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The lower division of oolite comprises; first, an imperfect dark brown limestone, much intermixed with sand and the oxide of iron; 2ndly, beds of sterile clay and fullers-earth; and, 3rdly, the great oolite, which is of considerable thickness, and yields freestone for architecture: it is composed of minute globules and broken shells, united by a yellowish earthy calcareous cement. With the lower division of oolites may also be classed, 4thly, the Stonesfield slate, which is a sandy calcareous stone, dividing into thin strata, accompanied with shale and carbonaceous matter. 5thly, forest marble: the beds are not numerous, and are chiefly composed of large fragments of shells; small entire turbinated shells abound in some of the strata. It deserves attention, that the univalve shells are most frequent in the thin beds, and the bivalves in the thicker beds, of this stone. 6thly, cornbrash. This is the upper part of the lower division of oolites; it does not compose beds of any considerable thickness, nor does it frequently occur in regular strata of any great extent, but generally in detached masses, cemented by clay: the external part of the stone is brown, but the inner part has often a gray or blueish colour. To Mr. Wm. Smith we are principally indebted for the first accurate account of the different beds of the oolite formation: he observed that though the total thickness of the cornbrash beds is but small, there is a considerable difference between the fossils in the upper beds and those in the lower ones.

Between the lower and the middle division of oolites, there are beds of dark blue clay called Oxford or Clunch clay; the thickness has been esti

mated at two hundred feet. Some of the beds are bituminous, and bear a near resemblance to lias clay; they abound in Septaria: other beds are much intermixed with calcareous earth. In the lower part of the Oxford clay, irregular beds of limestone occur, which have received the name of Kelloway rock, from being found near Kelloway bridge, in Wiltshire. The bones of one species of ichthyosaurus, different from those in the lias, have been found in the Oxford clay.

The MIDDLE DIVISION of oolite consists, 1st, of beds of siliceous and calcareous sand: 2ndly, the coral ragg, composed of loose earthy limestone, sometimes entirely formed of several species of branching madrepores; and 3rdly, the upper oolite: this agrees in many of its characters with the great oolite, but is more perishable; in some of the beds, the oolitic character is scarcely discernible, in other beds the globules are as large as peas; it has hence received the name of Pisolite. The total thickness of all the beds in this division has been estimated at two hundred feet.

Between the Middle and the Upper division of oolites, there occurs another thick bed of clay, which has received the name of Kimmeridge clay. It is a grayish clay passing into the state of shale, and is sometimes so bituminous as to be used for fuel; its thickness in some parts is more than one hundred feet. Bones of saurian or lizard-shaped animals have been found in this clay, and also bones of animals of a higher order allied to the whale or seal. The UPPER DIVISION of oolite comprises the beds of Portland stone, which have been well described

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as a calcareo-siliceous freestone, with beds and nodules of flint. In the Isle of Portland, where the middle bed of the Portland stone is quarried for architectural purposes, it is covered by a creamcoloured stone called cap, which is only burned for lime: under this, there are two beds of workable stone, each five feet thick, separated by gray flint, and a third bed of the best stone below. The total thickness of the three beds of building-stone varies from 17 to 24 feet. The Purbeck beds are by some geologists classed with the oolites; but they may more properly be regarded as a distinct formation, belonging to the iron-sand, as the fossils contained in these beds differ much from those in the oolite, and are supposed to be freshwater shells.

The calcareous sandy slate of Stonesfield, near Woodstock in Oxfordshire, is believed to form a member of the lower oolitic series; but its organic remains are so different from those in any known beds of oolite, that until it can be seen actually covered by some undisputed member of the oolite series, a doubt must be entertained whether it may not be a portion of a more recent formation out of its place, as we find chalk occasionally beyond the limits generally assigned to it.

The Stonesfield slate consists of two beds of yellowish or grayish oolitic limestone, each about two feet thick, and separated by a bed of loose calcareous sandstone about the same thickness. The Stonesfield slate on exposure to frost divides into thin plates, which are used for roofing. The stone is obtained by working horizontal galleries in the hill, which galleries communicate with deep per

pendicular shafts. It is to be regretted that no account has been yet published of the different strata of stone sunk through by these shafts, as we might hence derive decisive evidence, respecting the true geological position of the Stonesfield slate..

The fossil remains in the Stonesfield slate, consist of the impressions of the outer cases or elytra of winged insects, and the bones of animals of the opossum or didelphis genus, and also the bones of the megalosaurus or gigantic lizard, supposed to be analogous to the Monitor. From the size of these bones, it is estimated that the animal to which they belonged, was forty feet in length and twelve feet high. Legs and thigh bones of birds are also found in the Stonesfield slate, with the teeth, palates, and vertebræ of fishes, and two or three varieties of crabs and lobsters. Several varieties of marine shells and of plants occur in the same beds. The most remarkable circumstance attending these fossil remains, is, that they should occur in strata which are generally believed to have been deposited before the creation of terrestrial mammalia. If how ever, there were islands, inhabited by the higher class of animals, when the oolite beds were forming, their bones may have been carried down by rivers into the sea, and deposited with those of marine animals. But though this hypothesis might satisfactorily explain the occurrence of these remains in the Stonesfield slate, it would still be not less extraordinary, that similar remains should have been no where found in any of the upper secondary strata in England, nor in other countries; and that they are never met with, except in strata consi

derably above the chalk formation. The occurrence of wood, and beds of lignite (or wood coal) in oolite, confirms the opinion that dry land existed somewhere in the vicinity at the period when the oolitic beds were formed or deposited; but no indication that the land was inhabited by terrestrial quadrupeds has been hitherto discovered, except in the slate of Stonesfield. In the strata above the oolite, particularly in the iron-sand of Cuckfield, the bones of the megalosaurus and crocodile, and those of turtles, birds, and fish, present a similarity to the fossils of Stonesfield; but the bones of terrestrial quadrupeds are wanting, and many of the shells are fluviatile. But where was the island on which the animals lived and flourished, that have left their bones in the strata of Stonesfield? This question will be considered in the brief chapter I propose to give of the Geology of England.

OBSERVATIONS.

The oolites on the continent are frequently accompanied with beds of lignite: in England, lignite is not found in oolite, but in the thick beds of clay which separate the upper and the middle divisions of this formation. In returning from the county of Durham in 1820, I took a hasty morning survey of the oolite of the Cleveland Hills in Yorkshire, in the immediate vicinity of Thirk. I had not time to visit the coal mines; but from the specimens of coal I saw lying by the road side, I should consider it as a lignite, and not a true mineral coal: it is chiefly employed in burning lime, and is not used for domestic purposes, except by the poor. The oolite of the Cleveland Hills inclines to a light smoke gray colour; it is distinctly oolitic; the stone is more compact and hard than the oolites of Oxfordshire or Gloucestershire, and bears a near resemblance to some of the lim stone beds on the Jura, which I saw the same summer. The

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