176 THE VERMILION IRON-BEARING DISTRICT. 



are superimposed, giving the intricacy of structure already referred to. It 

 is of interest to note in connection witli this remarkably close folding of 

 the jasper ^ — some of the bands are actually folded upon themseh'es within 

 a radius scarcely greater than the width of the belt — that the jasper for the 

 most part has not l)een very much fractured. This is very clearly indica- 

 tive of the great depth at Avhich this formation lay at the time the folding 

 took place. This close folding without fracture can be explained only by 

 assiiming that the rocks were under such great pressure that they acted 

 practically as plastic bodies. North of Fall Lake the close folding of the 

 jasper is shown in one place where bands 4 to 6 inches in width have been 

 turned so' sharply that the two ends are noAv only 1 foot a^jart, and here 

 the jasper, usually considered a very brittle substance, shows no indica- 

 tions of fractures, but has comported itself as a viscous material. 



PI. VI, A and B, reproduced from sketches made by W. N. Merriam in 

 the field, from actual exposures near .Soudan, shows very well the extreme 

 intricacy of the folding. 



Both the longitudinal and the cross folding of the iron formation is 

 composite; that is, superimposed upon the major folds in each direction are 

 folds of the second order, and upon these are folds of the third order, and so 

 on down to minute plications. The pressure has been so great as to give all 

 variety of minor folds, including isoclinal and fan shaped. Moreover, these 

 varieties of folds may be seen almost equally well on a ground plan or on 

 a vertical cross section. They are beautifully shown at various places 

 about Tower and Ely, but perhaps the most extraordinarily complex folding 

 seen is that at the west end of the large island in the east part of Emerald 

 Lake. Figs. A and B of PL VI, which are upon the whole representative 

 of the district, show that the folding, notwithstanding the extremely brittle 

 character of the rock, was accomj)lished without major fracture. The 

 deformation, therefore, is deformation in the zone of rock flowage, and no 

 better instance is known to the writer of this kind of earth movement. 

 Frequently a solid belt of jasper is bent back upon itself within a radius 

 of its own width with no sign of fracture. 



Though the folding is so complex as to give even fan-shaped folds, the 

 turns are ordinarily round rather than angled, thus differing from those 

 acute-angled folds frequently seen in the Menominee district. The round- 

 ness of the folds is well illustrated in the fisrures. 



