; 
Geology. 427 
adual, not violent. We find that even while the Cretaceous conditions 
still existed, (during the deposition of No. 5 of the series*) the approach- 
ing close of that state of things, and the coming of the Tertiary era, 
were foreshadowed by the introduction of Fasciolaria, Pleurotoma, and 
Belemnitella, with many shells of other genera, quite as near in heir 
We even know from the presence of a few remains of Lycopodia- 
plants, and an occasional unbroken leaf of some Exogenous tree, that 
d 
meet with Ostrea, Corbula,-and Cerithiwm, mingled in the same bed wi 
Melania, Paludina, Physa, Cyrena, &c., all of tertiary types; while a 
little hicher in the series we find at some places only the remains of land 
and Radienace Mollusca. 
From the above facts, 
the true chalk. We are by no means inclined, h 
views of M. Alcide D’Orbigny, who regards all the Cretaceous formations 
of the United States and Western Territories as referable to a later epoch 
than the Green Sand, as the next succeeding formation below that of which 
we have just been speaking, (No. 4 of the series), is characte n 
country having been mingled together and described as if they occurred 
be 
previously stated, near the 
are not seen for a long distance below oe r 
view, They consist of the upper two members of the series (No. 5 an 
No. 4) which, in consequence ; 
nse higher and higher as we ascend the river, ak! 
close to the Missouri, between Milk and Muscleshell riv oy ge 
formations. Some four or five miles below the mouth of Muscleshe 
* For a secti i ks of this country, see a paper by James Hall and F. B. 
Meek in Gar Manabe yeiigets aiednd Sci. vol. 5, New Series. Likewise a paper 
by F.B. Meek and F. V. Hayden in Proceed. Acad, Nat. Sci. Philad, March, 1856. 
