240 
IOWA ACADEMY OF SCIENCE 
east of Canton and* a belt extending from south of Canton southwest 
through Beresford (Pig. 2).. 
In 1900, Professor Wilder studied the geology of Lyon county in the 
northwest corner of Iowa. 3 He accepted the mapping of the Dakota 
plain opposite Lyon county as Wisconsin, and further enlarged the area 
in two ways. He interpreted the Wisconsin moraine as crossing the Big 
Sioux river west of Granite and continuing southward along the east 
slope of the Big Sioux valley for 5 to 6 miles (Fig. 2). Concerning 
the Wisconsin border on the Dakota side Wilder says, “Prom the point 
where the moraine crosses the river west of Granite, to Sioux Falls it is 
easily traced as a well defined, boulder-strewn ridge. It passes east of 
Sioux Falls and crosses the river 2 miles northeast of town. * * * 
Thence for 10 miles it was traced nearly due north/’ The course of this 
border located from the statement just quoted is shown by the broken 
line on figure 2. • . . 
During the field seasons of 1910 and 1911 the, writer was engaged in 
a study of the Pleistocene deposits of northwestern Iowa for the Iowa 
Geological Survey. In connection with this work the Altamont moraine 
mapped by Professor Wilder in western Lyon county was investigated 
and the decision reached that it is. not Wisconsin moraine, and that in 
fact no part of the Wisconsin drift-plain of the Dakota lobe exists on the 
Iowa side of the Big Sioux river. 4 
Questions then arose as to the exact boundaries of the Wisconsin plain 
on the Dakota side, opposite Lyon county, for, as noted above, the state- 
ment of Professor Wilder concerning this boundary does not agree with 
the mapping of Professor Todd. It was also known that Professor 
Shimek, of the Iowa Geol. Survey, questioned the existence of the Wis- 
consin, drift-plain in the Shindlar region just opposite" Lyon county. 
These considerations led the writer to go into the Sioux Falls-Shindlar 
region during the latter part of the field season of 1911 to try to deter- 
mine the identity of the Wisconsin drift-plain, and to locate more exactly 
its boundaries. The time available for the study was very short and 
only a partial covering of the data, that is thought to exist was possible. 
The results of the investigation of Professor Shimek, unpublished at 
the time, the writer was in the field, appeared in the March, 1912, num- 
ber of the Bulletin of the Geological Society of America. Among the 
conclusions of Professor Shimek ’s paper (p. 154) are the following: 
1. ‘ ‘ There is no Wisconsin drift in the western part of Lyon 
county, Iowa.” 
"Wilder, F. A., Iowa Geol. Survey, vol. 10, 1900, pp. 137-141 and map p. 118. 
’Onlv a few weeks later Prof. Shimek of the Iowa Geol. Survey working- independent- 
ly of the writer and upon other problems, examined the so-called Altamont moraine 
of western Lyon county and reached the same conclusions concerning- it. 
