342 G. K. GILBERT AND F. P. GULLIVER — TEPEE BUTTES. 



talus profile is produced. The absolute steepness of the slopes is doubt- 

 less a function of the rate of the general degradation of the surrounding 

 surfaces. The height of each butte depends partly on the rate of degra- 

 dation and partly on the cross-section of the core, being greater as the 

 rate is rapid and the core large. 



The buttes are commonly from 25 to 35 feet high, and the largest 

 observed, in an embay ment of the gravel bluff northwest of Nepesta, 

 measures 75 feet. 



COMPARISON WITH BUTTES OF OTHER ORIGIN. 



The term butte is ordinarily applied to steep-sided hills with narrow 

 summits. More rarely it has been employed to designate mountains, as 

 ^' Shasta butte," but this use is probably obsolescent. Taking the word 

 in its narrower sense, we may contrast the tepee butte with neck, dike, 

 cinder, spring and mesa buttes. 



The butte marking the site of a volcanic neck, as, for example, Cabezon 

 butte. New Mexico, resembles the tepee in that it is occasioned by a hard, 

 cylindrical core. It differs in the material of the core. 



The dike butte also has a hard core, but this core has the form of a 

 vertical plate rather than of a cylinder, and hence the butte is elongated. 

 Example : Bird Tail butte, Montana. 



The cinder butte may have a hard core, but does not owe its form 

 thereto. It is essentially a constructional feature, and when freshly 

 formed has a crater at top. Example: Sunset butte, Arizona. 



The spring butte, formed by deposition from the Avater of geysers or 

 other springs, may resemble the tepee core in composition, but is a con- 

 structional rather than a degradational feature. Example : Soda butte, 

 Idaho. 



The mesa butte, being the remnant of a tabular outlier, is carved, like 

 the tepee butte, from a greater mass, but it has a hard cap instead of a 

 hard core, and thus its form is flat topped instead of conical. Example : 

 Haystack butte, Colorado. 



Acknowledgments. 



The investigation of the tepee buttes was incidental to the official work 

 of the United States Geological Survey, and this paper is published by 

 permission of the Director. 



The chemical analyses were made by Dr W. F. Hillebrand, chemist of 

 the United States Geological Surve}^, and the fossil mollusks were de- 

 termined by Mr T. W. Stanton, paleontologist of that bureau. 



We are indebted for laboratory facilities in the preparation and ex- 

 amination of microsections to the courtesy of the geological department 

 of Harvard University. 



