Page:Popular Science Monthly Volume 53.djvu/25

Rh 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



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