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ing of the valleys progresses even slower than the slow wasting away of the hill tops; the relief fades; the load offered to the streams lessens. The rainfall slowly decreases as a normal consequence of decrease of altitude; the ratio of river discharge to rainfall decreases; the small headwater branches shorten and dwindle away; the close adjustment of stream to structure is more or less lost, especially by the larger rivers, which meander and wander somewhat freely over the peneplain of denudation. Extreme old age or second childhood is, like first childhood, characterized by imperfect work; activities that were undeveloped in the earlier stage having been lost in the later stage.

All this should be so carefully imagined and so frequently reviewed that the orderly sequence of changes may pass easily before the mind. The mind should come to be in so close a sympathy with the progress of the cycle as to forget human measures of time and catch instead the rhythm of geographical development; even to the point of almost wishing to hurry to one place or another where some change of drainage or of form is imminent, for fear of failing to be in time to see it in its present stage.

Shore lines.—While the subaërial forces are denuding the surface of the land, the waves are beating on the shore and reducing the land mass to a submarine platform. They begin their work on a level line, contouring around the slope of the land mass as it is offered to them. The contour is simple if the sea lies on a rising sea bottom, evenly spread over with sedimentary deposits; the contour is irregular if the sea lies on a depressed land, more or less roughened by previous denudation. The waves of a great ocean work rapidly on a leeward shore, especially if it has a steep slope and if its rocks are not too hard: but if the descent to deeper water is very gradual, the waves may for a time spend their force chiefly on the bottom, building off-shore bars with the material they gather up, and thus deepening the water outside of the bars for a better attack on the land later on. The shore line is generally simplified, as the attack advances, but it may for a time become more irregular if the waves are strong and the land structure is of diverse resistances. Its changes deserve as care-