THE DIFFERENT KINDS OF COAL 119 



with little attention, and in many homes coal fires never go out 

 during the whole winter. 



Coal. Ages ago there grew in what are now the coal regions 

 of the United States, forests which were richer and more luxuri- 

 ant than the forests of to-day. The leaves, branches, and trunks 

 of these ancient forest trees fell to the ground, sank into the 

 soft moist soil, and gradually became completely covered with 

 wet earth. Slowly the heavy mass of vegetation was buried 

 deeper and deeper in the wet earth and became more and more 

 compressed by the tremendous weight of material accumulating 

 above it. The pressure, the absence of air, and the heat of the 

 earth's interior slowly decomposed the plant mass and brought 

 about changes similar to those brought about in the destructive 

 distillation of wood. In this process, gases were slowly given 

 off, for example, fire damp, the explosive gas so dreaded by men 

 who work in coal mines. After long ages, all that remained of 

 the buried vegetation was a black mass of carbon called coal. 



The different kinds of coal. The change of vegetable matter 

 into coal is a slow process ! Countless numbers of years are 

 required to change buried vegetation into coal. When the de- 

 composition has not progressed far, and only a small quantity 

 of gas has been given off, a substance called peat is formed. 

 Peat is a spongy mass of fibrous matter in which remains of 

 leaves or stems are sometimes seen. It is used for fuel in north- 

 ern Europe, particularly in Germany and Ireland, where hard 

 coal is scarce. 



When the decomposition of vegetable matter continues fur- 

 ther, more gases are driven ofF and a rocky mass known as 

 bituminous or soft coal remains. 



If the coal regions are not disturbed, more and more gases 

 are driven off, and finally almost pure carbon remains. This 

 carbon is in the form of a hard, brittle rock, and is called an- 

 thracite or hard coal. 



