Page:The Journal of geology (IA journalofgeology21894univers).pdf/102

stream in Florida, hardly incised in the low coastal plain, illustrates the faint relief permitted in surfaces that stand but little above their baselevel. The Colorado, in its canyon, is another example of an early stage of development, but it possesses an extreme intensity of relief because of the great altitude of its plateau; not an old valley, but a precocious young valley; not a vast work, except in our inappropriate human measures, but the good beginning of a vast work. The Elbe above Dresden offers illustration of a later stage than the three preceding; it has the beginnings of a flood plain, now on one side, now on the other side of the river; from which it is inferred that the deepening of the valley has practically ceased, that the river is graded, and that the slower process of valley widening is now the determining cause of topographic change.

View in the Jura mountains would serve as examples of adolescent forms, combining an interesting measure of consequent and subsequent features; but I have not yet succeeded in finding any satisfactory photographs of this region. Features of maturity, more or less advanced, are found in the retreating escarpments of the middle Ohio valley^[1] or of the central denuded region of Texas; and again in the minutely carved ranges of the central Alps. For yet older stages, it is difficult to find examples still in the cycle in which their old age was reached; but the plain of the middle Wisconsin river and the plateau of the middle Rhine are ideally satisfactory illustrations of baseleveled surfaces, one being an old plateau, and the other an old mountain region; although both have lately been brought into a new cycle by elevation, allowing their rivers to cut narrow trenches beneath their even surfaces. By selecting views in which only the plain surface is seen, these examples make appropriate closing members of the series here described. At a later time, when the complications of the cycle are in discussion, other views showing the dells of Wisconsin and the gorge of the Rhine may be presented, thus giving a new meaning to old examples.