Seen from a distance, the narrows has the appearance of an abrupt notch in the high ridge (Plate [IV]). Seen at closer range, the gap is still more impressive. It is in striking contrast with the other narrows in that there are no talus accumulations at the bases of the steep slopes, and in that the slopes are relatively smooth and altogether free from the curious details of sculpture seen in the other gaps where the slopes are equally steep.

The Upper narrows of the Baraboo at Ablemans (b, Plate [II]) is in some ways similar to the Lower, though less conspicuous because less deep. Its slopes are more rugged, and piles of talus lie at their bases as at Devil's lake. This narrows also differs from the Lower in that the quartzite on one side is covered with Potsdam conglomerate, which overlies the truncated edges of the vertical layers of quartzite with unconformable contact. So clear an example of unconformity is not often seen. Potsdam sandstone is also seen to rest against the quartzite on either side of the narrows (Fig. [26]), thus emphasizing the unconformity. The beauty and interest of this narrows is enhanced by the quartzite breccia (p. [18]) which appears on its walls.

Fig. 26. -- A generalized diagrammatic cross-section at the Upper narrows, to show the relation of the sandstone to the quartzite.
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One and one-half miles west of Ablemans (a, Plate [II]) is the third pass in the north quartzite ridge. This pass is narrower than the others, and is occupied by Narrows creek. Its walls are nearly vertical and possess the same rugged beauty as those at Ablemans. As at the Upper narrows, the beds of quartzite here are essentially vertical. They are indeed the continuation of the beds exposed at that place.

The fourth narrows is across the South range (i, Plate [II]). It is not now occupied by a stream, though like the others it was cut by a stream, which was afterwards shut out from it. Because of its depth, 600 feet, and the ruggedness of its slopes, and because of its occupancy by the lake, this pass is the center of interest for the whole region. So much has already been said concerning it in other portions of this report that further description is here omitted. The manner in which the pass was robbed of its stream will be discussed later (p. [138]).

The history of these several narrows, up to the time of the glacial period may now be summarized. Since remnants of Potsdam sandstone are found in some of them, it is clear that they existed in pre-Cambrian time, [6] and there is no reason to doubt that they are the work of the streams of those ancient days, working as streams now work. Following the pre-Cambrian period of erosion during which the notches were cut, came the submergence of the region, and the gaps were filled with sand and gravel, and finally the ridges themselves were buried. Uplift and a second period of erosion followed, during which the quartzite ranges were again exposed by the removal of the beds which overlay them, and the narrows cleaned out and deepened, and again occupied by streams. This condition of things lasted up to the time when the ice invaded the region.

Glens.—No enumeration of the special scenic features of this region would be complete without mention of Parfrey's and Dorward's glens (a and b, Plate [XXXVII], and Plate [XXV]). Attention has already been directed to them as illustrations of young valleys, and as places where the Potsdam conglomerate is well shown, but they are attractive from the scenic point of view. Their frequent mention in earlier parts of this report makes further reference to them at this point unnecessary.

WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. XXV.