r 



vi. 



Sigillaria and Stigmaria. 



THE short notice of M. Grand' Eury's admirable memoir on the 

 Geology and Palaeontology of the Coal Basin of the Gard,' to 

 a copy of which I am so fortunate as to have access, raises some 

 questions which the older workers on SigUlaria and Stigmaria had 

 supposed to be settled, and on which it may be useful to make a few 

 definite statements. 



I. It is quite certain that Stigmaria' are not "rhizomes which 

 floated in water or spread themselves out on the surface of mud.'' 

 Whether rhizomes or not, they grew in the soil or in the upper layers 

 of peaty deposits since changed into coal. The late Richard Brown 

 and the writer have shown that they grew in the underclays or fossil 

 soils, and that their rootlets radiated in these soils in all directions. - 

 In one of my papers I have figured a Stigmarian root penetrating 

 through an erect SigUlaria, and Logan in his Report of 1845 had 

 already figured a similar example. The penetration of decaying stems 

 by the rootlets of Stigmaria is a fact well known to all who have studied 

 slices of Carboniferous plants, j while Stigmaria are often found 

 creeping inside the bark of erect and prostrate trunks. Besides this, 

 as I have shown in " Acadian Geology," in the section of 5,000 

 feet of Coal-measures at the South Joggins (including seventy-six 

 distinct coal groups, and a larger number of soils with Stigmaria or 

 erect trees) SigUlaria and Stigmaria occur together, and the latter 

 nearly always either in argillaceous soils or sands hardened into 

 " Gannister," which are often filled with roots and rootlets, or on the 

 surfaces of coal-beds. On the other hand, the numerous bituminous 

 limestones, and calcareous and other shales holding remains of fi^shes, 

 crustaceans, and bivalve shells, do not contain Stigmaria in situ — 

 the only exception being two beds of bituminous limestone, the upper 

 parts of which have been converted into underclays. This section, 

 and that of North Sydney — two of the most complete and instructive 

 in the world — have afforded conclusive proof of this mode of growth 

 of SigUlaria and Stigmaria. 



1 Natural Science, March, 1892. 



» Quart, jfoicrn. Geo!. Soc, vol. ii., p. 394 (1846) ; Ibid., vol. iv., p. 47 (1847) ; 

 Ibid., vol. v., p. 355 (1849) ; Ibid., vol. v., pp. 23, 30. 



^ Williamson has noticed this in his excellent memoirs in the Phil. Trans. 



P 2 



