THE GROWTH OF COAL 247 



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/ while Stigmariae 

 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 eighty-one distinct coal groups, and a larger 

 number of soils with Stigmaria, or erect trees), Sigillaria and 

 Stigmaria occur together, and the latter nearly always either 

 in argillaceous soils, or sands hardened into ' Gannister,' which 

 are often filled with roots or rootlets, or on the surfaces of 

 coal beds. On the other hand, the numerous bituminous 

 limestones, and calcareous and other shales holding remains 

 of fishes, crustaceans, and bivalve shells do not contain 

 Stigmaria in situ — the only exceptions being two beds of bitu- 

 minous 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 Sigillaria 

 and Stigmaria. 



" The objection to calling the Stigmarioe roots and their 

 processes rootlets, appears to me a finical application of modern 

 botanical usages to times for which they do not hold. We 

 might equally object to the application of the term roots to 

 those which spring from the earthed- up stems of Calamites, 

 radiating as they do from nodes which, in the air, would pro- 

 duce branchlets. Grand' Eury's figures show abundant in- 

 stances of this. We might also object to the exogenous stems 

 described by Williamson, which belong to cryptogamous 

 plants ; and, unlike anything modern, are made up exclusively 

 of scalariform tissue. If the articulation and regular arrange- 

 ment of those gigantic root hairs, the rootlets, or 'leaves' of 



^ Williamson has noticed this in his excellent Memoirs in the Phil. 

 Trans. 



