es eee 
172 FV. Hayden on the Cretaceous rocks of. the West. 
In order that the geological relations of the Dakota group 
may be better understood, I have given a brief summary of the 
contiguous formations. 
nding the Missouri river we find near Fort Leaven- 
worth exposures of limestone which, up to the present time, we 
have regarded as belonging to the upper Coal-measures. ‘The 
beds are all nearly horizontal, with a slight, almost impercepti- 
ble, dip toward the northwest. As we continue up the Missouri, 
layer after layer of these Coal-measure rocks pass from view be- 
neath the water level of the river, and when we reach Fort Lisa 
they have entirely passed from sight and are overlapped by a 
bed of variegated friable sandstone. The sandstone undoubtedly 
_ exists, or has existed, as an underlying rock considerably lower 
down the river than Fort Lisa, probably nearly to Omaha City, 
but has either been removed by erosion, or concealed by the great 
thickness of superficial recent deposits which cover this country, 
sometimes entirely hiding from view the underlying basis rocks 
over large areas. Ascending the Platte valley we have the true 
Upper Carboniferous limestone nearly to the mouth of the Elk- 
orn. Before reaching that point, however, we observe a portion 
of No.1 resting directly upon the limestones, as the following 
section will show. 
At the mouth of the Elkhorn, the Carboniferous limestones 
have passed from view beneath the Cretaceous sandstones. The 
conspicuous westward from Fort Riley, are wanting in this region. 
The Dakota group as seen along the Missouri passes beneath the 
bed of the river about 30 miles above the mouth of the Big 
In an interesting memoir read before the American Philosop ical 
Society at Philadelphia, Prof. Hall, after describing numerous 
exposures of the variegated quartzites from St. Peters to Fort 
* Trans. Amer. Phil. Soc, 1861. _ 
