MAUVAISES TERRES. 201 
For a further and more detailed account of the comparative anatomy of the fossil 
mammalia collected on this Survey, the reader is referred to Dr. Leidy’s accom- 
panying Memoir. . 
The investigations connected with the geology of this curious country, and the 
natural history of its ancient Fauna, are invested with no small degree of interest, 
when we consider that, at the time these singular animals roamed over the Mau- 
vaises Terres of the Upper Missouri, the configuration of our present continents was 
very different from what it now is. Europe and Asia were then, in fact, no conti- 
nents at all, being represented only by a few islands, scattered over a wide expanse 
of ocean. The Atlantic seaboard of the United States, back to the mountain 
ranges, and up the Valley of the Mississippi as high as Vicksburg, was yet under 
water. Mount Etna, that remarkable volcanic cone of Sicily, nearly 11,000 feet in 
height, was yet unformed, and the fertile plateau of that island, more than 100 miles 
in circumference, was still deep under the Tertiary Mediterranean Sea. In Europe, 
during the period following the extermination of the eocene Fauna of Nebraska, 
the Alps have been heaved up nearly their whole height; and in Northern India, 
the whole Subhimalayan Range has been elevated. In South America, 9,000 feet 
have been added to the height of the Cordilleras, and the South Atlantic has been 
driven back 700 miles, while a district of country 2,500 miles in length, from the 
Great Plain of the Amazons to the Straits of Magellan, has emerged from the ocean. 
Some of my readers, who have not made Geology a particular study, may be 
curious to follow the course of reasoning by which geologists have arrived at such 
startling results—results which must, no doubt, appear to them incredible. 
In Europe, in Asia, and both North and South America, science has long ob- 
served and studied particular geological formations, which, in all these countries, 
have a certain degree of uniformity of organic remains therein embedded. These 
are, chiefly, an assemblage of marine shells and corals, which, though they differ, 
in most instances, in trivial minutise of form, yet bear a close resemblance to the 
very shells and corals now inhabiting our seas, and which are cast by thousands on 
our shores. 
It is not in a few rare instances alone, that these fossil shells are detected em- 
bedded in the substance of the rocks in question ; many of the strata, and especially 
those that contain much lime, actually teem with these exuvie; and, not unfre- 
quently, as in Florida and Mississippi, they are but an agglutinated aggregate of 
marine productions. We have, indeed, the most unequivocal proof, that all the strata 
composing this formation have been a succession of sediments or precipitates consoli- 
dated at the bottom of the ocean. Alternating with these beds there are also others 
interstratified, filled with the bones of quadrupeds which have perished on the 
banks and near the mouths of rivers, whence they have been swept into estuaries 
and bays, and entombed in the sediments there accumulating. In the occurrence 
of such mammalian remains, the geological formations to which the attention of 
the reader is now called, differ essentially from every other which underlies them, 
and which, therefore, are of more ancient date; since it is a self-evident fact, that 
6 
