BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 21, pp. 313-338, PLS. 18-2S JULY 2, 1910 



NOETH AMERICAN NATUEAL BEIDGES, WITH A DISCUS- 

 SION OF THEIE OEIGIN^ 



BY HERDMAN F. CLELAND 



(Presented before the Geological Society December 29, 1909) 



CONTENTS 



Page 



Introduction, with definition 314 



A. Natural bridges initiated by stream erosion 314 



1. By the perforation of the neck of an incised meander 314 



a. Rock bridge across Swifts Camp Creek Campton, Kentucky . 315 

 6. South Dalvota bridge 315 



c. Bridge at Attica, Indiana 317 



d. Pont d'Arc, France i 317 



e. Bridges of southeastern Utah 317 



f. Bridges of Le Perle Creek, Wyoming, and Buffalo Gap South 



Dakota 320 



g. Discussion of a former bridge of this type in Oklahoma 320 



2. By pot-hole action * 321 



a. Bridge spanning Kicking Horse River, British Columbia 321 



h. Lamoille River bridge, Vermont 321 



3. Erosion assisted by frost action 322 



a. Yellowstone Natural Bridge 322 



6. Remnants of lava stream roofs not included 323 



4. Travertine-cemented stream deposits undercut by stream erosion.. 323 



a. Bridges in Arcadia and Messina, Greece 323 



ft. Puenta del Incas, South America 323 



5. By the undercutting of a petrified log 323 



6. By the headward cutting of two streams 324 



» 7. By removal of unconsolidated material underlying a resistant 



M^ stratum 324 



^■j a. Switzerland 324 



P^r &. Big Bad Lands of South Dakota 326 



y c. Earth bridges 326 



I B. Bridges initiated by wave action 326 



C. Bridges initiated by solution 327 



1. By seepage 327 



a. The Virginia Natural Bridge 327 



, h. The Oklahoma Natural Bridge 327 



! c. The Massachusetts Natural Bridge 328 



d. Illustrations of bridges formed by the widening of a joint 329 



1 Manuscript received by the Secretary of the Society February 9, 1910. 



XXIII— Bull. Geol. See. Am., Vol. 21, 1909 (313) 



