THE FLORA OF THE COAL FORMATION. 429 



arc known to be coniferous, and they occasionally afford evidence that 

 we must not attach too much importance to the character <>i their 



markings. A very instructive specimen of this kind from Ohio, with 

 which I have been favoured by Professor Newberry, has in a portion 

 of its thicker end very fine transverse wrinkles, and in the remainder 

 of the specimen much coarser wrinkles. This difference marks, 

 perhaps, the various rates of growth in successive seasons, or the 

 change of the character of the pith in older portions of the stem. 



The state of preservation of the Sternbcrgia casts, in reference to 

 the woody matter which surrounded them, presents, in a geological 

 point of view, many interesting features. Professor "Williamson's 

 specimen I suppose to be unique, in its showing all the tissues of the 

 branch or trunk in a good state of preservation. More frequently, 

 only fragments of the wood remain, in such a condition as to evidence 

 an advanced state of decay, while the bark-like medullary lining 

 remains. In other specimens, the coaly coating investing the cast 

 sends forth flat expansions on either side, as if the Sternbcrgia had 

 been the midrib of a long thick leaf. This appearance, at one time 

 very perplexing to me, I suppose to result from the entire removal of 

 the wood by decay, and the flattening of the bark, so that a perfectly 

 flattened specimen may be all that remains of a coniferous branch 

 nearly two inches in diameter. A still greater amount of decay of 

 woody tissue is evidenced by those Sternbcrgia casts which are thinly 

 coated with structureless coal. These must, in many cases, represent 

 trunks and branches which have lost their bark and wood by decay ; 

 while the tough cork-like chambered pith drifted away to be imbedded 

 in a separate state. This might readily happen with the pith of 

 Cecropia ; and perhaps that of these coniferous trees may have been 

 more durable ; while the wood, like the sap-wood of many modern 

 pines, may have been susceptible of rapid decay, and liable, when 

 exposed to alternate moisture and dryness, to break up into those 

 rectangular blocks which are seen in the decaying trunks of modern 

 conifers, and are so abundantly "scattered over the surfaces of coal and 

 its associated beds in the form of mineral charcoal. 



Some specimens of Stembergia appear to show that they have 

 existed in the interior of trunks of considerable size. I have observed 

 one at the South Joggins, which appears to show the remains of a tree 

 a foot in diameter, now flattened and converted into coal, but retain- 

 ing a distinct cast of a wrinkled Sternbcrgia pith. (Pig. 1 GO, E.) 



Are we to infer from these facts that the wood of the trees of the 

 genus Dadoxylon was necessarily of a lax and perishable texture? Its 

 structure, and the occurrence of the heart-wood of huge trunks of 



