218 



MINERALS AND GEOLOGY 



they appear in certain intermediate forms ( Lycopodendron vascular e, 

 Sigillaria Defrancii, S. tesselata, &c.) to merge into each other. 

 Typically, the sigillarise have the outer surface marked with strongly- 

 defined, longitudinal ribs and furrows, whilst 

 these are absent in the lepidodendra ; but ribs 

 are also absent in many sigillarise, at least upon 

 the outer surface : whence the two groups cos- 

 tatce and acostatce of the latter, as commonly 

 adopted. The oval, rhombic, or other shaped 

 impressions on the stem-surface of both types, 

 indicate the original sites of leaves, and are 

 thus known as "leaf-scars." Within these, 

 generally towards the upper part, lie in most 

 FIG 120 cases, three small indentations known as " vas- 



Psiiophytum princeps cular scars," but in some genera only one is 



(Dawson). *P. elegans.(Id.) 



Devonian : Gaspe. present. Typically, in lepidodendra the central 

 vascular scar is more pronounced than the lateral scars ; whilst in 

 sigillarise the reverse of this occurs, or the central scar may be alto- 

 gether wanting. Very probably these extinct types represent con- 

 necting links between the higher cryptogams and the gymnosperms 

 of existing Nature. 



Remains of lepidodendroids are unknown in Ontario, but a species 

 of lepidodendron (Fig. 121) occurs in the Devonian rocks of Gaspe, 



FIG. 121. 

 Lepidodendron Gaspianum (Dawson). 



Devonian: Gaspe. 



together with impressions of long, narrow, parallel- veined leaves 

 referred to Cordaites* (Fig. 122). 



* Some of the more characteristic lepidodendroid and sigillarioid fossils of Devonian and 

 Carboniferous rocks, are comprised in the following synopsis : 



1. Lepidodendron : Stem-forms, often of great length, bifurcating, the surface marked with 

 oval, cordiform, or rhomboidal leaf-scars. Upper Silurian (?), Devonian, Carboniferous, 

 Permian. 



2. Lepidostrobus : Oval or cylindrical bodies with more or less distinctly hexagonal surfs 

 markings. Supposed " fruit cones " of lepidodendroids, Dev., Carb. 



3. Cordaites : Long-pointed leaves with comparatively broad base and parallel 

 Supposed leaves of lepidodendroids. 





nal surface- 

 1 venation- 



