GEOLOGY OF SOUTHWESTERN IOWA 531 



one layer, underlain by several feet of weathered shale. The 

 river at this point is only a few yards distant from the railroad 

 track and is flowing in a rapid, paved with many bowlders of 

 ^ay limestone evidently derived from the lower ledge. In the 

 hill south of the ravine Cretaceous shales only are seen reaching 

 ■ thirty feet above the railroad track. 



The correlation of the limestone ledges is difficult and is at- 

 tempted with hesitation, as the outcrop is meager. However, 

 fossils were collected both from the upper ledge and from a pier 

 of the old Keystone mill which evidently was constructed with 

 stone from the lower gray limestone whose outcrop, now con- 

 cealed, was only fifty feet distant. The fauna and lithology of 

 the limestones are not in close agreement with the limestones 

 near Essex. Lonsdale states that a deep drilling was done in 

 this immediate vicinity and it was claimed a coal seam eight 

 inches thick was found ninety feet below the river. If this rec- 

 ord is correct the coal without doubt is the Nodaway coal, and 

 the limestones can be correlated, the lower with the Burlingame 

 and the upper with the Fargo. The Rulo apparently is absent in 

 the Brownville syncline in Iowa. 



COMPOSITE SECTION ON RIVER SOUTH OF RED OAK. 



F'EET 



6. Shale, light gray, friable, with streaks of orange colored 



sandi 9 



5. Shale, arenaceous, micaceous, light gray, concretions. .. .11 to 27 



Unconformity 



4. Sandstone, yellow, unconformity, friablo, massive, with 



limonite concretions to IB 



3. Limestone, yellow, one layer 1 



2 Shale, blue 11 



1 Limestone, light gray, one layer l^/^ 



Total 491/2 



There is much of interest in these outcrops that extend along 

 the river for half a mile. Although now somewhat obscured they 

 show the unconformity between the Carboniferous and Creta- 

 ceous as well as one within the Cretaceous. 



. Four miles north of this locality and two miles north of the 

 city of Red Oak, at the site of the old Clark mill, on East Nish- 

 nabotna river, there is exposed above water level a ledge of lime- 

 stone eleven feet thick overlain by ten feet of dark yellow fri- 

 able Cretaceous sandstone. The limestone is impure, light gray 

 and yellow in color, unevenly weathered. Some layers are com- 

 posed of a mass of comminuted fossils and the whole ledge is 



