"From the study and comparison of these fossils, derived from such various sources, we may divide the Cretaceous period into three epochs, of which the middle one is the true Cretaceous epoch. The others, characterised almost exclusively by marine vegetables, are somewhat doubtful with regard to their true geological position; the one, more ancient than the Chalk, contains only the subcretaceous lignites of the neighbourhood of La Rochelle, and the Department of Dordogne; the other, superior to the Chalk, corresponds to the Sandstone with fucoides." The _subcretaceous_ epoch comprehends Algæ, Naiadeæ, and Coniferæ. "This small Flora is almost entirely founded on fossil plants, collected among the marine lignites of the Isle of Aix, near La Rochelle, long since described by M. Fleureau de Bellevue. "The difference of the vegetables does not appear to admit of connecting this Flora with that of the inferior chalk or greensand; but it would require to be more completely examined, both with regard to its precise geological epoch and the entire amount of vegetable species which it contains. The most abundant and characteristic of these species is the _Rhodomelites strictus_, whose branches, crossed and mingled with _Zosterites_, constitute the mass of these lignites with the wood of Coniferæ, which have not yet been studied, and small branchlets, very rare, of _Brachyphyllum orbignianum_. "I have referred to this period the two _Cystoseirites_, described by M. de Sternberg, and mentioned by him as found in the beds between the jurassic slates and the chalk in Transylvania. "Does this fossil Flora correspond to a formation almost entirely marine, but cotemporary with the Wealdean epoch? New investigations can alone determine this, but we may suppose an analogy between the Brachyphyllum of the epochs." _2d_, _Cretaceous Epoch_.--The Cretaceous epoch presents us, among the amphigenous cryptogams, with Algæ, some of which are doubtful; among the Acrogenous cryptogams, with ferns; the Monoctyledons are here represented by two species of palms; the Gymnospermous dicotyledons by the cycadeæ and coniferæ; the Angiospermous dicotyledons by a species of Acerineæ, a betulaceæ, a cupulifera, salicineæ, an acerineæ, and a juglandeæ; lastly, a few dicotyledons remain, but the determination of the families to which they belong is uncertain. "We ought, moreover, to notice at least from ten to twelve species of dicotyledonous leaves, indeterminate, and often imperfect, figured by Geinitz, Reuss, Corda, and Goeppert, or existing in collections. "This Flora, which contains from sixty to seventy species, is, as we perceive, remarkable in this respect, that the Angiospermous dicotyledons nearly equal the Gymnospermous dicotyledons, and in the existence of a pretty considerable number of well characterised Cycadeæ, which cease to appear at the Eocene epoch of the Tertiary formations.