30 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 2, 



organized inhabitants. These oscillations depended on gradual and 

 long-continued subsidence, alternating with elevatory movements, in 

 an extensive alluvial tract teeming vrith vegetable and animal life, and 

 receiving large supplies of fine detrital matter. On the one hand, 

 subsidence tended to restore the original dominion of the vraters ; 

 on the other hand, elevatory movements, silting up, and vegetable and 

 animal accumulation built up successive surfaces of dry land, or of 

 partially or occasionally inundated swamp. The results of these op- 

 posing forces no doubt always existed contemporaneously, so that by 

 mere change of place one could have passed from a coal-swamp to a 

 Modiola-lagoon or a tidal sand-flat ; but in each separate locality they 

 alternated with each other, with greater or less frequency ; and it is 

 probable that during a great part of the period the locality of our 

 section was near the margin of the alluvial tract in question, where 

 the various fortunes of the conflict would be more sensibly felt and 

 more easily recorded than nearer the open sea or farther inland. 



IV. Notices of New Facts relating to the Fossils of the Coal 

 Formation. 



1. Sigillaria and Stigmaria. — The identity of these plants, as the 

 trunks and roots of trees of the same genus, has been estabhshed by 

 Messrs. Binney and Brown, and is farther confirmed by facts already 

 noticed in this paper. I shall give, under this head, explanations of 

 some apparent difficulties, and facts bearing on the habits and struc- 

 ture of these singular plants. 



It has been asked, in reference to the Joggins section*, how it 

 happens that so many erect trunks show no roots, especially since 

 the great number of fossil soils would lead us to anticipate that the 

 former were less likely to be preserved than the latter. In answer I 

 remark : (1.) The underclays are usually more perishable than the 

 sandstones and arenaceous shales which contain the erect trunks, 

 hence the former are often cut away before the trunks are disclosed. 

 (2.) The roots, approaching to a horizontal position, have often been 

 compressed or converted into coal, when the erect trunks and vertical 

 rootlets have been preserved. There are cases, however, in which 

 the Stigmaria-roots are preserved in a horizontal position, and with 

 scarcely any flattening. Such roots were probably hollowed by decay 

 and filled with mineral matter before the beds were compressed by 

 the weight of newer strata. 



The greater number of the erect fossil trees in the section do not 

 show the markings of Sigillaria, but only furrows or ribs more or less 

 distinct. Were they all Sigillaria 1 I think it probable that most of 

 them were, and account for the disappearance of their external cha- 

 racters in the following ways : — (L) These trees being stony casts of 

 the interior of the bark, it is evident that if, when the sand or mud 

 forming the cast was introduced, thin films of wood remained adhering 

 to the inner surface, or if, on the other hand, a part of the bark itself 

 was removed by decay, in either of these opposite cases, an indistinct 



"^ Quait. Journ. Geol. Soc. vol. ii., President's Address. 



