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 ina 
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 cora. 
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 O. Davreuxiana (De Konninck) ; also, a 
small, undetermined species of Zerebratula. 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 : 
Shale, . ; ; é iis 
Siliceo-calcareous rock, 2 to 24 
Shale, . ; ; 1 
Band of bituminous limestone, and septaria, (?) 
Shale, with some imperfect coal and gray indurated clay, . 15 
Red ferruginous argillaceous bed, . : j 3 
Hidden in the slope, 
