In the flora of the secondary eras, all botanists agree that palms existed, although in Europe plants of the family of zamia and cycas together with coniferæ predominated, and must have given a peculiar aspect to the flora. As only 200 or 300 species of plants are known in all the rocks ranging from the Trias to the Oolite inclusive, our data are too scanty as yet to affirm whether the vegetation of this second epoch was or was not on the whole of a simpler organization than that of our own times.
In the Lower Cretaceous formation, near Aix-la-Chapelle, the leaves of a great many dicotyledonous trees have lately been discovered by Dr. Debey, establishing the important fact of the coexistence of a large number of angiosperms with cycadeæ, and with that rich reptilian fauna comprising the ichthyosaur, plesiosaur, and pterodactyl, which some had supposed to indicate a state of the atmosphere unfavorable to a dicotyledonous vegetation.
The number of plants hitherto obtained from _tertiary_ strata of different ages is very limited, but is rapidly increasing. They are referable to a much greater variety of families and classes than an equal number of fossil species taken from secondary or primary rocks, the angiosperms bearing the same proportion to the gymnosperms and acrogens as in the present flora of the globe. This greater variety may, doubtless, be partly ascribed to the greater diversity of stations in which the plants grew, as we have in this case an opportunity, rarely enjoyed in studying the secondary fossils, of investigating inland or lacustrine deposits accumulated at different heights above the sea, and containing the memorials of plants washed down from adjoining mountains.
In regard, then, to the strata from the cretaceous to the uppermost tertiary inclusive, we may affirm that we find in them all the principal classes of living plants, and during this vast lapse of time four or five complete changes in the vegetation occurred, yet no step whatever was made in advance at any of these periods by the addition of more highly organized species.
If we next turn to the fossils of the animal kingdom, we may inquire whether, when they are arranged by the geologists in a chronological series, they imply that beings of more highly developed structure and greater intelligence entered upon the earth at successive epochs, those of the simplest organization being the first created, and those more highly organized being the last.