OF THE NORTHWEST. 



73 



bed of the St. Peter's is there formed by ledges of soft brown sandstone (F. 1,/) ; 

 and from this up to White Rock, eighty miles up the river, sandstones of F. 1, and 

 magnesian limestone (F. 2), alone compose the bluffs, — the latter usually of buff 

 and salmon colours, containing casts of Euomphalus, besides a few other Lower 

 Silurian fossils, which will be found in the list in the Appendix. This is the " fawn- 

 coloured carboniferous limestone" of Mr. Featherstonhaugh. 



SECTION IT. 



TTS PALAEONTOLOGY. 



The St. Peter's Limestone is rich in organic remains. The most commonly 

 occurring species will be seen by consulting the tables, the Appendix, and details 

 of this Report. 



Many species, found both by Dr. Shumard and myself, in the lower shell limestone 

 of the Upper Mississippi, are identical with forms occurring both in the substratum 

 of gray limestone at Eagle Point, in the Dubuque District — figured and described 

 in my Report of 1839 — and in the blue limestone of the Ohio Valley. Those of 

 the upper division resemble rather the species found in the inferior beds of the 

 Upper Magnesian Limestone of that District. But all, so far as our examinations 

 have yet extended, are of a Lower Silurian type. 



SECTION III. 



TTS MINERAL CONTENTS. 



Some specimens of copper ore are reported to have been found in the vicinity of 

 the Falls of St. Anthony. If they have, it is not likely that they originated in 

 veins traversing this limestone formation, since neither it nor the underlying sand- 

 stone bear marks of being metalliferous. Probably they were erratic pieces trans- 

 ported from some copper locality lying to the north. The thickness, too, of these 

 calcareous beds is so inconsiderable, that even if they did contain metallic lodes, 

 these could not extend to any great depth, before they would dwindle in the 

 incoherent sandstones beneath. But the schistose structure of the rock itself is 

 altogether unfavourable to its metalliferous character. 



SECTION IV. 



ITS PHYSICAL AND AGRICULTURAL CHARACTER. 



High up on Turkey River, near the site of Fort Atkinson and the location of 

 the Winnebago Agency, this formation appears in the form of wonderfully symme- 

 trical, mound-like forms, with flat tops, as exhibited by the following illustration. 



in 



