30 



THE GEOLOGICAL HISTORY OF PLANTS. 



markings referred to PalcBOchorda, Palmphycus, and 

 ScoUthus 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 ScotoUthus, 

 Gyrophyllites, and As- 

 terophycus, are ex- 

 plained by the branch- 

 ing burrows of worms 

 illustrated by Nathorst 

 and the author. As- 

 tropolithon, a singular 

 radiating marking of 

 the Canadian Cambri- 

 an,* seems to be some- 

 thing organic, but of 

 what nature is uncer- 

 tain (Fig. 9). 



Rhabdichnites and 

 Eopihyton 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. \ Among these are 

 the singular bilobate forms described as Rusophycus 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 ArtJiropJiycus 

 and Orusiana. I have shown by the mode of occurrence 



Fio. 8. — Paloeophycua Seoertyensis (Bill- 

 ings), a supposed Cambnan Fucoid, 

 but probably an animal trail. 



* Supplement to " Acadian Geology.'' 

 t "Canadian Naturalist," 1864. 



