SOME SMALL NATURAL BRIDGES IN EASTERN 
WYOMING? 
V. H. BARNETT 
Natural bridges have been described at length by Mr. Herdman 
F. Cleland? in a paper read before the Geological Society of America, 
December 29, 1909, and less extensively from time to time by 
Walcott, Cummings, Pogue, and others. 
Small bridges observed by D. E. Winchester and the writer, in 
Weston and Converse counties, Wyoming, seem to justify a brief 
description, as they belong to a little different class from any 
discussed by these writers. Of the different types enumerated the 
bridges in Wyoming more nearly resemble the one formed by a 
petrified log spanning a ravine in the petrified forest of Arizona, 
described by Mr. Cleland,‘ but differ from it in that they owe their 
existence to indurated masses or concretions instead of to a petrified 
log as in the case cited by Mr. Cleland. 
The beds of the Fort Union and Lance formations of this 
district (eastern Wyoming) contain a predominance of soft sand- 
stone and sandy shale. Almost everywhere in the sandstone are 
inclusions of concretions and indurated masses. They present a 
great variety of forms. Some are nearly perfect spheres from the 
size of a marble to eighteen or twenty inches in diameter; others 
are more irregular and vary from the shape of a log to very irregu- 
lar masses sometimes several hundred feet in length. These larger 
t Published by permission of the Director.of the U.S. Geological Survey. 
2 Cleland, H. F., Bull. Geol. Soc. Am., XXI (1910), pp. 313-38, pls. 18-38. 
3 Charles D. Walcott, ‘‘The Natural Bridge of Virginia,’ Nat. Geog. Mag., V 
(1893), pp. 59-62; Herdman F. Cleland, “‘The Formation of Natural Bridges,” Am. 
Jour. Sci., 4th ser., XX (1905), pp. 119-24, 3 figs.; V. H. Barnett, ‘‘A Natural Bridge 
Due to Stream-Meandering,”’ Jour. Geol., XV (1908), pp. 73-75, 2 figs.; Byron, Cum- 
mings, ‘‘The Great Natural Bridges of Utah,” Nat. Geog. Mag., XXI (1910), pp. 157-67 : 
Joseph E. Pogue, ‘‘The Great Rainbow Natural Bridge of Southern Utah,” Jdid., 
XXII (1911), pp. 1048-56, 6 figs. 
4 Loc. cit. 
438 
