132 LE-DTUEES 



form of rafts to great distances and deposited at the mouths of rivers ; 

 the former, that a coal basin is the site of an ancient peat bog, th© 

 latter, that it is the position of an ancient estuary or delta. The 

 former opinion is called the ^^ peat hog theory," the latter the 

 " estuoA'y theory." 



Peat hog theory. — It is well known that in many countries, par- 

 ticularly in moist, cool climates, and damp, low grounds, certain 

 plants, such as ferns, mosses, &c., as well as trees which delight in 

 moist places, if allowed to grow undisturbed from generation to 

 generation will, by their decay, accumulate enormous masses of car- 

 bonaceous matter. Such a spot is called a peat hog. The theory of 

 this accumulation is as follows : Plants derive all their carbon from 

 the atmosphere. In the annual fall of leaf, and finally their own 

 death, they return to the earth the whole of the matter thus silently 

 extracted irom the air. Undisturbed vegetation, therefore, constantly 

 enriches the soil by adding to it what has been taken from the air. 

 Thus worn out lands improve by lying fallow. Thus the rich black 

 vegetable mould found covering the ground in forests continues to 

 increase from year to year. In all ordinary cases, however, there is 

 a limit beyond which this accumulation will not go. By decom- 

 position the organic matter is again returned to the atmosphere as 



: fast as it accumulates. But if by any means this decomposition is 



<:prevented the organic matter accumulates indefinitely. This is 

 precisely what takes place in peat bogs. The presence of water 

 in a great measure prevents the oxydation of the carbon. The 

 growth of plants now continually takes carbon from the atmosphere, 

 their death as continually deposits it upon the earth. Each genera- 



-tion rises, phoenix-like, from the ashes of the last, to become in its 

 turn soil for the next. Thus the ancestral accumulation continues 

 to increase, the funeral pile continues to rise, until pure carbonaceous 

 matter may in time accumulate to the depth of thirty or forty feet. 



. Such a mass of carbonaceous matter deprived of its water and com- 

 pressed to the density of coal, would make a seam of perhaps three 



■ or four feet in thickness. Now, according to the peat bog theory, it 

 is under such circumstances that the carbon of a coal seam has been 



; accumulated. 



The arguments in favor of this theory are : 1st. The purity of the 



. coal. It is true that coal is often found largely mixed with earthy 

 matter or mud. As we have already shown, every stage of gradation 



i may be traced between pure coal and pure shale. But by far the 

 larger portion of coal seems to be entirely free from foreign matter. 



' The amount of ash is not greater than five to ten per cent. ; that is, 

 not greater than might arise from the earthy matter of the plants 

 Irom which the coal was derived. This purity of the coal indicates 

 complete absence of sediment in the water in which the coal was 

 originally laid down. Now the water of peat swamps, though dis- 



. colored by organic matter in solution, is always entirely free from 

 sediment. In fact, this seems a necessary condition of the growth of 

 peat plants — an incursion of water containing mud is fatal to such 

 plants. If, then, a coal seam is the result of carbonaceous matter 



