96 NATURE TEACHING. 



CHAPTER V. THE SOIL. 



1. If we dig a hole in the ground we 

 usually notice certain changes in the appear- 

 ance of the earth which we remove as we go 

 deeper and deeper. That near the surface is 

 often dark in colour and loose or friable, below 

 this we come in succession upon material of a 

 lighter colour, then probably a rather compact 

 layer with stones,and finally hard rock. If we 

 look at a place where a deep trench has been 

 dug or where a heavy rush of water has cut 

 away the soil we see that there is a gradual 

 change in appearance from the upper to the 

 lower layers. The stones of the lower layers 

 are probably of a similar material to the rock 

 at the bottom, similarly the small stones and 

 even the finest particles which can be picked 

 out are recognisable as . fragments of the rock 

 which lies beneath. In other words we see 

 that soil largely consists of rock broken up 

 into small particles. 



2. This breaking up results from the 

 action of various agencies, but is very largely 

 due to water, containing carbon dioxide in 

 solution which dissolves carbonate of lime 

 (chalk) and which also attacks the mineral 



