How the Soil Is Made 63 



Plants also aid in breaking the rock. Often seeds are 

 dropped by the wind, and the rootlets of some of these seeds, 

 when they sprout, may find a crevice large enough and deep 

 enough for them to push their way into the rock. In these 

 crevices they find a little food and slowly grow larger and 

 stronger. By and by some of the roots are strong enough 

 to push apart large pieces of rOck. 



If the rock which we are studying is granite, we shall 

 after a time be able to pick out the different minerals of 

 which it is composed. We can tell the grains of quartz, 

 because they look glassy and remain very hard. Other 

 grains, which we caR feldspar, soften and change into clay,, 

 which makes the water muddy as it runs over the rocks. 

 We see also Uttle scales of yellow mica, sometimes called 

 "fool's gold," and a few grains of iron. There are tiny 

 quantities of other things which we shall not be able to 

 see, for the rainwater dissolves them and carries them 

 away. 



As the rock slowly crumbles to sand and clay, the bac- 

 teria begin to make their home in it. Hardy plants, that 

 are not particular about what they grow in, get a foothoM, 

 and when they die their stems and leaves decay and mix 

 with the rock particles until at last this material begins to 

 look like soil. It has become dark in color and rich in plant 

 food. Then, many other plants that require a good soil 

 take root there. The rock has at last completely disap- 

 peared under the layer of soil and its carpet of vegeta- 

 tion. 



Suppose, now, that we dig down and find how deep the 

 soil is and what lies below it. When we have gone down 

 two feet the soil is harder and of a lighter color, for there are 



