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of these strata is neglected. The quern stone, (a pudding-stone of silecious pebbles cemented by a ferruginous silecious paste) is also a production of the red sand. Our author mentions no

fossils peculiar to this stratum, though he says that we find most of the chalk fossils washed down, and imbedded in its upper surface.' This however must be merely accidental, as the sand stratum being inferior to the chalk, and consequently of earlier formation, cannot regularly contain any substance belonging to a stratum of more recent origin. These three beds of silecious sand make together a stratum, according to Mr. Townsend's calculation, at least 300 feet thick.

Beneath the sand we find a bed of clay, the thickness of which may be about 200 feet; but Mr. Townsend's account of this stratum is neither so ample nor so precise as it seems to deserve. He mentions that it is made use of for bricks, at Rowd near Devizes.

The superior oolite succeeds; being the first of three strata, which are distinguished by a structure resembling the roe of a fish, from whence the name is borrowed. They correspond with the marmor hammites of Linnæus, the roggen and hersenstein of the German mineralogists; and, from the ease with which they yield to the wedge, hatchet, and saw, in any direction, are generally called freestone wherever they are worked. The superior oolite has not been well examined. It occurs at Steeple Ashton, Calne, and Shotover, but its thickness, though scarcely less than 40 feet, is not correctly ascertained. Its characteristic fossils are echinites, particularly the mammellated species, but the attendant sand also contains nerites, strombites, pectinites, and oysters. A bed of clay separates it from another stratum, still less perfectly known, the calcareous grit, composed of silecious sand with a calcareous cement, which is followed by the coral rag, a blueish grey, hard, ponderous rock, consisting almost wholly of coral and shells, but so full of fissures and interstices as to be serviceable only for repairing the high roads, and for lime, to which purposes it is applied to the west of Calne. A bed of this rock contains fossil-wood charred into a species of coal. The thickness of the coral rag is about 30 feet, and the mytilus cristagalli, mammellated echinites, trigoniæ, pectinites, buccinites, mytilites, and pholades or fistulanas are abundant in every fragment: it beds upon a blue clay, and is sometimes succeeded by a second bed of calcareous grit.

Under these strata we have one called the clunch clay, with a mixture of marle, sand, shale, and even thin laminæ of coal.' This bed of clay, in which the Wilts and Berks canal runs, is at least 200 feet thick, and contains abundance of large gryphites, generally with a purplish stain, and belemnites, with other fossils, frequent in the alluvial gravel of Bedfordshire. The

thin seams of coal which occur, have given rise to numerous trials by soi-disant practical colliers,' at the expense of credulous and uninformed adventurers.

The Kelloway rock follows, so named from Kelloway Bridge, where it is quarried, for the purpose of mending the road. It is of a dark blue colour, probably stained by the clunch clay, strongly impregnated with iron, and abounds in petrifactions, particularly the gryphite of the clunch clay, numerous arnomites, mytilites, ostreæ, and beautiful ammonites in great variety. It appears to be from three to six feet in thickness, and rests on blue marly clay. Our author has traced its outcrop by Steeple Ashton, Trowbridge, Chippenham, Tytherton, Brinkworth, and Malmesbury, into Oxfordshire and Northamptonshire, and, if we mistake not, it also occurs to the north of Scarborough in Yorkshire.

The corn-brash which succeeds, is a pale yellow, shivered stratum, considerably thicker than the former, and applied only to repair the roads. Its fossils are, several species of anomia, particularly terebratula, spinosa, caput serpentis, and a nondescript, round, gibbous species, two or three species of pecten, mytilus modiolus, and some allied species which have not yet been named, echinus spatagus and mamellatus, with fragments of the pentracrinus, It extends from Temple Combe by Woolverton, Hinton, Tilsford, Melksham, Corsham, Grittleton, Malmesbury, Draycot and Sutton, to the northern borders of Oxfordshire, Buckingham, and Bedford. A bed of clay lies immediately beneath it, which frequently holds up the water, so as to render the corn-brash a very wet substratum; this may however generally be effectually remedied by judicious draining.

The forest marble is separated from the clay bed of the cornbrash by a bed of silecious sand and sandstone, which appears at the surface at Hinton. The forest marble has derived its name from having been first wrought for slabs and chimneypieces in the forest of Deane. It consists almost wholly of shells, so perfectly conglutinated as to admit of a perfect polish, while it precludes the possibility of determining to what species they belong; bits of charred wood frequently occur imbedded in this stratum, and bufonites, palates, and glossopetræ are not unfrequent. The stratum is divided into numerous beds, of different thicknesses, by intervening beds of clay; its thickness may amount to 40 or 50 feet, where all the beds are found, of which somewhat more than half is charstone; the substratum is a whiteish clay.

The second, or great oolite, better known by the appellation of the Bath freestone, lies beneath the forest marble, and appears by Mr. Townsend's account to be at least 140 feet thick, as is also the clay and fuller's earth on which it rests. The

upper beds however are frequently wanting, so that the depth is considerably diminished. It forms the summit of most of the eminencies around Bath, and to the facilities thus afforded to architecture, that city owes its splendour. The principal quarries which supply materials for building in its neighbourhood, are those of Claverton Down, Combe Down, Anthony Hill, Box, Bathford, Kingsdown, Pickwick, and Farley Down; but the stratum may be traced from Mells to Hampton Common and the Cotswold hills. Mr. Townsend suspects the quarries of Barnack to be in the great oolite, but Mr. Farey assigns them a superior situation. In case the latter should prove correct, it is probable that the Barnack ragstone is a solid bed of the cornbrash, which occasionally partakes of the oviform structure of the oolites; but at any rate the Bath freestone has been distinctly ascertained through Somersetshire, Gloucestershire, Oxfordshire, Northamptonshire, Rutlandshire, Lincolnshire, and Yorkshire. In the body of the rock fossils rarely occur, but on the upper surface they are abundant, particularly anomia reticularis, and sacculus, several ostreæ, and the singular pear encrinus. The stems of the latter are found adhering to the rock, so that the consolidation of the stratum must have been completed before any part of the superior bed of clay was deposited upon it. The uppermost beds of the great oolite, which consist almost wholly of fragments of shells, conglutinated by a calcareous cement, contain pieces of wood, bufonites, and palates; and the fuller's earth rock, a stratum which occurs beneath the fuller's earth, has numerous petrified reliquia, by which it is readily detected.

Under the great oolite, the third stratum which is distinguished by this inexplicable structure makes its appearance, and is termed by Mr. Townsend the inferior oolite The provincial name, where the great oolite is worked as freestone, is the bas tard freestone, being generally soft and full of cavities, occasioned by the removal of shells and coralline substances which had been imbedded in it. This stratum may be traced on the map, from Yeovil, by Castle Cary, Bruton, Doulting, Radstock, Midford, Lansdown Crescent in Bath, Swanswick, Crosshands, and Cheltenham, into Oxfordshire and Northamptonshire. Its thickness is about 40 feet, and it rests upon a bed of sand very discernible at Midford, to the south of Bath, and, in the immediate neighbourhood of that city, of at least equal depth.

This porous rock abounds with typolites, or casts of marine shells, which have vanished, and left vacuities unoccupied by cal careous spar. It has likewise numerous fossil shells, by some of which it may be distinguished from all other rock strata. The first of these, at least as far as my observations extend, is a large oyster, of a

transverse fibrous texture, consequently extremely brittle, and seldom found entire. Its fragments exhibit a striated calcareous substance, brown, and resembling asbestus...This rock is likewise distinguished by its shingle of white quartz, and by the anomia spinosa.... It may be identified by the bottom bed, charged abundantly with ribbed and studded trigoniæ, and with their casts, called hippocephaloides, immediately over which is a coral bed, which is compact, extremely hard, and susceptible of high polish... The coral bed contains the madrepora cinerascens, which is found recent in the Indian seas. One of these curious petrifactions was standing upright more than five feet high, and expanding nearly six feet, with a double cap, much fractured, but no fragment scattered to a distance. The remains are to be seen near Midford. In its cavities it contains numerous coated mytili, with their cables covered by a crust, on some of which corals have begun to build...... The covering of our coated mytilus is perfectly smooth, unless when the coral polypus builds his habitation on it.... Over the two beds of this rock which contain the corals and the trigoniæ... in the superior bed we have found nautilites, ammonites, volutes, trochites, turbinites, helix cochlea, helix decollata, arca noæ, madrepora porpita, a variety of the patella ungarica and ostrea diluviana. The sand bed immediately under this rock contains on its surface numerous and perfect specimens of the ostrea gibba, ostrea plica, ostrea edulis, one species of Venus, &c.' pp. 271-274.

With respect to the coated mytili, or fistulanæ, as Parkinson has called them, Mr. Townsend appears to us to be under a mistake, in supposing that the envelope which now surrounds them, formed part of the animal. The fact seems to be this. The mytili, like the recent pholades, bored holes into corals, thick shells, and stones. The first part of the petrifactive process, which took place at the time the stratum was formed, consisted in filling up the space between the shell and the inside of the cavity which it had bored. This furnished the coating now adhering to the shell, and, where the cavity had been formed in a madrepore, obtained an impression from the section of the madreporean structure, as exhibited in Parkinson's Organic Remains, Vol. II. Pl. XII. fig. 1. That this is the origin of what Mr. Townsend takes to be incipient habitations of the madreporean polypus, is confirmed by the circumstance that the striæ of the supposed coral are not perpendicular to the surface of the mytilus, but parallel to one another, and also by numerous similar casts in the surface of madrepores, the substance of which has been removed. The next process was the infiltration which furnished the calcareous spar of the shell itself; and the third removed the substance of the coral, shell, or rock, in which the cavities had been originally bored. Beneath the sand upon which the inferior oolite beds, we have a thin calcareous stratum called the Yeovil marble, and not far from it another, termed the marle stone, from having a fertile blue marle both above and

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beneath it. The total thickness of these beds is from 60 to 90 feet, and in some places probably much more.

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Most of the strata hitherto enumerated, exhibit a somewhat granular texture, seldom admitting of a polish, or possessing any extraordinary degree of hardness. The succeeding strata of lias limestone are of an even close texture, susceptible of a high polish, and equally esteemed in their recent state for repairing the roads, and, when burnt, for architectural purposes, particularly for water-works. Mr. Townsend mentions that the white lias may be readily engraved, and is now in request for the calicoprinters, for maps, and for some kinds of drawings, in which service it is a valuable substitute for copper-plates. The total depth of all the beds of lias cannot be much less than 100 feet, but individually few of them are above a foot in thickness, and most considerably less; they are separated by soft beds of clay, but the surface of the hard beds is far from even, being generally embossed with numerous protuberances; some of them are blue, others of a pale fawn colour. This stratum has been noticed on the south coast at Charmouth and Lyme Regis. From thence it may be traced by Chard, Castle Cary, Glastonbury, where it forms the base of the Tor, Chewton Mendip, Radstock, Farnborough, Stanton Prior, Keynsham, Cottham near Bristol, in the low country from Swansea bay to Cardiff and Newport, by Aberddaw, Gloucester, and Tewkesbury, around the Malvern hills by Dudley and Coalbrook Dale, south of Nottinghamshire, and through Yorkshire to the eastern coast at Tynemouth. The fossils of the lias are numerous and characteristic. Ostrea gryphus, ammonites of an enormous size, and some small oysters are very abundant, but the most remarkable are vertebræ, jaws, bones, and teeth of huge animals, probably species of the aligator. Mr. Townsend mentions one, in the possession of the Rev. P. Hawker, which was found near Bath, and with great industry extracted from its surrounding matrix.

The head is three feet long, and from the eye to the extremity of the jaw is two feet nine inches. It is furnished with one hundred and twenty teeth, which are an inch and an half long, sharp pointed and well preserved. At different times Mr. Hawker procured from the workmen fifty joints of the spine, measuring together six feet, and six joints of the tail, with many vertebræ, and some other bones not well defined.' pp. 275, 276.

Similar jaws are found at Charmouth, but Mr. Townsend gives the figure of one of a different structure, specimens of which are met with occasionally in the lias. The anterior part is polished, and neatly ribbed in a longitudinal direction. As far as we are acquainted with the skeletons of animals in general, we know of no instance of a bone or mandible with a similar surface being concealed beneath muscles and skin, while, on the other

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