204 FORMATION OF COAL. 



and strata associated with coal seams. Trees were also washed 

 down, and deposited where we now find them j so that in our 

 large rivers of to-day we are able to see a repetition of what took 

 place during the great coal forming era. Each flood of the 

 Mississippi deposits a layer of mud over the vegetation growing 

 in the submerged swamps, which, in time to come, will be a thin 

 layer of black organic matter, or if in sufficient mass, a bed of 

 coal 5 and the trees washed down by the river will remain as fossils 

 in, and above the coal. 



To return to the decomposition of vegetable matter. The 

 process of decay must have been restricted by submergence, we 

 see the process every day j stir up the stagnant water of a ditch, and 

 bubbles of gas are given off, showing that a chemical change is 

 going on. Vegetable matter is composed of Cellulose, the com- 

 position of which is Carbon 12, Hydrogen 20, Oxygen 10 ; and 

 when decomposition takes place certain gases are evolved, the 

 principal of which are Carbonic acid CO2, (the black damp of the 

 miner) ; Carbonic Oxide, CO, which we frequently see burning 

 with a blue flame in fire-places 3 and Marsh Gas, CH4, better 

 known as light Carburetted Hydrogen ; it has acquired the name 

 of Marsh Gas, from the fact of its being given off from Marshes 

 and beds of peat, sometimes in such volumes that it may be 

 lighted. 



Now imagine these gases to be given off from the submerged 

 vegetable matter, what will be the result ? For every molecule of 

 Marsh Gas given off, only one atom of Carbon will be parted with, 

 to four of Hydrogen, by this means the proportion of Carbon 

 would soon increase, while the proportion of the Hydrogen would 

 decrease, this is just what we have in our table. Much 

 the same thing would take place with regard to Carbonic Acid, 

 one atom of Carbon would be given off to two of Oxygen, 

 decreasing the proportion of the latter, but increasing the former. 

 This process could, however, only go on to a certain extent, viz., 

 as long as the Carbon could find Oxygen or Hydrogen with 



