22 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



red beds, between the La Bonte and La Prele, are some layers of fine white 

 amorphous gypsum. About ten miles from La Bonte we cross Spring 

 Creek, a small stream without wood, where travelers sometimes halt 

 for lunch or rest. The most conspicuous feature here is the bluff 

 wall of tertiary, which extends up westward so as to form the high hills 

 on the north side of the valley. The waters have worn deep into the 

 cream-colored marls, so that we have over a restricted area miniature 

 "bad lands." The dome-like hills and the numberless furrows down the 

 sides, the harder layers projecting out like verandahs, are well shown. 

 Three miles before reaching Fort Fetterman, the lignite beds make their 

 appearance from beneath the more modern deposits, exhibiting their 

 peculiar lithological characters in a marked degree. The strata dip 20° 

 northeast, and where seen in apposition, the White Biver tertiaries do 

 not conform. Seams of lignite and great quantities of brown iron ore 

 occur here. Some of the iron ore is quite rich, but most of it is very 

 lean. The prevailing constituent in all the rocks, sands, sandstones, 

 clays, &c, is iron, presenting every shade of color that can be derived 

 from that mineral, the yellow iron-rust color predominating. There are, 

 however, some layers of quartzite or coarse sandstone, which is very 

 compact and nearly black, and some of it contains a fair percentage of 

 iron. As soon as we come to these beds, the entire surface of the country 

 presents a somber hue, more rugged and less fertile ; due probably to the 

 greatly diminished amount of calcareous matter. Much of the country 

 has a burnt appearance, due, probably, to the oxidation of the iron. Fort 

 Fetterman is pleasantly located on a bench-like point between the La 

 Prele and the North Platte, near their junction. It commands a fine 

 view of the country in every direction, but more especially up the Platte 

 Valley, which can be seen for ten miles or more, with its sinuosities and 

 its pretty fringe of fresh green foliage. All the underlying rocks on 

 both sides of the Platte, as well as the La Prele, for several miles around, 

 belong to the eocene or lignite tertiary period. The soil everywhere 

 seems to be productive. Several of the officers at Fort Fetterman have 

 made experiments in raising vegetables in a small way with success. 

 It is the opinion of Colonel Chambers, the commander of the post, that 

 with suitable irrigation, all the more important crops can be raised with 

 ease. 



On the morning of the 17th we made a short side trip from the fort 

 up the valley, to the canon of the La Prele. Lieutenant O'Brien and 

 Captain Wells accompanied us to point out the location of a remarkable 

 natural bridge, which was said to rival the famous one in Virginia, with 

 which every school-boy is familiar. We found it even more wonderful 

 than we had anticipated, and it is a matter of surprise that so great 

 a natural curiosity should have failed to attract the attention it de- 

 serves. The canon is about ten miles from the fort, and is formed 

 by the passage of La Prele Creek through a long ridge that extends 

 from the La Bonte to Bed Buttes. The canon is one of upheaval and 

 erosion. The ridge is a long, local anticlinal or "puff," and the strata 

 incline from each side of the summit. The gorge is very irregular and 

 tortuous, filled with huge masses of rock that have fallen down, obstruct- 

 ing the passage. Where the stream has cut through the rocks direct 

 we have vertical walls on each side and a narrow gorge ; but where 

 the channel passes along a rift the valley expands out several hun- 

 dred feet. Where the La Prele emerges from the canon it cuts 

 through the limestones and red-beds at right angles, forming a regular 

 gorge, with walls fifty to one hundred and fifty feet high. At the head 

 of this gorge the stream has at some time changed its bed, passing 



