CONTAINED IN NODULES OF LIMESTONE. 
151 
scopical observers to be positive evidence of such coal being compressed vegetable 
tissue: on the contrary, the cellular and vascular tissues of our specimens, wherever 
they have decayed, present a homogeneous black or brown mass ; and where no such 
decomposition has supervened, the vegetable tissues are so preserved that their real 
nature is evident. We are not, however, prepared to lay any particular stress upon 
this point, because, even if it be allowed that these nodules present a fair sample of 
the vegetable constituents of the coal surrounding them, it does not follow that the 
same assemblage of species has formed other coals ; we may however remark, that 
with regard to some bituminous coals at any rate, we are inclined to regard the 
appearance of fibrous tissues as due to a molecular arrangement of the particles of 
that mineral, which no doubt had its origin in vegetable matter, but in which every 
trace of structure has been destroyed previous to, or during its mineralization. 
The absence of Calamites (one of the most typical and universal of coal plants) is 
another curious fact connected with these fossils ; the explanation is however very 
simple, for it has long been known to one of us, that some species of this genus repre- 
sent the casts of the hollow or cellular axis of SigUlaria and Calamodendron, and 
perhaps of many other genera, as Sternbergia does of Dadoxylon. ; this is a subject 
however to which we shall recur at another time, when, having completed the analysis 
of the specimens of Calamodendroyx contained in these nodules, we shall hope to lay 
the results before the Royal Society. In the mean time we shall proceed to describe 
the structure of Trigonocarpon, the most interesting of the genera which we have 
named. 
The usual form in which IWgowocarpow occurs is well known, and has been repeatedly 
figured. That this, however, was that of an incomplete organ has long been con- 
sidered probable, and almost confirmed by the discovery of such specimens as those 
oiT.ovatum, figured in Lindley and Hutton’s ‘Fossil Flora’ (tab. 142a), and in the 
‘Records of the Geological Survey of the United Kingdom’ (vol. i. p. 430). There 
have also been found in the coal shales compressed Trigonocarpons surrounded by a 
disc, as if lying in the concavity of a scale, and suggesting the possibility of these 
fruits having been detached from a cone similar to that of a pine. In none of the 
specimens preserved in the limestone nodules are any such appearances presented ; 
and it may be assumed that the appearance in question is due to the compression of 
the fleshy coat of the Trigonocarpon. The presence of this integunjent and of various 
others was stated in a notice printed in the ‘ Proceedings of the Royal Society’ for 
March 30, 1854, and was one of the first results of our examination of these fossils : 
the more detailed analysis and figures were, as was then stated, reserved for an after 
communication. 
Plate IV. fig. 1 represents a very beautiful specimen of Trigonocarpon, exposed by 
breaking a nodule of limestone. It is crossed by a fissure, dividing it into portions 
A. and B., and to understand its structure it is necessary to refer to fig. 2, which 
represents the same fossil, with the portion A. removed ; fig. 3 represents the under 
Y 2 
