130 THE VERMILION IRON-BEARING DISTRICT. 



rated from tlie next succeeding series by a great unconformity. The 

 formations will be taken up in order of age and described separately in the 

 following pages. 



SECTION II.— ELY GREENSTONE. 



FEATURES OF THE GREEISTSTONE. 



In the Vermilion district there is a great complex of igneous rocks 

 whose members possess one general character in common. They are 

 almost universally colored some shade of green ; hence, for want of a better 

 one, the descriptive term " greenstone " is applied to the complex. To judge 

 from microscopic examination, no chemical analyses having been made, 

 the rocks constituting this complex vary in chemical character from inter- 

 mediate to basic rocks. They likewise possess vai'ied physical characters. 

 The various parts of this complex are not of exactly the same age, as in a 

 number of places one member of the complex intrudes other members ; 

 nor are the rocks all of exactly the same mode of origin, as some are 

 effusive and others intrusive, although all are igneous. These differences 

 in age and mode of formation are, however, only such as we normally expect 

 to find in rocks belonging, as these do, to one great period of eruptive 

 activity which certainly extended over a great length of time. 



Finally, a number of patches of fragmental rock are found in the midst 

 of the Ely greenstones. These patches are too small to be shown on the 

 accompanying maps. Moreover, it is still doubtful whether these are tuffs 

 contemporaneous with and interbedded with the flows, or normal conglom- 

 erates derived from the greenstones and infolded in them. It is probable 

 that both of these rocks are present, but owing to the imperfect exposures 

 it was impossible to distinguish them. 



As a unit the Ely greenstones bear the following general relations to 

 the rest of the rocks of the district. They are in all cases older than the 

 other rocks. From them have been largely dei'ived the later elastics and 

 upon them rest all of the sediments. Through them have been intruded 

 all of the remaining igneous rocks. The Ely greenstones are all 

 Archean, or, if a more general term is desired, they form the basement 

 complex of the Vermilion district. This complex is very well developed m 

 the immediate vicinity of Ely, the largest city of the district, which is 

 literally built upon a firm foundation of these greenstones, and the complex 



