IOWA ACADEMY OF SCIENCE 
241 
2. ‘‘The ridges -southwest, , east and southeast of Sioux Falls and 
south of Canton are not a part of the Altamont moraine, but are 
Kansan. ’ ’■ 
3. “The plain extending from Shindlar to Canton, South Dakota, 
is Kansan and not Wisconsin. 
With the first and second of these conclusions the writer agrees. 
But, with the third., which is, that the plain from Shindlar to Canton, 
is Kansan, the writer does not agree, and it is against this conclusion 
that most of this paper is directed. 
The western part of Lyon county, Iowa, is v-ery rugged with a sub- 
ma timely dissected topography. The divides' are narrow, standing at 
an altitude of 1,400 to 1,480 feet, and below this, a relief of 100 to 150 
feet exists. The surface material is loess and such drift exposures 
as occur are of yellow Kansan clay. The eastern portion of Lincoln 
county, South Dakota, opposite Lyon county, is however a relatively 
level plain, sloping gently to the south and east. Near its eastern mar- 
gin- at the Big Sioux a. ' few ' narrow valleys occur, but the dominating 
feature of the region is the relatively level plain. This, plain does 
not have a. loiess covering. The high divides on the east side of the 
river, from the state line south to a point opposite Canton, have a 
uniform elevation of about 1,460 feet. Opposite the state line, the 
elevation of the Dakota plain is about 1,400 feet, which is about 150 
feet above the river and about 60 feet below the Iowa divides. But 
the elevation of the plain decreases southward more rapidly than the 
fall of the river, and north of Canton the edge of the plain overlook- 
ing the valley has an elevation of only 1,320 to 1,340 feet, which is 
only 80 to 20 feet above the river and more than 100 feet below the 
divides of the Iowa side. These contrasts in the topography and 
elevation of the areas on opposite sides of the Big Sioux river are 
well shown in the northeast corner of the Canton topographic sheet 
of the United States Geological Survey. 
This relatively level plain extending from the north border of Lin- 
coln county southward to Canton and east to the Big Sioux valley is 
an area included by Chamberlin, Todd and Wilder in the Wisconsin 
drift-plain but which Shirnek would make a Kansan plain. 
Passing directly eastward from Sioux Falls, the topography is ero- 
siona.l, with a relief of 50 to 75 or even 100 feet (Fig. 3). The distance 
between the two limbs of the northward loop of the Big Sioux valley 
is here only 4 to 5 miles, and the small creeks have cut back from 
either direction until all the area is well drained. The slopes are 
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