Irving apparently regarded these shear zones as originally beds of a different character from the adjacent quartzite, and his conclusion is fully borne out by the thin sections. The microscope shows that the grains of quartz are of small size, and separated to a greater or a less extent by interstitial clayey material. Because of this partial separation of the grains of quartz, they have not been granulated to the extent that one would expect from the schistosity of the rock, most of the original cores being plainly visible. They, however, often show wavy extinction and even cracks, but not to a greater degree than the grains in the massive quartzite; for in the latter the full stress of the pressure has been borne by the grains in full touch, not separated by a plastic matrix, as are the grains of quartz in the argillaceous layers. In the matrix of the schist are numerous small flakes of muscovite, arranged with their longer axes in a common direction, much finely crystalline quartz, and a good deal of iron oxide. It is concluded that the clayey character of the beds, and, consequently, the greater ease of movement within them, has located the slipping-planes and shear-zones, necessary in order to accommodate the beds to their new positions. On the south range, near Devil’s Lake, these shear-zones are generally not more than six or eight inches wide. They may be well seen just back of the Cliff House, and on the Northwestern Railway, about one-half mile south of this house. All of these shear-zones are parallel with the bedding, and illustrate the possibility, so far as I know first mentioned by H. L. Smyth, that a crystalline schist, with schistosity parallel to bedding, may be produced by shearing along the bedding-planes.