SOUDAN FORMATION. 191 



the proof in favor of his view that the cherty iron carbonate is the original 

 rock of the iron-bearing formations. In the Vermihon district tlie iron 

 carbonate is present in very' small qiiantity, but it is significant that we 

 find siderite in large quantity in the ranges east of this but in line of its 

 strike, for instance near Port Arthur and in the Michipicoten district. 



No proof of the supposition that a cherty iron carbonate is the original 

 rock of the Soudan formation has been found in the Vermilion district. 

 From the analogy of this with the other iron-bearing districts of the 

 region it seems most probable that in this, as in the districts above referred 

 to, the cherty iron carbonate was the chief original rock of the iron-bearing 

 formation. In the monographs cited above, details are given which will 

 enable the reader to follow the various changes which, by leaching and 

 deposition, transform the cherty iron carbonate into chert, jasper, and ore. 



While stress has been laid upon the formation of the jas2Der as the 

 result of secondary jDrocesses acting upon an originally ferruginous rock, it 

 must be stated that in certain places in the district the jasper doubtless 

 owes its origin to processes of secondary infiltration. Such jasper occurs 

 in vein-like form and in irregular bunches. It may occur also as the 

 cement of the brecciated greenstones, and is found occasionally lying 

 between the greenstone ellipsoids. The possibility that some of this 

 jasper may- be due to secondary action must of course be admitted. 

 This is admitted, however, only for very small masses. These masses 

 were probably formed by infiltration in openings in the greenstones, from 

 above, during the time that the overlying cherty iron carbonates were 

 being changed to the present condition of the iron-bearing formation. That 

 the infiltration is of relatively recent date in one particular instance is 

 shown by the presence of chert veins in an acid porphyry which cuts the 

 jasper and the greenstone north of Mud Creek Bay. Had iron been present 

 in this siliceous solution jasper with small masses of ore instead of the 

 veins of chert might very well have been formed. 



RELATIONS OF SOUDAjST FORMATION TO ADJACENT FORIVIATIONS. 



RELATIONS TO THE ELY GREENSTONES. 



From a scientific point of view one of the most interesting problems 

 confronted in the study of the Vermilion district is that of the relation of the 

 iron formation to the Ely greenstones. From an economic standpoint this 

 is also one of the most important problems. It was likewise most puzzling 



