134 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. 20, 



In regard to beds destitute of Stigmarian underclays, the very 

 few cases of this kind apply only to shaly coals filled with drifted 

 leaves, or to accumulations of vegetable mud capable of conversion 

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

 the carbonaceous shales and bituminous limestones abeady referred 

 to. It will be observed in the section that in a few cases such beds 

 have become sufiiciently dry to constitute underclays, and that con- 

 ditions 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 Sigillarice sometimes grew singly or in scattered 

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

 stances they must have grown close together, and with a dense un- 

 dergrowth of ferns and Cordaites, forming an almost impenetrable 

 mass of vegetation. 



From the structure of Sigillarice 1 infer that, like Cycads, they ac- 

 cumulated large quantities of starch, to be expended at intervals in 

 more rapid growth, or in the production of abundant fructification. 

 I adhere to the belief expressed in previous papers that Brongniart 

 is correct in regarding the SigiUarice as botanically allied to the 

 Cycadacece, and I have recently more fully satisfied myself on this 

 point by comparisons of their tissues with those of Cgcas revoluta. 

 It is probable, however, that when better known they will be found to 

 have a wider range of structure and afiinities than we now suppose. 



There are some reasons for believing that the trees described by 

 Corda under the names of Di^loxylon, Myelopithys, and Heterangium, 

 and also the Anahathra of Witham, are Sigillarice. Much of the 

 tissue discribed by Goeppert as Araucarites carhonarius is probably 

 also Sigillarian. 



4. Calamodendron. — The plants of this genus are quite distinct 

 from Calamites proper. A Calamodendron as usually seen is a striated 

 cast with frequent cross lines or joints ; but when the whole stem is 

 preserved, it is seen that this cast represents merely an internal pith- 

 cylinder, surrounded by a woody cylinder composed in part of scalari- 

 form or reticulated vessels, and in part of wood-cells with one row 

 of large pores- on each side.. External to the wood was a cellular bark, 

 and the outer surface seems to have been simply ribbed in the manner 

 of Sigillaria. It so happens that the internal cast of the pith of 

 Calamodendron, which is really of the nature of a Sternbergia, so 

 closely resembles the external appearance of the true Calamites as to 

 be constantly mistaken for them. Most of these pith-cyhnders of 

 Calamodendron have been grouped in the species Calamites approoci- 

 matus ; but that species, as understood by some authors, appears also 

 to include true Calamites* y^N^Aoh, however, when well preserved, can 

 always be distinguished by the scars of the leaves or branchlets which 

 were attached to the nodes. 



Calamodendron would seem, from its structure, to have been closely 

 allied to SigiUaria, though, according to linger, the tissues were dif- 



^ See Geinitz, " Steinkolilenformation in Sachsen." 



