FOSSIL COAL PLANTS. 223 
The oblique position in which, for the most part, these enormous stems of Sigillarid 
are disposed, in the floor or south wall of the coal seam, is unfavourable for determining 
their longitudinal extent: nor shall we ever ascertain it, until a much larger area is 
uncovered. During the length of several hundred feet in this gallery, not a single case 
is presented, either of the commencement or the termination of a stem of Sigillaria. 
With the exception of the one flexuous dichotomous species, mentioned above, the whole 
are singularly straight, and present no apparent diminution of their breadth, towards 
their superior extremities. Five or six of these Sigillaires have thirty feet of their length 
laid bare; and one other has forty or fifty feet long, exposed; without any perceptible 
change in width during that space. We regret the necessity of leaving so much unde- 
termined. ‘The actual lengths of these noble trunks can only be ascertained whenever, 
in the future operations of the mine, the coal shall be more extensively removed. 
More than one hundred of these straight Sigillaria are shown in our drawing. These 
are only the best defined among them; selected for illustration. At least double that 
number exist in that space; but there would have been no advantage gained by intro- 
ducing them into our sketch. As to their thickness, it may be stated that few stems are 
so small as two feet wide: many are three feet diameter: four or five of them are four 
feet; one or two others are four and a half feet; and two are five feet broad, each: differ- 
ing little, probably, from the original thickness of the living trunks. All these may be 
verified by consulting our diagram; which was drawn to a scale, from the actual admea- 
surements of the stems, at the time of discovery. 
The exterior or epidermal, and the cortical covering, are in these specimens converted 
into coal. ‘This carbonizing process, during the imperfect crystallization of the coal, 
tends greatly to ambiguity; for by this circumstance we are deprived of the only certain 
mode to which we can resort for determining species. The obscurity, occasioned by this 
modification of surface, has added to our embarrassments in examining these fossils, and 
has occasioned no slight hesitation in establishing their specific identity. Where the 
thickness of bark is considerable, as in Stgillaria pachydermata of Brongniart, and the 
Lepidodendron rimosum of Sternberg, the characteristic marking of the cicatrices, when 
converted to coal, is nearly obliterated. In the case of the species before alluded to, 
Sigillaria elegans, the carbonized bark appears to be only one twenty-fifth part of an inch 
thick; and, when removed, shows that the inferior surface still bears a modified resem- 
blance to the outer covering. 
It seems highly probable that a large proportion of the bulk of the coal itself was 
derived from the stems and leaves of Sigillaria; for by the appearances which yet 
remain, they must have stood as thickly crowded, as any of our most densely wooded 
forests. M. Brongniart has stated that the great number of leaves which the Sigillaires 
bore, extending along their entire length, and which had evidently been disarticulated 
and had fallen before the stem was buried in the strata, announce a life of no ordinary 
duration, and a growth which has required a considerable lapse of time. Notwithstand- 
ing this, we observe that the inferior extremity of the trunk presents flutings and cica- 
trices, which agree, as to size, with those near the top of the same stems, and which are 
nearly as strongly marked. The trunk has undergone, then, no considerable change or 
increase in its diameter; nor any remarkable alteration in the state of its surface, towards 
