614 PALaSONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 



would, if they were transformed into coal, produce three to five feet of 

 hard mineral coal. 



For a better understanding of the different features and various ap- 

 pearances of coal, it is necessary to remember that the woody substance 

 in its decomposition or slow burning, and befoi'e arriving at its harden- 

 ed state of mineral coal, is ordinarily subjected to a softening process. 

 The low part of a bed of peat is, in most cases, a black paste. In the 

 old lignite deposits of Germany, large trunks of trees, perfectly black- 

 ened, are heaped and flattened into beds of six feet to nine feet thick, 

 and their woody substance has become so soft that the workmen 

 can easily cut it with their shovels; hence the flattening of all the 

 stems in the coal and the shales; the remarkable appearance of im- 

 mense pieces of bark rolled and pressed together, like sheets of paper; 

 hence, again, the compactness of some coals ; the evident stratification 

 or lamination of others; the remarkable action of the sulphuret of 

 iron, in transforming into pyrites whole flattened stems, or in preserv- 

 ing in the cannel coal of Breckinridge the outlines of the stigmaria, and 

 of their leaves, with such neatness that they look as if they had been 

 painted in yellow, on a ground of black. 



The thickness of a coal bed, notwithstanding contrary assertions, is 

 scaicely a reliable guide for identification; though as it has been pre- 

 viously explained, the coal is formed on a continuous surface, and not 

 deposited here and there in hollows of various extent, depth, and di- 

 rections — for this thickness depends on the evenness of the bottom 

 upon which it rests. When a bottom of sand, or of any other loose 

 substance whatever, has been for a long time covered by a deep sea, it 

 is mostly even and unbroken; a bed of coal formed upon it is gener- 

 ally of continous and of equal thickness. But when two beds of coal 

 are only separated by a thin formation of sandstone, and consequently 

 have been formed at a short interval from each other, the sandstone 

 covering the lower bed often bears, on its surface, numerous wrinkles 

 and furrows, as an evidenoe of the action of turbulent waters. In this 

 case, the coal formed above it is only piecemeal, in separate payers, 

 thick in places, then rapidly thinning until it disappears, to be again 

 found at a distance of a medium thipkness, and continue for a while. 



