188 THE VERMILION IRON-BEARING DISTRICT. 



been extremely altered, and with the recrystallization of the elements tlaere 

 may have taken place complete destruction of the original structures, with 

 the exception of banding, which is still evident, and, in fact, this may have 

 been further emphasized by the rearrangement of the constituents. 



OEiGiisr. 



The banded structure of the iron-bearing formation is exceedingly 

 regular throughout the district. It is difficult to say how persistent the 

 individual bands are, however, for the outcro^js do not allow them to be 

 traced over very long distances. Most of the bands seen at a particular 

 exposure persist entirely across the exposed surface. A. few, however, 

 ran out to a feather edge even on small exposures, and thus disappear. 

 The presumption is that all the bands feather out within a shorter or 

 longer distance. This banding is so well marked and so eminently 

 characteristic that from its presence alone one is fully warranted in making 

 the statement that the structure of the formation is essentially that of a 

 sedimentary rock. Furthermore, the composition and texture of the rocks 

 making up the formation are such that we can assert with confidence that 

 none of the members are of igneous origin. It has already been stated 

 that in places the iron formation proper — that is, the interbanded iron 

 oxides, cherts, and jaspers — overlie conformably a series of clastic rocks, 

 beginning at the bottom with a conglomerate and grading upward into 

 finer material, and also that we find similar fine clastic matei'ial interbanded 

 with the iron oxides, cherts, and jaspers. This • clearly indicates that the 

 rocks of the iron formation are of sedimentary origin. The presumption 

 is that the elastics were first formed; that there was then a period with 

 changing conditions, during which the slates and iron-formation rocks were 

 interbedded, and that finally the conditions controlling the deposition of 

 rocks of the iron-bearing formation became more persistent when the orig- 

 inal rocks of the iron-bearing formation were deposited. This enables us 

 to explain certain characteristics of the contact between the green- 

 stone and the iron formation which, in view of the known relations 

 of these rocks, could not otherwise be explained. At a point 2,000 paces 

 east, 700 paces south of the soiitheast corner of sec. 17, T. 62 N., R. 13 

 W., there is an exposure of jasper on the south side of massive green- 

 stone. At this exposure there seems to be a gradation of the greenstone 



