The beds of limestone, like those of the sandstone beneath, are horizontal or nearly so, and the upper formation lies conformably on the lower. The limestone does not contain water-worn pebbles, and the surfaces of its layers are rarely if ever ripple-marked; yet the arrangement of the rock in distinct layers which carry fossils of marine animals shows that the limestone, like the sandstone beneath, was laid down in the sea. The bearing of this origin of the limestone on the development of the present valleys is the same as that of the sandstone. _Origin of the topography._--The topography of the plain surrounding the quartzite ridges, especially that part lying west of Devil's lake, is then an erosion topography, developed by running water. Its chief characteristic is that every depression leads to a lower one, and that the form of the elevations, hills or ridges, is determined by the valleys. The valleys were made; the hills and ridges left. If the material carried away by the streams could be returned, the valleys would be filled to the level of the ridges which bound them. Were this done, the restored surface would be essentially flat. It is the sculpturing of such a plain, chiefly by running water, which has given rise to the present topography. In the development of this topography the more resistant limestone has served as a capping, tending to preserve the hills and ridges. Thus many of the hills, especially in the southwest portion of the area shown in Plate II, are found to have caps of the Lower Magnesian formation. Such hills usually have flat tops and steep or even precipitous slopes down to the base of the capping limestone, while the sandstone below, weathering more readily, gives the lower portions of the hills a gentler slope. The elevations of the hills and ridges above the axes of the valleys or, in other words, the relief of the plain is, on the average, about 300 feet, only a few of the more prominent hills exceeding that figure. The topography east of the line between Kilbourn City and Prairie du Sac is not of the unmodified erosion type, as is made evident by marshes, ponds and lakes. The departure from the erosion type is due to a mantle of glacial drift which masks the topography of the bedded rock beneath. Its nature, and the topographic modifications which it has produced, will be more fully considered in a later part of this report. [Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V., PL. IV. The Lower Narrows of the Baraboo from a point on the South range.] II. THE QUARTZITE RIDGES.