278 c. R. keyp:s — carboniferous strata of central iowa. 



Very recently a detailed section (plate 9) was made from Harvey, in the 

 southeastern part of Marion county, along the line of the Des Moines river 

 to the capital city and thence up the Raccoon river to DeSoto, in Dallas 

 county, a distance of sixty-five miles. The circumstances for its con- 

 struction have been made very favorable by the numerous excellent ex- 

 posures afforded by railway lines that have been built nearly the entire 

 distance on each side of the two streams. These railway cuts, taken to- 

 gether with the natural outcrops on the rivers, permit the stratigraphy of 

 the district to be very satisfactorily traced in all the minor particulars. 



Along the line just specified, more than two hundred exposures were ex- 

 amined and measured, the different beds being carefully correlated in the 

 field by direct passage from point to point. Out of this number, ten of the 

 most instructive and typical sections have been selected, and descriptive 

 notes are appended, indicating the salient characters of the various strata. 

 Each is marked on the accompanying general section, the base of which is 

 the low-water limit in the Des Moines river. It is thought that the two 

 methods of illustration will adequately present, in the briefest possible manner, 

 the leading geological features of the region. The stratigraphical relations 

 of the several beds will find further explanation beyond. 



The Quaternary deposits have not yet been differentiated with sufficient 

 care to warrant the separation, in a general section, of the drift sheets and 

 the loss. 



Description of Sections. 

 L Harvey Exposure. — Quarry in S. W. qr. N. W. qr. Sec. 4, T. 75 K, E. 18 W. 



3. Drift and loss (exposed) . . . . .10 feet. 



2. Gray and ash-colored marl, with abundant fossils: Spirlfera 



keokuk, Hall ; Pentremites koninckiana, Hall ; Zaphrentis 

 spinulijera, Hall ; Athyris suhquadrata, Hall ; Productus 

 marginocinctus, Prout ; and others . . . 5 " 



1. Blue limestone, weathering brown in places, thinly bedded 



above (exposed) . . . . . . 12 " 



//. Coalport Section.— S. E. qr. S.W. qr. Sec. 4, T. 76 N., R. 19 W. 



6. Heavily bedded sandstone, with lepidodendrids, sigillarids, 



filices and calamites below (exposed) 

 5. Dark-colored clays and shales, sandy in places 



4. Coal (mined at this place) ..... 



3. Dark clays and bituminous shales .... 



2. Coal, rather impure . . . . 2 to 3 " 

 1. Sandstone, very thinly bedded, and sandy shales (exposed 



to water's edge) . . . . . . 8 " 



No. 6 of this section is not exposed on the river bluff* at this place, but 

 crops out in a ravine some distance inland. 



15 



feet. 



30 



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5 



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14 



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