THE LOWER SILURIAN ROCKS. 567 



quartzite bluffs at Necedah, and in one or two very small and somewhat doubtful eap- 

 pings of limestone in the southwestern towns of Juneau county, the Lower sandstone is 

 the surface rock. 



i The larger portion of the district presents the character of a level plain, which has, 

 for the most part, a surface of loose sand derived directly from the disintegration of the 

 Lower sandstone, but showing many marshes, some of very large size, and occasionally 

 prairies. Except on the marshes, and the few small prairies, this plain is nearly every- 

 where covered with a growth of stunted oaks, with which, towards the north, small 

 "jack- pines " intermingle. It is traversed centrally from north to south by the Wiscon- 

 sin river, and is surrounded on all sides by higher ground. The elevation on the north 

 is due merely to the gradual rise of the plain in that direction, the general altitude on 

 the southern edge, along the Lemonweir river, being about 300 feet, that along the north 

 line of Juneau county, 400 feet. The high ground on the east is also due to a steady, 

 but very much more rapid, rise of the plain in that direction, the dividing ridge along 

 the line of Adams and Waushara counties having an altitude of some 200 feet above 

 the Wisconsin. On the south, southwest and west, however, the edge of the plain is 

 very sharply defined by a narrow and much indented dividing ridge, which is especially 

 marked in the southwestern towns of Juneau county, where it has on its western side 

 the deeply carved valley of the Baraboo, with its numerous branch ravines. 



Dotting the central plain, and rising quite abruptly from its most level portions, are 

 the isolated mounds and castellated peaks of rock that constitute its most marked and 

 peculiar characteristic. Except the quartzite mound at Necedah, these are altogether 

 of sandstone, being the only portions that have been left from the denudation of the 

 Lower sandstone. Although none of them exceed 300 feet in height, and but few 200 

 feet, they register a denudation of fully 500 feet; that is to say, over the larger part of 

 this plain there has been at one time a thickness of 500 feet of rock, wluch no longer 

 exists, and possibly there has been a much greater thickness than this. There are two 



FIG. 35. 



OUTLINES OP ROCHE A Cms AND FRIENDSHIP MOUND, AS. SEEN FROM PILOT KNOB. 

 Seale 2.480 feet to the inch. 



classes of these remarkable outliers : the larger and more prominent ones, which reach 

 elevations of from 150 to 300 feet, have lengths of from ^ to 1 mile, and show more or 

 less vegetation on top; and the smaller and less conspicuous ones, which are from 30 to 

 100 feet in height, often of bare rock, and cover comparatively small areas. The larger 

 outliers are few in number, and are, for the most part, quite distant from one another. 

 Two of these are especially prominent, showing from any point on or around the plain 

 high enough to be above the tree tops. These are the Roche a Oris and the Friend- 

 sliip Mound in the southwest part of T. 18, R. 6 E., Adams county. Their prominence 

 is due both to their heights above the plain at their bases and to the comparatively 

 great elevation of the portion of the plain on which they stand. The Roche a Cris is a 

 thin, wedge-shaped mass of rock, without pinnacles, having a length of about mile, 

 and a height of 225 feet above its base, or about 660 feet above Lake Michigan, and 

 standing up like a fragment of a great wall. Friendship Mound is about half a mile 

 south from Roche & Cris, which it exceeds in height by 50 feet, having also a much 

 greater length and thickness and a more rounded contour. The outline of these two 

 bluffs, aa sketched from the summit of Pilot Knob, 10 miles east, is given in Fig. 35. 

 Amongst the other large outliers may be mentioned the very large wooded mound, in T. 



