Fune 16, 1870] 
NATURE 
1B ae) 
FOSSTL MAMMALS [N NORTH AMERICA 
The Eatinct Mammalian Fauna of Dakota and Ne- 
braska ; together with a Synopsis of the Mammalian 
Remains of North America. By Dr. Leidy. With an 
Introduction on the Geology of the Tertiary Forma- 
tions of Dakota and Nebraska ; witha map. By Dr. 
Hayden. (Philadelphia, 1869.) 
R. LEIDY’S new work on the extinct mammalia 
and fauna of Dakota and Nebraska, to which is 
appended a Synopsis of the Mammalian Remains of North 
Amcrica, fills a wide gap in Paleontology. It occupies 
the whole of the seventh volume of the Journal of the 
Academy of Natural Sciences of Philadelphia, and is ac- 
companied by a preface on the geology of the Tertiary 
Strata of Dakota and Nebraska, by Dr. Hayden. Alto- 
gether it forms the most important contribution to our 
knowledge of fossil mammals which has been made since 
Prof. Gaudry published his famous “ Animaux Fossiles 
et Geologie de l’Attique.” These two books, indeed, 
stand in close relation to one another, for in the one the 
chief interest centres in the Miocene fauna, which is the 
subject matter of the other. I propose to give an outline 
of Dr. Leidy’s work, and to show the relation which the 
American Mammalia bore to those of Europe, from 
the Miocene down to the “ Quaternary,” or Post-glacial 
epoch. 
At the close of the Cretaceous period, writes Prof. 
Hayden, the ocean which had “rolled uninterruptedly 
across the area now occupied by the Rocky Mountains” 
began to grow shallow, until at last a long barrier of land 
gradually rose above the waves, and separated the Atlantic 
from the Pacific. This elevatory movement culminated 
in the Rocky Mountain range in the United States, and 
probably has been going on from the Cretaceous period 
down to the present day. In the early Tertiary epoch 
enormous lakes occupied the basin of the Mississippi. 
The “ great lignite basin,” for instance, extends far south- 
ward, possibly even to California, westward far over the 
mountains to Utah, and possibly to the Pacific, and north- 
ward probably to the Arctic Sea, interrupted here and 
there by the upheaval of mountain ranges.” The strata 
which testify to the former existence of this great jake, 
consist of layers of clay and sand, and numerous beds of 
lignite, varying in thickness from a few inches to twelve 
or fifteen feet. In its lower portion an oyster is the 
characteristic fossil, which by its stunted growth implies 
a change from salt to brackishwater, while in the rest of the 
formation there are freshwater shells of the genera Melania 
and Corbicula. “The occurrence of immense fan palms, 
and many other plants now growing only in tropical 
climates, points directly to the conclusion that along the 
shores of this great lake there grew most luxuriant forests, 
equalled only by those now existing in Central America 
or Brazil.” The date of this lignite formation is possibly 
Eocene, and certainly pre-Miocene. Some of these lakes 
continued to exist as late as the Pliocene epoch. 
The “White River group” of rocks consists of white 
indurated clays, sandstones, and conglomerate marls 
and sands, upwards of a thousand feet thick, which 
occupy an area of at least 100,000 square miles on the 
Eastern flank of the Rocky Mountains. It is purely 
a fresh-water formation. In Nebraska it is eroded by 
pluvial and torrential action into quaint pinnacles and 
fantastic shapes of every sort, and into deep barren ravines 
that recall to mind Dr. Falconer’s description of some parts 
of the Sevalik Hills. From the difficulty of traversing the 
5,000 square miles which are cut up in this way the district 
is known to the Canadian voyagers as “ Mauvaises Terres,” 
and to the Indian hunters as the “Bad Grounds.” It has 
furnished the larger portion of the Mammalia described 
by Dr. Leidy, and is unequivocally of Miocene Age. The 
Loup River Strata resting on the White River group, 
consist of sand and a few layers of limestone, and 
contain the remains of land and fresh water Testacea 
and Mammalia. In Nebraska, the sand is so incoherent 
that it forms a series of ever shifting dunes, which occupy 
an area of not less than 20,000 square miles. The remains 
of Elephant and Mastodon and others show that it 
belongs to the Pliocene, irrespective of the stratigraphical 
evidence. The Post-tertiary deposits are represented in 
the same region by a yellow siliceous marl, most fully 
developed along the Missouri River, and in the valley of 
the Plate. It is from three to five hundred feet in thick- 
ness, and contains well-known Post-glacial fossils. 
In treating of the Mammalia yielded by these different 
formations, Dr. Leidy has followed the example of Prof. 
Agassiz in the needless multiplication of species. Natu- 
ralists fall into two classes, according to the ideas which 
they bring to bear on their work: the one fix their attention 
on the variability and points of resemblance manifested by 
suites of organic remains, and stretch the name of species 
as far asit will go; the other give specific value to minute 
differences of size and form, which, in a larger series of 
specimens, either recent or fossil, would be found value- 
less in classification. IA this work Dr. Leidy has joined 
himself to the latter class, and has marked every small 
variation by a specific, and, in some cases, even a generic 
name, and by so doing has added, without any necessity, 
to the heavy burden of synonyms which scientific litera- 
ture has to put up with. He believes that the American 
is a “peculiar fauna,” and, that even if no difference be- 
tween European and American fossils can be detected, 
their geographical separation is evidence that they be- 
long to different species. For example, in the description 
of a new species, Egwzs excelsis, he admits that “itis not 
improbable that part of the specimens looked upon as 
fossils may be the remains of the Mustang, or recent wild 
horse of our western wilderness.” Nevertheless, he holds 
to his own undefined specific name. This fault is carried 
to an extreme, in the case of the extinct family Anchi- 
theriide, On the small foundation of one tooth, which, 
“in general proportions and construction,” and “in size,” 
is “nearly the same as the teeth of Anchitherium 
Aurelianense,’ a new genus, Anchippus, is based; while 
four milk molars, which “in form, mode of insertion, and 
general constitution and size, bear a near resemblance to 
those of the same species,” constitute the basis of 
the second new genus Parahippus. This mode of treat- 
ment runs more or less throughout the work, and renders 
it of less value than might have been expected from the 
importance of the subject-matter. But, nevertheless, it 
is a mine of information to which Tertiary naturalists will 
resort for many long years to come. 
I will now pass on to the consideration of the leading 
features of the Miocene fauna. On the borders of the 
ancient Miocene lake, from which the Mauvaises Terres 
