Page:Popular Science Monthly Volume 78.djvu/427



LTHOUGH there are more than fifty natural bridges of considerable size in North America, comparatively few persons have ever seen one, the reason being that, with the exception of the Virginia bridge and the natural bridge in North Adams, Mass., most of them are more or less inaccessible.

A bridge, according to the usual definition, is a structure that permits one to pass from one side of a depression to another, whether that depression be a railroad cut, a street or a river. As used in this article a natural bridge is a natural stone arch that spans a valley made by running water; a natural arch being a structure that does not span a valley of erosion.

Although a number of descriptive articles on natural bridges have