628 TIIE GEOLOGY OP MINNESOTA. 



[Red till. 



moved mostly toward the south and southeast, bringing the dark bluish till, 

 weathered above to yellow, which covers this area. The following include 

 all the observations of red till which have come to my knowledge in west- 

 ern Minnesota and eastern Dakota. 



In the N. W. J of section 24, T. 123, E. 48 (the west township of Prior), a red till was 

 found at the bottom of J. P. Edward's well, 77 feet below the surface, underlying yellow and 

 blue till. The section of this well is stated on page 629. 



About two miles west of Big Stone City, the lower part of a newly undermined bluff on the 

 north side of the Whetstone river consists of till which has the same red color that characterizes 

 the till of northeastern Minnesota. The upper portion of this bluff, to a depth of about 20 feet, 

 is yellowish gray till; and this is directly underlain by red till, exposed along a distance of a 

 third or a half of a mile, with a vertical thickness of 20 or 30 feet, and extending below. The 

 same bluff of till reaches a half mile farther east, but has there become obscured by falling down. 

 Its top, about 50 feet above the river, is probably 40 or 50 feet below the average surface of the 

 drift-sheet. 



This red till appears to extend southwesterly, under the yellow and blue till, nearly or quite to 

 the foot of the Coteau des Prairies. It is reported by Alonzo Wardall, who lives in the S. W. } of 

 section 12, T. 12O, R. 5O, in Grant county, Dakota, seventeen miles west-southwest from Big 

 Stone City. He has bored about seventy-five wells within that county and Big Stone and Lac qui 

 Parle counties, frequently finding red till in considerable thickness in the bottom of deep wells. 



At Montevideo, in Chippewa county, a mile northeast from the east end of Lac qui Parle 

 county, an excavation for a cellar in the base of the bluff at the east side of Main street exhibited 

 the section, about 15 feet in depth and 40 feet in length, shown by fig. 51. This is the east bluff 

 of the valley that is now occupied by the Chippewa river. It is composed 

 of till, and rises nearly a hundred feet above this excavation, to the general 

 |t.level of the adjoining country. The position of the section here seen, and 

 the order and character of its materials, suggest that they are probably a 

 f a ll en down since the valley was eroded. Here and there this cut 



FIG ECTION IN 



MONTEVIDEO. shows thin layers of sand, and in part its diverse tills are imperfectly strati- " 



fled, with contorted bedding; but they are gravelly and stony clay, and doubtless the bluff above 

 this point embraces three corresponding kinds of unmodified glacial drift. Next below the soil 

 is a dark gray till, from 2 to 6 feet in thickness. This rests for its greater part upon yellowish 

 till, of which a thickness of 6 to 12 feet is exposed, having the color usually seen near the sur- 

 face; but on the west the latter abuts upon a small ridge five feet high and scarcely twice as 

 wide, which also underlies the dark gray stratum and is composed of red till, identical in color 

 with that of Minneapolis and Saint Paul and northeastern Minnesota. A little projection of red 

 till appears to have extended here in the form of a ridge from north to south, for it was exposed 

 with nearly the same dimension and relation to the rest of the section at the south side of this 

 excavation, twenty feet distant. 



These observations seem to have their most probable explanation in supposing that during 

 an early glacial epoch an ice-sheet was pushed west-southwesterly from the region of lake Supe- 

 rior qi.ite across Minnesota, bringing these deposits of red till. This may have been when the ice 

 reached its greatest extent, covering all of this state except its southeast corner, which lies within 

 a driftless area. Some of its till, derived in large part from the red shales and sandstones, retained 

 a distinctly reddish color; but we must suppose that at such distances the admixture of other drift, 

 brought by convergent glacial currents from the north and northwest, would commonly give to 

 the deposits of that ice-sheet a prevailing bluish color, like that of the till spread over this region 

 by the southeasterly-flowing ice of the last glacial epoch. Nuggets of copper, which were almost 

 certainly transported from the region of lake Superior when the ice had its maximum extent, are 

 found rarely west of the driftless area in the till of southern Minnesota and of Iowa. The direc- 

 tions of the strite, and the course of the terminal moraines of the last ice-sheet, show that these 

 masses of copper could not have been brought from their northeastern source during the last gla- 

 cial epoch. It seems thus to be proved that ice flowed farthest southwestward from lake Superior 

 at an earlier date; and that ice-sheet is believed to have deposited the red till found in this district. 



