790 



THE POPULAR SCIENCE MONTHLY. 



and unquiet time, and, except in certain bands of iron-ore and some 

 dark slates colored with carbonaceous matter, we find in it no evidence 

 of vegetation. In tlie Cambrian a great subsidence of our continents 

 began, Avhich went on, though with local intermissions and reversals, 

 all through the Siluro-Cambrian or Ordovician time. These times 

 were, for this reason, remarkable for the great "abundance and increase 

 of marine animals rather than of land-plants. .Still, there are some 

 traces of land vegetation. 



The oldest plants known to me, and likely to have been of higher 

 grade than algae, are specimens kindly presented to me by Dr. Alleyne 

 Nicholson, of Aberdeen, and which he had named Jhdhotrepliis Hark- 

 nessii * and H. radlafa. They are from the ISkiddaw rocks of Cum- 

 berland. On examining these specimens, and others subsequently col- 

 lected 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 refer them not to algre, but probably to rhizocarps. 

 TJiey 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 ai'e parts 

 of one plant, and for this I have 

 proposed the generic name Prot- 

 annularia (Fig. 1). Somewhat 

 higher in the Siluro-Cambrian, in 

 the Cincinnati group of America, 

 Lesquereux has found some mi- 

 nute radiated leaves, referred by 

 him to the genus Sphenophyllum, 

 which is also allied to rhizocarps. 

 Still more remarkable is the dis- 

 covery in the same beds of a stem 

 with rhombic areoles or leaf- 

 bases, to which the name Proto- 

 stigina has been given. f If a 

 plant, this may have been allied 

 to the club-mosses. This seems 

 to be all that we at present know 

 of land-vegetation in the Siliiro- 

 Fi(i.\-Protniir,n>m-ii iTari-nr^m (Niciioi<.on\ a Cambrian. So far as the remains 



probable Uiiizocuij) (,1 the Onloviciui) period. . ,. , 



go, they indicate the presence of 



the families of rhizocarps and of lycopods. 



If we ascend into the Il'pper Silurian, or Silurian proper, the evi- 

 dences of land-vegetation somewhat increase. In 1859 I described, in 

 The "Journal of the Geological Society," of London, a remarkable 

 tree from the Lower Erian of Gaspe, under the name Prototaxltes, but 



* " Geological Magazine," 18C9. f Protostigma siffillarioidcs, Lesquereux. 



