PRE-CARBONIFEROUS FLORAS. 477 



series, whilst the Upper Cretaceous series is linked on by its 

 plants to the Tertiary formations. The line, therefore, between 

 the Age of Gymnosperms and the Age of Angiosperms must 

 be drawn between the Lower and Upper Cretaceous, and not 

 at the base of the Cretaceous series. 



CHAPTER XLIV. 

 PRE-CARBONIFEROUS FLORAS. 



CAMBRIAN PLANTS. The Laurentian and Huronian deposits 

 have as yet yielded no remains of plants ; but the occurrence 

 of graphite in large quantity in the former of these would 

 strongly support the view that the Laurentian period was not 

 without an abundant vegetation. The Lower Cambrian Rocks 

 have yielded many so-called " fucoids ; " but these are almost 

 invariably to be referred to the tracks and burrows of marine 

 worms. The only apparently unequivocal plant of the Lower 

 Cambrian period is the Eophyton (fig. 378) of the "Fucoidal 

 Sandstone " of Sweden. 



The singular fossils referred to this genus consist of straight, 

 furrowed, and striated stems, which can hardly be anything else 

 than the remains of plants. The affinities, however, of these 

 ancient fossils are quite undetermined, except that it seems 

 pretty certain that they cannot be referred to the Alga. 



In the Upper Cambrian Rocks (Potsdam Sandstone) of 

 North America occur various so-called " Fucoids " (PalcBOphy- 

 cus, &c.) The true nature of these, however, is in many cases 

 very doubtful, and it is questionable if any of them can really 

 be regarded as plants. 



Here, also, we may briefly consider certain remains dis- 

 covered by the author in the Skiddaw Slates of the North of 

 England, a formation which is probably referable to the Upper 

 Cambrian, but which good authorities regard as belonging to 

 the Lower Silurian series. The remains in question were 

 originally referred provisionally to the genera Buthotrephis and 

 Eophyton, and the fossils which led to the former determina- 

 tion appear to be indubitable plants. They are thus described 

 by Dr Dawson in a note communicated to the author : 



I. Biithotrephis Harknessii, This consists of what have been cylindrical 

 branches, given off from a central stem, and producing a few branchlets in 

 the manner of Pinnularia. Under the microscope the branches show a 



