302 . THE VERMILION IRON-BEAEING DISTRICT. 



zone about 3 feet wide. In the midst of this zone there is a horse of the 

 country rock. Around it the material is sheared and brecciated, and the 

 infiltration of silica has taken place subsequent to this shearing. The 

 beds in the sediments on both sides of the fault have been bent. The 

 amount of displacement could not be measured, but seems to have been 

 slight — a very few feet at the most. 



The schistosity and cleavage which have been produced are well 

 marked on the slates. They show the variable relations to the bedding 

 planes which are shown by Van Hise " to be consequent upon their mode 

 of formation, and are clearly the result of the compressive forces which 

 caused the folding. Thus they may be essentially parallel to the bedding 

 on the flanks of the folds, and vary from this position to a position at right 

 angles to it, near the apices of the folds. This cleavage can be well seen 

 on the good exposures southwest and west of the portage from Moose into 

 Flask Lake. South of Ogishke Muncie Lake, where the beds strike N. 25° 

 to 30° W., the schistosity strikes N. 60° E. The difference in the behavior 

 of the soft and hard beds — that is, the weak and the strong beds — under 

 the same condition of pressure are well brought out at one place, upon 

 Ogishke Muncie Lake. At the southwest end of the long point ]3rojecting 

 southwest into sec. 27, T. 65 N., R. 6 W., at the southwest end of Ogishke 

 Muncie Lake, there are in the slate near the water's edge alternating bands 

 of harder and softer materials. In the softer bands, cleavage running 

 parallel to the bedding has been produced, while in the harder ones cross 

 joints have been formed, running practically perpendicular to the cleavage 

 in the soft beds. This difference is evidently due to the difference in the 

 elastic strength of the two rocks. The one, the slate, practically flowed 

 under pressure, while the other was fractured. The deformation evidently 

 took place wliile these rocks were in the zone described as the combined 

 zone of flowage and fracture.'' 



Excessive crumpling is very noticeable in the cherty layers and in the 

 slates. This crumpling is especially well shown on the portage between 

 Fox and Agamok lakes, and is illustrated in fig. 1, PL Y, Minnesota 

 Greological Survey, Vol. IV. The bands here are fractured along planes 



a Principles of North American pre-Cambrian geology, by C. R. Van Hise: Sixteenth Ann. Kept. 

 U. S. Geol. Survey, Pt. I, 1896, pp. 573-874. 

 6 Ibid. 



