, EVIDENCE OF THE FOSSIL FLORA. 189 



tinct when viewed at arm's length than when microscopically 

 examined ; but enough remains to show that it must have 

 been a terrestrial, not a marine plant. The accompanying 

 print (fig. 63) may be regarded as no unfaithful representa- 



Fig. 63. 



FEKN ? OF THE LOWER (MIDDLE) OLD EED SANDSTONE. 

 (Natural size.) 



tion of this unique fossil in its state of imperfect keeping. 

 The vegetation of the Silurian system, from its upper beds 

 down till where we reach the zero of life, is, like that of the 

 Old Red Sandstone, almost exclusively fucoidal. In the older 

 fossiliferous deposits of the system in Sweden, Kussia, the 

 Lake Districts of England, Canada, and the United States, 

 fucoids occur, to the exclusion, so far as is yet known, of every 

 other vegetable form ; and such is their abundance in some 

 localities, that they render the argillaceous rocks in which 

 they lie diffused capable of being fired as an alum slate, and 

 exist in others as seams of a compact anthracite, occasionally 

 used as fuel. They also occur in those districts of Wales in 

 which the place and sequence of the various Silurian forma- 

 tions were first determined, though apparently in a state of 

 keeping from which little can be premised regarding their 

 original forms. Sir Roderick Murchison sums up his notice 



