354 ANNUAL OF SCIENTIFIC DISCOVERT. 



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 SigiUaruc and Calcunitea?, but especially 

 the former. 



2. The woody matter of the axes of S/'yillaricv and Calami tecc., and of con- 

 iferous trunks, as well as the scalariform tissues of the Lepidodcndrw and 

 UlidodendrcB, and the woody and vascular bundler of Ferns, appear princi- 

 pally in the state of mineral charcoal. The outer cortical envelop of these 

 plants, together with such portions of their Avood and of herbaceous plants 

 and foliage as were submerged \vithout subaerial decay, occur as compact 

 coal of various degrees of purity, the cortical matter, owing to its greater 

 resistance to aqueous infiltration, affording the purest coal. The relative 

 amounts of all these substances found in the states of mineral charcoal and 

 compact coal depend principally upon the greater or less prevalence of sub- 

 aerial decay occasioned by greater or less dryness of the swampy flats on 

 which the coal accumulated. 



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 Calamitece, tall and branchless, and clothed only with rigid linear leaves, 

 formed dense groves and jungles, in which the stumps and fallen trunks of 

 dead trees become 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 sur- 

 face, 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 true 

 conifers show rings of growth not larger, or much less distinct, than those 

 of many of their northern congeners.* The SigiUarice and Catamites were 

 not, as often supposed, succulent plants. The former had, it is true, a very 

 thick cellular inner bark ; but their dense woody axes, their thick and ncarly 

 imperishable outer bark, their scanty and rigid foliage, would indicate no 

 very rapid growth. In the case of Sigillaria?, the variation in the leaf-scars 

 in different parts of the trunk, the intercalation 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 sev- 

 eral years must have been required 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 overthrown 

 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 Siyillaricc, and therefore an 

 undisturbed condition of forest-growth enduring through many centuries. 

 Further, there is evidence that an immense amount of loose parenchymatous 

 tissue, and even of wood, perished by decay; and we do not know to what 

 extent even the most durable tissues may have disappeared in this way ; so 

 that in many coal-scams we have only a very small part of the vegetable 

 matter produced. 



Lastly. The results stated in this paper refer to coal-beds of the middle 



* Taper on Fossils from Nova Scotia, Proc. Geol. Soc., 1847. 



