90 Cretaceous. 



]ine to New Mexico, but on the Lower Missouri, where it was first ob- 

 served by geologists, it never reaches a thickness of more than 150 or 

 2U0 feet. In New Mexico it occurs as tlie most conspicuous of the 

 Cretaceous divisions, and along the line of the Kansas Pacific Railway. 

 in Kansas, it has yielded large quantities of the most remarkable rep- 

 tilian remains. 



The Niobrara Group is found, in some form, whereverthe Cretaceous 

 beds occur, from the north line to New Mexico, and probably much 

 farther. As it is developed on the Lower Missouri, and southward 

 throuo-h 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 

 buildino- purposes; but along the flanks of the mountains, or in the 

 far west^ it never reveals its chalky chai'acter. It is found in thin, 

 slaty, calcareous layers, but universally characterized 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. 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. 



The Fort Pierre G-roup 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 this 

 group. This group covers a vast area of country, perhaps 5,000 

 square miles or more, and wherever it prevails, it gives to the sur- 

 face 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 evap- 

 orates, the surface is covered with a deposit of the salt varying from 

 an inch to several inches in thickness. The water that flows throug'h 

 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, 3'et they are b}^ no means 

 destitute of vegetation. The various species of chenopodiaceous shrubs 

 and herbs, that are peculiar to the west, find their natural habitat in 

 these clays, and grow most luxuriantl}'. The Sarcobatus reaches its 

 highest growth in this region. The somber appearance given to the 

 country by the black clays is unfavorable to it. At the Great Bend 



