556 GEOLOGY OF CENTRAL WISCONSIN. 



bia and Dane counties. In the former, it is met with in the north- 

 east corner of the county, in the towns of Randolph and Conrtland, 

 with a thickness of only 20 feet, and forming strips not more than a 

 few rods wide around several areas of Trenton limestone. Further 

 south its main area lies altogether east of Columbia county, but it is 

 found again in the southeastern the towns of Columbus arid Hamp- 

 den, with the same small thickness and distribution in a narrow belt 

 around an area of Trenton limestone. The St. Peters is absent every- 

 where else in Columbia county, except in live small patches on the 

 high prairie of Arlington, and in a still smaller area, but with a thick- 

 ness of 125 feet, in the high peak known as "Gibralter Bluff," in the 

 town of West Point. In Dane county, the St. Peters is found under- 

 lying the Trenton on both sides of the Catfish valley, sometimes 

 coming to the surface as a narrow band only, at other times having 

 quite a surface spread, as in Sun Prairie, Medina, Cottage Grove, 

 Deerfield, Fitchburg, Oregon, Montrose, and Verona; these larger 

 areas including a number of small patches of Trenton limestone, 

 which caps the summits. On the west side of Sugar river, though 

 having its full thickness, the St. Peters comes to the surface only in 

 narrow bands, forming the sides of deep and narrow valleys. The 

 same is true of the south side of the valley of Black Earth creek in 

 Cross Plains and Middleton. In Berry, Springfield, and northern 

 Middleton, the St. Peters occurs only in a few limited areas on the 

 highest ground. The whole surface spread of the St. Peters, in Col- 

 umbia and Dane counties, is not more than 225 square miles, all but 

 6 or 8 of which is in the latter county. 



In eastern Columbia and Dane counties the St. Peters sandstone 

 does not contribute any marked topographical features to the coun- 

 try, being comparatively thin and generally drift covered. Where it 

 occurs in narrow bands around the Trenton areas, its place is not un- 

 commonly marked by an abrupt change of level. On the west side of 

 Dane county, however, and especially west of Sugar river, which 

 forms the western boundary of the region of the Glacial Drift, the St. 

 Peters affects the scenery of the country in a marked degree. Here 

 we find it having its full thickness of 80 to 100 feet, and producing, 

 by its friability, abrupt, and not infrequently precipitous and rocky, 

 valley sides, whose summits are capped by the Trenton limestone, 

 whilst the valley bottoms are on the Lower Magnesian. In the val- 

 leys themselves, isolated towerlike rocks of the St. Peters occur, of 

 varying size, and occasionally of greater area at top than at bottom. 

 Some of these contain the full thickness of the St. Peters, and are 

 crowned with the lowest layers of the Trenton. 



