604 



FOSSIL PLANTS OF THE SECONDARY STRATA. 



are replaced by a few ferns and their allies. Plants of the Zamia 

 tribe occur along with some Coniferae. The pinnated frond called 



Pterophyllum (fig. 811), appears to be- 

 long to a Cycadaceous plant allied 

 to Zamia, while Voltzia (fig. 812) 

 and Pence seem to be Coniferous 



*" ^\ xN ^lp^" ^' ' genera. In the secondary formations, 



f ^^Ns^^BJ!^^^^ L J generally, there are no true coal fields, 



although carbonaceous matter, in the 

 form of imperfectly bituminized lignite, 

 is found deposited occasionally. Not- 

 withstanding the absence of true 

 coal, the sandstones and shales of the 

 Oolitic system contain numerous fossil 

 plants, which in their form and char- 

 acter seem to be a transition between 

 the Palaeozoic flora, and that of more 

 recent formations. In the upper Oolite 

 at Portland, there is a bed of earthy 

 brown matter, about a foot in thickness, 

 commonly known as the Dirt-bed, in 

 which there is an assemblage of silici- 



fied stumps of large trees (fig. 813). They are generally in an erect 

 position (fig. 814), and appear to be in situ. They are probably Cyca- 



Fig. 811. Pterophyllum Pleiningerii, apparently the frond of a fossil Cycadaceons plant allied 

 to Zamia. 

 Fig. 812. Voltzia heterophylla, one of the fossil Coniferse of the Triassic system. 



