114 COAL FORMATIONS. 



The extent of these strata it is impossible to conceive; but parts 

 of those brought to light by the labors, prompted by the necessities of 

 man, afford a glance at the resources with which vegetable nature has 

 thus supplied the wants of mankind. No example of the providence 

 of nature is more signally remarkable than this. The world of living 

 vegetable existences, when viewed in this connection, appears little 

 more essential to the necessities and happiness of our nature than the 

 world of dead vegetable matter. 



The decay of vegetable substances and the conversion of woody 

 fibre into humus, mould or coal, is one of the most remarkable pro- 

 cesses in the decomposition of organic bodies. By decay, dead vege- 

 table substances give off the oxygen so essential to their living exist- 

 ence. This takes place when in a moist state and exposed to the ac- 

 cess of air, when the air is excluded and when covered with water in 

 contact with other putrefy ing substances. 



It is not possible to explain in detail the processes which vegetable 

 matter has undergone in the formation of coal, during a period ex- 

 tending far, very far, beyond that commonly alloted to the existence of 

 our earth ; but proximate causes may be percieved in known chemical 

 phenomena and in a notice of the fact, always to be borne in mind, that 

 the same causes which have heretofore produced extraordinary changes 

 in our earth, are still in operation. 



Vegetable substances, on the application of heat, are known to give 

 off their water, while their gummy resinous matter remains incorpora- 

 ted with their carbon. If this heat be gradual, as it undoubtedly has 

 been in the interior of the earth, especially in the latitudes where coal 

 is mostly found, the processes of decomposition of vesetable struc- 

 tures and the combinations of the juices and solid matter of vegeta- 

 bles are especially adapted to the formation of coal. This heat, so im- 

 portant here, is well understood to have existed since the formation 

 of the crust of the earth. It increases in the ratio of one de- 

 gree for every 60 or 70 feet towards the interior from about 40 feet 

 below the surface, though it differs in different places upon the earth ; 

 so that at the depth of 45 or 50 miles it is sufficiently intense to melt 

 or dissolve granitic rocks. But it is not less true that the latitudes in 

 which coal most abounds have been, at a comparatively early period 

 of our earth exposed to a tropical climate, and the superficial heat has 

 therefore facilitated the processes in the production of coal. 



Vegetable juices thus exposed to heat precipitate a black product 

 called extractive matter, and the action of air on vegetable solids also 

 produces h umus. Most vegetables acted on by water in contact with 

 other decaying bodies, undergo that slow process of combustion essential 

 to the formation of peat and coal. Peat, indeed, and the gradual car- 

 bonization of parts of vegetable remains, like the trunks of trees, are 

 evidences of the progressive formation of coal. When no more oxygen 



