| Peat Dismal Swamp | Lignite Texas | Bituminous Coal Penn. | Anthracite Penn. | |||||
| Moisture | 78 | .89 | 14 | .67 | 1 | .30 | 2 | .74 |
| Volatile matter | 13 | .84 | 37 | .32 | 20 | .87 | 4 | .25 |
| Fixed carbon | 6 | .49 | 41 | .07 | 67 | .20 | 81 | .51 |
| Ash | 0 | .78 | 6 | .69 | 8 | .80 | 10 | .87 |
2. The vegetable remains associated with coal are those of land plants.
3. Coal accumulated in the presence of water; for it is only when thus protected from the air that vegetal matter is preserved.
4. The vegetation of coal accumulated for the most part where it grew; it was not generally drifted and deposited by waves and currents. Commonly the fire clay beneath the seam is penetrated with roots, and the shale above is packed with leaves of ferns and other plants as beautifully pressed as in a herbarium. There often is associated with the seam a fossil forest, with the stumps, which are still standing where they grew, their spreading roots, and the soil beneath, all changed to stone ([Fig. 303]). In the Nova Scotia field, out of seventy-six distinct coal seams, twenty are underlain by old forest grounds.
The presence of fire clay beneath a seam points in the same direction. Such underclays withstand intense heat and are used in making fire brick, because their alkalies have been removed by the long-continued growth of vegetation.
Fuel coal is also too pure to have been accumulated by driftage. In that case we should expect to find it mixed with mud, while in fact it often contains no more ash than the vegetal matter would furnish from which it has been compressed.
Fig. 303. Fossil Tree Stumps of a Carboniferous Forest, Scotland