274 GEOLOGY OF EASTERN WISCONSIN. 



Toward the top, there are to be found some very sandy layers that appear to rest, in a 

 measure, unconformably upon a worn surface beneath, and probably represent the St. 

 Peters sandstone, which would naturally be calcareous in such a situation. 



A portion of the rook of this dome is a coarsely brecciated, very hard crystalline dolo- 

 mite, but the greater part belongs to the more common class of coarse, impure magne- 

 sian limestone that characterizes this formation. 



Passing by a number of minor exhibitions of the same phenomena, we find, in the 

 vicinity of Ripon, this peculiarity developed to a wonderful extent. Just west of the 

 Ceresco Mills, in the lower part of the city, there rises a rock hUl, having an elongated 

 oval contour, somewhat enlarged and curved at the eastern extremity. Its .base is 

 sldrted on the east and north by streams above which its crest rises to an average height 

 of about one hundred feet. Its axis lies east and west, and does not much exceed one- 

 fourth of a mile in length. It is tenninated at the west by a deep ravine, beyond which 

 rises a second ridge of similar form and height, and somewhat greater length, but which 

 is less conspicuous because of its connection with the plateau on the south. The ridge 

 first mentioned is nearly isolated by a deep ravine on the south, which reveals its form, 

 though the rock exposures are chiefly confined to the eastern end. On the northeast 

 slope, thick, heavy, rough beds of Lower Magnesian Kmestone show a dip of 15° to 18° 

 to north of east. On the easternmost point, the dip is 18° to the eastward, while on the 

 southeast curve a slant of 25° to 30° to the southeast is observed, and farther along the 

 south side of the hill, a more southward and southwestward dip seems to be indicated, 

 though the exposures are very unsatisfactory. A small quarry above the limekQn, and 

 near the top of the hiU, shows within itself dips of 3° E., 12}4° N. B., and 7° N. W., 

 with all intermediate inclinations. This uTegularity is not caused by the folding or con- 

 tortion of even bedded layers, so much as by the thickening and thinning of irregular 

 ones. Great lumps, as it were, occur at certain points, swelling two or three fold the 

 thickness of the layer, or causing it to disappear entirely in a structureless mass. The 

 rook is greenish blue, somewhat argUlaoeous, aud contains a few fossils. 



Down the slope from this quarry, and within six rods of it, a bed of St. Peters sand- 

 stone lies immediately against the flank of the Lower Magnesian arch, the top of the 

 sandstone beiitr/ 30 feet beloto the crest of the ridge. The actual junction of the sand- 

 stone with the limestone was not visible at the time of either of my visits, but I was 

 credibly informed that in a filled portion of the sajid pit it had been previously exposed. 



Wells in the vicinity show that the surface of the limestone descends to at least 100 

 feet below the top of the hiH. There is here then within a horizontal distance of less 

 than one quarter of a mile, a rise and fall of the upper limits of the Lower Magnesian 

 limestone of not less than 100 feet. 



Pig. 29. 



INoBTH AND South Section, near Eipon. 

 1. Lower Magnesian limestone. 2. St. Peters sandstone. 3. Trenton limestone. 



Within less than a half mile south of this arch, the Lower Magnesian strata again 

 mount into the Trenton horizon, more than 100 feet above the intervening depression, 

 and agam to the south, less than half a mile, another arch appears, but passes 

 under the bluff to the west before attaining so great an altitude as the two preceding 

 ones. The rock forming this one is unusually kregular in hardness, and weather out 

 into the most fantastic shapes, so that the loose worn masses are much admured as lawn 

 ornaments. 



The accompanying figure will assist in illustrating the foregoing facte. The irregu- 



