224 FOSSIL COAL PLANTS. 
the base. These views confirm the remark which has been here already made, respect- 
ing the singular maintenance in size, of the diameter of the Sigillaires of our own coal 
fields. 
Respecting the class of plants to which these enormous trunks appertained, we have 
good authority for placing them among the numerous families of the group of ferns. It 
is impossible, M. Brongniart contends, to admit that these stems had belonged to 
vegetables of the class of dicotyledons. No wood of dicotyledonous or monocotyledonous 
plants, properly speaking, have been found in the coal fields; nor is there any dicotyle- 
donous plant, actually existing, which shows stems regularly grooved, and bearing the 
organs, which, after their fall, leave cicatrices at all analogous to those of the Sigillaires. 
The ancient surface, therefore, during the growth of our Pennsylvania coal strata, was 
overshadowed by groves of gigantic ferns, rivalling in magnitude the trees of our present 
forests.* 
THE NORTH WALL, OR ROOF. 
We turn now to the examination of the north wall, or rock roof, of our coal seam. 
Here an entirely different aspect presents itself; well worth the recital. Instead of an 
interlaced mass, composed of innumerable thinly compressed and flattened stems, dis- 
played upon a comparatively smooth surface of black clay shale, we have a series of long 
bifurcating columns whose dark forms are relieved against the lighter coloured conglo- 
merate. We are struck with the fact, that unlike those on the opposite wall, excepting 
in one species, none of these stems are straight: they all possess remarkable curvatures. 
Their bark, originally very thin, and since converted into coaly lamina, readily falls 
away under the operations of the miner. Much was probably destroyed at a vastly 
older period amidst the turbulence which attended their prostration. Of this we have 
some evidence in the occasional marks of rubbing which some of these stems appear to 
have received. Both circumstances contribute to the difficulty of identifying the species. 
All these trees appear to belong not only to one genus, but to a single species, Less 
numerous—inasmuch as they indicate such only as lived at that remarkable epoch, when 
the diluvial waters, heaving along enormous masses of sand, and gravel and pebbles, 
swept over the surface,—less numerous, I say, than that earlier vegetation, which slowly 
and quietly accumulated at the base of the coal, in the position we have just been consi- 
dering them,—these prostrated overlying trunks, present even a more interesting specta- 
cle. Seldom has it occurred to witness an exhibition of antediluvian vegetation, like this, 
of which we have given but an imperfect sketch. 
Facilitated by the gradual advance of the work, under his immediate direction, the 
writer had abundant leisure for observing these remains; and opportunities were not lost 
to prepare a faithful picture of the most interesting. Ample as apparently were the 
* The clay floor of the coal, bearing these magnificent traces of tropical vegetation, exhibits, when broken, in its 
interior, the grass-like leaves of Lyeopodiolite, and Stigmaria. One of the family of Sigillaria, also, (S. Lepidendri- 
folia,) bears leaves which are not greatly dissimilar to those of the former. Leaves of the other and smaller ferns, 
are not very frequent here. Stigmaria is less abundant than usual in other seams, and has contributed brt little 
towards the composition of the mass of coal. 
