THE SOIL, HOW MADE, AND FROM WHAT 21 



the one hand, and on the other, the fine-grained valley 

 or "alluvial" soils, prized for their fertility all over the 

 world. 



Break up a piece of clay or very soft rock ; limestone 

 will do. Put the pieces in a bottle of water, cork it, 

 and then shake it hard for some time. Notice how the 

 sharp edges become rounded. This is what happens to 

 pieces of rock when ground together by running water. 



FIG. 12. Valley and stream. 



Figure 12 shows a stream and valley. If we had to build 

 a railroad straight across this valley, we should have to cut 

 through the hills, and we could then see what sort of soil 

 there is in them. Figure 12 a shows a cut of this sort made 

 deep enough to show the soil in the valley as well as in the 

 hills. The little mark right under the words " flood plains '" 

 stands for the river. On each side of it (under the word 

 " bench ") is fine soil brought by the river for a long distance 



