236 THE GROWTH OF COAL 



vegetable muck accumulated in ponds and similar places. 

 Such vegetable matter, once accumulated, requires only pressure 

 and the changes which come of its own slow putrefaction to be 

 converted into coal. 



But in order that it may accumulate at all, certain conditions 

 are necessary. The first of these includes the climatal and or- 

 ganic arrangements necessary for abundant vegetable growth. 

 The second is the facility for the preservation of the vegetable 

 matter, without decay or intermixture with earthy substances ; 

 and this, for a long time, till a great thickness of it accumulates. 

 The third is its covering up by other deposits, so as to be com- 

 pressed and excluded from air. It is evident that when we have 

 to consider the formation of a bed of coal several feet in thick- 

 ness, and spread, perhaps, over hundreds of square miles, many 

 things must conduce to such a result, and the wonder is perhaps 

 rather that such conditions should ever have been effectively 

 combined. Yet this has occurred at different periods of geo- 

 logical history and in many places, and in some localities it has 

 been so repeated as to produce many beds of coal in succes- 

 sion. 



Let us now question our block of coal as to its origin, sup- 

 posing it to be a piece of ordinary bituminous coal, or still better, 

 a specimen of one of the impure somewhat shaly coals which 

 one sometimes finds accidentally in the coal bin. In look- 

 ing at the edge of our specimen we observe that it has a " reed " 

 or grain, which corresponds with the lamination or bedding of 

 the seam of coal from which it came. Looking at this carefully, 

 we shall see that there are many thin layers of bright shining 

 coal, and the more of these usually the better the coal. These 

 layers, in tracing them along, we observe often to thin out and 

 disappear. They are not very continuous. If our specimen is 

 an impure coal, we will find that it readily splits along the sur- 

 faces of these layers, and that when so split, we can see that each 

 layer of shining coal has certain markings, perhaps the flattened 



