THE ORIGIN OF COAL.

New Zealand Tablet, Volume II, Issue 69, 22 August 1874, Page 8

THE ORIGIN OF COAL.

Coal, according to the modern hypothesis, is merely a trausmuted vegetable soil which accumulated, not under water, but under the trees composing primeval forests. These forests stood on areas which were subjected to repeated changes of level in relation to that of the ocean. It must be understood that though the ground beneath us is popularly regarded as the type of everything steady and immoveable, this earth of ours is far from deserving the character for stability with which it is thus fully accredited ; absolute rest is all but unknown to it. It happens that even at the present day there are certain regions, such as those subject to volcanic disturbances, whose tendencies are always to move upwards, like the more aspiring of our youths, while there are others, such as the coral regions, which are steadily sinking like those less fortunate youths who have failed in the voyage of life. So it was in the olden time. The coal beds appear to have accumulated on the latter class of areas — areas of depression — geographical regions in which the earth had a tendency to sink below the level of the ocean. Mud and silt had collected upon such areas until the deposits thus formed reached the surface-level of the water ; and then came what appears to have been necessary to the growth of the coal-plants, namely, a bed of peculiar grey mud. We do not know why that mud came there, or whence it was derived. That it was very different from the ordinary depoeits, the sandstones and shales, which accumulated in the carboniferous ocean, is shown by the physical qualities which it still possesses, and which they do not possess-' properties which fit it for the purpose to which it is now devoted, of being manufactured into fire-bricks, whenoe its common name of fire-clay. That this grey mud was the soil preferred by the great majority of the plants constituting the carboniferous forests is as obvious as the oak woods of Herefordshire and the sunny south will not flourish upon the cold soils of the Luncashiro uplands. Minute spores, representing the seeds of the plants which afterwards became coal, were floated to this mud by wind and waior; and finding there a suitable soil, they germinated, look root, and soon converted the swamp area into a magnificent forest. As the trees grew they shed showers of their miacroscopic spores, which often fell in such vast quantities as to constitute an ! important contribution to the accumulating vegetable soil, but along with them tLere fell other and more bulky objects, such as might be expected to accumulate under a semi-tropical forest. The dead leaves, broken branches, und prostrated stems, alike contributed a share to the decaying vegetable mass. In the tropical regions of the present day such ucuumululions become rapidly decomposed, aod pass away in gaseous forms j bnt such does appeur to have been the case in the carboniferous age— at least, not in the same degree. Even in Lancashire, notwithstanding all tho influences tending to diminish the bulk or" the vegetable mass — such as atmosphoiio decomposition — chemical changes occurring during the latter processes of mineralization, and tho presence of super-imposed rocks prolonged throughout all subsequent ages, we hnvo coal scams six and seven feet in thickness, whilst they occur in America, as for example in the oolitic coalfield on the Juu.cs River, with the surprising thickness of between thirty and forty et. Such accumulations of vegetable soil as these thicknesses of solid

coal represent, almost exceed comprehension, and must indicate enormous periods of undisturbed forest life. But at length a change came over the sylvan Bcene ; the land sank— whether suddenly or slowly we have no means of saying. The numbers of dead fishes found on the roofs and upper portions of some coals seems to indicate a sudden rush of pure water over the land, followed by the quick destruction of the fishes, poisoned by the bituminous mud in which they found themselves entangled. In other cases the roof of clean blue shale, devoid of all appearance of either animal or vegetable remains, and resting immediately upon a defined surface of pure coal, is suggestive of a slower submergence, allowing time for the destruction and obliteration of all traces of growing vegetation upon its surface.— ' Macmillan s Magazine.'