"But these localities, so diverse, are referrible to very different stages of the Oolithic series, and perhaps will constitute, when they are better known, and more fully explored, distinct epochs. "The distinctive characters of this epoch, comprising the whole extent we have assigned to it, from the Lias to the Wealdean formation exclusively, are; among the Ferns, the rarity of ferns with reticulated nervures, so numerous in the Lias; among the Cycadeæ, the frequency of _Otozamites_ and _Zamites_, properly so called; that is to say, Cycadeæ most analogous to those of the existing period, and the diminution of _Ctenis_, _Pterophyllum_, and _Nilsonia_, genera much more remote from living species; finally, the greater frequency of Coniferæ, viz., _Brachyphyllum_ and _Thuites_, much rarer in the Lias. "_Wealdean Epoch._--This epoch affords, Amphigenous cryptogams, the Algæ; among Acrogenous cryptogams, Ferns, _Marsileaceæ_, and _Equisetaceæ_; among Gymnospermous dicotyledons, _Cycadeæ_ and _Coniferæ_; lastly, some Carpolithes as plants of a doubtful class. "This enumeration results principally from discoveries made, in recent years, in the Wealdean formations of the north of Germany, at Osterwald, Schaumberg, Buckeburg, Oberkirke, &c., of which the fossil plants were first described by M. Ræmer, and afterwards in a more complete manner by M. Dunker, in his monograph of these formations. To these species must be added others, less numerous and varied, previously discovered in the _Wealds_ of England, near Tilgate Forest, and Hastings in Sussex, and which are so well described by M. Mantell." This same formation has likewise been found in France, near Beauvais, by M. Graves, who observed there _Lonchopteris Mantelli_, and some other plants, of which M. Brongniart has not seen specimens, and which he quotes from Graves on the geology of the department of the Oise. "These species, 61 in number, enumerated above, appear to be all peculiar to this formation, with the exception, perhaps, of _Baiera Huttoni_, which seems to be identical with the species of the Bayreuth Lias and Scarborough Lias; but their generic forms are almost all the same as those of the Lias and Oolitic formations. The Cycadeæ, however, already appear less numerous relatively to the ferns.