178 The American Geologist. March, 1892 
Cretaceous times, almost, if not quite uninterruptedly a land arew 
subjected to denudation; that, at the beginning of Carboniferous 
times the land was already eroded beyond the stages of youth 
nearly to topographic maturity; that, when the Cretaceous period 
began, it found the Carboniferous area a low-lying base-levelled 
area, a peneplain skirting a moderately low and not strikingly 
diversified highland of older and harder rocks; and that the 
Cretaceous ocean completely covered this region, depositing there- 
on a considerable thickness of Cretaceous rocks. The encroach- 
ment of the Cretaceous sea was rapid as is indicated by the pe- 
culiar Trinity conglomerate, which is apparently hurriedly worked 
over land debris. The final chapter in the history was the post- 
Cretaceous elevation, which first raised this region above the sea, 
because its former elevation was in part indicated in the topog- 
raphy of the Cretaceous ocean even through the blanket of Cre- 
taceous strata which covered it. Being the first to be raised 
above the sea it was the first to be eroded, and consequently now, 
over large areas, shows no signs of the former covering, either in 
remnants, Quaternary debris, or in unadjusted stream courses. 
NOTES UPON NEBRASKA TERTIARY. 
By F. W. Russet, Chicago, Il. } 
In the January (1890) number of the GEOLOGIST the writer pre- 
sented some preliminary observations upon certain geologic forma- 
tions of central Nebraska. Obtaining many of these data from re- 
connaissance a desired degree of accuracy could not be attained. 
Subsequent examination has served to reveal more completely 
certain criteria for the study of this central record. One hiatus 
is closing but we can not, as yet, proceed along an unbroken 
sequence. Most noticeable does this become when we endeavor 
to intercalate certain beds between the inferior Tertiary limestone 
and the superior loessian formation. These beds, as far as seen, 
do not contain data for exact horizonal determination. The 
problem then resolves itself into placing them from their relations 
to the other formations. Briefly then to get the sequence in mind 
let us consider our material. We shall find at the base the un- 
questioned Tertiary buttes. The writer has examined all the 
