"Plants are composed chiefly of cellulose and proteins. The former, comprising by far the larger bulk, constitute the framework, whereas the latter are concerned in the vital functions. With these are associated many other substances, among which are chiefly starch, sugars, and fats and oils, constituting reserve foodstuffs; waxes, resin waxes, resins, and higher fats, performing mainly protective functions.... These components differ widely in their resistance to various agencies. Those substances involved in the life function and the support of the plant are relatively very stable under the conditions imposed upon them. "At the death of the plants, governed by conditions imposed in the bog, a partial decomposition, maceration, elimination, and chemical reduction begins, brought about by various agencies, chiefly organic, mainly fungi at first and bacteria later. The most labile are removed first, the more resistant next, and so on, as the conditions require, leaving the most resistant behind in a residue called peat. "The process of decomposition, elimination, and chemical reduction begun in peat, chiefly by biochemical means, is taken up and continued by dynamochemical means into and through the various successive later stages, and results in the various grades of coal, as lignite, sub-bituminous, and cannel coal, and anthracite." The principal chemical elements involved in the changes which take place are carbon, oxygen, and hydrogen, as shown by the following analyses of about average samples of each member of the so-called "coal series." =========================+========+========+==========+========= The "coal series" | Carbon | Oxygen | Hydrogen | Nitrogen -------------------------+--------+--------+----------+--------- Wood (cellulose) | 50 | 43 | 6 | 1 Peat | 59 | 33 | 6 | 2 Lignite | 69 | 25 | 5.5 | 0.8 Bituminous coal | 82 | 13 | 5 | 0.8 Anthracite coal | 95 | 2.5 | 2.5 | trace Graphite | 100 | .. | .. | .. -------------------------+--------+--------+----------+--------- From this table it is seen that the oxygen relatively diminishes while the carbon relatively increases, though, of course, all three elements actually decrease during the chemical change from cellulose to coal. These three elements disappear mainly in the form of gases, such as water vapor, marsh gas, and carbonic acid gas. The final or graphite stage is almost reached by the graphitic anthracite of Rhode Island, which is so nearly pure carbon as to be really useless as coal.