266 GEOLOGY OF EASTERN WISCONSIN. 



21. Soft, friable, dirty yellowish sandstone of very uniform medium grain. Thicb- 

 ness, 6 feet. 



The concretions above refeiTcd to are globular aggregations of quartz sand cemented 

 by calcareous material, in size and form, resembling a boy's marbles. They are fre- 

 quently attached to each other, producing odd and fantastic forms. 



On Mt. Maria, two and a half miles southwest, the mam exposure is the Lower Mag- 

 nesian hmestone, but at the base of it, at some poiuts, sandstone is exposed and con- 

 tains ScoHthus tubes within two and a half feet of the hmestone above. On the eastern 

 slope of the hill the calcareous shales of the Mendota horizon may be seen. 



Near the center of section 24 of the same town the guUey of the road exposes imper- 

 fectly a considerable portion of the Mendota foi-mation, which is here more shaly than 

 at Bartholomew's Bluff and does not expose any fiiin thick layers of limestone, the sec- 

 tion being composed chiefly of shales and sandstones, as follows : 



1. Coarse yellow crystaUine limestone, graduating into sandstone. 1 foot. 



2. Green and orange sandstone with calcareous matter in seams and aggregations. 

 2 feet. 



3. Green calcareous sandstone. 6 inches. 



4. Orange sandstone, 1 foot. 



5. Slope, covered, about 3 feet. 



6. Whitish sandstone containing Scohthus, 3 feet, 3 inches. 



7. Orange calcareous sandstsone, 8 inches. 



8. YeUow sandsbme containing spherical concretions, 1 foot. 



9. Calcareous sandstone, 1 foot. 



Farther south the section is extended upward about 86 feet, by aneroid measm-ement, 

 and consists of arenaceous and calcareous shales, interstratified with and graduating into 

 green sandstone, and, more rarely, into gray sandstone. Some of the shales appear 

 highly argillaceous, and some near the middle pass into an impure limestone. An ad- 

 jacent hUl is capped with Lower Magnesian limestone, to whose enduring character it 

 owes its existence. 



Less than a mile west of this. Bow's Hill, Kkewise indebted to a protecting cap of 

 Lower Magnesian limestone for its origin, presents along its slopes partial exposures of 

 the formation under discussion. At this point, red and purple shales are found, associ- 

 ated with the various varieties of rock described at the previous localities. These red 

 and purple shales have already been described as a characteristic of the Mendota group, 

 but as shown by the previous sections, they are not always present. These shales are 

 well shovrn in the town of Dayton, Sec. 27, N. W. qr. of S. W. qr., in a little quarry 

 along the brook not far from the road. 



Fig. 25, 



Profile section from X. W. to S. E., across Green Lake, showing (1, 8 and 3) Potsdam group, (2) 

 Mendota beds, (fl) Madison sandstone, (4) Lower Magnesian limestone, (5) St. Peters sandstone, 

 and (6) Trenton limestone. 



They are again seen on the shores of Green Lake, toward its western extremity. On 

 the south side of the lake they occur as a low exposure at the water's edge, covered by 

 drift. On the opposite .side, north of Norwegian Bay, there is a more considerable dis- 

 play of Mendota strata. The chff has a protecting cap of Lower Magnesian limestone. 



