SMITHSONIAN EXPLORATIONS, I93O 



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Fig. 25. — View down stream across Natural Bridge, Arizona. The flat 

 cultivated land is merely a (ill of algal limestones under which a huge natural 

 bridge was subsequently dissolved by the creek. The flower stem of a century 

 plant stands in the immediate foreground. (Photograph by Resser.) 



a fc*»* 



Fig. 26. — One of the excellent new mud volcanoes that developed last 

 spring near the Dragon's Mouth, Yellowstone National Park. (Photograph 

 by Resser.) 



