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THE POPULAR SCIENCE MONTHLY 



and the travertine strong enough to arch over the creek and buttress 

 itself on the opposite bank, thus forming a natural bridge. The 

 deposition does not seem to be going on as actively now as formerly, but 

 in one place the lime is being deposited so rapidly that hats, shoes and 

 other objects left in the spray are coated over with a thick layer of lime 

 in a few months. Underneath the bridge are caves of considerable size 

 adorned with stalactites and stalagmites. 



The greatest natural bridges of the United States, and of the world, 

 are found in southeastern Utah. These were formed in a manner so 

 simple that the explanation may, at first, seem inadequate. The streams 

 which they now span have great bends and formerly had greater ones. 

 As they deepened their beds they kept cutting away on the inside of 

 these curves. In some cases the streams probably cut through the necks 

 of these meanders without the formation of bridges, but in four in- 

 stances the stream perforated the neck of the bend, forming natural 

 bridges. These Utah natural bridges are enormous, varying in height 

 from 108 to 308 feet, and in length of span from 186 to 275 feet. The 

 bridges are made of red sandstone and occur in a high plateau in which 

 the streams have cut canyons hundreds of feet deep. 



An interesting bridge of a similar origin spans Swifts Camp Creek 

 (Figs. 9 and 10) in the mountains of eastern Kentucky. Although the 

 top of the bridge is but 15 or 20 feet above the surface of the stream 

 and the length of the span is only 50 feet, yet it illustrates as well as 

 the great Utah natural bridges the manner in which the stream has 

 worked to accomplish this result. The greatest natural bridge in Europe, 

 the Pont D'Arc across the Ardeche has a similar origin, as can readily 



Fig. 12. A Natural Bridge below Creelsboro. Russel Couxty, Kentucky, 



formed as shown in Fig. 11. 



