Jurassic Period, 76 



the Pterophyllum of the Keuper appear anew, with slight 

 specific differences in the Wealdean formations. The equise- 

 tites of the Keuper extend to the mean oolithic formation ; 

 the baiera of the Lias likewise recurs in the Wealdean beds 

 of the north of Germany ; the Sagenopteris and the Camp- 

 topteris likewise appear in the Keuper, Lias, and Oolite. 



" Yet these common characters, which indicate a great 

 analogy between the Floras of each of these epochs of for- 

 mation, do not prevent each of them having characters of its 

 own, and often an assemblage of species, almost all peculiar 

 to each particular epoch. We ought, therefore, to distin- 

 guish here those various subdivisions, the number of which 

 will perhaps be afterwards multiplied, when we become better 

 acquainted with the vegetables of each of the stages of the 

 Jurassic formations. 



** Keupric Epoch. — M. Brongniart then gives an enumera- 

 tion of the vegetables of the Keupric epoch, which, in regard 

 to the Amphigenous cryptogams, consist of Algse ; in regard 

 to the Acrogenous cryptogams, of Ferns and Equisetacese ; in 

 the case of the Gymnospermous dicotyledons of Cycadese and 

 Coniferae ; lastly, of two doubtful monocotyledons {Paloeoxyris 

 and Preisleria') 



" On comparing this Flora with that of the variegated sand- 

 stone of the Vosges, and with that of the Lias, we perceive 

 that it has nothing in common with the first except the palse- 

 oxyris, which appears very nearly related to that of the varie- 

 gated sandstone ; on the contrary, it resembles the Flora of 

 the Lias or Oolite in the ferns, many of which are specifically 

 identical, or nearly allied in the Nilsonia and Pterophyllum, 

 which are likewise either identical, or very nearly connected 

 specifically with the Lias. 



" Lias Epoch. — The Liasic epoch furnishes Amphigenous 

 cryptogams, consisting of Algae, mushrooms, and lichens; 

 Acrogenous cryptogams, such as Ferns, Marsileacese, Lyco- 

 podiacese, and Equisetaceae ; Gymnospermous dicotyledons, 

 represented by the Cycadeae and Coniferae ; finally, doubtful 

 monocotyledons, consisting oi Proacites and Cyperites. 



" The essential characters of this epoch are therefore, 1*^, 

 The great predominance of Cycadeae, already well established. 



