168 
THE GEOLOGIST. 
when carefully traced over the surfaces of accumulation, are found to present the 
outline of flattened trunks. This is also true to a certain extent of the finer 
varieties of slate-coal ; hut the coarse coal appears to consist of extensive laminse 
of disintegrated vegetable matter mixed with mud. When the coal (especially 
the more shaly varieties) is held obliquely under a strong light, in the manner 
recommended by Goejipert, the sui-ftices of the lamina? of coal present the forms of 
many well-known coal-plants, as ^ir/il/nria, Siigmaria, Poacitcs (or Nceggerathia), 
Lepidodendron, Ulodendrun, and rough bark, perhaps of Conifers. When the coal 
is traced upward into the roof-shales, we often find the laminae of compact coal 
represented by flattened coaly trunks and leaves, now rendered distinct by being 
separated by clay. 
The relation of erect trees to the mass of the coal, and the state of preservation 
in which the wcjod and bark of these trees occur, — the microscopic appearances of 
coal, — tlie abundance of cortical tissue in the coal, associated with remains of 
herbaceous ])lants, leaves, &c., are next treated of 
The author offers the following general conclusions : — 
(1.) With respect to the plants which have contributed the vegetable matter of 
the coal, these are principally the SiyiUarice and Calamiteic, but especially the 
former. 
(2.) The woody matter of the axes of Sir/lllaricB and CaJamitem and of coniferous 
trunks, as well as the scalariform tissues of the axes of the Lepidodendrece and 
Ulodendrece, and the woody and vascular bundles of fems, appear principally in 
the state of mineral charcoal. The outer cortical envelope of these plants, together 
witii such portions of their wood and of herbaceous plants and foliage as were 
submerged mthout subaerial decay, occur as com))act coal of various degrees of 
purity, the cortical matter, owing to its greater resistance to aqueous infiltration, 
att'onling the i)urest coal. The relative amounts of all these substances found in 
the states of nuneral charcoal anil compact coal depend principally upon the 
greater or le.ss prevalence of subaerial decay occasioned by greater or less diyne.ss 
of the swamjiy flats on which the coal accunmlated. 
(3.) The structure of the coal accords with the view that its materials were 
accumulated by growth without any driftage of materials. The Sigillarice and 
Calamitew, tall and branchless, and clothed only with rigid linear leaves, formed 
dense groves and jungles, in which the stujnps and fallen trunks of dead trees 
became resolved by decay into shells of bark and loose fragments of rotten wood 
which currents must have swept away, but which the most gentle inundations, or 
even heavy rains, could scatter in layers over the surface, where they gradually 
became imbedded in a mass of roots, fallen leaves, and herbaceous plants. 
(4.) The rate of accumulation of coal was very slow. The climate of the period, 
in the northern temperate zone, was of such a character that the tme conifers 
show rings of growth not larger, or much less distinct than those of many of their 
northern congeners.* The SiyiUariw and Calaviites were not, as often sujjposed, 
succulent plants. The former had, it is tnie, a very thick ceUular inner bark ; 
but their dense woody axes, their thick and nearly imperishable outer bark, their 
scanty and rigid foliage, would indicate no very rapid growth. In the case of 
Sigillaria, the variations in the leaf-scars in different parts of the tnmk, the inter- 
calation of new ridges at the surface representing that of new woody wedges in 
the axis, the transverse marks left by the successive stages of upward growth, all 
indicate that at least several years must have been rei^ iired for the growth of 
stems of moderate size. The enormous roots of these trees, and the conditions 
of the coal-swamps, must have exempted them from the danger of being over- 
thrown by violence. They probably fell, in successive generations, from natural 
decay ; and making every allowance for other materials, we may safely assert that 
every foot of thickness of pure bituminous coal implies the quiet growth and fall 
of at least fifty generations of SigillaricB, and therefore an undisturbed condition 
of forest-growth enduring through many centuries. Further, there is evidence 
that an immense amoimt of loose parenchymatous tissue, and even of wood, 
perished by decay ; and we do not know to what extent even the most dui-able 
• Paper on Fossils from Nova Scotia, Proc. Geol. See. 1847. 
