208 The American Naturalist. [March, 
out of the overlying beds, by the slow process of denudation, 
presents a remarkable, not to say, sepulchral appearance. 
Toward the interior of the Bad Lands, midway between the 
White and Cheyenne rivers, side branches of the main can- 
yons have cut their way entirely through the dividing ridges 
and have produced particularly picturesque effects. Charac- 
teristic among these are the Devil’s Tower, at the south end of 
Sheep Mountain, in the eastern portion of the Bad Lands; 
Chimney Rock, near their center, and the Tabled Rocks along 
_ their western border. 
The location of such especially characteristic Bad Land 
scenery, in this particular region, is doubtless due to the near 
approach of the White and Cheyenne rivers to each other at 
this place. Since the Miocene deposits of this region are 
essentially horizontal, and form the summit of the divide 
between these two streams; this divide would be of essentially 
the same altitude, in reference to the beds of these streams, 
whether the latter were near together or far removed from each 
other. Therefore these streams upon approaching nearer to 
each other, as they do in this region, where they are only 
about 20 miles apart, would greatly reduce the length of their 
respective, intervening tributaries, without decreasing the 
height of the divide which separates them. This would nec- 
essarily increase the average rate of fall of the tributaries, and 
correspondingly the rapidity of the flow of their waters, 
therefore the erosive power of the latter. , 
In various portions of the Titanotherium beds there are 
numerous vertical veins of chaleedony running through the : 
beds in every direction. These veins vary in thickness from ri 
that of a sheet of paper to about two inches. On first thought 
the writer was inclined to attribute their origin to mud cracks, 
any particular region where they now occur having been wr : 
short periods, during seasons of low water, above the water 
level and subjected to the action of the atmosphere and the 
heat of the sun became baked and cracked ; just as we now 80 
