70 
ON THE GEOLOGY AND NATURAL HISTORY 
Formation No. 1 of the Vertical Section. 
In ascending the Missouri, No. 1 is first seen in the form of outliers overlapping the 
Carboniferous limestones near the mouth of the Platte. At De Soto it occupies the whole 
country, though concealed for the most part by grassy slopes. The first exposure along 
the Missouri occurs near Wood’s bluffs, right bank, about one hundred and seventy miles 
above the mouth of the Platte. We have here a yellowish gray friable sandstone, twenty 
to thirty feet exposed, and overlying this, a recent deposit of water-worn pebbles, ce¬ 
mented by the hydrated oxide of iron, very deep rust color, 6 to 8 feet. Succeeding this 
in ascending order, 30 to 40 feet of yellow silicious marl. At Chalk bluffs about forty 
miles below the mouth of Big Sioux river, occurs the finest exposure of No. 1 along the 
Missouri. 
Feet. 
1. Eight inches of earthy lignite, resting upon twelve inches of yellowish drab arenaceous clay, this in turn 
underlaid by eight inches of impure lignite. 
2. Ferruginous rather coarse-grained friable sandstone, . . . . . . . . GO to 80 
8. Yellow plastic or unctuous clay, toward the top becoming grayish blue, contains flat argillaceous iron con¬ 
cretions. Seen only during low water, ............ 2 
Overlying bed 1 are eight to twelve feet of ash-colored clay, which I suspect belongs to 
formation No. 2 of our general section. If so, it is an outlier, and the first indication of 
its appearance in ascending the river. 
At this place I was unable to discover any well-preserved organic remains. In small 
seams of clay interstratified with the sandstone some traces of vegetable impressions were 
observed, and in some ferruginous concretionary sandstone some imperfect fragments of a 
plant resembling an Equisetum. 
The next exposure of No. 1 is in a range of hills about two miles below the mouth of 
Big 8ioux river, on the left bank of the Missouri. The sandstone at this point is quite 
variable in its character and structure. The whole forms a large concreted mass of rock 
of a dark dull reddish color, sometimes red or yellow, differing according to the amount 
of ferruginous matter contained in it. Only about twenty feet are exposed at this point. 
About fifteen feet above the base of the exposure, the rock has a compact silicious charac¬ 
ter, and from this portion is obtained the stone for building purposes. Near the top it 
becomes a friable coarse-grained ferruginous sandstone with dark purple nodules. These 
nodules possess merely a thin shell and are formed by concretionary action. A thin 
stratum occurs at this locality, filled with shells, of which casts only are obtained. The 
calcareous matter which formed the substance of the shells has been dissolved away, so 
