64 Conservation Reader 



fewer plant remains in it. This poorer, lighter-colored soil 

 we call subsoil. If we dig a little deeper, we shall find pieces 

 of rock in the subsoil. Below these we come to soft, crum- 

 bling rock and last of all the solid rock. 



The soil that is found resting on the rocks from which it 

 was formed is known as residual soil. This name is given to 

 such soil, because it is what remains after long years of rock 

 decay during which the rains have washed away a part of 

 the finer material. 



What has become of the soft earth that the water washed 

 away ? The muddy rivulet has already told us its interest- 

 ing story. We have learned that a part of this earth (or 

 soil) is borne to the distant ocean. There it is forever lost 

 unless the sea bottom should some day become dry land. 

 Stranger things than that have happened on this ancient 

 earth of ours. The part of the soil which the water carried 

 away to form the rich valley lands and deltas is known as 

 alluvial soil. 



Long ago the northern, part of our country was covered 





£/. S. Department of Agriculture 

 A flood plaifl^ where alluvial soil has been depoated by the river. 



