There are few topographical features that excite greater interest than natural bridges. This is due, no doubt, to some extent to their rarity and to some extent to the questions which arise as to the force or forces which have been at work to produce such structures. Although rare, the total number on the North American continent is quite large. In this paper, which does not include a description of all the natural bridges of North America, thirty-eight are mentioned.
The terms “natural bridge” and “natural arch” have been so often used as synonyms, both in common parlance and in scientific literature, that it will be necessary to define the terms. In the restricted sense in which the term “natural bridge” is used in this paper, a natural bridge is a natural stone arch that spans a valley of erosion. A natural arch is a similar structure . . .