278 Notices of Memoirs — De Sajjorfa — Jurassic Plants. 



which M. Schimper has recently recognized a veritable Haliseris. 

 The Fucacese, properly so called, on the contrary, would apparently 

 have still been absent, and this absence would support the opinion of 

 those who recognize in them the most highly organized of all the 

 Alg(S. The same appearance is not presented on the land; we may 

 say that it varies according to the groups we examine. The per- 

 sistency of the structure of Equisetum is well known; those of the 

 Jurassic epoch are distinguished by their great height, sometimes 

 relatively gigantic, a characteristic nevertheless that would not apply 

 to all the species. The Ferns present a singular combination of 

 extinct types, and types whose affinity to those of the present day 

 cannot be mistaken. ClatJiropteris, Thaumatopteris, and several 

 other genera with reticulated nerves, whose fructification have 

 recently been observed, are scarcely distinguishable from the living 

 Drynarice, with which we should perhaps have classed them if there 

 had been fossil species. We might state also that several TcBuiop- 

 teridce range themselves without much effort by the side of Marattia 

 Dancea and Angiopteris, and consequently amongst the Marattiacece ; 

 but besides these partial assimilations, which the discovery of organs of 

 reproduction has legitimized, there exist a number of types that we 

 are compelled to group artificially, so uncertain are we still on the 

 •subject of their true affinities. Eespecting many of them, one would 

 be even compelled to believe that they are really without any actual 

 affinity to any of the living genera capable of being compared to 

 them. Hence the method of classification, founded by M. Ad. 

 Brongniart, and based solely on the characteristics of the nervation, 

 takes the precedence, and ought to be exclusively employed as the 

 only one which does not lead to erroneous results. 



The Jurassic Ferns of France comprise a moderately large num- 

 ber of species, and even of entirely new genera. I would here offer 

 an explanation of those differences whicli are calulated to strike the 

 miud when one proceeds to enumerate the different local vegetations. 



Several of the localities whence the French fossils come, amongst 

 others that of Hettange (Moselle), of Chatillon-sur-Seine, of Lour- 

 dines (Vienna), of Saint-Mihiel (Meuse), etc, represent ancient 

 sea-shores where the mere action of the water washing away the 

 earth and of the wind have contributed to carry the plant to the 

 bottom of deep creeks and bays filled perhaps with a pure chalky 

 slime or fine mud hereafter converted into sandstone. The plants 

 collected under these conditions differ more or less from those which 

 we meet with in the marly and bituminous schists which must have 

 been deposited at the bottom of the peaty lagoons or estuaries of 

 that epoch. It is to the formation of this last kind that it is ex- 

 pedient to ascribe the Ehsetic Flora of Franconia, and that of the 

 Oolite of Scarborough. These floras have transmitted to us the 

 vestiges of a fresh and luxuriant vegetation, whose growth was 

 favoured by the influence of the waters, and which was without 

 doubt quite distinct from that which covered the interior of the 

 lands. It is, on the contrary, that second vegetation to which I may 

 naturally apply the name of sylvan, because it extended uniformly 

 over the surface of the Jurassic regions, of which the fossils collected 



