STE. GENEVIEVE FORMATION 
241 
THE STE. GENEVIEVE FOEMATION AND ITS STRATI- 
GRAPHIC RELATIONS IN SOUTHEASTERN IO.WA. 
STUART WELLER AND FRANCIS M. VAN TUYL. 
In hi^ report on the geology of Lee county^ Keyes described 
a fine-grained, compact limestone at the top of the St. Louis 
formation, resembling lithographic stone in texture. Gordon^ 
reported a similar limestone characterized by Spirifer littoni 
(=Spi^fer pellaensis Weller) and Pugnax ottumwa at the same 
horizon in Van Buren county. Bain^ subsequently recognized 
this member in Keokuk county and named it the Pella because 
of its typical development at the town of this name in the neigh- 
boring county of Marion. This name has been adopted by Sav- 
age in his geology of Henry county^ and by Miller in the Marion 
county report.® Until 1900, when Nickles and Bassler® referred 
the Pella to the Ste. Genevieve upon the basis of its bryozoan 
fauna, the St. Louis age of the formation was accepted without 
question. Weller^ subsequently pointed out the Ste. Genevieve 
affinities of the Pella fauna in 1909, and recent field studies 
have now likewise demonstrated that the Pella is formationally 
distinct from the underlying St. Louis, it being separated from 
that formation by a disconformity and by a characteristic basal 
sandstone in every Iowa locality which has come under obser- 
vation. 
Areal Distribution . — In general, the exposures of the Pella 
beds in Iowa are confined mainly to the southeastern part of the 
state. In the belt of Mississippian rocks, which extends north- 
westward from this region, the higher formations of the system 
are concealed by the Coal Measures, except for locally exposed 
areas in Story, Webster and Humboldt counties, where the over- 
lying beds have been removed by erosion. Little is known as 
to the extent of the Pella in this direction, but the finding of a 
good Pella fauna by Wilder® in certain marls overlying the St. 
Louis limestone in Webster county indicates that the Pella seas 
extended at least as far northward as Fort Dodge. 
Ua. Geol. Survey, Vol. Ill, 1893, p. 349. 
Ua. Geol. Survey, Vol. IV, 1894, p. 217. 
Ua. Geol. Survey, Vol. IV, 189'4-, p. 282. 
Ua. Geol. Survey, Vol. XII, f901, p. 265. 
Ua. Geol. Survey. Vol. XI, 1900, p. 143. 
«U. S. Geol. Survey Bull. 173, pp. 166 and 188. 
'^JOur. Geol., Vol. XVII, p. 278. 
8Ia. Geol. Survey, Vol. XII, 1901, p. 78. 
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