BIG STONE AND LAC QUI PARLE COUNTIES. 625 



Terraces. Interglacial modified drift.] 



between the lake and the bluff is about forty rods wide, and rises some 40 feet in this distance. 

 On the Dakota shore of Big Stone lake, similar foot-slopes of till, below the steep bluffs, vary from 

 an eighth to a half of a mile in width, along the greater part of the southeastern half of the lake, 

 but they are wanting farther northwest. 



A deposit of alluvium, consisting mostly of sand and clayey silt, brought into the valley by 

 Whetstone river, forms a nearly level bottomland about a mile wide at the foot of Big Stone lake; 

 and a similar deposit extends two or three miles next below Lac qui Parle, having been brought 

 by the river of the same name. Other portions of the Minnesota valley on the borders of these 

 counties generally have an alluvial flood-plain an eighth to a fourth of a mile wide, while the 

 greater part of the area enclosed between the bluffs is till, somewhat modified at the surface by 

 the waters that eroded the valley. 



Terraces. Southeast from the village of Brown's Valley, the railroad in its ascent from 

 the base to the top of the bluff is located upon an inclined terrace which rises southeastward 

 along the side of the bluff at the rate of about 40 feet to the mile, extending three miles. Where 

 this terrace is crossed by the carriage road a mile easterly from the northwest corner of Big Stone 

 county, its width is some forty rods, in which distance its hight from its verge to the base of the 

 higher part of the bluff rises some 25 feet. On the west side of the valley, a terrace of similar 

 width but approximately horizontal, lying at half or two-thirds of the hight from the base to the 

 top of the bluff, extends from opposite Brown's Valley nearly to Big Stone lake. "Along this lake, 

 also." Prof. Winchell writes, "are terraces that have a slope or dip striking across the bluff. One 

 may be seen at Mr. Hurley's; ... it can be traced three or four miles, passing, in that 

 distance, down from union with the prairie level to the bottoms, or so far down as to be blended 

 in the bottomland. A similar vanishing terrace can be seen on the Dakota side'' [a few miles west 

 from Mr. Hurley's] .... "Within the space of about three miles, its form can be seen to 

 pass obliquely across the face of the main bluff, from top to bottom, sloping to the east or south- 

 east, and disappearing in the bottomland." 



At Ortonville and for a mile or more southeastward, a terrace occurs about 75 feet above the 

 lake and 50 feet below the top of the bluff. It varies from a few rods to an eighth of a mile in 

 width, and in this width ascends 10 or 15 feet. The rise of 50 feet thence to the highest land is 

 by an irregular slope, less steep than the bluff below this terrace. These features, however, are 

 much broken by gullies and ravines. A similar narrow bench in the bluff of till on the opposite 

 side of the Minnesota valley is seen in the northwest part of Yellow Bank township along a dis- 

 tance of four miles next southeast from Whetstone river and Big Stone City. 



Professor Winchell has noted other terraces farther southeast in this valley, and attributes 

 their form to erosion in Cretaceous strata which are supposed to be only thinly covered by drift. 

 "A terraced condition of the bluffs may be seen at a little lake, caused by the enlargement of the 

 river on T. I2O, R. 44, [Marsh lake,] as well as in the bluffs of Lac qui Parle. Here an obser- 

 vation was made that plainly indicates the origin of these benches. They exhibit a slope or dip 

 toward the S. E., running successively down to the bottoms, higher ones occurring in their places. 

 This can plainly be seen from the opposite bluff. This slope is believed to be due to the dip of 

 the rocks of the Cretaceous, though no outcrop of these rocks was seen at that place, the bluffs of 

 the river and of all ravines being smoothly turfed over." 



Modified drift of the earlier glacial epoch. In the report of Brown and Redwood counties 

 (page 582) mention is made of a cut in the bluff southwest of New Ulm, where the amount 

 of drift deposited in the last glacial epoch appears to be a bed of till, 16 to 18 feet thick, over- 

 lying a bed of stratified gravel and sand of about the same thickness, which was probably formed 

 during the recession of an earlier ice-sheet. A closely similar section was observed on the Hast- ' 

 ings & Dakota railroad, about fifteen rods south of Mr. Oehler's brick-yard at Big Stone City. 

 Here a cut is made through a ridge of drift which belongs to the general drift-sheet, but has been 

 left by erosion as a level- topped plateau jutting southward toward the Whetstone river. The cut 

 is about 45 feet deep and twenty-five rods long. At the top is a stratum, 15 feet in thickness, 

 composed of yellowish sand and gravel, fine above but coarse in its lower three to five feet. Un- 

 derlying this is unstratified boulder-clay or till of the usual character, forming a bed 15 to 18 feet 

 thick, its maximum thickness being at the east end of the cut. This has the dark bluish color 

 usually characteristic of the deep portion of the till, except that at each end of the cut, next to 

 the face of the slopes bounding this plateau, it has the ordinary yellow color of the upper part of 



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