THE TOMAH AND SPARTA QUADRANGLES 633 



between the Oneota and the St. Peter and thus might be considered 

 a distinct formation. Some of the sandstones are locally so case- 

 hardened as to resemble quartzite, and these form a residual float 

 over the surface of the Oneota. In many cases the sandstones are 

 so little cemented as to be quarried for sand. Except for the basal 

 layers, the sands are clean, well sorted, and well rounded. A large 

 proportion of the grains are of high sphericity. The strata imme- 

 diately above the residuum are fairly well bedded. Higher strata 

 have all degrees of cross-lamination and cross-bedding. 



The known thickness of the St. Peter in this area does not 

 exceed 70 feet. No fossils have been found in the St. Peter sand- 

 stones of this area or, for that matter, in any part of Wisconsin 

 known to the writers. In eastern Minnesota the St. Peter has 

 yielded fossils.^ 



Conditions of origin. — While all the facts relating to the origin 

 of the St. Peter have not yet been completely evaluated .and more 

 data are being collected, it does not appear probable to the writers 

 that any part of the St. Peter sandstones in either of the two 

 quadrangles is of marine origin. The basal portions are certainly 

 of residual origin and as this residuum extends over the tops of the 

 St. Peter hills it proves the absence of marine-wave wash during 

 the deposition of all material up to the tops of these hills. The 

 shales and sandstones immediately overlying the basal residuum 

 appear to be of stream deposition. The higher, clean, cross- 

 laminated sands have characteristics which suggest their modifica- 

 tion and deposition by the wind. 



CONCLUSION 



With the St. Peter formation the Paleozoic section of the 

 Sparta and Tomah quadrangles is concluded. That other Ordo- 

 vician and also Silurian formations once extended over this region 

 is strongly suggested, if not proved, by the ragged edges of strata 

 of these two systems which are found at comparatively short 

 distances to the south and west. It is possible that formations 

 younger than the Silurian were once present; but, if so, evidence 

 of their former existence has not been discovered. 



' F. W. Sardeson, Bull. Minn. Acad. Nat. Sci., IV, No. i (1896), pp. 64-88. 



