OF THE UPPER MISSOURI. 
71 
that most of their specific characters have been obliterated. The most abundant fossil 
is the Pcctunculus Siouxensis , Hall and Meek. Great quantities of sulphuret of iron are 
found throughout the bed. 
Passing up the Big Sioux river, about two miles above its mouth, the bed of lignite 
before mentioned is seen, two to two and a half feet in thickness, underlaid by sandstone, 
the same as seen at Wood’s bluffs, Chalk bluff, &c. Here I found in considerable num¬ 
bers a species of Cytherea. The lignite bed is exposed for several miles up the Big Sioux. 
Six miles above its mouth we have impure lignite, about twelve inches in thickness, under¬ 
laid by alternate layers of ferruginous sandstone, loose sand, yellow and ash-colored arena¬ 
ceous clays, and fine whitish clay. The strata containing clay have quite distinct impres¬ 
sions of leaves, which belong to dicotyledonous trees. There were also some fine impres¬ 
sions in a dark gray though concretionary silicious rock. Two miles below the mouth of 
Iowa creek, on the Missouri, is a fine exposure of No. 1, in a bluff cut by the river; it 
contains at this locality large numbers of sandstone concretions, arranged in the coarse 
sand in horizontal strata. Great quantities of the sulphuret of iron are seen here in crystals 
or in large tabular masses, a fresh fracture of which has much the appearance of cast iron. 
In the Platte valley, about four miles above the mouth of the Platte, No. 1 is first seen 
in a thin outlier, resting directly upon the limestones of the upper Coal measures. At the 
mouth of Elkhorn river, the limestones pass beneath the water-level, and No. 1 occupies 
the country until we reach a point about thirty miles above the mouth of Loup fork, where 
it is in turn concealed by the overlapping edges of No. 3, and the Pliocene and Miocene 
Tertiary beds of the Bad Lands of White river. Continuing a northwest course we do 
not meet again with No. 1 until we reach the valley of Old Woman’s creek, a branch of 
the south fork of the Shyenne. It is here exposed over a small area by upheaval, and 
presents the same lithological characters as on the Missouri. Around the Black hills are 
a series of beds, supposed to belong to No. 1, exposed by the uplift of the mountains in 
the form of a belt or zone, which attain a thickness of 200 to 250 feet. 
Returning again to the Missouri river, we take leave of the sandstone, which forms the 
type of our No. 1, near the mouth of Iowa creek; then succeed in regular order Creta¬ 
ceous formations Nos. 2, 3, 4 and 5, and the Tertiary beds of the lignite basin. Near the 
mouth of Milk river, Cretaceous formation No. 4 rises to the surface, but 2 and 3 are 
wanting in this region. Near the mouth of Little Rocky Mountain creek, a bed of coarse¬ 
grained gray sandstone, variable in color and structure, rises above the water’s edge from 
beneath the well-known Cretaceous formation No. 4 of section. In its lithological charac¬ 
ters this bed of sandstone seems to resemble our No. 1, with which we have placed it 
provisionally, though we have no certain evidence that a single species of organic remains 
was common to both. 
