

538 



NOTES UPON THE GEOLOGY OF SOME PORTIONS OF MINNESOTA, 



Without going farther into detail at the present time regarding the character and dis- 

 tribution of these formations, we may, I think, deduce a few general conclusions respect- 

 ing the geological structure of the country described. 



I conceive it to be sufficiently demonstrated that the quartzites at Bedstone Ferry, on 

 the Minnesota, — those near the sources of the Little Cottonwood, extending thence north 

 and south, — together with those of the escarpments of Pipestone and of the streams flow- 

 ing into the Sioux River, — arc of the same age. These quartzites I regard as of the age 

 of the Huronian formation of Canada, and the quartzites of Wisconsin. 



The eroded anticlinal is occupied, as far as we know, only by newer formations, from 

 Redstone Ferry, near New Ulm, to its opposite side, forty miles distant ; while at a point 

 forty or fifty miles further north, the ancient Laurentian rocks appear in the bottom of 

 this old erosion, and upon these the newer formations lie unconformably. 



A section across the country would present the following features, on looking to the 

 northward, and proceeding from east to west: 



(Geological section from the Minnesota River at New Ulm to the western limit of the Slate.) 



a. Quartzites cast of the Minnesota, at Ecdstono Ferry, dipping eastward. 



b. The outcrop of quartzites near the source of the Little Cottonwood, dipping to the westward. 



c. The outcrop of quartzites at the Pipestone locality, dipping to the eastward. 

 /. The place of the Pipestono stratum. 



d. The interval between a and b made by the eroded anticlinal, which is now occupied by Cretaceous and other modern 



formations, along this lino.* 



e. Tho lower country to the west of the Pipestono-iocality, occupied by modern formations similar to d. 

 R. Minnesota River. R' '. Sioux River. 



The space between the upper two linos of tho section is intended to represent the prairie (urination. 



- The country between b and c is occupied by a synclinal axis of Huronian quartzites ; 

 and we have the western margin of another similar synclinal at a. We have therefore 

 in this apparently undisturbed region of country.most satisfactory evidence that the more 

 elevated portions are occupied by synclinal axes ; while the lower portions are the places 

 of eroded anticlinals, as at d and e. 



The space between b and c is the southern extension of the Coteau des Prairies, which, 



* Note from Section. An cast and west section forty miles to the north of this point shows the continuity of 

 the Cretaceous formation interrupted by numerous prominences of the Laurentian gneiss. 



