Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/266

148 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. broader than the oval or elliptical tripunctate areoles, and are striated longitudinally. The woody axis has both discigerous and scalariform tissues, arranged in wedges, with medullary rays as in exogens; the pith is transversely partitioned in the manner of Sternbergia; and the inner bark contains great quantities of long and apparently very durable fibres, which I have, in my descriptions of the structures in the coal, named 'bast-tissue.' The outer bark was usually thick, of dense and almost indestructible cellular tissue. The trunk, when old, lost its regular ribs and scars, owing to expansion, and became furrowed like that of an old exogenous tree."

It will be understood that this statement refers to the main stems of the ribbed Sigillarioe of the type of S. reniformis and S. Brownii, so abundant in the coal-formation of Nova Scotia, and that it is made with especial reference to the conditions of the accumulation of coal in that province. The evidence on which it is based may be stated under the following heads:—

Erect Trunks.—The numerous erect stumps of Sigillarioe occurring at the South Joggins, and at Sydney, Cape Breton, are usually preserved as casts in sandstone, the only part of their organic substance remaining being the outer bark, which exists in the state of compact coal. Still the interior structures have not altogether perished, but may be recognized as a layer of mineral charcoal in the bottom of the stony column, under the sand and other foreign matters subsequently introduced. Occasionally the bark of the tree has collapsed before it could be filled with sediment, and the only remains of the trunk consist of the little mound of carbonaceous matter derived from the tree itself. Cases of this kind are mentioned in my paper on the South Joggins*. In addition to the coaly matter showing structure, we can also occasionally find in the interior of such erect trees a transversely striated sandstone cast (Sternbergia) representing the medullary cylinder. In one instance only have I found the medullary cylinder calcified in such a manner as to show its structure, and surrounded by the woody cylinder also in a calcified state. This specimen was that described, but not adequately figured, in my paper on the Structures in Coal, and I now propose to figure it more in detail (Plate X.). Ordinarily the coaly mass consists of confused fragments of mineral charcoal derived from the wood and the fibrous tissues of the bark; but these often retain their structure very perfectly.

After collecting and examining the woody matter thus remaining in twenty or more of these erect trees, I have found that, with one exception, it consists of tissues of a uniform character, presenting only such differences as might be expected in trees generically allied. The tissues observed are discigerous or porous wood-cells with from one to four rows of pores, pseudo-scalariform tissue, and elongated structureless cells of the bark (the "bast-tissue" of my former papers). These structures indicate that the woody parts of these trees were identical in character with those of the calcified axis above-mentioned.


 * Quart. Journ. Geol. Soc. vol. x. p. 1.