AND COAL-MEASURES OF IOWA. 125 
level, near our encampment of the 9th of September, as designated on the Chart. 
Not far from this place we encountered two granite boulders, the first large erratics 
we observed in our ascent of the Des Moines. A chalybeate spring issues from 
under the coal-banks. 
A short distance from this section, ridges one hundred to two hundred feet high, 
composed chiefly of sand, gravel, and drift deposits set in, concealing the carboni- 
ferous stata, so that they only appear at long intervals. It was not until after 
passing the Boone Fork, that an opportunity was offered of again inspecting the 
rocks. 
A short distance above the mouth of Brushy Creek, micaceous sandstones, of the 
coal formation, are exposed, at an elevation of from fifteen to twenty feet; and two 
miles further, on the right bank, a bluish gray clay is seen near the water's edge, 
charged with fragments of argillaceous iron ore, together with an impure gray 
calcareous rock, and loose pieces of soft sandstone; but the exact order of super- 
position cannot be seen, by reason of the thick vegetation and deep alluvion. 
Five miles above Brushy Creek, argillaceous shale, with nodules of ironstone, is 
overlaid by slaty sandstone, which latter is about fifteen feet above the water-level. 
(See Section No. 61, D.) About a quarter of a mile beyond, hard, black, bitumi- 
nous shale, splitting into sheets, rises from beneath the water-level, and soon attains 
an elevation of from fifteen to twenty feet, covered by erratic deposits, which con- 
tinue to accumulate in proceeding towards the north. The shales enclose large 
angular masses of compact black calcareous rock, which may answer for an hydraulic 
cement. 
About half to three-quarters of a mile above this locality, a conspicuous boulder 
of porphyritic granite lies in the river, near the left bank. Ten miles above the 
Boone Fork of the Des Moines, solid ledges of sandstone, containing vegetable 
impressions, and embracing some thin, interpolated layers of conglomerate, present 
themselves to view. These sandstones gradually increase in thickness on approach- 
ing the great easterly bend of the “Burnt Woods District,” where the current of 
the Des Moines strikes mural escarpments of thirty to fifty feet on alternate sides, 
as it is deflected from one high point of land to another. Twenty to twenty-five 
miles above the Boone Fork, they even attain the height of one hundred and ten 
feet. (See Section No. 62, D.) 
Near the termination of these bluffs, just below our encampment of the 5th 
September, in sight of the Burnt Woods, there is a good deal of hydrated oxide of 
iron, but rather too much impregnated with sandy particles to be of practical value. 
The sandstones, with some shaly intermixtures, continue within sight of Lott’s 
Rapids, about five miles below the point where the north and south line, between 
Ranges 28 and 29, crosses the Des Moines. Here, limestones can be seen at a low 
stage of water, covered with a multitude of boulders, which fill the channel; and 
these so obstruct the navigation, that it was with difficulty we succeeded in floating 
the bark canoe containing our provisions and camp equipage, over the shoals, 
although the river was high. 
It seems as if an accumulation of drift had taken place, from some local cause, 
such, perhaps, as the stranding of an iceberg loaded with erratics ; since above and 
