pact than those of the preceding epochs, and often oolitic. The following Table exhibits the names and order of the various beds in this formation, as they have been determined by English geologists. 1. Lower oolite. a. Lias, and lias marl. b. Calcareo-siliceous sand. c. Numerous oolitic strata, occasionally subdivided by their argillaceous beds, and distinguished by various local names. a. Great Oxford clay, or clunch clay. 2. Middleb. Calcareous sand and grit. oolite.c. Oolitic strata associated with coral rag (pisolite c. of Smith.)! a. Argillo-calcareous formation of Kimmeridge and the vale of Berks (oak-tree clay of Smith.) 3. Upper b. Calcareous sand (Shotover Hill.) oolite. c. Oolitic strata of Portland, Tisbury, and Aylesbury. d. Argillo-calcareous Purbeck strata. The lias seems to be the same as the muschelkalk of Werner; it is the lowest bed of the series, and lies immediately over the new red sandstone. It consists chiefly of carbonate of lime, but it is tougher than common limestone. 3. The formation lying immediately over the oolite has received the name of green sand, from the green colour which it frequently displays. This formation is of no great extent. It lies immediately under the chalk. It consists of the following beds, lying over each other, beginning with the lowest : (1.) Beds of sand highly charged with peroxide of iron, associated occasionally with coarse limestone. The iron sand of the English geologists. (2.) Blue marl. (3.) Beds of sand usually coloured green, but occasionally brown, containing many petrifactions in the state of chalcedony. (4.) Marl. The sand of this formation often assumes the form of a kind of sandstone, to which the name rag is given, with some epithet indicating the locality; for example, Kentish rag. 4. The last of the horizontal secondary formations is the chalk, so extensively distributed in the south of England and in France, and constituting so beautiful a district of country. It consists almost entirely of low hills, remarkable for their smooth rounded outline, and for the deep hollows and indentations in their sides. The highest chalk hill in England is rather ས་, under 1000 feet. The chalk formation consists of three subordinate beds. The lowest is called chalk marl. It is a mixture of clay and chalk, and is easily distinguished by the property which it has of falling to pieces when moistened with water and allowed to dry. The second subordinate bed is called hard chalk. It has the aspect of chalk, but the hardness of limestone. The finest exhibition of this formation is the hard chalk in the north of Ireland, in the county of Antrim, immediately under the great trap deposit. It contains as many flints as usually occur in the soft chalk. The third and uppermost subordinate bed is the soft chalk, which, in the south of England and in France, is by far the thickest and most abundant of all the beds belonging to this formation. IV. The beds lying above the chalk have been particularly examined in the neighbourhood of Paris, the neighbourhood of London, the Isle of Wight, and one or two other places. They consist of a numerous series of beds, differing very much from each other in different places, and the identity only recognisable by means of the fossils which they contain. V. Still newer than the beds over the chalk are certain deposits in caverns, which Dr Buckland considers as having been formed at the time of the deluge, and which, therefore, he calls diluvial deposits. VI. The newest deposits of all, are those that are still going on at the sea-shore, on the banks of rivers, at the bottom of lakes, &c. in consequence of the slow action of water: these are called alluvial. Such is a rapid view of the different rocks of which this globe, so far as it has been examined, is composed. Let us now see how the different petrifactions are distributed through them. This constitutes the most important point of investigation, because it alone can enable us to determine the changes to which the earth has been subjected since its original creation, and the length of time which may have elapsed before it became fit for the habitation of man. I. Vegetable remains. The secondary formations below the coal beds are very poor in vegetable remains; since only fourteen different species have been hitherto observed-of these four are fuci, obviously sea plants. They all occur in limestone, except the fucoides circinatus, which is found in the sandstone which constitutes the base of Kinnekulla, a transition hill in Sweden. Two are equisetums; five are ferns; two lycopodiums; and one cannot be referred to any known order of plants. The coal formation contains a vast number of fossil vegetables. Indeed, there can be no doubt that the coal itself is entirely derived from decayed and altered vegetables. The opinion of Deluc is the most probable, that it was originally similar to our present mosses, and that it has been converted into coal by being exposed to great pressure, while at the same time the vegetables underwent a species of decomposition. Not a single sea plant occurs in the coal beds; but almost all the fossil plants found in them are cryptogamous. Not a single dicotyledonous plant has been met with, and only a very small number of monocotyledonous plants. Three species occur which have been referred to palms, one to cannæ. But 130 different species of fern have been made out, and fourteen species of calamites. These Brogniart, from the structure, has referred to equisetums. They are quite gigantic, such as nowhere can be met with at present. The ferns all belong to the genera that occur in the torrid zone. Not a single species similar to those which at present vegetate in European climates has been met with. Sixty-eight species of lycopodiaceæ, and seven species of marsileaceæ, have been observed in the coal beds; all of them, likewise, of the kind that belong exclusively to the torrid zone. It would seem from this, that when coal was formed, no dicotyledonous plants existed, and that almost the only plants existing were cryptogamous. The equisetums and ferns found in the coal beds are much larger than any known at present. Many of them formed trees, and the stems of the equisetums are often as large as those of trees. Is it not probable from this, that at the time when coal was deposited, the dry land was but little elevated above the level of the sea? It is obvious that the coal was only deposited on the dry land, as no traces of sea plants ever occur in it. If these conjectures be well founded, it is probable that the formation, or at least the elevation, of the primary strata, took place at a time subsequent to the formation of coal. The magnesian limestone, which lies immediately over the coal, is very poor in fossil vegetables. Only eight species have been observed in it. They are all fuci, and of course sea plants. Twenty species of fossil plants have been made out in the new red sandstone near Strasburg, and described by M. Voltz. Of these, three are equisetums, six ferns, five coniferæ, two lileaceæ, and four doubtful, but belonging to monocotyledonous plants. Thus the plants in the new red sandstone differ completely from those in the coal. The great oolite and lias formation is rather poor in plants. Twenty-two species in all have been made out. Of these two are equisetums, seven ferns, one lycopodium, eleven cycadeæ, and one uncertain. The coniferous plants are entirely wanting in this formation, though they occur in the preceding. The greensand and chalk contain fifty-two different species. Of these three are fuci, one equisetum, twenty-one ferns, one lycopodium, seventeen cycadeæ, six coniferæ, two lileaceæ, and one doubtful. The chalk contains scarcely any but marine plants, viz. two coniferæ, eleven fuci, four nayades. In the formations above the chalk, the fossil plants approach much nearer to those at present existing on the earth. They are very numerous; but, from the state in which they occur, it is almost impossible to refer them to any particular species. As far as we are entitled to draw conclusions from these fossil vegetable remains, we seem warranted to affirm, that the nature of the vegetables on this globe has undergone four different changes. 1. The first period extends from the first traces of fossil vegetables to the formation of coal. The plants which existed at that period seem to have been chiefly vascular cryptogamous plants. The temperature of the earth, even in Iceland, must at that time have been at least as high as it is at present in the torrid zone. An equable climate seems to have existed everywhere, and that as high as the equator is at present. 2. The second period corresponds with the deposition of the new red sandstone. The earth at that time seems to have been mostly covered by the sea; for the fossil plants found are mostly sea plants. 3. The third period begins with the great oolite, and continues till the deposition of the chalk. It is distinguished by the great number of cycadeæ, joined with ferns and coniferæ. 4. The fourth period is distinguished by the preponderance of dicotyledonous plants, and by the absence of plants, differing from those actually existing at present. Such are the inferences to be drawn from the vegetable fossils. Those from the animal fossils are still more decisive with respect to the alterations which the earth has undergone, and the alterations in its inhabitants which have taken place. II. Animal Remains. The animal fossils in the transition rocks belong to the lowest order of animals; corals, and different species of shells, being the only ones that occur. The shells are ammonites, orthoceratites, nautilites, conolaria, and perhaps a few others. These petrifactions occur most abundantly in the transition limestone. No animal of a higher order than corals or shell-fish occurs. In the mountain limestone, which lies under the coal, the species of corals, univalve and bivalve shells, are more numerous than in the transition limestone. The animals inhabiting these shells seem to have been possessed of a power very rarely found in the shell-fish of the present times, a power of rising and sinking at pleasure in the water. Several of that curious tribe of animals, to which the name trilobites has been given, occur in the mountain limestone. Some obscure traces of fish have been met with in the mountain limestone; but none of them has been referred even to a genus, if we except what has been considered as the snout of the xiphias or sword-fish. The animal remains found in the coal beds are chiefly orthoceratites, terebratula, ammonites, and some species of the genera lingula and unio. In a bed of ironstone at Crosbasket, near Glasgow, two species of mussel-shells occur in a very perfect state, but not referable to any species of that genus at present existing. It is in the magnesian limestone lying over the coal that the first animal of a higher order than shell-fish occurs. For in the bituminous marl slate of Thuringia, which is connected with the magnesian limestone, there is found the remains of an amphibious animal, belonging to the genus monitor. The shells of this formation have not been much studied. The productas, donax, arca, anomią, and unio, are the most common. At Sunderland the remains of a fish, of the genus chalodon, have been found imbedded in this formation. The great oolite formation, which comes next, has been subdivided into the lias, the lower and upper oolite. In the lias, corals are rare. It contains but few multilocular univalves, chiefly ammonites, nautilites, belemnites, and terebratulas. The bivalves are numerous, and the most common are ostrea, gryphea, plagiostoma, plicatula, avicula, mya, and cardita. Several species of crustaceous animals occur in it, but always in an imperfect state. Bones and palates of the turtle have also been found. But it is chiefly distinguished by two genera of oviparous qua drupeds, differing in structure from all the genera at present known, and in such particulars as must have fitted them to liv entirely in the sea. These are the ichthyosaurus and the ple siosaurus. live The lower oolite contains traces of alcyonia, and a variety of corals. The crinoid family are rather conspicuous in it. The most common shells belong to the genera pecten, ostræa, terebratula, modiolus, trochus, unio, tellina, modiola, lutraria, trigonia. The remains of vertebral animals are rare. Vertebræ are said to have been found, belonging to marine lizards, nepad 1 In the upper oolite, besides the shells above enumerated, and some others, teeth, vertebræ, and palates of fishes, are found, and also several species of tortoise. Several oviparous quadrupeds |
