





The Plant World 



A MONTHLY JOURNAL OF POPULAR BOTANY. 



Vol. n. NOVEMBER, 1898. No. 2. 



IN A COAL SWAMP. 

 By F. H. Know It on. 



THE vegetable origin of coal is no longer a disputed fact; indeed 

 almost all of the steps may be traced between the growing 

 plant and the compact anthracite. It is known that when vege- 

 tation is excluded from the air, as when covered with water, it 

 does not decay and crumble to dust, but gives ofE a portion of the 

 lighter gaseous materials of which it is composed, leaving the carbon 

 behind. In a peat-bog for example, the plants, such as mosses and 

 sedges, may be growing at the surface, while below their stems and 

 leaves have died away and are being compacted into peat. If this 

 process goes on for a long period the weight of the mass becomes 

 very great and the material at the bottom is forced to give off more 

 and more of the volatile substances composing it, leaving the carbon 

 behind in an increasingly pure state. This process goes on step by 

 step until at the end almost all trace of plant structure is lost and we 

 have the hard, brittle anthracite. 



The largest and most important deposits of coal were laid down 

 during what is known geologically as the Carboniferous age, or age of 

 ferns. This age is the middle one of the seven principal divisions 

 into which the geological history of the world is divided. The con- 

 ditions at that time were very different from any now existing. The 

 North American continent as we know it was not half completed and 

 the Appalachain and Rocky mountains were probably only long, nar- 

 row islands in the midst of a great sea The land area within which 

 coal was deposited consisted of broad, low swamps filled with shallow, 

 stagnant or slow-moving salt or brackish water. In these swamps 

 grew probably the most luxuriant vegetation the world has seen, a 

 luxuriance permitted by the superabundance of carbonic acid in the 

 atmosphere and by a moist, warm climate. Some idea of this wealth 

 of vegetation may be gained when it is known that more than a thou- 



