AND COAL-MEASURES OF IOWA. 



129 



of the country towards the great central valley, and to the excavation of the Des 

 Moines. This river falls one hundred and eighty-three feet in its descent from the 

 Raccoon Fork to the Mississippi, a distance of two hundred and four miles by the 

 meanders of the river, and one hundred and twenty miles in a direct line. 



It becomes a question, too, whether the carboniferous rocks of the Des Moines, 

 are not the attenuated margin of the great Illinois coal-field, with which it was at 

 one time connected ; and, if so, whether all the strata above the Archimedes lime- 

 stone of St. Francisville, represent only the Yoredale rocks and Millstone Grit of 

 Great Britain, and not the coal-measures proper. 



After replenishing our stores at Fort Des Moines, and allowing my voyageurs to 

 recruit somewhat from their fatigues and sickness, I commenced an examination of 

 the Raccoon Branch of the Des Moines. From the low stage of the water, we were 

 not able to ascend it beyond the first " Main Fork," a distance of forty-five miles. 

 The exposures of rock are not so frequent as on the main branch. 



At the first high ground on the right bank, a seam of coal has been exposed, in 

 digging a foundation for a mill, about fifteen feet above the river. Six inches of 

 the coal is exposed, covered with ferruginous clay and soil. This coal is probably 

 not in its original position, but has slid from above. A little higher up, some coal 

 has been dug out, but the crumbling argillaceous debris prevented an examination. 



Four miles by the meanders of the river, and about one mile and a half in a 

 direct line from the mouth, a disintegrated bed of clay, including some imperfect 

 coal, lies at an elevation of forty-five feet. There seems to be another bed of coal 

 at a lower level, fifteen to twenty feet above the bed of the river ; but the excava- 

 tions at this place have not extended deep enough to uncover it. 



At the rapids, fourteen miles above the mouth, there is limestone in the bed of 

 the river, overlaid by sandstone. In a ravine near by, shale and dark schistose 

 limestone are partially exposed. The limestone contains Productus com. 



Ten or twelve feet above the base of a bluff, on the left bank, at a bend two or 

 three miles higher, shaly layers are associated with an impure calcareous rock. 



In a long bend of the Raccoon Fork, twenty-eight miles from its mouth, a 

 brownish gray limestone was observed, charged with Productus Flemingii, minute 

 Entrochites, and an Orbicula, allied to 0. Davreuxiana (De Konninck) ; also, a 

 small, undetermined species of Terebratida. This limestone seems to correspond to 

 the productal limestone found on the Main Fork, near Keeth's Rapids. 



The best section which I saw on the Raccoon River, was eight or ten miles 

 below the First Forks. Forty feet of strata are exposed by a slide, in the following 

 order from above downwards : 







Feet. 



Shale, .... 





o 



Silicco-calcareous rock, 





•1 to 21 



Shale, . . 





1 



Band of bituminous limestone, and 



septaiia, 



(0 



Shale, with some imperfect coal and 



gray indurated clay, . 



15 



Red ferruginous argillaceous bed, . 





. 3 to 5 



Hidden in the slope, 





35 



17 



