1868.] DAWSON — THE COAL FLORA. 369 



into impure coal. The origin of these beds is the same with that 

 of the carbonaceous shales and bituminous limestones already 

 referred to. It will be observed in the section that in a few 

 cases such beds have become sufficiently dry to constitute under- 

 clays, and that conditions of this kind have sometimes alternated 

 with those favourable to the formation of true coal. 



There are some beds at the Joggins, holding erect trees in situ, 

 which show that Sigillarise sometimes grew singly or in scattered 

 clumps, either alone or amidst brakes of Calamites. In other 

 instances they must have grown close together, and with a dense 

 underground of ferns and Cordaites, forming an almost impene- 

 trable mass of vegetation. 



From the structure of Sigillariae I infer that, like Cycads, they 

 accumulated large quantities of starch, to be expended at intervals 

 in more rapid growth, or in the production of abundant fructifi- 

 cation. I adhere to the belief expressed in previous papers that 

 Brongniart is correct in regarding the Sigillariae as botanically 

 allied to the Cycadacese, and I have recently more fully satisfied 

 myself on this point by comparisons of their tissues with those of 

 Cycas revoluta. It is probable, however, that when better known 

 they will be found to have a wider range of structure and 

 affinities than we now suppose. 



*P »K »J» »T« 



Genus Lepidodendron, Sternberg. — This genus is one of the 

 most common in the Coal formation, and especially in its lower 

 part. Any one who has seen the common Ground-pine or Club- 

 moss of our woods, and who can imagine such a plant enlarged to 

 the dimensions of a great forest tree, presenting a bark marked 

 with rhombic or oval scars of fallen leaves, having its branches 

 bifurcating regularly, and covered with slender pointed leaves, 

 and the extremeties of the branches laden with cones or spikes of 

 fructification, has before him this characteristic tree of the coal 

 forests, — a tree remarkable as presenting a gigantic form of a 

 tribe of plants existing in the present world only in low and 

 humble species. Had we seen it growing, we might have first 

 mistaken it for a pine, but the spores contained in its cones, 

 instead of seeds, and its dichotomous ramification, would unde- 

 ceive us ; and if we cut into its trunk, we should find structures 

 quite unlike those of pines. As in Sigillaria, we should perceive 

 a large central pith, and surrounding this a ring of woody 

 matter ; but instead of finding this partly of disc-bearing wood 



