180 THE VERMILION IRON- BEARING DISTRICT. 



Minnesota Iron Company's warehouse. The presence of these graphitic 

 slates with the iron formation probably accounts for the large masses of 

 graphitic rock on the twelftli level in No. 8 shaft at Soudan. There is a 

 mass of this graphitic rock 10 feet long and from 6 to 8 feet thick 

 completely lying in the soap rock. It was cut in a third dimension for 1 1 

 feet, and how much farther it may extend in this direction is unknown. 

 This gi-aphitic rock was tested, it is said, by Mr. John H. Eby, sometime 

 mining engineer of the Minnesota Iron Company, who reported it as 

 graphite. 



These clastic sediments are iuterbedded with the jasper and other 

 materials constituting the iron formation proper. Toward the iron 

 formation the bands apparently become more frequent, and the clastic 

 sediments decrease in amount, and there is thus a gradual transition into 

 the iron formation proper. 



The lower clastic portion of the formation is by no means characteristic. 

 It is rarely present, and when present is very thin. In one place about 

 40 feet of sediments, chiefly conglomerate, were seen, but the exposures 

 were so poor that it was impossible to tell whether the beds were duplicated 

 by folding or not It is possible that some fairly wide areas separating 

 jasper exposm-es from greenstone exposures may be underlain by the 

 clastic formation, but this is not probable, for the practical absence of the 

 formation, which is fairly resistant throughout the district, shows that it 

 must have been very subordinate. Yet, in spite of its subordinate position 

 quantitively, this clastic portion of the formation is of great stratigraphic 

 importance, as no matter at how few places it has been found or how thin 

 it may be, it nevertheless is clear proof of a very important change in 

 conditions, marking the transition from the period of volcanic activity in 

 which the greenstone had its origin to the period of sedimentary de^^ositiou 

 in which the Soudan formation was laid down. 



inCKOSCOPIO CHARACTERS OF THE ERAGMENTAL PORTION OE THE SOUDAN 

 FORMATION. 



The conglomerate and normal fine-grained sediments, belonging for the 

 most part below the iron-bearing formation proper, show nothing under the 

 microscope which is worthy of detailed description. The conglomerates 

 are clearly recognizable in the field as elastics, and rnider the mici'oscope 



