408 THE AMERICAN NATURALIST. 
bitten off limbs, mixed accumulations in fine uniform sediments, 
are inexplicable on the lake hypothesis. 
3. The character of the clays is exactly what the loess would 
probably assume on consolidation, and does not agree with the 
Niobrara chalk, a deposit similar in origin to that proposed by 
the lacustrine theory for the White River clays, except that the 
water was salt instead of fresh. 
4. The great extent and uniformity of the White River and 
the details of its distribution appear to the writer to agree with 
that of the loess, but to be difficult to explain on the theory of 
lake deposition. 
This view of the origin of the White River beds involves a 
great change in our notions of the climate and conditions of 
the west in the later Tertiary. If it be correct, these must 
have been much like those now prevailing in the same region ; 
and our ideas as to the probable appearance and habits of these 
extinct animals can be made much more definite and certain. 
This theory has probably little or no application to the 
Eocene beds west of the Rockies. These do not contain the 
fine unstratified chalks ; they are in well-defined basins enclosed 
by mountain ranges and drained by great canyons; land tortoises 
are as rare in them as water tortoises in the White River; alli- 
gators, etc., occur frequently, and the characteristic plains types 
of mammals of the White River are small, scarce, or undevel- 
oped. Furthermore, before the Sierras and Coast Range were 
elevated, the rain now falling on the Pacific Coast must have 
fallen where the Great Basin now is; while we have no known 
adequate cause for so great a change in the climate of the 
plains between the Oligocene: and the present time. The 
Eocene deposits are probably a mixture of lake and fluviatile 
sediment—what proportion of each would not be easy to 
determine. 
