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POPULAR SCIENCE MONTHLY. 



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 moun- 

 tain 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 carry- 

 ing power of the water will be very great, and we shall hope to find 

 evidence of its work in transporting the products of rock weather- 

 ing 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 com- 

 mon, but the accompanying geological phenomena are, notwithstand- 

 ing, none the less interesting, and the conclusions to be drawn from 

 the evidence thus presented are none the less valuable. 



