had in pre-Cambrian time, for they are still partially buried by younger beds. _The narrows in the quartzite._--There are four narrows or passes in the quartzite ridges, all of which are rather striking features. One of them is in the South range, one in the North range near its eastern end, while the others are in an isolated area of quartzite at Ablemans which is really a continuation of the North range. Two of these narrows are occupied by the Baraboo river, one by Narrows creek, and the fourth by Devil's lake. From Ablemans to a point several miles east of Baraboo, the Baraboo river flows through a capacious valley. Where it crosses the North range, six miles or more north of east of Baraboo, the broad valley is abruptly constricted to a narrow pass with precipitous sides, about 500 feet high (c, Plate XXXVII). This constriction is the Lower narrows, conspicuous from many points on the South range, and from the plains to the north. Beyond the quartzite, the valley again opens out into a broad flat. [Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. XXIV. Talus slope on the east bluff of Devil's lake.] 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 ( which appears on its walls. [Illustration: Fig. 26.--A generalized diagrammatic cross-section at the Upper narrows, to show the relation of the sandstone to the quartzite.] 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.