Page:Popular Science Monthly Volume 53.djvu/25

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Plate I, when the newly formed bay gradually becomes filled with mud or the washes of the land.

Valleys even in mountain regions are almost independent of the undulations of the strata, in that the courses of the streams frequently

PSM V53 D025 Valley at philipsburg st martin.jpg
Plate 1.—Valley at Phillipsburg, St. Martin. Lower portion occupied by shallow salt ponds, beneath which more than thirty feet of mud have already been deposited. Beach in front of ponds formed by wave action.

occupy the crests of folds, while the geological troughs are represented by features in bold relief, as is illustrated in Fig. 3. It is easily shown that valleys, even among mountains, whether parallel