228 PHYSIOGRAPHY. [chap. 



even the lime salts by which they are hardened are dis- 

 solved away ; and the-solid animal fabric returns to swell the 

 sum of the fluids and gases from which, through the plant, 

 it has been derived. But, under like conditions to those 

 which have been mentioned in the case of the plant, the 

 bones may be covered up and projected from further decay, 

 or may become infiltrated with calcareous or siliceous matters ; 

 and thus, as a " fossil bird," a pigeon may form an integral 

 part of the solid crust of the earth. 



It will be apparent that pigeons and peas, or more broadly, 

 the animal and the plant, respectively represent, in the world 

 of life, the destructive and the reparative powers of the not- 

 living world — the forces of denudation and of upheaval. 

 The animal destroys living matter and the products of its 

 activity, and gives back to the earth the elements of which 

 such matter is composed, in the form of carbonic acid, am- 

 moniacal and mineral salts. The plant, on the contrary, 

 builds up living matter, and raises the lifeless into the world 

 of life. There is a continual circulation of the matter of the 

 surface of the globe from lifelessness to life, and from life 

 back again to lifelessness. 



If pigeons and peas were the only forms of life, the 

 balance of solid and fluid constituents of the globe would 

 hardly be affected by their existence. Every pigeon and 

 every pea, as has been seen, represents a certain amount 

 of liquid and gas transmuted into the solid form; but, under 

 ordinary circumstances, the sohds thus withdrawn, return to 

 the fluid and gaseous states within a short time after the 

 death of the body which they constitute. It is hardly con- 

 ceivable that, under any circumstances, fossil pigeons or 

 fossil peas should make a sensible addition to what may, 

 at any rate in a relative sense, be termed the permanent 

 crust of the earth. 



