90 THE GLACIAL LAKE AGASSIZ. 



shale or clay, 20 feet; and white and gray sandy sliale or sandstone, 20 feet, 

 in which the well stopped, not reaching the Archean rocks. ^ These strata 

 above the source of the artesian water are probably equivalent to the dark 

 beds of the Tracy well, while the lower strata coi'respond to the white and 

 kaolinic lower beds there. 



Comparing the elevations of the top of the kaolinic deposits in these 

 wells, there is seen to be a slight dip of the strata toward the north-north- 

 west, amounting to about 240 feet in the distance of 112 miles from Tracy 

 to Browns Valley. Another comparison is afforded by a well near Sleepy 

 Eye, which is 45 miles east of Tracy and 1,034 feet above the sea, pene- 

 trating 182 feet of drift; then 79 feet of white and gray Cretaceous clay, 

 containing one thin stratum of brownish-red clay, together cori-esponding 

 apparently to the lowest 79 feet of the Cretaceous beds in the Tracy well, 

 and lying, like those beds, on Archean red granite." These observations 

 indicate a slight westward dip, amounting to about 60 feet, in the Creta- 

 ceous strata between Sleepy Eye and Tracy. The resultant inclination 

 satisfying both these sets of observations is a dip of about 3 feet per mile 

 to the northwest, being thus directed away from the ridge of Algonkian 

 quartzite, 1,300 to 1,700 feet above the sea, which outcrops in northern 

 Cottonwood County, on the east flank of the Coteau des Prairies, and in 

 Pipestone and Rock counties, on its west side. 



Above the strata thus far described, a hard, gray, somewhat calcareous 

 and concretionary sandstone, probably representing the Niobrara formation, 

 is seen iii a few low outcrops near Alta Vista, in the northeast corner of 

 Lincoln County, and A\ithin 7 miles eastward, having an elevation approxi- 

 mately 1,175 to 1,150 feet above the sea. These outcrops are 30 to 35 

 miles northwest from Tracy, and occupy nearly the same stratigraphic 

 horizon with the gravel bed, between 145 and 165 feet in depth, in the well 

 at that place. The only organic remains detected in this sandstone are 

 particles of lignite and traces of wood. 



Clay or shale, containing fossils characteristic of the Fort Pierre and 

 Fox Hills formations, the upper members of the marine Cretaceous series, 

 has been encountered in numerous instances bv wells in the same region. 



' Oeol. and Nat. Hist. Survey of Minnesota, Fourteenth Annual Report, p. 11. 

 -Ibid., p. 1.5. 



