little or nought behind. But if the air be excluded, the oxi- 

 dation is very partial, and the other ingredients of the vege- 

 table matter — carbon and hydrogen mainly — unite with each 

 other and with the oxygen present in the vegetable matter it- 

 self to form a great variety of compounds, gaseous, liquid, and 

 solid. There is however in all organic matter an excess of car- 

 bon as compared with the oxygen and hydrogen; and as the 

 slow process goes on, the gaseous and liquid products gradually 

 escape, and a residue is left that becomes progressively richer 

 in carbon until finally only pure carbon remains. 



The exclusion of the air, and hence of its oxygen, may be 

 caused in various ways, by covering up the vegetable matter, 

 either by water or by a deposit of earth, clay, or sand. The 

 latter is the process artificially employed in the manufac- 

 ture of charcoal, wherein all the gaseous elements present in the 

 wood are eliminated in combination with part of the carbon, 

 the rest of which remains in a nearly pure state as charcoal, but 

 retaining perfectly the form and texture of the wood In al- 

 most the same way. though on a gigantic scale and through 

 long ages of time, have the hardest coals been formed from veg- 

 etable deposits. The covering by water, however, permits us 

 to observe the natural process as now going on in peat-swamps. 

 Peat represents a young stage of coal-production; but it is 

 formed only, or chiefly, from moss-deposits of a peculiar kind- 

 the so-called *S'p/ia(/n?/m mosses. These grow in low wet ground, 

 and have no roots, but keep growing above and dying below. 

 Hence the green carpet that covers the surface of the peat- 

 swamp passes down at a very short distance into a mass of 

 half-decayed and blackish stems matted together; at a greater 

 depth, this becomes a dark pasty mass full of dead stems, etc. ; 

 and this in turn may pass into a compact deposit, black or dark 

 brown in color, and approaching some of the softer varieties of 



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