600 GEOLOGY OF CENTRAL WISCONSIN. 



south shore of Lake Monona, near the S. E. corner of Sec. 26. On the south line of the 

 town of Madison, Sec. 33, a large quarry on the Lower Magnesian shows the following 1 , 



beginning above : 



Ft. In. 



1. Concretionary and irregularly bedded, yellowish-gray limestone 10 



2. Chert layer; sometimes forming a continuous nodular- surfaced layer, at 



others occurring in a row of separate nodules; internally, the chert 

 (644) is brown-and-white-banded, and jaspery; externally it has a soft, 

 white, silicious coating 3 



3. Compact, heavily bedded, flinty-textured, gray limestone (644) containing a 



few geodic cavities lined with dolomitic crystals; composed of silica, 

 1.09; alumina, 0.44; iron peroxide, 0.43; iron protoxide, 0.63; lime 

 carbonate, 66.82; magnesia carbonate, 30.40; water, 0.35=100.16; thick- 

 ness 4 



4. Chert layer, like No. 2 2 



5. Very heavily bedded limestone, like No. 1 5 



Throughout the quarry there is a marked local dip of 10 to 15 southward. The 

 quarries have been opened for 20 years, the etone being used altogether for burning into 

 lime, of which about 20,000 bushels are made annually in two large kilns. 



On the west shore of Lake Kegonsa, near the center of Sec. 26, Dunn, a large ex- 

 posure shows the following: 



Fed. 



I. White sandstone with brownish stains 1 



II. Greensand layer 2 



III. Light-colored, soft, thin-bedded, calcareous sandy layers, with specks of green- 



sand and geodic calcite 1 



IV. Whitish layer, more calcareous than the preceding ... 2 



V. Heavily-bedded, light yellowish sandstone (693); fine-grained, firm, nearly 



one-half soluble, the residue made up of angular to subangular white sand; 



in parts cross-laminated 12 



VI. Sandy, yellowish, fine-grained limestone 12 



30 



The lowest layers are unmistakably Mendota, which is here much less sharply defined 

 than usual from the Madison. One-half mile north, friable, brownish, entirely non- 

 calcareous, Madison sandstone is seen on the hill side, corresponding to the uppermost 

 layers of the foregoing section. A similar sandrock shows near the roadside on the 

 north line of the N. W. qr. of Sec. 27, at the Town House, on the center of the south 

 line of Sec. 21, and in the field near the middle of the S. E. qr. Sec. 21, the last named 

 lying near to, and about 15 feet below, one of Lower Magnesian. All of these exposures 

 appear to carry the Madison to an unusual thickness, 50 or 60 feet, 



On the divide Itetweem the Catfish and Sugar river valleys, in Middleton, Verona, 

 Fitchburg, Montrose and Oregon, the Trenton is the rock most commonly quarried, be- 

 ing obtained from the tops of isolated ridges whose sides often show large exposures of 

 the St. Peters. Amongst other quarries may be named those on the S. E. qr. Sec. 27 

 (662, 663, 669), and the S. E. qr. Sec. 35 (664, 665, 666), Middleton; the very large 

 quarries on Sees. 7, 15 and 18, Fitchburg; those on Sees. 13 and 26, Montrose; those on 

 Sees. 4 and 24, Oregon; and those on Sees. 28 and 35, Rutland. All of these are in the 

 Buff beds, generally close to the St. Peters. 



In the Sugar river valley and its branch valleys the Trenton is quarried at a few 

 points, but the St. Peters makes very frequent natural exposures of large size. ClifS? 



