21 



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 constituent 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 conjoined 

 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 black- 

 ened. The phenomenon 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, are splintered or 

 flaked in a remarkable manner. The jaspers especially are often broken in 

 such a way that they appear as spawls from rude implements of art, or even 

 resemble the latter. Some of them are certainly the work of primitive man, 

 but the vast proportion, often scattered over miles of surface, are probably 

 accidental forms. These I suppose to have been produced by stones striking 

 one another in the descent from declivities as they have been carried down, 

 perhaps by glacial movement. The softer rocks of the buttes, those which 

 are too soft for stone works of art, are also observed broken in the same way 

 as the hard ones. In experimenting on some large splintered slabs of jasper 

 from the buttes of Dry Creek Canon, I found that a quick blow of a hammer 

 would send off, with a ringing sound, a long sharp flake, reminding me of the 

 primitive knives or scrapers of the stone age of man. 



Between the well-finished implement and the accidental spawl every gra- 

 dation of form may be observed among the scattered stones of the plains and 



* Perhaps much of this soluble silica may have been supplied by hot springs still so 

 frequent in Wyoming and other Western Territories. Cold springs, slightly alkaline, 

 may have also contributed to the petrifying silica. In Pioneer Hollow, fifteen miles 

 west of Fort Bridger, I observed a dozen springs within the distance of a mile, the 

 water of which reminded me of the congress -water of Saratoga, New York. It is cool 

 and clear, highly carbonated, slightly alkaline, and agreeable to the taste. The springs 

 are circular, from 1 to 15 feet across, and are surrounded with dome-like craters from 

 1 to 3 feet high. The craters are formed of a siliceous sinter, which has been slowly 

 deposited from the spring-water, and is probably the accumulation of ages. The sinter 

 is brown from the presence of iron, though the water has no perceptibly ferruginous 

 appearance or tasto. 



