CONSTRUCTION OF THE EAKTH. 151 



Then, to make another bed of coal, there was an eleva- 

 tion for another growth, which was in its turn sub- 

 merged, to be covered by a rocky deposit. Where there 

 are many beds of coal there must have been many of 

 these alternate movements. 



234. Pebbles, Sand, and Earth. In several different 

 connections I have remarked upon the ways in which 

 the rocks are worked up into pebbles, sand, and earth. 

 You have seen that, while other agencies are at work, 

 water, either directly or indirectly, is the grand agent 

 directly by its own erosive power, and indirectly by 

 grinding fragments of rock, from the large to the mi- 

 nute, against each other. By these means chiefly has 

 the soil all been prepared ; and it is nothing but commi- 

 nuted rock, with soluble matter from some of the rocks 

 dissolved in the water diffused through it. It is true 

 that when seeds are put into the soil thus prepared ad- 

 ditions are made to it from the decay of vegetable mat- 

 ter, but this is a mere return of such matter to the min- 

 eral condition. All was originally mineral earth, wa- 

 ter, and air ; and in plants and animals we have life act- 

 ing only upon mineral matter, giving it, for the time be- 

 ing, new properties. It is a very important item in the 

 construction of the earth for man that the soil should be 

 thus prepared, by what may, in one sense, be considered 

 a destructive process, but in another the putting the 

 material of which the rocks are composed into a special 

 form for a special purpose. If this were not done, vege- 

 tation and animal life could have flourished, at best, to 

 but a scanty extent. 



235. Earth-worms and Ants. These animals, apparent- 

 ly so insignificant, are real geological workers, accom- 

 plishing in the aggregate great results in preparing the 

 soil to produce food for man and beast. The earth- 

 worm burrows in the earth, loosening it, and leaving his 

 casts here and there. He is not confined to loose soils, 

 but is ever encroaching upon hard spots, especially if 





