FIELD WORK 129 



page 3, represents the Altamont moraine as crossing the Big Sioux River 

 into L3^on County, Iowa. He also refers to pre-Wisconsin gravels (page 

 3), and presents again the Otis Mill section opposite Chatsworth. 



Finally, L. H. Harvey," incidentally discussing the geology of south- 

 eastern South Dakota and northwestern Iowa in connection with the 

 plant ecology of the region, and proba])ly not writing from personal 

 knowledge, refers to the Altamont moraine between the Big Sioux and 

 the Missouri rivers and mentions the oUiteration of the "questional)le 

 pre-Kansan." 



The foregoing references indicate clearly that the ridges and knobs in 

 the region immediately east and southeast of Sioux Falls have been re- 

 garded as a part of the early Wisconsin Altamont moraine; that this 

 moraine was extended into Iowa; that the flat plains along the west side 

 of the Big Sioux Eiver between Canton and Sioux Falls were considered 

 a part of the Wisconsin plain; that the great gravel beds along the Big 

 Sioux were regarded as Wisconsin gravel trains; that two drifts were 

 recognized near Sioux Falls, of which the upper was Wisconsin and the 

 lower probably Kansan, and that the gravel, sand, and silt beds between 

 these two drifts were viewed as equivalent to the Buchanan. 



Recent developments resulting from the study of the Pleistocene de- 

 posits in western Iowa raised a doubt as to some of the foregoing conclu- 

 sions, and an investigation was undertaken by the writer in connection 

 with the work of the Iowa Geological Survey. 



Field Work 



The writer visited repeatedly the region in question during the past 15 

 years, and, not venturing to dissent from the opinion of expert geologists, 

 concluded several years ago that if the ridges near Sioux Falls and oppo- 

 site Granite are parts of the Altamont moraine, then the latter must ex- 

 tend on the Iowa side along the Big Sioux Eiver at least to the uplands 

 opposite Canton, for these ridges are topographically and structurally the 

 same. 



The investigation of the Aftonian deposits, which is being carried on 

 by the writer for the Iowa Geological Survey, made it necessary to see 

 this region again, and about a month (with several subsequent visits, each 

 covering from two to five days) was spent in the field during the summer 

 of 1910 along the Big Sioux River between Sioux Falls and Canton, and 

 later the work was continued down the Bior Sioux to connect with the 



^1 Floral succession in the prairie-grass formation of southeastern South Dakota. 

 Botanical Gazette, vol. 46, 1908, p. 83. 



