SECONDARY STRUCTURES OF BARABOO QUARTZITE 265 



These movements were in the direction of the anticlinal axis of the 

 fold for an upper bed with reference to a lower bed, and in the direc- 

 tion of the synclinal axis for a lower bed with respect to an upper bed. 

 More deformation took place in weak beds than in strong beds; more 

 in highly tilted, beds than in slightly tilted beds. Other factors also 

 influenced the movement. For instance, a large amount of readjust- 

 ment took place at the contact of the quartzite and the underlying 

 igneous rocks. It may be that this was due to the absence of easy 

 planes of slipping in the massive igneous rocks and that consequently 

 a large part of the required amount of movement took place at the 



Norl-h 



5 ou t" h 



Fig. 2. — Diagrammatic north-to-south section of the quartzite formation. Scale 

 of cross-section: f inch = i mile. A and B represent sections of cubes in the beds 

 before deformation. 



contact of the two formations. Fig. 2 represents a diagrammatic 

 north-to-south section of the quartzite formation. The arrows 

 indicate the direction of movement in the beds in the process of fold- 

 ing. A and B represent sections of cubes in the beds before deforma- 

 tion. After deformation, the cubes will be deformed into parallelo- 

 pipeds, and the sections A and B will be deformed into parallelograms. 

 Spheres inscribed in the original cubes are deformed into ellipsoids 

 called the strain ellipsoids. Fig. 3 represents A of Fig. 2, a vertical 

 section of a cube normal to the strike, and the parallelogram resulting 

 from the deformation of ^; the circle inscribed in A, and the resulting 

 ellipse of strain. Fig. 4 represents a similar section on the North 

 Range where the bedding is vertical. The arrows indicate the direc- 

 tion of slipping between the beds. 



