Field-Labourers 63 



cause of their fertility — they have been regularly 

 manured for ages. 



But besides manuring the land during their lives, the 

 animals must have left their bones to enrich it also, 

 whenever they escaped being devoured. Small dead 

 bodies must have been covered up by leaves, or buried, 

 as we shall see, either by the castings thrown up by 

 worms or by the burying beetles, whose office it 

 especially is to act the part of sexton to the smaller 

 wild animals. 



Burrowing animals have also been especially useful 

 in more ways than one. In the iirst place, they have 

 added to the organic matter of the soil, and, in the 

 second, to the mineral matter also ; and besides this 

 they have done much to drain the soil, and expose it 

 to the iniluences of the sun and air. 



The organic matter which they have added, besides 

 their own droppings, consists of the materials which 

 they use to line their nests, principally leaves and 

 grass, and also the remnants of their food, nuts, 

 grain, acorns, and sometimes the whole of their winter 

 stores. 



They have added also to the mineral matter of the 

 soil by helping on the decay of the underlying rocks. 

 These are seldom at any great depth beneath, for the 

 loose materials with which they are covered are but as 

 a film of dust compared with the thickness of the solid 

 mass. The soil at its very thickest is measured only 

 by feet, while the solid crust of the earth is measured, 

 at least, by hundreds of miles ; and in most cases the 

 soil is actually only a few, often a very few, feet 

 thick. 



Burrowing animals often carry their tunnels down 



