30 



THE GEOLOGICAL HISTORY OF PLANTS. 



markings referred to Palceochorda, Palceopliycus, and 

 Scolithus have their places here. Many examples highly 

 illustrative of the manner of formation of the impressions 

 are afforded by Canadian rocks (Fig. 8). 



Branching forms referred to Licrophycus of Billings, 

 and some of those referred to Buthotrephis, Hall, as well 



as radiating markings 

 referable to Scotolithus, 

 Gyropliyllites, and As- 

 terophycus, are ex- 

 plained by the branch- 

 ing burrows of worms 

 illustrated by Nathorst 

 and the author. As- 

 tropolitlion, a singular 

 radiating marking of 

 the Canadian Cambri- 

 an,* seems to be some- 

 thing organic, but of 

 what nature is uncer- 

 tain (Fig. 9). 



Rhdbdichnites and 

 Eophyton belong to im- 

 pressions explicable by 

 the trails of drifting 

 sea-weeds, the tail-markings of Crustacea, and the ruts 

 ploughed by bivalve mollusks, and occurring in the Silu- 

 rian, Erian, and Carboniferous rocks, f Among these are 

 the singular bilobate forms described as Rusopliycus by 

 Hall, and which are probably burrows or resting-places 

 of crustaceans. The tracks of such animals, when walk- 

 ing, are the jointed impressions known as ArtJiropliycus 

 and Crusiana. I have shown by the mode of occurrence 



FIG. 8. Palceophycus Beverly ensis (Bill- 

 ings), a supposed Cambrian Fucoid, 

 but probably an animal trail. 



* Supplement to " Acadian Geology." 

 f "Canadian Naturalist," 1864. 



