V ON THE FORMATION OF COAL 161 



She is paid back principal and interest at the 

 same time ; and she straightway invests the car- 

 bonic acid, the water, and the ammonia in new 

 forms of life, feeding with them the plants that 

 now live. Thrifty Nature ! Surely no prodigal, 

 but most notable of housekeepers ! 



197 



