FORMATION OF COAL. 



that grew millions of years ago, but we can observe certain 

 changes taking place in our peat swamps. We may learn much 

 from experiment, although we cannot follow nature closely, so 

 far as the time element is concerned, and we have to assume, 

 to a certain extent, the conditions that then prevailed. Deduc- 

 tive reasoning, after all, throws most light on the subject, but 

 we must be careful not to confound facts with fancies. 



So far as can be ascertained, the plants that went to form 

 our coal seams required damp places, such as reeds, mosses, and 

 ferns. Swampy plants spread out laterally in search of water 

 rather than vertically, for even a small thickness of peat ren- 

 ders respiration for plant life impossible. 



With compression, and the elimination of 

 some of the oxygen and hydrogen, as carbon 

 dioxide and carburetted hydrogen, peat may 

 completely change its nature. In peat bogs, 

 we may see the moss growing at the surface, 

 while at the bottom it is so altered that it is 

 difficult to distinguish the vegetable matter. 

 Under a pressure of 6000 atmospheres, peat is 

 converted into a hard, black, brilliant sub- 

 stance, having the physical aspect of coal, and 

 showing no trace of organic structure. Ap- 

 parently pressure and increased terrestrial 

 movements cause carbon dioxide and car- 

 buretted hydrogen to be given oft 7 , and as 

 these gases escape, the percentage of carbon 

 increases. In Pennsylvania, U.S.A., the 

 coal becomes more anthracitic as it passes 

 into regions that have undergone great plica- 

 tions. At Mons, France, the same seam that 

 yielded bituminous coal at the surface gradu- 

 ally passed downwards into anthracite. The 

 deepest collieries in New South Wales are 

 known to be the most fiery. A seam may be- 

 of one kind of coal on one side of a parting, 

 and another kind on the other side. 



Ordinary bituminous coal is generally made 

 up of layers of Wight and dull coal. The 

 bright coal is supposed to be made up of peaty 

 material, while the dull is composed of 

 sapropels, which is a mud formed by the 

 decay of vegetable matter, and its presence indicates 

 submergences due to floods. Bands of slate of vary- 

 ing thicknesses may also occur in coal seams, but a seam must 

 not be condemned on account of it partings, provided they can 

 be easily separated from the productive part of the seam. Some- 

 times when the coal is green, i.e., freshly mined, these bands 



Fig. 13- 

 Ta?niopteris 

 daintreei. 



