Page:The Journal of geology (IA journalofgeology11893univ).pdf/370

than the belts of schist. Consequently, at the upper narrows of the Baraboo no evidence was found of faulting which could reduce the estimated thickness of the quartzite as given by Irving.

As Irving clearly saw, bearing strongly in favor of the theory of a great fold, is the increasing steeper dip of the layers in passing north. The phenomena of movement and metamorphism corresponding so exactly to those required by a simply fold, the question may be asked if these are not evidence of some weight in favor of the general correctness of Irving's conclusion as to the structure. Had monoclinal faulting extensively occurred, it would not have been necessary to have had so great a readjustment of the beds as has been shown to occur by the schists, cleavage, and the exceedingly intricate macro-fracturing and micro-fracturing of the rock beds and their constituent particles.

In addition to the phenomena described by Irving, in summary, the Baraboo quartzite ranges show results of dynamic metamorphism as follows: A fine example of the Reibungs Breccia may be seen. A fault zone of limited throw exists. All phases are exhibited, between a massive quartzite, showing macroscopically little evidence of interior movement through a rock exhibiting in turn fracture and cleavage, to a rock which macroscopically is apparently a crystalline schist. The foliation of the schists is parallel to the original stratification, being consequent upon the movements of the beds over one another, readjustments occurring mainly in the softer layers. In thin sections the schists still give clear evidence of their fragmental origin, but also show the mechanical effects of interior movement. These same effects are apparent within the heavy beds of quartzite, some readjustments of the particles to their new positions being here also necessary. There is no evidence that the semi-crystalline character of the schist and quartzite are due to high heat. Nowhere are the particles fused. So far as they are destroyed it is by fracture, and the rock is again healed by cementation.