626 TIIE GEOLOGY OF MINNESOTA. 



[Buried moraine. 



the till to a depth of thirty feet from the surface at the west and fifteen feet at the east. It is 

 bounded by definite, nearly level lines both above and below, and is underlain by obliquely bed- 

 ded yellow gravel and sand, which has a thickness of about 15 feet exposed to the grade of the 

 track and also extends deeper. My interpretation of these deposits would refer the lower gravel 

 and sand to an interglacial epoch, their origin being from the earlier ice during its departure; the 

 till was quite surely deposited by the last ice-sheet; and the overlying gravel and sand is prob- 

 ably modified drift belonging to the immediately succeeding epoch of its recession and final 

 melting. 



A buried moraine. There are many reasons for believing that several 

 successive ice-sheets have been accumulated and pushed forward upon the 

 northern part of the continent, repeatedly overspreading nearly all of Min- 

 nesota; and if this be true, some of them doubtless formed terminal mo- 

 raines, which were afterward covered and their mounds and hills of coarsely 

 rocky drift spread in a nearly level stratum by the more extended ice-sheet 

 of a later epoch. Such a buried moraine is exposed by the deep channel 

 of the upper Minnesota river. The till here is found to contain, at a depth 

 of 40 to 50 feet below the general surface, a stratum that abounds in 

 boulders, usually producing a narrow shelf or terrace upon the bluffs. 



About Correll station, in Big Stone county, this rocky layer in the till has caused an exten- 

 sive plain to be left in the process of erosion, some 50 feet below the top of the bluffs and 50 to 75 

 feet above the river. The west end of this plain is in section 6, T. 1 2O, R. 44, about three miles 

 west of Correll; and it thence extends eight miles east to the Pomme de Terre river, having a width 

 of one and a half to two miles in its western half, and expanding to a greater breadth farther east. 

 Its first one and a half miles at the west is not remarkably sprinkled with boulders, but has one 

 immense block, thirty feet or more in diameter, on section 5, about one and a half miles west of 

 Correll station. Very abundant boulders, however, are found on the southern verge of this part 

 of the plain, covering the upper ten or twenty feet of the escarpment, 50 to 60 feet high, which de- 

 scends to the bottomland in the southeast part of section 6, and near the south line of section 5. 

 A little farther east, probably in the northwest comer of section 9, and about three-quarters of a 

 mile southeast from the large boulder before mentioned, another was observed in the escarpment 

 of this plain, measuring twenty feet in diameter, and consisting of gray granite, in which are 

 seen at one side several fragments of hornblende schist up to three and four feet in diameter. A 

 great profusion of boulders occurs here along the margin of this plain through a distance of two 

 miles or more, and the same feature probably continues all the way east to the Pomme de Terre 

 river, near which it was again observed in section 19, Appleton. On the south, in the region of 

 Marsh lake, are occasional knolls and short ridges, composed mainly of boulders, extending ten 

 to twenty rods and rising ten to fifteen feet above the marsh. For a mile west from Correll sta- 

 tion, and all the way east to the Pomme de Terre river, this plain is much sprinkled by boulders 

 of all sizes up to six or eight feet. Between Five Mile creek and the Pomme de Terre river, the 

 east part of this area somewhat loses its plain-like contour, and becomes in part quite undulating 

 and broken, having numerous knolls and ridges twenty to forty rods long, running mostly from 

 west to east, five to twenty feet high, so thickly strown with boulders of all sizes up to five or ten 

 feet in diameter that often they cover three-quarters of the surface. These small elevations and 

 depressions have been shaped by the eroding action of water, being more regular in their outlines 

 than typical terminal moraines, which they resemble in their multitude of boulders. It appears 

 that here a terminal moraine, accumulated in one of the early glacial epochs of the great ice age, 

 has been crossed by a later ice-sheet. Partly leveled and buried under the later till, a section of 

 it is exposed to view by the excavation of this valley. 



The ancient water- courses, now deserted, which are found in Chippewa county northeast 



