THE EARTH'S CLOTHING. 9 



the rocky floor of the continents from sight, and upon 

 it we live ; and from it come plants, each having a value 

 and beauty of its own after its kind. This skin, or mask, 

 that hides the rocks that cover all the planet is, com- 

 pared with the whole thickness of the earth, infinitely 

 thin. It is at best only a few feet deep, often only a 

 few inches deep. It is as if we % had placed a blanket 

 of the thinnest cloth over the back of the largest ele- 

 phant we could find. The rocky crust of the earth, 

 from the top of the highest mountain to the bottom 

 of the deepest mine, compared with the thickness of 

 the earth from the surface to the centre, is as one is to 

 four hundred. If the crust we are able to measure is 

 only 4 Ju of the thickness to the centre, how thin is the 

 soil compared with the mass of the earth? However, 

 we are ourselves but specks and mites compared with 

 the whole mass of the globe, so we need not trouble 

 ourselves concerning the comparative thinness of the 

 skin of our planet-home. We wish now to study the 

 many-colored coat of the world, and to do this we 

 must begin with the rocks. We wish to study the soil, 

 because from it come plants, fruits, clothing, foods, 

 flowers, and wealth ; and the soil is the child of the 

 rocks. 



in. SURFACE INDICATIONS. The miner pros- 

 pecting through the country in search of valuable 

 metals is guided in part by what he calls the " surface 

 indications." If the water in the brooks is deep red, 

 there may be iron in the hills. If bits of worn and 

 weathered coal lie half hid in the grass at the foot of 



