SOUDAN FORMATION. 179 



In spite of the intricacy of the folding of the iron formation, it has been 

 possible to determine that in general the axes of the major folds strike east- 

 northeast to west-southwest, the clearest instance of such a large fold being 

 the syncline at Ely. The dip of the axial plane of these folds appears 

 almost without exception to be steep to the north, indicating that the close- 

 ness of the folding has been very great and overturns are common results 

 of this. It is interesting to find that this axial plane has been subject to 

 torsional movement, as in the case of the plane of the Ely syncline. This 

 upon the west end dips to the north, but underground explorations at the 

 east end show that it has here a reversed dip to the south. 



PETROGRAPHIC CHARACTERS. 

 MACROSCOPIC CHARACTERS OF THE FRAGMENTAL PORTION OF THE SOUDAN FORMATION. 



The Soudan formation may be divided into a fragmental series of 

 sediments and into the iron formation proper, whose origin is not distinctly 

 clastic. 



The clastic portion of the formation will be described first, for the 

 reason that it always underlies the iron formation proper. The very few 

 occurrences of these clastic sediments are so widely separated froin each 

 other areally that it is impossible to say that they all belong to the same 

 beds, although they everywhere bear the same relation to the iron forma- 

 tion. And in this connection it must be borne in mind that there is a 

 possibility that the different bauds of the iron foi'mation are not of exactly 

 the same age, but represent stages of deposition of slightly different age, 

 although all of the same general period. The sediments of the clastic 

 division of the iron formation are grayish green and black in color, and 

 consist of a conglomerate at the base, grading upward into the finer-grained 

 deposits. The conglomerate lies next to the greenstone, and consists — both 

 matrix and pebbles — of the material derived therefrom and some pebbles 

 of vein quartz. The finer sediments are chiefly finer material of the same 

 character, derived from the same source. The exception to this statement 

 would be certain soft, black, graphitic slates which are found associated with 

 the jaspers. Such may be observed, for example, upon the westernmost 

 exposures of Lee Hill, just back — that is, north — of the houses of Tower. 

 A somewhat similar graphitic slate is found on the southern slope of Soudan 

 Hill, about 200 yards northeast of No. 12 shaft, which is northwest of the 



