CHAPTER III. 



THE ERIAN OK DEVONIAN FORESTS — ORIGIN OF PETRO- 

 LEUM — THE AGE OF ACROGENS AKD GYMNOSPERMS. 



Iisr the last chapter we were occupied with the com- 

 paratively few and obscure remains of plants entombed 

 in the oldest geological formations. We now ascend to a 

 higher plane, that of the Erian or Devonian period, in 

 which, for the first time, we find varied and widely dis- 

 tributed forests. 



The growth of knowledge with respect to this flora 

 has been somewhat rapid, and it may be interesting to 

 note its principal stages, as an encouragement to the hope 

 that we may yet learn something more satisfactory re- 

 specting the older floras we have just discussed. 



In Goeppert's memoir on the flora of the Silurian, 

 Devonian, and Lower Carboniferous rocks, published in 

 I860,* he enumerates twenty species as Silurian, but these 

 are all admitted to be Algge, and several of them are re- 

 mains which may be fairly claimed by the zoologists as 

 zoophytes, or trails of worms and mollusks. In the Lower 

 Devonian he knows but six species, five of which are 

 Algae, and the remaining one a Sigillaria, but this is of 

 very doubtful nature. In the Middle Devonian he gives 

 but one species, a land-plant of the genus Lepidodendron. 

 In the Upper Devonian the number rises to fifty-seven, 

 of which all but seven are terrestrial plants, representing 



6 



* Jena, 1860. 



