in the same latitudes, for the older floras of the temperate zones exhibit in many respects a tropical aspect. In the cretaceous and tertiary periods, the flora embraces many genera of the existing flora of the temperate zones. In the successive faunas also, even of the ocean bed, we are to take into consideration the existing physical conditions. In the very early periods coarse and fine sediments are found, indicating, if not shore lines, at least shallow and disturbed water on one side, and deeper seas with quiet water and finer sediments on the other. The geographical extension of species does not always correspond with the nature of the sediments; for while in the Trenton period we have a large number of brachiopoda extending over wide areas, even as far west as the formation is known, the same is not true of the Hamilton group, although the physical characters of the two formations appear to have been equally uniform. This fact, however, does not furnish an argument in favor of gradual climatic or other permanent changes; for again in the carboniferous period certain forms of brachiopoda have even a wider range than in any preceding period.—The causes affecting the distribution of the faunas and floras of the several geological periods cannot be discussed in a sketch like the present; but that these have successively appeared and disappeared is ascertained in every part of the habitable globe. Of the succession or coming in of new species we have everywhere abundant evidence; and in a great proportion of instances they could not have been derived from sources very far from where we find their imbedded exuviæ.
| TABULAR ARRANGEMENT OF THE GEOLOGICAL FORMATIONS, WITH THE NAMES OF SOME OF THE CHARACTERISTIC ORGANIC REMAINS. | |||
MODERN
OR QUATERNARY. |
Post-tertiary. Recent and post-pliocene. |
Alluvial deposits, peat, calcareous tufa, glacial and modified gravel, with remains of man; associated plants together with extinct fossil mammalia—elephas, mastodon, megatherium, mylodon, glyptodon, &c.: with shells, &c. | |
CENOZOIC OR TERTIARY.
|
TERTIARY.
|
Pliocene. | Mostly marine shells, bivalves and univalves in great numbers, and largely of living forms. The fossil flora indicating a warmer climate than the present. |
| Miocene. | The upper part with some extinct mammalian remains, elephas, mastodon, sivatherium, hexaprotodon. The fossil flora contains species of acer, platanus, smilax, &c. The marine fauna with a mixture of extinct and existing species (India). The lower miocene has a greater proportion of extinct forms, and is remarkable for its great number of extinct mammalian remains, especially in the western part of this continent, among which are rhinoceros, oreodon, brontotherium, titanotherium, palæotherium, anchitherium, archæotherium, machærodus, &c. | ||
| Eocene. | In the upper part, land and fresh-water shells, with mammalian remains; marine shells, corals, foraminifera. Many remains of sharks of enormous size. Cetaceans (whales, zeuglodon, &c.), herbivores, carnivores, ruminants, pachyderms, monkeys, &c., first appear. | ||
MESOZOIC OR SECONDARY.
|
CRETACEOUS.
|
Upper cretaceous (Maestricht chalk, white chalk, and chalk marl). | Characterized by remarkable forms of saurians of several genera, mosasaurus, &c., chambered shells (ammonites), univalve and bivalve shells, echinoderms, and corals; brachiopoda, mostly rhynchonellidæ and terebratulidæ; and the remarkable family rudistes; and in America by a fossil flora analogous to the tertiary and recent forms, as maple, willow, beech, poplar, elm, sassafras, &c. |
| Lower cretaceous or Neocomian (Wealden). |
Many cephalopods, including ammonitoid shells in a great variety of forms, with many peculiar forms of bivalve mollusca, as well as the ordinary forms. Fishes allied to the garpike. A remarkable fresh-water saurian (iguanodon). The flora is characterized by a great number of coniferæ cycadeæ, and ferns. First appearance of deciduous trees. Bony fishes (teliosts) become common; crocodiles and cetaceans (whales). | ||
JURASSIC.
|
Oölite, Upper. Middle. Lower. |
Marsupial and insectivorous mammalia—amphitherium, phascolotherium. A remarkable form of bird, archæopteryx. Flying reptiles (pterodactyls). Large numbers of fishes, insects, crustaceans resembling the common crawfish, chambered shells (ammonites, belemnites, &c.), univalve and bivalve shells. Brachiopoda, echinideæ, crinoidea, corals, &c. Among the fossil plants the cycadeæ predominate (zamia being the prevailing genus), with coniferæ and ferns. | |
| Lias. Lias (limestones and slates). |
The lower (liassic) beds are characterized by remains of gigantic saurians, ichthyosaurus, pterosaurus, &c.; fishes of the shark family and others; insects, with mollusks of the several orders, and extravagant forms of crinoidea, &c. | ||
TRIASSIC.
|
Upper, middle, and lower trias.
Red sandstones of Connecticut valley. Shales, sandstones, and beds of bituminous coal. |
Mollusca numerous; the cephalopods chiefly of the genera ceratites, ammonites, and orthoceras, the latter genus becoming extinct in this formation. Last appearance of the brachiopodous family spiriferidæ. One form of encrinite abundant. Fish teeth and saurian remains. A remarkable batrachian form, the labyrinthodon. First appearance of mammalian remains in microlestes and dromatherium. Tracks of saurians and birds (?) both in Europe and America. First appearance of crawfish-like crustaceans. A remarkable coal field near Richmond, Va., with an abundant fossil flora. All classes of the vertebrata, viz., fishes both of the cartilaginous and bony forms, reptiles, amphibia, birds, and mammals, are represented in this epoch. | |
