410 Geological Society. 



lield obliquely under a strong light, in the manner recommended by 

 Goeppert, the surfaces of the laminae of coal present the forms of 

 many well-known coal-plants, as Sigillaria, Sligmaria, Poacites (or 

 Noeggerathia), Lcpidodendron, Ulodendron, 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 wood and bark of these trees occur, — 

 the microscopic appearances of coal, — the abundance of cortical 

 tissue in the coal, associated with remains of herbaceous plants, 

 leaves, &c., are next treated of. 



The author offers the following general conclusions : — 



(1) With respect to the plants which have contributed the vege- 

 table matter of the coal, these are principally the Sigillaricc and 

 Calamitef£, but especially the former. 



(2) The woody matter of the axes of Sigillarice and Calamitca 

 and of coniferous trunks, as well as the scalariforra tissues of the 

 axes of the LepidodendretE and Ulodendrece, and the woody and vas- 

 cular bundles of Ferns, appear principally in the state of mineral 

 charcoal. The outer cortical envelope of these plants, together with 

 such portions of their wood and of herbaceous plants and foliage as 

 were submerged without 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 mine- 

 ral charcoal and compact coal depend principally upon the greater 

 or less prevalence of subaerial 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, tail and branchless, and 

 clothed only with rigid linear leaves, formed dense groves and jun- 

 gles, in which the stumps 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 cli- 

 mate 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 Sigillarice and Calamites 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 nearly imperishable outer 

 bark, their scanty and rigid foliage would indicate no very rapid 

 growth. In the case of Sigillarice, the variations in the leaf-scars 

 in different parts of the trunk, the intercalation of new ridges at the 



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



