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, by the illustration on page 104. 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 
