CHAPTER, II. 



LOCAL SECTIONS ON THE UPPER MISSISSIPPI. 



a. Above the Mouth of the Wisconsin. — For the purpose both of investigating the 

 mineral contents of the Lower Magnesian Limestone and Lower Sandstone of Wis- 

 consin, Iowa, and Minnesota, and at the same time tracing out the elements of 

 stratification of these formations, and their pala3ontological details, I was instructed 

 to make minute local sections, at various points in the Valley of the Mississippi, the 

 results of which are contained in this chapter. 



My observations commence at the Falls of St. Anthony, where F. 2, c, forms the 

 base of the sections capped with the shell-beds of F. 3, A. 



On the east side, the different members of that formation occur in the following 

 order, above the white sandstone. 



Feet. 



1. Grayish buff-coloured layers of Magnesian limestone, containing 

 numerous casts of Leptccna, Terebratula, Orthis, Spirifer, Ortho- 



cer atites, Plcurotomaria, &c, ...... 6 



2. Ash-coloured argillaceous limestones, in' thin layers, containing 



but few fossils, ........ 5 



3. Highly fossilifcrous shell limestone, of a bluish-gray colour, . . 23 



From three to four feet of the upper beds of the section are above the top of 

 the cascade. The whole height of the perpendicular fall is sixteen feet. 



Many of the organic remains of the upper bed are identical with the Trenton 

 limestone, Utica slate, and Hudson River group of the New York system, and their 

 western equivalent, the blue limestone of the Ohio Valley. 



The most characteristic species in these beds are Leptcena alternata, L. planum- 

 bona, L. sericea, Orthis testudinaria, 0. tricenaria, 0. disparilis, Terebratula modesta, 

 Atrypa capax, Bellerophon bilobatus, Plcurotomaria lenticidaris, P. suhconica, P. um- 

 bilicata, Orthoceratite (species undetermined), Calymene senaria, Isotelus gigas, Lichas 

 trentonensis{?) , Ceraurus pleuvexanthemus, Chcetetes lycoperdon. 



About a quarter of a mile below the cascade, the lower beds of the shell lime- 

 stone are better exhibited than at the last section, and they rest here on the white 

 sandstone (F. 2, c). The section is as follows : 



