INDIAN TRIBES OF THE MISSOURI VALLEY. 367 
part of the remains of vertebrata, which have been described by Prof. Joseph Leidy in the 
Proceedings of the Academy of Natural Sciences, Philadelphia. They all belong to ex- 
tinct species, representing with a good degree of completeness the mammalian Fauna of a 
district. All the remains of Turtles appear to belong to a single species, but the indivi- 
duals are very numerous and of large size, some of which were estimated to weigh from five 
hundred to one thousand pounds. The materials of which the rocks are composed are light- 
colored clay, grits, and marls, more or less indurated, and worn into these fantastic shapes 
by atmospheric agencies. The presence of land and fresh-water shells, and the absence of all 
indications of marine origin, show this region to have been a vast inland lake some time 
during the Miocene Tertiary period. For some distance up the White River Valley from 
its mouth, the country is very fine, and clothed with an excellent growth of vegetation, 
but towards its source for two or three days’ march the sandy desert prevails, and travelling 
is very difficult. Passing across the country to the Niobrara, toward the Platte, the prairie 
assumes its usual character, and travelling is much better; and though much of that region 
is occupied by patches of bad lands and denuded places, still the greater portion is clothed 
with good grass, and has a cheerful appearance. Along the Platte, Loup Fork, and por- 
tions of the Niobrara, are the Sand Hills, a large area of not less than twenty thousand 
square-miles, composed of loose sand, which has been thrown up into hills and ridges fifty 
to two hundred feet in height by the wind. The material is derived from the eroded 
portions of the more recent Tertiary beds in this region, and as the winds are mostly from 
the west and northwest, this loose sand is slowly moving onward toward the east and 
southeast. Though totally unfit for agricultural purposes, this tract of country cannot be 
said to be destitute of vegetation. In the valleys and depressions among the hills are 
many fine spots of grass, and sometimes the hills are covered with varieties of grass 
adapted to so meagre a soil. The soap plant, Yucca angustifolia, grows here very abun- 
dantly, and sending its roots deep into these sandy hills, protects them from being dimi- 
nished by the winds. The sand plum, Prunus pumila, grows very abundantly all through 
the Sand Hills, and supplies an astringent but not unpalatable fruit. On the head of Loup 
Fork, and between that stream and the Niobrara at various localities, are numerous saline 
and fresh-water lakes. ‘The fresh-water lakes contain a great profusion of various species 
of water-plants and their peculiar animal life, while those that are impregnated with 
saline matter present the appearance of desolation, no vegetation growing in their vicinity 
except a few weeds adapted toa saline soil. In former years these Sand Hills were a 
famous resort for the buffalo, and even at this time a few may be found, but they have 
been for the most part driven away by the Indians to other and less frequented parts. 
Among the many objects which come under the observation of the traveller in the 
Dakota country, none are of more interest than the numerous villages of the prairie dog, 
VOL. X11.—47 
