364 The American Geologist. June, i9uo 
NONCONFORMITIES AT THE MOUTH OF THE 
PLATTE RIVER, 
By Charles Newton Gould, Lincoln, Nebraska. 
In eastern Nebraska there are three well marked geolog- 
ical horizons representing the three eras, Paleozoic, Mesozo- 
ic, and Comanche. To the Paleozoic belongs the Carbonif- 
erous, to the Mesozoic the Dakota, and to the Cenozoic the 
drift and loess of the Glacial epoch. The deposits of these 
three horizons differ much in thickness. The Carboniferous 
rocks being lowest in the scale extend to the depth of several 
hundred feet below the surface. The maximum thickness of 
the Dakota in the state is probably not to exceed three 
hundred and fift}' feet, and along its eastern border on the 
Platte river, less than one hundred feet are exposed. The 
drift and loess vary from a few feet to perhaps two hundred 
feet in thickness. 
Between these deposits, in the region under consideration 
ma\- be observed a marked nonconformity, each representing 
a time limit and a period of upheaval and consequent eros- 
ion. The amount of rock which has been removed in any- 
one instance is largely- conjectural, although by comparison 
with neighboring regions, fairly accurate estimates may be 
obtained. 
The Platte river in its course across the plains from the 
mountains to the Missouri, flows nearly the entire distance 
through a broad, shallow valley. A little below the mouth 
of the Elkhorn, the \-alle)' suddenl)- narrows, and the bluffs 
on either side become very pronounced. F'rom this point to 
the mouth of the river, a distance of thirty miles, the river is 
characterized by a valle)' scarcely more than a mile wide, from 
which steep and often rocky bluffs rise abruptly. The reason 
for the sudden contraction of the valley ma\' be found in the 
character of the rock through which the channel has been 
carved. Throughout its entire course the river encounters 
only loess and alluvium until it strikes the harder material — 
sandstones and limestones, which form the bluffs near its 
mouth. It is along these bluffs that the nonconformities, 
which form the subject of this article, may be best studied. 
The abundance of invertebrate fossils, as well as the 
character of the rock, testif\' to the fact that the Carbonif- 
