GEOLOGICAL SURVEY OF THE TERRITORIES. 91 



line to New Mexico, and probably much farther. As it is developed on 

 the Lower Missouri, and southward through Nebraska, Kansas, into 

 Texas and the Indian Territory, it contains thick, massive beds of 

 chalky limestone. On the Kansas Pacific Railway, at Forts Hays and 

 Wallace, this limestone is sawed into blocks of any desirable size with 

 a common saw, and used for building purposes ; but along the flanks of 

 the mountains, or in the far West, it never reveals its chalky character. 

 It is found in thin, slaty, calcareous layers, but universally character- 

 ized by the presence of the oyster, Ostrea congesta, and also some 

 form of Inoceramus, or a few fish remains, but the little oyster is 

 ubiquitous. We have spoken briefly of the lower series of cretaceous 

 rocks, as shown in the section. In these three divisions there seems to 

 be no well-marked line of separation, and the more we study them the 

 more intimately do they seem to be blended together. We shall here- 

 after refer to the seams of coal that have been found in the Dakota 

 Group ; and we will state just here that one local bed of carbonaceous 

 clay, which was used to some extent as fuel, was found in No. 2, on the 

 Nebraska side of the Missouri, about thirty miles above Sioux City. 

 In no other portion of the West have we ever seen anything that ap- 

 proached coal in this group. 



The Fort Pierre Group begins to overlap the Niobrara Group below 

 the mouth of the Niobrara, and above that point, although the river cuts 

 deep down into the chalk limestone, and long lines of cone-like bluffs 

 extend up nearly to the Great Bend, yet the distant hills on either side of 

 the river show plainly the dark, shaly clays of No. 4. This formation cov- 

 ers a vast area of country, perhaps fifty thousand square miles or more, 

 and wherever it prevails it gives to the surface the aspect of desolation. 

 The entire thickness of the group is filled with the alkaline material 

 which is so well known in the West, and wherever the water accumulates 

 in little depressions and evaporates the surface is covered with a deposit 

 of the salt varying from an inch to several inches in thickness. The 

 water that flows through these clays is usually impregnated with these 

 salts and thus rendered unfit for use. Although these clays seem to be 

 so sterile, and in the dry season are typical of extreme aridity, yet they 

 are by no means destitute of vegetation. The various species of clien- 

 opodiaceous shrubs and herbs that are peculiar to the West find their natu- 

 ral habitat in these clays, and grow most luxuriantly. The sarcobatus 

 reaches its highest growth in this region. It is probable, however, that 

 the country underlaid by rocks of this group will prove fertile when 

 it can be irrigated. The somber appearance given to the country by 

 the black clays is unfavorable to it. Nowhere except on the Upper 

 Missouri have I seen this formation so well defined or so fruitful in or- 

 ganic remains. The two zones mentioned in the section may be said to 

 exist geographically as well as geologically. At the Great Bend there 

 is a large thickness of the strata filled with concretions that are made 

 up mostly of an aggregate of fossils, as Ammonites, Baculites, &c. Near 

 Chain de Roche Creek these concretions have been swept down into the 

 Missouri by the swift current during the spring floods, and in the low 

 water of autumn they present a picturesque appearance, as is shown in 

 Fig. 3. 



This fossil zone extends across the country in a nearly east and west 

 direction. Passing above this point very few fossils, except here and 

 there a baculite or bones of the Mosasaurus, are found for one hundred 

 and fifty to two hundred miles, when another belt or zone of fossils ex- 

 tends across the country in the same direction. These zones undoubtedly 

 represent certain depths of the waters in the great cretaceous sea, which 



