"II. _Permian Period._--The nature of the vegetables which appear peculiar to this epoch, is far from being determined in a positive manner; for the few localities where the fossils we consider as belonging to it, have hitherto been found, are not perhaps really of a formation very identical and truly contemporaneous. For it may be asked, whether the bituminous and copper slates of the county of Mansfield, classed by all geologists with the zechstein, and the sandstone of Russia, placed by M. M. Murchison and Verneuil in their Permian formation, are really contemporaneous? Finally, is there greater reason for classifying the slates of Lodève, considered by M. M. Dufresnoy and Elie de Beaumont as depending on the variegated sandstone, but so different from the same sandstone of the Vosges in its _flora_, in this period, which would thus be a kind of passage from the coal period, so well characterised, to the vosgian or variegated sandstone, which differs from it in so decided a manner?" On account of these doubts, M. Brongniart indicates these three floras separately; _1st_, The Flora of the bituminous slates of Thuringia, composed of algæ, ferns, and coniferæ; _2d_, The Flora of the Permian sandstones of Russia, which comprehends ferns, equisetaceæ, lycopodiaceæ, and noeggerathiæ; _3d_, The Flora of the slates of Lodève, which is composed of ferns, asterophylliteæ, and coniferæ. "We perceive that there are great specific differences between the plants of these localities, and that hitherto no species common to them has been found. Must we ascribe these differences to the influence of the great diversity of geographical position, or is there, besides, a difference in the period of their origin among these formations? The only character which tends to bring these two latter Floras near each other, is the relation which both of them bear to the coal-formations, of which they seem to be a kind of extract, reminding us more especially of the most recent beds. "With regard to the plants of the bituminous slates of the Mansfeld district, they are so few in number, and appear to have been deposited in conditions so different, that we can with difficulty compare them with the two other Floras. Yet the species of Sphenopteris are extremely like each other in the three formations, and an exact comparison would perhaps establish the identity of many of them. The Pecopteris crenulata of Ilmenau, is only perhaps an imperfect state of the Pecopteris abbreviata of Lodève; lastly, the Callipteris of the Permian formation of Lodève have a very close connection between themselves and the Callipteris of the coal-formation. "We may add, with regard to the bituminous slates of Thuringia, that many of these fossils appear to be marine plants, whose numbers would become much more considerable if we did not suppress all the imperfect impressions which have been described as such, and which are nothing more than fragments of ferns or altered coniferæ.