600 GEOLOGY OP CENTRAL WISCONSIN. 



Prairie and Medina, its eastward descent having carried it here far below the altitudes 

 at which it is found on the west side of the county. It lies also at the bottom of the 

 valley of Sugar river and its numerous branch valleys, crowns the outlying bluffs of the 

 Wisconsin valley, and occurs also in several small isolated patches, within the Potsdam 

 area of the Catfish valley. The thickness of the Lower Magnesian in Dane county seems 

 rarely to be more than 80 feet, whilst its very irregular upper surface brings it often into 

 the horizon of the next formation above. The St. Peters sandstone occupies a large 

 tract on the east side of the Catfish valley, where it appears to be never more than 50 

 feet in thickness. It is found, also, forming a narrow band around the Trenton areas 

 of York, Bristol and Windsor. West of the Catfish valley it occupies much of the high 

 ground forming the divide from the valley of the Sugar river. In the last-named valley 

 and its branches the St. Peters forms the lower part of the -bluff sides, having its full 

 thickness of 80 to 90 feet. It occurs also in several detached areas in the high country 

 north of Black Earth creek. The Trenton limestone occurs in detached areas, mostly of 

 considerable size, capping the high ground on both sides of the Catfish valley. Some of 

 the areas, however, are quite large, covering one or two townships, as in Middleton, 

 York, Christiana and Albion. In Springdale and Primrose the narrow ridges between 

 the streams, carry the whole thickness of the Trenton limestone, being at times capped 

 by the Galena. For the most part, the Trenton areas of Dane county include only the 

 lower part of that formation. The Galena limestone occurs only as a capping on tho 

 higher parts of the ridges of Springdale and Primrose, and in two or three small areas 

 in Christiana. 



Cross sections- for Dane county, both north and south, and east and west, are given 

 on Plates XXIV and XXV, showing both the surface contour, and the succession and rela- 

 tions of the several strata. Two other sections through the county, drawn on a larger 

 scale, will be found attached to Plate XIII of the Atlas. These sections, with the col- 

 ored map, render unnecessary any further general descriptions. 



On the east side of the county the lower or Buff portions of the Trenton shows in nu- 

 merous quarries, many of which yield a good building stone. Amongst many quarries 

 we may list the following: N. E. qr. Sec, 25, York; N. E. qr. Seo. 26, Medina, a large 

 quarry with a 12 feet face; on Sees. 29, 35 and 36, Decrfield; N . E. qr. Sec. 22, N. E. 

 qr. Sec. 24, and N. E. qr. Sec. 23, Christiana, the last one showing 15 feet of regular, 

 heavy layers; N. W. qr. Sec. 2, N. E. qr. Sec. 15, S. W. qr. Sec. 2, N. W. qr. Sec. 27, 

 Albion; S. E. qr. Sec. 30, Dunkirk, where there is a 15 feet face; S. W. corner Sec, 3, 

 N. W. qr. Sec. 4, N. E. qr. Sec. 10, where there are 10 feet of even, heavy layers, S. E. 

 qr. Sec. 13, N. E. corner Sec. 14, N. W. qr. Sec. 35, S. E. qr. Sec. 36, Pleasant Springs; 

 Sec. 4, Cottage Grove; N. W. qr. Sec. 14, N. E. qr. Sec. 23, Sun Prairie; N. W. qr. 

 Sec. 17, N. E. qr. Sec. 30, and in the north part of Sec. 34, Bristol; S. E. qr. Sec. 14, 

 N. E. qr. Sec. 23, Windsor; S. W. qr. Sec. 2, S. W. qr. Sec. 26, N. W. qr. Sec. 35, 

 Burke; N. E. qr. Sec. 14 and N. E. qr. Sec. 11, Windsor. 



The quarry on the N. W. qr. Sec. 35, Pleasant Springs, is on the western edge of 

 a Trenton area, and shows 15 feet of the lowest part of the formation. The upper 

 layers are thin, whilst the lower six feet are taken up by two very heavy firm layers, 

 between which is a persistent thin seam. 2 inches thick, which affords large regular 

 paving slabs. The limestone is yellowish, much marked by dendritic oxide of man- 

 ganese, and is easily trimmed into smooth blocks. The thin upper layers show numer- 

 ous nests of crystals of limonite, pseudomorphous after pyrite, as also large casts of 

 orthoceratites. The top layer is glaciated, the striae running almost due south. At the 

 bottom of the quarry, the junction with the St. Peters is exposed. A wnll near by 

 is 58 feet in the latter formation. The quarry is an old one, having been opened 22 

 years, during which time 4,000 cords of stone have been removed. 

 The quarry in the north part of Sec. 4, Cottage Grove, shows 20 feet of tliin, and 



