[Illustration: Fig. 4.--Diagram made by plotting the different dips now at hand along a section from A to B, Plate II, and connecting them so as to show the structure indicated by the known data. The full lines, oblique or vertical, represent the beds of quartzite. The continuous line above them represents the present surface of the quartzite, while the dotted lines suggest the continuation of the beds which completed the great folds of which the present exposures appear to be remnants.] [Illustration: Fig. 5.--A diagrammatic section showing the relation of the sandstone to the quartzite.] [Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. VII. The East Bluff at the Upper Narrows of the Baraboo near Ablemans, showing the vertical position of the beds of quartzite. In the lower right-hand corner, above the bridge, appears some breccia.] [Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. VIII. Vertical shear zone in face of east bluff at Devil's lake.] Near the shear zones parallel to the bedding planes, there is one distinct vertical shear zone (Plate VIII) three to four feet in width. It is exposed to a height of fully twenty-five feet. Along this zone the quartzite has been broken into angular fragments, and at places the crushing of the fragments has produced a "friction clay." Slipping along vertical zones would be no necessary part of folding, though it might accompany it. On the other hand, it might have preceded or followed the folding. Schistose structure probably does not always denote shearing, at least not the shearing which results from folding. Extreme pressure is likely to develop schistosity in rock, the cleavage planes being at right angles to the direction of pressure. It is not always possible to say how far the schistosity of rock at any given point is the result of shear, and how far the result of pressure without shear. Schistose structure which does not appear to have resulted from shear, at least not from the shear involved in folding, is well seen in the isolated quartzite mound about four miles southwest of Baraboo on the West Sauk road (f, Plate II). These quartzite schists are to be looked on as metamorphosed quartzite, just as quartzite is metamorphosed sandstone.