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CARBONIFEKOUS LIMESTONES 



On approaching the Missouri, the hills bordering its extensive bottoms, known 

 as Council Bluffs, attract particular attention, not only from their contour, but 

 from their geological formation. Where vegetation has been removed from their 

 slopes, they are seen to be composed chiefly of a fine, ash-coloured, siliceous marl, 

 or loam, effervescing with acids. In favourable situations, many species of ter- 

 restrial and fluviatile shells were discovered, of the same species as are found in 

 similar deposits in the Wabash Valley, which are considered contemporaneous with 

 the Loess of the Rhine. 



The most abundant species are, Helix thyroideus, H. alternata, H. monodon, 

 Helicina occidina, Succinea campestris (?), and Pupa armifera. The base of the hills 

 under this marl is gravel and drift ; the whole resting on carboniferous strata, which 

 show themselves at intervals near the bed of the Missouri, and in a few places at 

 the base of the bluffs. 



The bottoms of the Missouri at Council Bluffs vary from eight to twelve, or even 

 fifteen miles in width. Towards the narrows of the Nishnabotna, these bluffs con- 

 tract in width, until, below the mouth of Nodoway River, they are only two or 

 three miles apart. The highlands throughout this distance present great uniformity 

 of outline, appearance, and composition, proving that within these limits, embracing 



HILLS OF SILICEOUS M A K L, COUNCIL BLUFFS. 



nearly two degrees of latitude, the waters of the Missouri, many hundred miles from 

 their embouchure, have been pent up into vast lake-like expansions, at the bottom 



