NATURE AND ORIGIN OF THE SOIL. 9 



outer surface is softer than the interior. In other places the rock 

 is just under the surface. In some places we have to go very deep 

 to find the rock, but it is always there to be found if w r e only go 

 deep enough. All of our sand and clay have come from these old 

 rocks, sand from one kind of rock, white clay from another kind of 

 rock, blue clay from another. The nature of the soil will therefore 

 depend largely upon the nature of the rock from which it came. 

 This sand or clay may have come from the breaking up of the 

 rocks that are found just under the soil; in that case the soil is 

 likely to be shallow. But usually it has come from rocks at a dis- 

 tance, a long distance it may be, and has been carried to its pre- 

 sent place by water and ice, and spread out over the old rocks. 



Figure i. 



Soil formed from a rock at a distance. <i is solid rock cf a hill or mountain. Rock at f 

 has been broken off by rain and frost and thrown down to foot of hill. Finest soil is being 

 Washed into stream to be carried away to build farms elsewhere. 



In this latter case the soil may be very deep and mixed, we can 

 now explain why the soil in some places is quite different in its na- 

 ture from the rocks under it, and why there is such a variety in the 

 the same locality and on the same farm. One field may be clayey, 

 and across a stream we may find a sandy soil. They have come 

 from different places, and have been washed down by the water and 

 spread out at different times. 



A step farther back can now be taken. We go to the hills, to 



