248PI,EIBTOCENE GEO~OGY OF NORT~WESTERN IOWA Iowa"/6 which also mapped O'Brien and Clay counties together with parts of Lyon, Osceola, Dickinson, Oherokee and Buena Vista counties as "Wisconsin" lying outside the "Wisconsin Moraine" ' . Su.bsequent work to the south evidently did not bear out the earlier conclusions concerning this extra-morainic Wisconsin area for in the report on Oherokee and Buena Vista counties 17 Cherokee county, to the south of O'Brien, was mapped 'as "Older Drift (Kansan)" except for a triangular area between Mill creek and the Little Sioux which was called '''Wisconsin Overwash Gravel" (figure 27) . . The west part of Buena Vista county also was mapped as Kansan drift, which consequently abl1t;. on the north against the ';Wisconsin Drift'" area of the Clay county map. The central and east parts of Buena Vista county were mapped as '~Wisconsin Drift",. but without a morainic belt ~i.long the boundary. . The . prevIous assignment of the drift of O'Brien and Clay counties to the Wisconsin epoch was questioned (page 319), with the suggestion that it might prove to be earlier Wisconsin or even older. The problem was evidently considered the same as that in Plymouth connty to which report "the reader is referred." In the' Plymouth .county report the drift had been provisionally referred to the Iowan epoch. l8 As a part of the report on Oherokee and Buena Vista counties P.rofessor Macbride discussed "The Margin of the \ Wisconsin Drift')19 in northwestern Iowa, and mapped the course of 1 the Altamont moraine (figure 28), a course which shows little relation to that of the same moraine on the county maps north of .
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