10 ON THE GEOLOGY AND NATURAL HISTORY 
soft yellowish white limestone fully charged with Jnoceramus problematicus and fish remains. 
Near the north side of the Omaha reserve another bottom commences, averaging about 
five miles in width—greatest width ten miles—extending up the Missouri, above the vil- 
lage of St. John’s. Dacota City is located on this broad level bottom. 
At Sioux City, on the Iowa side, is a fine quarry in formation No. 1, which has yielded 
much excellent building-stone, and many attempts have been made to convert it into lime. 
The simple application of an acid would have shown it to be nearly destitute of calcareous 
matter. The whole bed presents the variation in color and structure peculiar to this 
rock. ‘The more compact stratum extends below the water level, and will at some future 
day form a superior landing for steamboats. A few fossils have been found at this locality, 
impressions of leaves like the common willow, and some molluscous remains. Scattered 
over the high hills are exposures or outliers of formation No. 3, the rock of which is ex- 
tremely calcareous, and is eagerly sought after by the inhabitants and converted into lime. 
I saw a load of this lime sold at Sioux City for the enormous price of one dollar and 
twenty-five cents per bushel. In the valley of the Big Sioux river, about three miles 
above its mouth, a bed of lignite is exposed, eighteen inches to two feet in thickness, but 
very impure. This is the same stratum seen near the Omaha Mission, at Omadi and other 
points along the river. As we pass up the valley of the Big Sioux, we see the different 
Cretaceous beds, Nos. 1, 2, 3, and 4, represented with a few of their peculiar fossils. No. 
1 contains a Pectuneulus, a Cytherea, a Pholas, with numerous vegetable remains ; Nos. 2 
and 3 contain Ostrea congesta, Inoceramus problematicus, and abundant fish remains; No. 
4 has yielded nothing characteristic as yet at this locality, and is only thinly represented 
on the summits of the bluffs. 
As we pass the mouth of the Big Sioux, latitude 423°, longitude 964°, the country 
begins gradually to lose, to a certain extent, its fertile character; many kinds of trees, as 
the soft maple, several varieties of oaks, one species of elm (Ulmus fulva), butternut, black 
walnut, wild locust, &c., reach their limits, and many others have already ceased to appear. 
From thence to the mountains not more than five or six species of forest trees are seen, 
and these appear very seldom except along the borders of streams. 
Returning again to join the expedition at Omaha City, I found the travelling very diffi- 
cult and was much delayed. A severe storm of rain had swollen all the small streams to 
an enormous extent, so that the bridges were all swept away. The yielding nature of the 
alluvial banks of streams, and the want of firm rock foundations, render it difficult to erect 
permanent bridges which will resist the strong power of the current of the rivers when 
swollen to their greatest height, as they frequently are in the months of May and June. 
After an examination of that portion of Nebraska already occupied by settlers, I came 
to the following conclusions : 
