58 GEOLOGICAL SUEVEY OF THE TERRITOKIES. 



covers a large region, at least 100,000 square miles, and from isolated , 

 patches on both sides of the Missouri Eiver, I would infer that this 

 great fresh-water lake must have spread over 150,000 square miles. It 

 is this latter formation which covers the greater portion of Western 

 Nebraska. The colors on the geological map will show the area. The 

 Cretaceous beds occur along the Niobrara for eighty to one hundred 

 miles above its mouth ; then the loose sandy and marl beds of the Ter- 

 tiary basin overlap them. From thence to the source of the Niobrara, 

 about three hundred miles, the river runs through the Tertiary deposits 

 only. 



This stream forms the northern boundary of the State. All of Ne- 

 braska west of longitude 101° is occupied by the sands and clays of the 

 fourth basin. 



The " Bad Lands of White Eiver" are so called because, being com- 

 posed of indurated sands, clays, and marl, they have been so cut up 

 into ravines and canons by streams, rains, and other atmospheric agen- 

 cies, as to leave cones, peaks, isolated columns, and towers, presenting 

 the appearance in the distance of a gigantic city in ruins. 



It is so exceedingly rugged and difficult of access that it is only within 

 a few years that any route but the Laramie road, which runs through 

 the middle of them, was considered passable. Of late years it has been 

 shown by various expeditions, both public and private, that any portion 

 of the great West can be traversed with teams, if necessary. 



The Cretaceous beds of the Fort Pierre group extend along White 

 Eiver from its entrance into the Missouri, except about fifty miles near 

 the forks, where the White Eiver Tertiary overlaps them. 



Even now some isolated patches of Tertiary are seen, as Medicine and 

 Bijoux Hills. 



From the forks or the junction of Little White Eiver with the larger 

 streams the Tertiary beds occupy the whole country to its source. All 

 the intervening country between White and Niobrara Elvers is covered 

 with the sands, clays, and marl of the White Eiver deposits, but along 

 portions of the Niobrara and south of that river the lower sands of the 

 Loup Eiver deposits make their appearance. Here we find a singular 

 region of country called the " Sand Hills," which occupy an area of 

 about twenty thousand square miles. These hills lie mostly betweea 

 the Niobrara and the Platte, though a portion of them extend north- 

 ward of that river. 



On the south side of the Niobrara the Sand Hills commence atEapid 

 Eiver and extend westward about 100 miles. Along Loup Fork they 

 commence near the forks or the junction of Calamus branch with Loup 

 Fork. 



The whole surface is dotted over with conical hills of moving sand. 

 These hills often look like craters or small basins, the wind whirling 

 and, as it were, scooping out the sand, leaving innumerable depressions 

 with a well-defined circular rim. There is a great deal of vegetation 

 scattered through this portion, grass and plants peculiar to sandy dis- 

 tricts. 



Many of the hills are so covered with a species of yucca that their 

 sides are well protected from the winds by their roots. It is the favorite 

 range for buffalo and antelope, and these animals become very fat, 

 and from this fact we may infer that this district may be adapted for 

 grazing purposes. It can never be used for jjurely agricultural pur- 

 poses. 



Traveling is also very difficult among these hills ; the wheels sink 

 deep into the loose sand, rendering it impossible to transport loaded 



