20 THE GEOLOGICAL HISTORY OF PLANTS. 



scribed, under the name of Eophyton, certain impressions 

 on old Cambrian rocks in Sweden, and which certainly 

 present very plant-like forms. They want, however, any 

 trace of carbonaceous matter, and seem rather to be 

 grooves or marks cut in clay by the limbs or tails of some 

 aquatic animal, and afterwards filled up and preserved by 

 succeeding deposits. After examining large series of 

 these specimens from Sweden, and from rocks of similar 

 age in Canada, I confess that I have no faith in their 

 vegetable nature. 



The oldest plants known to me, and likely to have 

 been of higher grade than Algse, are specimens kindly 

 presented to me by Dr. Alleyne Nicholson, of Aberdeen, 

 and which he had named Buthotrephis Harknessii* and 

 B. radiata. They are from the Skiddaw rocks of Cum- 

 berland. On examining these specimens, and others 

 subsequently collected in the same locality by Dr. G. M. 

 Dawson, while convinced by their form and carbonaceous 

 character that they are really plants, I am inclined to re- 

 fer them not to Algae, but probably to Rhizocarps. They 

 consist of slender branching stems, with whorls of elongate 

 and pointed leaves, resembling the genus Annularia of 

 the coal formation. I am inclined to believe that both 

 of Nicholson's species are parts of one plant, and for 

 this I have proposed the generic name Protannularia 

 (Fig. 1). Somewhat higher in the Siluro-Cambrian, in 

 the Cincinnati group of America, Lesquereux has found 

 some minute radiated leaves, referred by him to the genus 

 Sphenophyllum,\ which is also allied to Ehizocarps. Still 

 more remarkable is the discovery in the same beds of a 

 stem with rhombic areoles or leaf -bases, to which the 

 name Protostigma has been given. J If a plant, this may 



* " Geological Magazine," 1869. 



f See figure in next chapter. 



J Protostigma sigillarioidcs, Lesquereux. 



