THE PLANT. 19 



turned, so the carbonic acid sent into the atmosphere 

 by burning, decay, or respiration, becomes a per- 

 manent stock of constantly changeable material, 

 until it shall be locked up for a time, as in a house 

 which may last for centuries, or in an oak tree 

 which may stand for thousands of years. Still, 

 when these decay, the carbon which they contain 

 mu.-t be again resolved into carbonic acid. 



The coal-beds of Pennsylvania are mines of car- 

 bon once abstracted from the atmosphere by plants. 

 In these coal-beds there are found various fornir- <>t' 

 organized matter. These existed as living things 

 before the great floods, and it is the theory of some 

 geologists that at the breaking away of the barriers 

 of the immense lakes, of which our present lakes 

 were merely the deep holes in their beds, they were 

 washed away and deposited in masses so great as to 

 take fire from their chemical changes. It is by 

 many supposed that this fire acting throughout the 

 entire mass (without the presence of air to suj>j_>1if 

 oxygen except on the surface) caused it to become 

 incited carbon, and to flow around those bodies 

 which still retain their shapes, changing them to 

 coal without destroying their structures. This coal, 

 so long as it retains its present form, is lost to the 

 vegetable kingdom, and each ton that is burned, by 

 being changed into carbonic acid, adds to the ability 

 of the atmosphere to support vegetation. 



Thus we see that, in the provisions of nature, car- 

 bon, the grand basis, on which all organized matter 

 is founded, is never permanent in any of its forms. 



