220 THE GEOLOGY OF MINNESOTA. 



[Shakopee limestone. 



It is everywhere distinct as an important limestone formation, and is every- 

 where separated from the other great calcareous member of the same 

 formation by a sandstone as distinct and continuous, and as clearly recog- 

 nizable, as the St. Peter sandstone. There seems much reason to believe 

 also that it exists across the Mississippi, in the state of Wisconsin, but at 

 this time there is no distinct published notice of its occurrence there. The 

 Lower Magnesian in Wisconsin has been divided by Prof. R. D. Irving, of 

 the geological survey of Wisconsin, into three parts, as exemplified near 

 Madison (American Journal of Science and Arts, June, 1875,) but there 

 is reason to believe that his proposed subdivisions do not include the 

 Shakopee limestone at all, and that the distinctions which he mentions 

 are wholly confined to the St. Lawrence limestone of Minnesota. This 

 subject was discussed by the writer in the Bulletin of the Minnesota Academy 

 of Natural Sciences, for 1875, when this hypothesis was first published. It 

 is rendered still more plausible from the fact that even in Houston county 

 the St. Lawrence exhibits variations of composition and lithology which 

 are comparable to those Prof. Irving describes. 



The characters of the Shakopee in Houston county are not noticeably 

 different from those in counties further west. The aggregate thickness, 

 however, is less than seventy-five feet. 



This formation does not appear in the bluffs of the Mississippi river, in 

 Houston county, nor in those of Root river generally; but its line of strike 

 is some miles back in the country away from the immediate bluffs. This is 

 due to the more crumbling nature of the Jordan sandstone, which underlies 

 it, and which operates, in that respect, to tear down the Shakopee in the 

 same manner, and for the same causes, as the St. Peter on the Trenton. To 

 this fact, and to its general resemblance to the St. Lawrence limestone, may 

 be attributed the non-discovery of this limestone by the United States geolo- 

 gists who have reported on the geology of the state, or by others, whose ex- 

 aminations were largely confined to the main water-courses, before the 

 general settlement of the state and the construction of good roads. Its 

 area is embraced on the colored map of the county, in the same color with 

 that of the St. Lawrence limestone and Jordan sandstone. 



This limestone may be seen frequently in the central portion of the 

 county, in the upper reaches of the ravines which radiate in all directions 



