A NATURAL BRIDGE DUE TO STREAM MEANDERING 



V. H. BARNETT 



Natural bridges were originally referred to the agency of caverns, 

 as explained in Scott's Geology"- and most of the less recent works. 

 Scott gives the Natural Bridge of Virginia as an example of this 

 method of formation, and it was not until 1893, when Walcott^ des- 

 cribed the bridge, that it was considered as having been formed in 

 another way. Cleland^ has reviewed several methods of origin in 

 an article in the American Journal of Science, but so far as the writer 

 knows none have ever been described as being due to stream 

 meandering. 



The bridge here described is located south of the White River 

 below the mouth of Porcupine Creek, in South Dakota, and was 

 visited by the writer in 1905, while working as field assistant to Pro- 

 fessor E. S. Riggs, of the Field Columbian Museum. It is formed 

 of White River beds. The opening of the archway is about 12 feet 

 high by 8 feet wide, and the thickness of the arch is something like 

 10 feet in a vertical direction by 7 feet in a horizontal. The left 

 side of the picture (Fig. i) is the canyon wall, while on the right a 

 pillar supports one end of the arch. The stream which formed this 

 natural bridge once flowed on the outer side of the pillar, but making 

 a sharp bend, it flowed just in front of the pillar to a point immediately 

 under the near edge of the arch, where it turned and flowed along the 

 foot of the wall toward the front of the picture. The position of this 

 bridge is such that it was very difficult to photograph it so as to show 

 its true relation to the stream. Between the foreground on the right, 

 covered with weeds, and the pillar, one side of which only is shown, 

 is the old channel of the stream. The gorge is about 30 feet deep, 



1 W. B. Scott, An Introduction to Geology, pp. 90, 91. 



2 National Geographical Magazine, Vol. V, 1893, p. 59. 



3 American Journal 0} Science, 4th ser., Vol. XX, 1905, pp. 119-24; 3 figs. 



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