552 GEOLOGY OF CENTRAL WISCONSIN. 



nearly pure limestone to a nearly non-calcareous sandstone being quite Ft. In. 

 abrupt (cut on Chicago and Northwestern road, Sec. 35, Madison; also, 



cut on same road at Mendota Station, Westport). Thickness 15 



II. White oolitic chert layer (Madison quarries) 6 



I. Greensand layer (Madison quarries) 6 



Total . . 71 



The bold bluff that rises from the mouth of Honey creek, Sauk 

 county, has already been cited as giving an unusually complete sec- 

 tion of the upper part of the Potsdam series. It shows, also, the 

 largest continuous exposure of the Lower Magnesian that I have ever 

 seen a vertical cliff over 50 feet in height. The following is a de- 

 tailed section of this cliff, beginning above: 



Ft. In. 



1. Heavy layer of brown- and-yellow-mottled limestone, which leaves on solu- 



tion 2.2 per cent, of very fine clayey residue 1 



2. No good exposure 5 . . 



3. Heavy layer of very close-textured, nearly white, limestone, with many 



dendritric markings; residue 9.09 per cent, and clayey 1 2 



4. Thin layers, 3 to 4 inches each, of limestone like the last; residue 5.8 per 



cent., clayey 3 .. 



5. Thin layers of brown-and-gray-mottled limestone with minute crystal-lined 



cavities; residue 2.9 per cent., clayey 6 



6. Heavy layer of light gray, close-textured limestone, with cavities like No. 



5; residue 8.35 per cent., clayey 3 6 



7. Two heavy layers like No. 6; residue 6 per cent., clayey 5 2 



8. Shaly layers of porous, yellow- and-gray-mottled, crystalline limestone; 



residue 7-2 per cent., clayey 2 3 



9. Three layers of yellow-and-gray-mottled, close-textured limestone; residue 



18.85 per cent., clayey 3 



10. Heavy layer of yellowish, sandy limestone; residue 40.17 per cent., fine, 



gray sand 2 



11. Heavy non- arenaceous layer, with very indistinct subordinate bedding 3 6 



12. Very irregular, brownish, close-textured Limestone, occurring in thin broken 



layers, the cracks being lined with white stalactitic lime carbonate; resi- 

 due 4.38 per cent., clayey 1 6 



13. Two heavy layers of brownish- gray, close- textured limestone; residue 3. 42 



per cent., clayey 2 6 



14. Irregularly thin bedded, very close- textured chonchoidal- fracturing gray 



limestone; residue 9.3 per cent., clayey 1 4 



15. Very indistinctly bedded, nodular- weathering, close-textured, mottled lime- 



stone; residue 7 . 17 per cent., clayey 8 8 



16. Very irregularly bedded, rough-surfaced, close-textured, gray limestone; 



residue 28.97 per cent., fine sand and clay 3 6 



17. Thick layer of porous, brecciated, highly-crystalline limestone; residue 



13 .67 per cent., fine sand and white clay 1 9 



18. Thick layer of compact, yellowish brown, granular, smooth-fracturing 



Limestone, with much dendritic manganese oxide; residue 16.65 per 



cent., clayey 1 7 



Total . . 52 5 



