128 
GEOLOGICAL SKETCH OF THE ESTUARY AND FRESH WATER DEPOSIT 
tions of sandstone. The evidence is quite clear that the surface of No. 1 was much eroded 
prior to the deposition of No. 4. We also find that Formations Nos. 2 and 3 which are so 
well developed between the Great Bend and mouth of Big Sioux River, are entirely want¬ 
ing in this region. Some uncharacteristic fragments of large bones were found in the debris 
near the water's edge, which appear to have been washed from No. 1, and doubtless belong 
to some immense saurian animal. Thus far up the river we have observed no indications 
of disturbance of strata by subterranean influences; but on reaching a point about five 
miles above Grand Island, a great thickness of rocks not before seen, is uplifted so as to ex¬ 
hibit the beds, inclining at every angle from a horizontal to a vertical position. The beds 
are composed of variegated sands, clays, and earthy lignite, and some of them are fully 
charged with organic remains. Toward the north the Bear’s Paw and Little Rocky Moun¬ 
tains are full in view, rising out of the midst of the prairie, and toward the south we can 
see the Square Buttes, Judith, Girdle and Snowy Mountains, revealing at once the fact 
that the elevating forces, which uplifted these mountain peaks, disturbed the surrounding 
strata also. 
The local sections already given, will show with sufficient clearness the lithological cha¬ 
racters of the formation upon which the fresh water and estuary beds rest. A large num¬ 
ber of local sections of the fresh water and estuary strata were taken at different points, 
and from them the following general section has been constructed; which, though future 
examination may modify to some extent, will be sufficiently accurate for our present 
purpose. 
