198 NATURE-STUDY REVIEW [15:5— May, 1919 



blown away, until the bare rock lies exposed. This has led the 

 people of those countries to place their scant supply of soil in 

 narrow terraces, protecting the outer edges with stone walls. In 

 some mountainous regions soil is so scarce that the people build 

 their homes in the rocky dliffs in order to leave every inch of it for 

 crops. In such places spots of soil no larger than a bath-towel are 

 cultivated. 



Soil is no more permanent than the rock from which it comes. 

 It is continually changing. It sometimes even travels far from 

 where it was first produced. Frequently it takes a water- journey, 

 and from the mountain and hillslide slopes it is carried by the 

 streams and rivers down to valley and prairie lands. Much of the 

 soil in the Mississippi Valley has traveled far and arrived by 

 several different routes. The Grand Canyon of the Colorado is an 

 excellent example of the part that water plays in the production of 

 soil. The rushing, plunging, tearing Colorado river has eroded its 

 way down from a high level plateau through the reck for a mile — 

 a mile straight down through the rock! The canyon walls on 

 which it carved its story as the centuries rolled by stand thirteen 

 miles apart at the top. And all that lay between these walls of 

 rock was ground to atoms, mingled with the water, until the river 

 was like liquid mud, and was then carried on toward the Gulf of 

 California. Twenty thousand square miles of soil is carried 

 across two states, finally to become food for water-plants. 



Nature knew right in the beginning that the thing we call force 

 is something that man could not get along without, and she so 

 arranged that he has an unlimited supply. The great storehouse 

 for force isn't in the earth at all but in the sun, and notwithstanding 

 the distance which separates the sun and the earth. Nature has 

 established lines of transportation by which it is conveyed to man. 

 It is the best possible system of transportation, for it is always 

 working. There are two lines, one direct, when the sun's rays 

 come in contact with man, the other indirect, through the mediimi 

 of atoms stored up in plant and animal life, by which man is 

 physically nourished, and also in the various fuels used to supply 

 artificial heat. 



Soil — the food for plant-life — like our own, must be nourishing. 

 Nature understood this long before we did. She probably did not 

 think in terms of calories, but in producing food for plants which 

 would in turn feed man she did turn out a rational, well-balanced 

 and adequate supply of soil-nourishment. There doesn't appear 



