, Description of part of Wyoming Territory. 273 



Uin talis. In many cases tbe drift completely covers the terraces or 

 buttes, descending upon the declivities so as entirely to conceal their 

 structure. Usually, however, it accumulates in the ravines of the 

 declivities, leaving bare the intervening ridges of light-colored clays 

 and sandstones. Many of the buttes are nearly" or quite free of drift 

 material ; some again are strewn with fragments of rocks, consisting of 

 the harder materials from the terraces themselves, and these likewise 

 occur mingled with the drift -pebbles and bowlders from the mountain 

 heights. 



The stone fragments from the buttes consist of harder siliceous and 

 calcareous clays, impure limestones, jasjiers, and less frequently agate 

 and chalcedony. In some instances they consist of singularly black, 

 incrustated and rounded sandstones, somewhat of the character of the 

 septaria. Specimens of these occasionally bear a resemblance to fossil 

 turtles, and when found with the harder crust broken, they look like 

 turtle-shells filled with a sandstone matrix. 



In the buttes in the vicinity of Carter Station, on the Union Pacific 

 Railroad, I observed many large nodular and cylindroid masses of 

 agate. These have a concentric arrangement of layers resembling that 

 of fossil wood, for which they ai'e taken. Many of the masses con- 

 tain a nucleus of amber-colored crystals of calcite. 



Nodules of chalcedony, with dendritic markings, occur in some of the 

 buttes. These, together with the condition of many of the fossils of 

 the buttes, indicate the presence of a considerable proportion of soluble 

 silica in the waters of the ancient lake. In some of the sandstones 

 the fossil shells have had their lime completely replaced by clear 

 chalcedony. 



Occasionally, strata of limestone, mostly impure, from the admixture 

 of clay and sand, are found in some of the buttes. A frequent con- 

 stituent also is fibrous arragonite, or satin spar, in thin seams. Many 

 of the bare mounds of clay among the buttes are thickly strewn with 

 fragments of this arragonite. 



The stones imbedded in the surface of the plains and buttes, in some 

 positions favorable for the purpose, are highly polished from the con- 

 joined action of the wind and sand, and when seen in the slanting 

 light of the early morning or evening sun, appear like myriads of 

 scattered mirrors. In many positions the stones, no matter what may 

 be their composition, are all blackened. The phenomena I could not 

 explain. 



In many places the stone fragments from the declivities of the 

 terraces, strewn over the lower buttes, or distributed over the plains, aiT 

 splintered or flaked in a remarkable manner. The jaspers, especially. 



