[Footnote 1: Witness the Argentine and Alaska boundary disputes.]
Thus the first sign of a mountain range will be a series of undulations upon the surface of the supposed plain. These undulations will be roughly parallel to one another. We call the direction of their parallelism the strike of the ranges. From the moment the wrinkling movement begins, a set of forces is put in operation tending to level the wrinkles and fill up the hollows or valleys between them. These are the forces of denudation. People often vaguely speak as though mountains were first elevated to their full height and then only began to be pulled down; but of course the process of mountain sculpture is due to the simultaneous operation of the elevating and destructive forces. Every mountain is being pulled down in the very process of its elevation. It grows only because it is elevated faster than the destructive forces avail to level it. For all we yet know, some of the mountain ranges which seem most rapidly disintegrating may, in fact, still be growing. No one has yet divided the mountain ranges of the world into those which have not yet reached and those which have passed their maturity. When that has been done we shall doubtless find some clearly marked difference in aspect between them which now we do not know enough to recognise. The visible difference once discovered, the two groups will raise different kinds of emotion in the man who sees them. He will note the aspect of growth in one set and of decay in the other, and will be correspondingly affected, as we all now are by the young leaves and buds of spring and the fruits and faded foliage of autumn. Sad folk will love the fading and sanguine folk the growing hills. There will arise a new subject for poets and a new group of similes for preachers and moralists. In this way also science enlarges the material of art.
But we must return to our nascent mountain group, as yet a mere series of parallel wrinklings, higher here, lower there, with lines of depression between them. Rain falling will need to drain away, and in doing so will form pools in hollows, and will run along the furrows till it reaches the open country and can turn away. Thus the first streams of a nascent group of mountains follow and do not flow across the strike. Only the rivulets that actually flow down the slopes will flow in a direction perpendicular to the strike, and will be tributaries to the main lines of drainage that flow along the strike.