968 The American Naturalist. [November, 
bones which recall the camels and the alpacas ; forms which are 
intermediate between the rats and the squirrels, and others which 
may be the granddaddies of the horse. Then there were still 
others which fed on these grass-eating species: tigers with enor- 
mous canine teeth, and the still larger Hyznodons with teeth 
which close together like shears. It was a wonderful fauna 
which inhabited Nebraska and Dakota in the ages long past. 
Will the Bad Lands ever be exhausted of fossils? The treas- 
ures of this region and of the larger bad lands of Dakota adorn 
the museums of the east, and every year collectors are at work. 
Of course the specimens which are weathered out can soon be 
picked up, but there are quantities left. In fact, the beds may be 
said to be inexhaustible. Each spring a new crop may be 
expected. What has been the history of the region? How did all 
these animals accumulate here? What makes the land bad? Why 
is it not like disintegrating rock elsewhere? These are some of the 
questions. There are few problems in geology which give their 
“answer in a plainer manner. It is a veritable classic and pony. 
= These regularly stratified beds, layer after layer of marly, 
material, twelve or fifteen hundred feet in thickness, must have 
been deposited on the bottom of an inland sea, while the charac- 
ter of the fossils—for mollusks occur here and there—shows that 
the water must have been fresh. To-day these strata are nearly as 
level as when they were first laid down. The eye cannot detect 
any departure from the horizontal ; and in the Buttes to the north 
can be traced layer for layer the same beds which occur in the 
Buttes to the south. There is, however, a slight dip in the strata 
caused by the upthrust of that strange mountain region, the 
Black Hills, to the north. 
This lake drained the region around, but the geological history 
of all that region known as the plains shows that then, as now, 
the streams largely ran from west to east. Hence the principal 
“affluents of this Miocene lake must have come from the west. 
The climate then was probably different from that to-day, for 
nowhere within two hundred miles is there rainfall sufficient to 
maintain such a lake as this. 
On the shores of this lake and on the banks of the tributary — 
streams lived those animals whith > the fossils of Ba co 



