104 ON THE GEOLOGY AND NATURAL HISTORY 
Qd. Les Mauvaises Terres, or Tertiary Basin of White and Niobrara rivers. 
This most remarkable lacustrine deposit has been, comparatively speaking, but recently 
made known to the scientific world, wonderful not alone for its unique scenery, but also for 
the abundance and importance of its organic remains. ven at this time it has been but 
partially explored, yet it has already revealed a profusion of Mammalian and Chelonian 
remains belonging to species, and in many cases to genera, which though closely allied differ 
from all known living forms, which has now rendered it classic ground to the geologist 
and paleontologist. A history of the progress of its exploration up to 1858, with elabo- 
rate descriptions of the vertebrata known from this deposit up to that date, may be found 
in a magnificent memoir written by Prof. Joseph Leidy, and published by the Smithsonian 
Tnstitution. 
In its lithological characters this deposit differs very materially from the lignite basin, 
being composed of whitish clays and calcareous and silicious marls and grits, and entirely 
destitute, so far as we now know, of any vegetable remains, except very rare fragments of 
silicified wood. It is chiefly remarkable, however, as a vast deposit, in which were en- 
tombed immense numbers of Mammalian and Chelonian animals, for the beauty and per- 
fection with which these remains have been preserved, and its unique rugged scenery. ‘The 
few molluscous fossils which have been found in it, show most conclusively its freshwater 
origin, being confined to the genera Helia, Planorbis, Limnea, &e. 1 have already em- 
bodied the principal details in regard to this interesting deposit in a preceding chapter, 
and in a subsequent portion [ will briefly state such evidence as I have been able to 
secure, to show that it is of Miocene age. ‘The following vertical section comprises all the 
beds known up to this time, and it is not probable that future explorations will modify it 
materially. 
VERTICAL SECTION, SHOWING THE ORDER OF SUPERPOSITION OF THE DIFFERENT BEDS OF THE TERTIARY 
BASIN OF WHITE AND NIOBRARA RIVERS. 
SUBDIVISIONS. LocaLitizs. 
Estimated 
thickness 
Yellow silicious marl, similar in its character to| Most fully developed along the Missouri 
the Loess of the Rhine, passing down into varie-| river, from the mouth of the Niobrara to 
gated indurated clays and brown and yellow fine | St. Joseph; also in the Platte valley and 
erits; contains remains of extinct quadrupeds, | on the Loup Fork; also largely exhibited 
mingled with those identical with recent ones; | in the valley of the Mississippi and in and 
also a few mollusca, mostly identical with recent | over the Southwest. 
species so far as determined. 
POST PLIOCENE. 
300 to 500 feet. 
| 
