FOSSIL PLANTS. 841 
Generally, this agglomeration of broken tissue preserves some 
outline by which the genera, even the species to which the remains 
belong, can be recognized at first sight: leaflets of ferns, stems of 
Calamites, bark of Stigmaria, Lepidodendron, etc. But besides 
this, the coal itself, though more rarely, is marked with distinct 
prints of the plants of which it isa compound. This case is espec- 
ially observable in a kind of hard, laminated, flint coal, obtained 
in Mercer county by Mr. H. A. Green, which bears on the hori- 
zontal surface of its crystalline lamellae, however thin they may be 
cut, the outline and nervation of leaves and branches of ferns, 
and other vegetables of the coal; and these are so distinctly 
marked, that the most delicate parts are as easily identified as 
those of plants preserved in shales 
The great abundance of these remains show that the whole mass 
of this coal, which is true coal and burns freely, is a compound of 
them. In the cannel coal which has been formed under water 
from more decomposed vegetables, the forms are more rarely rec- 
ognizable. Yet the cannel coal of Breckenridge, Ky., is marked 
through its whole mass by stems and leaves of Stigmaria and 
Lepidodendron, rendered distinct by infiltration of sulphuret of 
iron. Even in the anthracite coal of Penn., whose matter has 
been subjected to heat and fused to cohesion ‘ise the transforma- 
tion of vegetable matter into coal, one can easily discover an 
abundance of remains of plants whose genera and even species are 
sometimes recognizable. These facts, which cannot be overlooked, 
may be taken into account in examining new theories in relation 
to the formation of coal. 
VEGETABLE REMAINS PRESERVED IN SHALE.—It is in the clay 
or silicious shale that the fragments of plants of the coal epoch 
have been more generally preserved. When a bed of vegetable 
matter heaped for the formation of a coal has begun to cease its 
growth, its top indicates a greater scarcity of vegetable remains, 
mixed with a larger proportion of earthy or clayey matter. The 
coal then becomes a less homogeneous mass, easily separating in 
layers of heaped fragments of vegetable and foreign matter. By 
and by, the vegetation becoming scarcer by superabundance of 
water upon the surface of the bogs, the clay is more thickly depos- 
ited, and the vegetable remains, more rare and scattered, are more 
_ distinct, and more easily recognizable. When preserved in that 
