514 NATURE STUDY. 



even rock a little. Show how muriatic acid (obtained from 

 drug-store) placed in the water helps it dissolve such rocks 

 as mortar, limestone, and marble. Most water in the ground 

 contains a little acid. Many rocks, such as mortar, sand- 

 stone, and granite, consist of insoluble grains held together 

 by parts which are soluble. When the latter dissolves, 

 the other portions fall apart and make soil. 



If the school is near a large body of water, with a 

 pebbly beach, the children can easily see how the stones 

 are rolled back and forth, and gradually worn into soil, by 

 the waves. 



THE DECAY OF LEAVES TO MAKE SOIL. 



Evidences. This can be best seen after there have been 

 some weeks of spring weather. Collect, or better, have 

 the children collect, and bring to school, leaves or leaf 

 mould in different stages of disintegration. Note their 

 dampness, and the earthworms usually abundant among 

 them. Collect also some leaves from dry places, which 

 have not disintegrated. 



Recall the story as studied last fall of the work of the 

 leaves for the trees during the summer, of their coloring 

 in the autumn to make the world beautiful, of their falling 

 to cover the seeds and buds (and the baby earthworms) 

 through the winter's cold. Now they have another work, 

 to make food, the very best food, for the plants' roots. 

 They are changing into something which will be drawn in 

 by the roots, travel up to the buds, and help to make new 

 leaves and flowers and seeds. 



Causes. Compare the wet and dry leaves. Compare 

 the decayed leaves with those collected and pressed last 

 fall. Surely water had much to do in turning the leaves 

 into food for the plants. The earthworms helped by chew- 

 ing them, and breaking them into pieces. 



