152 B. SHIMEK PLEISTOCENE OF SIOUX FALLS AND VICINITY 



gravel terraces above Sioux Falls and none above the terrace island, which 

 is only a short distance above these ridges of gravel, and this suggests tliat 

 a great mass of gravel deposited by the Kansan in the rough area under 

 discussion was the source of the gravels which largely make up the river 

 terraces, and that the present knobs and ridges are a mere remnant of the 

 original mass. 



Additional plausibility is given to this conclusion by the fact that the 

 terraces are highest immediately below and opposite these ridges and 

 gradually decline as we go down the river. The following table of eleva- 

 tions, given in feet, shows this : 



I II 



Sioux Falls 1,?,97 80 



Brandon 1,333 + 25 75 



East Sioux Falls 1,323 45 



Canton 1,246 +4 27 



Fail-view 1,216 + 20 30 



Hudson, South Dakota 1.224 



Hawarden, Iowa 1,182 23 



Chatsworth, Iowa 1,104 22 



The first column contains the elevations above the sea of the tracks of 

 the Chicago, Milwaukee and Saint Paul Eailway at the several stations 

 named as given by Gannett. At Sioux Falls the terrace is below the city, 

 but at about the elevation of the Illinois Central depot. Brandon is about 

 25 feet lower than the terrace to the west. At Canton the terrace is not as 

 distinct as it is across the river at Beloit, where it is about 4 feet higher 

 than the Canton depot. At Fairview the terrace is 20 feet above the sta- 

 tion, and at all the other points the depot is on the terrace level. 



The second column represents the height of the terrace above the river 

 at the respective points. It will be noticed that the altitude of the Hud- 

 son depot is greater than that of Fairview, and while the height of the 

 terrace above the river was not determined it also seems to be greater. 

 This is probably due to the accumulation of similar gravels which came 

 down the valley of Eock Eiver, which empties into the Big Sioux opposite 

 Hudson. 



South of Chatsworth the terraces become still less conspicuous and 

 practically disappear before the Missouri Valley is reached. 



Furthermore, the numerous upper benches, with their capping strata 

 of gravel, and the strata of silt overlying the Kansan in Sioux Falls (see 

 plate 10, figure 2), as far as observed practically at the same level, 

 suggest that the waters of the Big Sioux below Sioux Falls luid been 

 dammed by the great gravel mass, thus raising the water level and mak- 

 ing possible the deposition of sand and silt at what are now rather high 



