DA-\TtClC — SIGlXtAEIA, CALAMIIES, AKD CAIAMOEEKDEOX-. 147 



2. On iTie Stetjcttjee and Appimties of SiGiEiAELi, Calamites and 

 Calamodendeon. By J. W. Dawsok, LL.D., P.R.S., F.G.S., 

 Principal of M'^Gill TJniversity. 



(Read May 11, 1870*.) 

 [Plates VII.-X.] 



1. Sigielaeia. 



The difficulty of arriving at a correct knowledge of the structure 

 of these curious trees is caused principally by the unequal durability 

 of the different parts of the stem. It arises from this that some 

 portions have usually perished, while others were in process of 

 mineralization, and the portions which remain have in a great 

 degree lost their original form and arrangement. The outer bark, 

 while extremely durable, was too impenetrable to be preserved in 

 any other way than as compact coal. The fibres of the bark and 

 of the woody axis are often mineralized or imperfectly preserved as 

 mineral charcoal. The cellular portions of the bark and of the axis 

 have usually entirely disappeared. Still, imperfectly preserved stems 

 can be obtained in great abundance in any coal-field by those who 

 are content to work on such unpromising material. 



Probably the finest specimen of a ISigillaria hitherto described is 

 that of S. elegans, so admirably figured by Brongniart, and which 

 has long served, to give to the student of palseobotany his ideas of 

 the structure of the genus. Unfortunately, however, Brongniart's 

 specimen represents a small or young stem belonging to the some- 

 what aberrant subgenus Favtdaria ; so that it fails to give an adequate 

 idea of the structure of the typical fossil Sigillarice, which are 

 much more common and important, at least in the coal-fields of 

 Nova Scotia. The structure of these last, as observed in specimens 

 obtained at the South Joggins, was, I believe, first described by me 

 in my paper on the "Vegetable Structures in Coal, published in the 

 'Journal' of this Society in 1859. The specimens subsequently 

 figured in the ' Journal ' of this Society, and in the ' Transactions ' 

 of the Eoyal Society, by Mr. Binney, under the name of S. vascidaris, 

 belong, in part at least, to types of structure quite distinct from that 

 of the true Sigillariasf. 



My own results as to the typical Sigillarice are thus shortly 

 summed up in my paper on the " Conditions of Deposition of 

 Coal" J : — "In the restricted genus Sigillaria the ribs are strongly 

 developed, except at the base of the stem ; they are usually much 



* For the cliscussiol^ on this paper see Quart. Journ. Geol. Soc. vol. xsvi. 

 p. 490. 



t It would seem that the specimens figured by Mr. Binney as Sigillaria 

 vascularis (Philos. Trans. Tol. cIt.) belong in part to the axis of a remarkable 

 Sigillarioid tree, of which specimens have been kindly shown to me by Prof. 

 Williamson, and in part (especially pi. xxxt. figs. 6 & 6) to the wkole stem 

 of a Lepidodendron. The latter plant has been described by Mr. Carruthers as 

 Lepidodendron selaginoides. 



X Quart. Journ. Geol. Soc. vol. sxii. p. 129. 



l2 



