GEOLOGY OF SOUTHWESTERN IOWA. 359 



No. 15. Light yellowish, indurated marl 4 feet. 



No. 14. Yellowish, siliclous limestone, with flinty concretions. . . 2^ feet. 

 No. 13. Yellowish, marly shale, with concretions of impure lime- 

 stone 3 feet. 



No. 12. Compact limestone » 1 foot. 



No. 11. Yellowish, marly shale 2 feet. 



No. 10. Gray limesto ae, in thick layers 3 feet. 



No. 9, Bluish, clayey shale % root - 



No. 8. Yellowish, silicious limestone lJh* feet. 



No- 7. Compact, gray limestone, with marly partings 16 feet. 



No. 6. Bluish, shaly clay 1% feet. 



No. 5. Compact layer of limestone % foot. 



No. 4. Bluish, shaly clay 2^ feet. 



No. 3. Compact, bluish limestone 2 feet. 



No. 2. Bluish clayey shale 4 feet. 



No. 1. Fine-grained, micaceous sandstone 1 foot. 



Total 80f| feet. 



The lowest member of the foregoing section, No. 1, is only 

 a few feet above the general level of the flood-plain, and 

 many of the other members appear snccessively above it in 

 the face of the bluff that fronts the flood-plain near Mr. 

 Wilson's residence, while the higher members are fonnd in 

 the bed and banks of a small rivulet that comes down from 

 the uplands through the bluffs at this point. Along the base 

 of the bluffs above this point, as far as the north boundary 

 line of the county, frequent exposures are seen of strata 

 which are equivalent to a large part of those that constitute 

 the lower half of the section at Wilson's. Southward from 

 Mr. Wilson's, along the base of the bluffs, several exposures 

 of the lowest members of that section are seen at long inter- 

 vals, always holding about the same relative position above 

 the level of the flood-plain, all the way to the town of 

 Hamburg, in the southwestern part of the county. The fine 

 grained micaceous sandstone of No. 1, of the foregoing 

 section, is seen at the village of Plum Hollow, a couple of 

 miles below Mr. Wilson's, and also at Hamburg, and several 

 intermediate points. A few strata were found resting upon 

 it at all these points, but none were observed beneath it. It 

 is therefore stratigraphically, the lowest stratum found in 



