THE ATMOSPHERE EARTH'S TREASURY. 267 



watery vapour, the ammonia, the carbonic acid 

 take wings, and soar, it may be, to vast ele- 

 vations from the earth, as though they would 

 never more come into active duty on its surface. 

 But in process of time they must return again, 

 and take their allotted place in the operations 

 of the universe. Millions of animals may die, 

 leaving their putrefying carcases to rot in the 

 wilderness, or in the jungle, or in the depths of 

 the caves of the earth ; and it might be thought 

 that all the valuable constructive materials 

 which entered into their composition were ibr 

 ever removed from usefulness. But it is not so. 

 Every wind that sweeps over these remains 

 bear away the volatile portions round about 

 the world. The gentle rain comes down and 

 washes the soluble parts away, supplying a 

 fertilizing fluid to the roots of distant plants. 

 The interchange of ingredients never ceases. 

 Millions of animals feed upon the vegetation 

 nourished by the decay of former myriads. 

 Their time is then completed; their period of 

 utility is ended : they die. The air again 

 receives their elements, and again with con- 

 tinually succeeding generations do these enter 

 into activity in the economy of the "world. 



