The rocks of the old red sandstone period supply the earliest satisfactory remains of plants. The ferns, sigillarke, lycopodites, and calamites, so abundant in the coal measures, make their appearance the newer of these beds, and even fragments of dicotyledonous wood have been observed. The various sections of the invertebrata are well represented, but the remarkable characteristic in the animal life of the period is the abundance, of strange forms of lieterocercal-tailed fish, whose buckler-shields, bard scales, or bony spines occur hi the greatest abundance in sonic beds. The reptiles and reptile tracks in the red sandstone of Moray, originally referred here, are now univer sally considered as belonging to the new red measures.
The striking feature in time rocks of the carboniferous period is the great abundance of plants, the remains of which occur throughout the whole series, the coal-beds being composed entirely of them, the shales being largely charged with them, the sand stones containing a few, and even the limestones not being entirely without them. These plants were specially fitted for preservation, the bulk of them being vascular cryptogams, a class which Lindley and Hutton have shown by experiment to be capable of long preservation under water. They are chiefly ferns; some are supposed to have been arboreseent lycopods. while others (sigillaria, calamites, and asterophylliteR) are so different from anything now known, that their position cannot be definitely deter mined. though it is most probably among the higher cryptogams. Several genera of conifers have been established from fossilized fragments of wood; and some sin gular impressions, which look like the flowering stems of dicotyledonous plants, have been found. The limestones are chiefly composed of crinoids, corals, and brachio potions shells. The corals attain a great size, and the 'crinoids arc extremely abundant, their remains making sometimes beds of limestone 1000 ft. thick, and hundreds of square miles in extent. Many new genera of shells make their appearance. The trilobites, which were so abundant in the earlier rocks, are reduced to one or two genera, and finally with this period. Fish with polished bony scales are found; and others, like the Port Jackson shark, with pavements of flat teeth over their mouth and gullet. fitting them to crush and grind the shell-protected animals on which they fed. Strange fish-:ike reptiles existed in the seas, and air-breathing species have been found on the continent and in America. 'The wing-cases, and parts of the bodies of insects, have also been found.
The permian period is remarkable for the paucity of its organic remains, but this may arise from our comparative ignorance of its strata. The plants and animals are on the whole similar to those found inthe carboniferous measures, and a great proportion of them belong to the same genera. Many ancient forms do not pass this period, as the gig/War/a among plants, and the prodit eta among animals.
The red sandstones of the triassie period are remarkably destitute of organic remains —the iron, which has given to them this color, seems to have been fatal to animal life.
In beds, however, on the continent, in which the iron is absent, fossils abound. These fossils present a singular contrast to those met with in the 5Ider rocks. The paleozoic forms had been gradually out, and the few that were still found in the permian strata do not survive that period. while in their place there appear in the trios many genera which approach more nearly to the living forms. Between the organisms of the permian and t•iassic periods there exists a more striking difference than is to be found between those of any previous periods. Looking at. this life-cha•acter, the rocks from the permian downwards have been grouped together under the title paleozoic; while from the bias upwards the whole of the strata liave received the name of neozoic.
The extensive genera of ammonites and belemnites make their first appearance in the trios. Several new forms of cestraciont fish occur, and the reptiles increase in number and variety; among them is the huge hatrachian labyrinthodon, and the singular fresh water tortoise, dicynodou. The bird-tracks on the sandstones of Connecticut are by some referred to this age. Small teeth of mannalia, believed to be .those of an insec tivorous animal, like the myrmecobius of Australia, have been found in the keeper has of Germany and Somerset.
In the oolitic series we have an abundance of organic remains, in striking contrast to the scanty traces in the permian and triassic periods. Many new genera of ferns take the place of the paleozoic forms, and a considerable variety of conifers make their appearance, some of which have close affinities with living species, one, indeed, being referred to a still existing genus. The same approximation to living types is to he fount! in the animal kingdom. Several of the foraminifers. are referred to living genera. Among the corals, the representatives of two living families make their appearance. No new genera are found among the brachiopoda; but the conchifera and gasteropoda show a great addition of new genera, some of which are still represented by living species, while not many new added to the cephalopoda, though they were individu ally very abundant. In some places the lies shale consists of extensive pavements of belemnites and ammonites. The crinoids give place to the increasing variety of sea urchins and star-fishes. • Numbers of insects have been found. The cestracionts continue to be represented in the oolitic seas, but with them are several true sharks and rays; and the homocereal-tailed fish become Labyrinthodont reptiles abouud: the huge mcgalosaur and its companions occupied the land; while the seas were tenanted with the remarkable ichthyosaur and plesiosaur, and the air with the immense bat-like pterodactyl. Seven genera of mammalia have been found, all believed to be small carnivorous or insectivorous marsupials except the stereognathus, which Owen considers to have been a placental mammal, probably hoofed and herbivorous.