128 



CARBONIFEROUS 



LIMESTONES 



slides. These, perhaps, conceal a third bed of coal, corresponding to that seen near 

 the Lizard Fork. The shale contains many small crystals of selenite, but no beds 

 of plaster-stone can be seen overlying the shales. Ferruginous alum-waters ooze 

 from the bank, like that tested above the Raccoon Fork. 



A corresponding section of shaly beds and coal presents itself to view at a 

 westerly bend of the river, in sight of the "Great Slide," as exhibited in the 

 annexed vignette. This is the last out crop of coal-measures which we witnessed on 

 the Des Moines River. 



LAST EXPOSURE OF COAL, UPPER DES MOINES. 



Beyond this, the stream enters and meanders through an open prairie country, 

 presenting to view low drift knolls, similar to those represented, high up on the 

 Iowa, on the illustration page. The bed of the Des Moines soon becomes contracted 

 to about fifty yards, and canoe navigation is rendered difficult by shallow rapids, 

 over pavements of boulders. 



Having arrived at that part of the Des Moines, beyond which there was little 

 prospect of tracing much further the carboniferous rocks, as I judged, both from 

 the aspect of the country and the representation of hunters ; finding also that our 

 store of provisions was almost exhausted ; that I was myself in a disabled condition, 

 from a gun-shot wound received in the arm, as stated in the Introduction ; that my 

 men were exhausted by fatigue and exposure, so that all but one had contracted 

 intermittent fever ; I decided upon returning to Fort Des Moines. 



In reviewing the general features of the carboniferous rocks of the Des Moines, 

 as indicated by local sections, it appears, that without taking into account the 

 numerous smaller disturbances, there are three principal axes of depression ; one 

 at Raven Cliff, one at Elk Bluff and Red Rock, and one below the Burnt Woods, 

 near the great bend of the Des Moines, a few miles south of the Second Correction 

 Line ; while the chief axes of upheaval are about St. Francisville, Sweet Home, 

 Bentonsport, and Dam No. 15, above Ottumwa, where the underlying limestones 

 attain their greatest thickness. It must be remarked, however, that the elevation 

 of these rocks above the water-courses is in a great measure due to the scooping out 



