606 THE GEOLOGY OF MINNESOTA. 



Later moraines. Modified drift 



Ancient water-courses. Definite channels, which appear to have been formed by drainage 

 during the final melting of the last ice-sheet, are found extending from northwest to southeast at 

 three places in Yellow Medicine county. One of these, lying about a half mile from the Minne- 

 sota valley west of Granite Falls, and another at the outcrops of rock in section 17, Omro, have 

 been described on pages 592 and 598. The third, situated in Wergeland and Burton, has been 

 traced farther than either of the others, but its full extent in either direction remains to be 

 explored. It reaches from the East branch of Lac qui Parle river in section 5, Wergeland, south- 

 easterly through sections 9, 15, the south part of 14, and the north part of 24, in this township; 

 and thence in a nearly east-southeast course, through sections 19, the south edge of 20, the north- 

 east part of 29, and through 28, 27 and 35, in Burton, to the south half of section 1, Eidsvold, in 

 Lyon county. In section 28, Burton, and for the next two miles southeastward this depression is 

 followed by Mud creek, and in section 1, Eidsvold, it is crossed by the North branch of Yellow 

 Medicine river, and lies on its south side. This ancient river-course, now dry or occupied by 

 insignificant streams, has along this explored extent of twelve miles a width that varies from a 

 quarter to a half of a mile, consisting of a nearly flat bottomland whose subsoil is gravel and sand, 

 bordered by areas of moderately rolling or morainic till, which average 30 to 40 feet higher. A 

 large river is believed to have flowed southeastward here during the departure of the ice-sheet 

 after the formation of its third moraine, which seems to cross this channel at the southeast cor- 

 ner of section 19, Burton. The receding ice-fields on the northeast prevented drainage from 

 taking its present courses, and their melting supplied unusual floods. Beyond this water-course 

 the ice-margin southeastward to Faribault county was bordered by a long and shallow lake, which 

 overflowed by the way of Union slough in Iowa (page 461). Similar water-courses were afterward 

 channeled, alongside the west border of the melting ice-fields at successive stages of their reces- 

 sion, in Omro, and near Granite Falls, respectively seven and twenty-three miles farther northeast. 

 The fourth, fifth and sixth terminal moraines of the last ice-sheet,* formed at successive 

 stages in its recession, clearly exhibited farther east in the vicinity of Kiester, Elysian and Waco- 

 nia, seem to be represented in this district by the morainic knolls and mounds of drift, with more 

 than the ordinary proportion of boulders, which are found associated with the water-courses men- 

 tioned in Omro and near Granite Falls. A morainic belt, apparently reaching a considerable 

 distance from northwest to southeast, was crossed in section 30, Tyro, a few miles east of the 

 Omro valley; and another, described on page 592, probably representing the fifth and sixth mo- 

 raines, lies at the west side of the eastern channel, and consists of prominent smooth swells, 

 occupying a width of two or three miles from three to six miles west of Granite Falls, and 

 expanding farther south in Wood Lake, Sioux Agency and Echo, to a width of six miles. 



Modified drift. No extensive areas of modified drift were observed in this district. In a 

 few places, however, small deposits of gravel and sand, partly kame-like, form the surface. A 

 noteworthy cut in such beds was seen near Balaton, in southern Lyon county. A sixth of a mile 

 southeast from this station, close southwest of the railroad, in a rounded hillock, an excavation 

 has been made for ballast to a distance into the hillock of a hundred and fifty feet, the section 

 exposed being twenty rods or more in length and about 20 feet high in its highest part. It con- 

 sists of gravel, yellowish and in many portions ferruginous, mostly very coarse and containing 

 abundant pebbles up to six or eight inches in diameter, nearly all of them plainly water-worn or 

 rounded. At 4 to 7 feet below the top. for a length of a hundred feet or so at the highest part, the 

 material is fine, sandy gravel, obliquely bedded in slopes of 5 to 25 eastward. At the east end of 

 this a portion 10 to 15 feet below the top and 20 feet long is represented in fig. 50. The central 

 mass here is sand while the enclosing strata are gravel, mostly with pebbles less than three inches 

 in diameter, but in some places holding pebbles up to five or eight inches 

 in diameter. The lenticular mass of sand occurring here shows two small 

 faults at its center, each of three or four inches, the lower side being at the 

 east. The stratification of this deposit is conformable with the slope of 



Fig 60. Section in modified 



drift, near Baiuton. its surface, showing that it remains nearly or quite in the same form as it 



was left by the glacial floods. 



Only two fragments of rock that exceeded a foot in diameter, were seen in this excavation. 

 These were one and a half and three feet long. About one-third of the pebbles here, both large 

 and small, are limestone; nearly all the rest are granite and crystalline schists; only a few pebbles, 



'Compare pages 461, 463 and 581; and chapters xxi and xxn. 



