Kansan deposits 149 



was manifest evidence of later disturbance. No other formation ever 

 intervenes, so far as observed, and it is not within the range of probability 

 that any other formation will ever be found in this intermediate position. 

 In view of this fact it is reasonable to conclude that the drift which here 

 so frequently lies immediately under the older loess is Kansan. 



Perhaps the most puzzling feature of the Kansan in this area is it^ 

 occurrence on both the plain south of Sioux Falls on the South Dakota 

 side of the Big Sioux Kiver and on the opposite Iowa uplands, which rise 

 more than 150 feet higher. The writer is not prepared to give an expla- 

 nation of the fact, but suggests that it may be found in advances of the 

 Kansan ice-sheet at different times and in different directions on opposite 

 sides of the Big Sioux valley, in our territory. There is evidence that 

 such different movements did occur. The generally accepted opinion is 

 that a great part of the western Kansan sheet moved in a southwesterly 

 direction, yet on the plain in question there was undoubtedly a movement 

 in a southeasterly direction. On the flat area near the state line, on both 

 the Iowa and South Dakota sides, which is practicall}'^ an extension of the 

 plain on the west side of the river, there are numerous glacial striae on 

 the Sioux quartzite, which here comes to the surface over large areas. 

 The striae of one of these sets extend in a direction varying from north 10 

 degrees to 15 degrees west, and those of the other set vary from north 30 

 degrees to 40 degrees west. Similar strise having the same general direc- 

 tion appear on the Sioux quartzite at the foot of the slope north of section 

 16, at Sioux Falls. The general direction of the movement of the ice-sheet 

 which passed over the plain was therefore southeasterly, while the upland 

 Kansan on the Iowa side and on the South Dakota side south of Canton 

 probably came from the northeast, and possibly at an earlier time within 

 the Kansan period. 



The Kansan plain. — The plain on the west side of the river has been 

 referred to the Wisconsin because of its topography. The writer re- 

 peatedly traveled over various portions of this plain between the uplands 

 south of Sioux Falls and those south of Canton and between Harrisburg 

 and the river, and found that while the general surface of the plain is 

 flat it is much more uneven than appears from a distance, and that its 

 drainage is quite well developed along long draws, which culminate in 

 such valleys as that of Spring Creek southeast of Shindlar and Beaver 

 Creek southward. There are few entirely inclosed basins containing 

 swamps and ponds, and the general character of the surface is very 

 similar to that of the Kansan in O'Brien and Osceola counties in Iowa. 



The plain slopes gradually to the southeast and east. The fall from 



