540 GEOLOGY OP CENTRAL WISCONSIN. 



from the lime-capped bluffs at the northwestern corner of Marquette 

 county, are other bluffs, showing large exposures of the limy layers 

 that come immediately beneath the Mendota. One and a half miles 

 northwest from here, on Sec. 3, T. 17, R. 7 E., across an intervening 

 level stretch of sand, is one of the towers of sandstone that char- 

 acterize the central plain known as Pilot Knob. This peak rises 

 25 feet above the top of the calcareous layers seen just across the 

 valley, and 65 feet above their base, and yet from its summit down 

 for 150 feet, we find only altogether non-calcareous sandstone, much 

 of which is highly ferruginous, and all of which is quite unlike anj 

 of the layers that are usually found within 200 feet of the base of the 

 Mendota. Moreover, two fossil horizons, yielding Ptychaspis Mitiis- 

 caensis, and other forms, supposed to be characteristic of the middle 

 portion of the lower sandstone, occur in this exposure. We have, 

 then, here, to some extent, a repetition of the anomalous occurrences 

 of the Baraboo region noncalcareous, red, ferruginous sandstone, with 

 fossils indicating a horizon full 300 feet below the Mendota, rising 

 through the horizon of the upper calcareous beds, into that of the 

 Mendota. Some nine miles west of Pilot Knob, near Friendship, 

 Adams county, occur other similar sandstone towers, all showing en- 

 tirely non-calcareous, friable rock. On the summit of one of them, 

 the Roche a Cris, is to be recognized the uppermost of the fossil 

 horizons of Pilot Knob, the lower one of which, marked by a 

 peculiar lithological character, is still more unmistakably to be re- 

 cognized on another bluff, some five miles south of Friendship. Both 

 of these horizons indicate a slight rise of the layers eastward towards 

 Pilot Knob. Still another one of these outliers, the Friendship 

 Mound, rises 85 feet higher than the Roche a Cris near by, carrying 

 the light-colored, friable, non-calcareous sandstone all the way. The 

 horizon of the summit of this bluff is, then, 85 feet above that of the 

 summit of Pilot Knob, or, if the latter rises into the horizon of the 

 Mendota, as high as the position that would be expected for the 

 Low r er Magnesian, from its occurrences in northeast Marquette 

 county. 



At the southern end of Adams county, the Wisconsin passes the 

 gorge known as the Dalles. At the northern end of the gorge is 

 another of the large sandstone outliers like those just mentioned 

 the Elephant's Back. This bluff, with the walls o the gorge below, 

 gives a nearly continuous section of 310 feet. At Kilbourn City, two 

 miles below, an Artesian boring penetrates into the underlying Arch- 

 aean. Combining the results of the section and boring, we have the 

 following general succession : 



