the force of chemical action in six and a half million years. We can not, however, give a time equivalent for the destruction of a mountain range, since decay, and consequent disintegration, is only one of the many forces acting to sap the strength of solid rocks and to tear them asunder. The above figures are given merely to make plain that the time necessary to accomplish the leveling of a mountain chain is but a small part of the earth's existence as such, great as this period may seem from the standpoint of human history.
We shall, if possible, time the second excursion immediately after a heavy rain, and we shall select for our objective point a place
Fig. 3.—Temporary Wet-weather Delta.
where the rain water, in its efforts to reach a stream, is forced to run down some steep declivity. Under such circumstances, the carrying power of the water will be very great, and we shall hope to find evidence of its work in transporting the products of rock weathering and other material broken up by the action of frost. A little diligence will soon reward us with the evidence which we seek. A local inequality of the ground, perhaps only a few feet across, is found filled with water—a minute, temporary lake caused by the recent heavy rainfall. Such little water bodies are extremely common, but the accompanying geological phenomena are, notwithstanding, none the less interesting, and the conclusions to be drawn from the evidence thus presented are none the less valuable.
