately. It 

 must in each case be clearly understood that the conglomerates of the two 

 areas are geologically contemporaneous and that the same contemjDoraneity 

 exists in the case of the slate formation. The Agawa formation is present, 

 however, only in the Knife Lake area and can not be correlated with any 

 definite formation in the western area. The areas will be described 

 separately in the following pages. 



