266 GEOLOGY OF EASTERN WISCONSIN. 



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

 ness, 6 feet. 



The concretions above referred to are globular aggregations of quaiiz 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 fonns. 



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

 nesian limestone, but at the base of it, at some points, sandstone is exposed and con- 

 tains Scolithus tubes within two and a half feet of the limestone 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 gulley of the road exposes imper- 

 fectly a considerable portion of the Mendota formation, which is here more shaly than 

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

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



1. Coarse yellow crystalline 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 Scolithus, 3 feet, 3 inches. 



7. Orange calcareous sandstsone, 8 inches. 



8. Yellow sandstone containing spherical concretions, 1 foot. 



9. Calcareous sandstone, 1 foot. 



Farther south the section is extended upward about 36 feet, by aneroid measurement, 

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

 owes its existence. 



Less than a mile west of this, Bow's Hill, likewise 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 shown 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 N. W. to S. E., across Green Lake, showing (1, 2 aud 3) Pofsdara group, (2) 

 Mendota beds, (3) Madisou sandstone, (4) Lower Magnesiau 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 cliff has a protecting cap of Lower Magnesian limestone. 



