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physiological sources, viz, the causes of the production of heat | a small piece of amadou or tinder. The tube now being full in living beings.

of air, the piston is quickly and forcibly driven to the bottom Mechanical Sources. The friction of two bodies against each by the hand; the compressed air then instantly inflames the other develops a quantity of heat which increases with the amadou, wbich will be seen burning, if the piston be instantly pressure and velocity with which they are are rubbed. For and rapidly withdrawn from the tube. The inflammation of example, the axle-boxes of carriage wheels, by their friction the tinder in this experiment implies at least a temperature of against the axle, are frequently heated so much as to take 300° Cent. or 572° Fahr. At the instant of compression, it fire. Sir H. Davy partly melted two pieces of ice by rubbing produces a very sensible light, which was at first ascribed to them together in an atmosphere below the freezing point. By the high temperature to which the air has been carried; but boring a mass of bronze under water, Count Rumford found it has been discovered to arise from the combustion of the oil that in order to obtain 250 grammes (about half a pound and with which the piston is greased. an ounce) of filings, the heat developed by the friction was It is by the elevation of temperature which it generates, sufficient to raise 25 kilogrammes (about 55 pounds) of water that pressure is sufficient to produce the combination, and from 0° to 100Cent. In the tinder-box apparatus, it is by consequently the detonation of a mixture of oxygen and the friction of the steel against the flint that the metallic par- hydrogen. The heat disengaged by compression is explained ticles,

which are detached, are so heated as to take fire in the by the closer bringing together of the particles, which causes air. The heat disengaged by friction is attributed to a vibra- a certain portion of latent heat to pass into the state of sensible tory motion thus communicated to the particles of bodies. heat. Percussion is also a source of heat, as may be proved

It has been supposed that a cast-iron stove could be made by hammering a malleable metal on an anvil. The heat thus so as to hear the whole of the air of an apartment by the single disengaged arises not only from the closer bringing together of operation of a motion of rotation. This ingenious process has the particles, but also from a vibratory motion ; for lead, which not only been proposed, but even put in practice in some part is not increased in density by percussion, is a metal which does of America; but it is evident that this could only be useful not admit of being thus heated. where moving power was abundant and of very little value, as Physical Sources. Of all the sources of heat known to us, in certain mountainous regions, where waterfalls are very | the most intense is the sun. Of the cause of the heat given considerable, and where, free from the action of frost by their out by the sun, we are ignorant: some consider it as a faming velocity and temperature, they can be found at every step. mass liable to immense eruptions; while others say that it is The following is a representation of a fire-place heated by the composed of strata which chemically re-act on each other, like friction of a mill-stone, and answering the purpose of cooking the couples in the voltaic pile, and that thus electric currents victuals and warming the house. See fig. 224.

are generated which are the sources of the solar light and

heat. On either hypothesis, the incandescence of the sun Fig. 224.

would have its limit. Experiments have been made in order to measure the quantity of heat annuelly emitted by the sun. M. Pouillet, by means of an apparatus which he calls the pyrheliometer (sun-fire-measure), has calculated that if the quantity of heat which the earth receives from the sun in the course of a year, were entirely employed in melting ice, it would be capable of melting a stratum of it round the globe of about 34 yards in depth. Now, according to the surface which the earth presents to the radiation of the sun, and according to the distance between them, the earth receives only mydoooou part of the solar heat.

If we had the sun always at our disposal, howerer feeble his rays might become at certain times of the year, we could still, by means of very simple artifices, draw from it a sufficient quantity of heat for the purpose of heating our apartments. Thin and transparent bodies, particularly squares of glass, possess with regard to the solar rays a very singular property which cannot be too extensively known. For instance, if we take a box, see fig. 226, having one of its sides open, close

Fig. 226.

When a body is compressed in such a manner that its density is increased, its temperature rises with the diminution of its volume. This phenomenon, which is scarcely sensible in liquids, is manifested in solids to a considerable degree; and in gases, which are extremely compressible, the disengagement of heat is still greater. The powerful development of heat which is produced by the compression of a gas, is shown in the Tachopyrion, or Fire-syringe. This instrument is composed of a thick glass tube or brass cylinder, in which a piston, covered with leather, moves so as to be air-tight.

See °At the bottom of the piston is a small cavity, in which is put

fig. 225.

Fig. 225,

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241 this opening with a square of glass, and then expose it to the the mean temperature at the surface to be 10° Centigrade or sun, the rays will immediately strike against it. These rays 50° Fahrenheit, a depth co, of about 200 feet will give a temwill not all penetrate into the interior of the box, but the perature of 12o Centigrade or 53o.6 Fahrenheit ; a depth A A, greater part of them will pass through the glass and tend to of about 1,600 feet will give a temperature of 25° Centigrade heat the interior. If the opening were not closed by a square of glass, the rays having once reached the interior would go out

Fig. 227. as freely as they entered, and apart from the influence which they might have on the sides, the temperature of the interior of the box would be the same as that of the exterior. But things happen otherwise in the case of the glass square. The calorific rays have no longer the same facility in going out which they had in going in. The square performs the office of & valve which only opens inwardly. If there be only one square for the rays to pass through, a considerable number of them manage to escape ; but if there be a number of squares in succession for the rays to pass through, the more will they be prevented from escaping, and a greater number of rays will remain prisoners. This process will be continually taking place with new rays, and the longer the machine is placed in the sun, the more will they collect, and the more will the heat increase inside. Moreover, the stronger the heat becomes, the greater will be the number of squares necessary to preserve it. But with a sufficient number of squares we can, in a small stove, develop a heụt strong enough to cook eggs or to prepare beef-tea. The construction of hot-houses is founded on the observation of these phenomena, the knowledge of which remounts to a remote epoch, but the explanation of which was reserved for modern physics. Terrestrial or Central Heat.-The temperature of the interior of the earth is in winter always higher than the temperature of the surface. If we take, for example, the air which has penetrated into caves or still “deeper cavities, and make it ascend by proper channels into the interior of houses, we shall be able in fact to mitigate the rigour of the cold, although in a very limited manner. In some mills driven by water, for the purpose of preventing the moving power from freezing, and the motion of the wheels from being stopped, it is usual to pass a stream of water through the earth before it reaches the sluice; this water is heated in its subterranean passage, and prevents or 970 Fahrenheit; and a depth B B, of about 3,000 feet will give the cold water with which it is mixed from freezing in the a temperature of 38° Centigrade or 1009.4 Fahrenheit. In the Water-course which supplies the mill. This mode of warm- artesian wells of Grenelle, at the depth of 1,798 feet, the teming is the most economical that can be imagined; but unfor- perature is 27°.8 Centigrade or 82° Fahrenheit. tunately its applications are of too limited an extent. It

Various hypotheses have been framed in order to account includes

, however, the germ of a principle which should create for the central heat of the globe. That most generally adopted an immense revolution in our means of warming buildings. by philosophers and geologists is, that the earth existed at first It is well known that the farther we dig into the interior of in a liquid state, by the action of an elevated temperature, and the earth, the more is the temperature found to be elevated. that by radiation the surface was gradually solidified so as to The terrestrial globe, in fact, possesses a heat of its own, form a solid crust, which is in reality only about 45 miles in which is denominated the central heat. At a depth not very thickness, the central mass being stiil in a liquid state. As to the great below the surface, and which varies with the country | process of cooling, this can only be extremely slow, on account where the shaft is sunk, we meet with a stratum of earth of the weak conducting power of the terrestrial strata. It is whose temperature remains the same in all seasons of the on this account, also, that the central heat does not appear to Fear; whence we conclude that the solar heat only penetrates raise the temperature of the surface of the ground by more underground to a certain determinate depth. Then, below than one thirty-sixth part of a degree Centigrade, or onethis stratum, which is denominated the invariable stratum, it is twentieth of a degree Fahrenheit. found that the temperature increases at a mean, by 10 Centi- Heat of Molecular Phenomena.—The phenomena of molecular grade for every 30 metres deeper that the shaft is sunk; that action, such as imbibition and absorption, capillary action, etc., be 10 Fahrenheit for every 56 feet. This law of the increase are in general accompanied by the development of heat. M. of temperature underground has been verified at great depths Pouillet has found that whenever a liquid is poured on a puldepth of 3,828

yards

, the temperature of the stratum has been according to the nature of the substances. With non-organic The existence of the

central heat is confirmed by that of ther- rise in the temperature is from two to three-tenths of a degree; mal springs and volcanoes. As already observed, the depth of but with organic matter, such as sponge, farina, starch, be invariable stratum is not the same at all points on the liquorice-root,

dried membranes, etc, the increase in tempeearth's surface. At Paris

, it is 294 yards, and the temperature rature varies from one to ten degrees. The absorption of gases this depth is constantly the same, namely, 110.8

Centigrade by solid bodies presents the same phenomenon. M. Dobe330-24 Fahrenheit. Fram the preceding data, we can calcu- reiner found that if powdered platinum, such as may be

to what depth it will be necessary to sink obtained in the state of a chemical precipitate, under the name dabast in order to obtain water of a certain degree of heat; of Platinum black, be placed in oxygen, this metal will absorb fed if this water were once brought to the surface

, it would about 260 times its bulk of that gas, and the temperature will lehet eges, by passing it through pipes to a limited distance. Spongy platinum, which is obtained by precipitating the chioin the following diagram, fig. 227, there is a representation of ride of platinum with sal-ammoniac (chloride of ammonium), forum 3,200 feet, showing the interior strata and three artesian takes fire by the disengagement of the heat due to the absorp: pela terminating at different depths, and sending up to the tion. On this principle is constructed the hydrogen lamp: surface water of three different temperatures.

Supposing | This apparatus is composed of two glass vessels, fig. 228.

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The upper vessel, A, is inserted in the lower vessel B, by | Lower Greensand of the chalk iormation, you come to a group means of a ground tubular neck, which is rendered air-tight, of rocks called the police (pronounced 60-0-lite). The name At the end of this neck is a mass of zine, z, immersed in water of this sytem of rocks is derived from two Greek words-wòv, charged with sulphuric acid. The reaction of the water on the 00-un, an egg, and sites, lithos, a stone-eggy-stone, er the acid and the metal, produces a disengagement of hydrogen, egg-rock. The rock is called oolite on the ground that, where which at first finding ro n-eans of escape, drives the water of it was first especially examined, the slons consisted of diminuFig. 228.

tive egg-like grains, much resembling the roe of a fish; and hence called, sometimes, the roe-stone. Each of these egga like grains has within it a microscopical fragment of sand, or worn coral, as a nucleus, around which, as the grain was rolled along in a stream of limy water, layers of calcareous matter gathered arɔund it, and when it became too heavy for the water, it sank into the calcareous bottom, and formed what is now called oolite.

The oolite group of rocks is sometimes called the Jurassic System, from the fact that they form the great mass of the

Jura mountains, which separate the north-east of France from OD

Switzerland. But when the system is bælled Jurassic, it comprehends the lias, on which the colites rest.

The colitic system is generally divided into three great
groups, called the Upper, the Middle, and the Lower,
UPPER.

\ A. Portland Stone and Sand.
B. Kimmeridge Clay.

Coral Rag.

Z

MIDDLE. ( 0. Oxford

Clay,

B. Cornbrash.

F. Forest Marble.
LONER.

e. Great Oolite, or Báth Stone. the vessel s into the vessel a, until the zinc is no longer im

H, Stonesfield Slate. inersed in it; the cork of the upper vessel is employed laterally

1. Fullers' Earth. so as to allow the air to escape as the water ascends. A short

3. Interior Dolite, or Cheltenham Stone. copper tube, i, fixed on the side of the vessel B, carries a All the colitic strata develop themselves as you travel from small conical piece, E, having an orifice, above which, in a London to Bath. On that route you find that the different capsule, p, is placed spongy platinum. Now, as soon as the clays and limestones have given rise to high escarpments and stop-cock which closes the copper tube is opened, the hydro- wide valleys. Between each valley covered with clay, the gen is disengaged and burns in contact with the platinum. limestone beds, whether they be of chalk or oolite, form hills Great care must be taken not to present the platinum to the and mountains, which terminate abruptly towards the west, current of hydrogen, until this gas has expelled all the air while from underneath them the clays are seen to rise. This which is in the vessel B, otherwise there would be a strong is represented in fig. 6, detonation arising from the combination of the oxygen and hydrogen contained in the vessel B. The heat produced by 1. LITHOLOGICAL CHARACTER OF THE OOLITE. the changes in the state of a body have been already invesrigated under the heads of “Solidification" and “Liquefac.

J. THE UPPER OOLITE. tion," in a former Lesson; and as to the heat developed by A. PORTLAND Stone. -The Portlarid stone is well known electricity, this must form part of our separate chapter in as supplying a valuable building material, which is especially Physics, under that title,

adapted to ornamental architecture. Large quarries of it have been opened at Purbeck, in Dorsetshire, and at Fonthill

and Tisbury, in Wiltshire. This bed has, in reality, three LESSONS IN GEOLOGY.--No. LIV.

seams or layers. 1. The uppermost, which is of a yellowish

colour, is called by the workmen the cap, and is burned for By Txos, W. JENKYN, D.D., F.R.G.S., F.G.S., &c. lime. 2. The middle, which supplies the very best building CHAPTER V.

stone. 3. The lower, which contains the casts of shells, and

is, on that account, not so fit for being tooled. THE CLASSIFICATION OF ROCKS.

B. KIMMERIDGE CLAY.-Kimmeridge is the name of * SECTION VII.

village in a small bay of the isle of Purbeck, where this clay THE OOLITES.

is best developed. The clay is slaty in texture, blue and

yellowish in colour, and consists of calcareous or limy inatter IMMEDIATELY underneath the Purbeck beds of the Wealden, abounding with vegetable and animal remains. or, where there is no Wealden, immediately underneath the Some beds of this clay are very much like peat, and so

Fig. 6. Dolitic Strata between London and Bath.

IY

A Lonlon Clay, D. Chalk. c. Gault.

D. Upper Oolite.

. Kimmeridge Clay, i, Lower Colite. I. Lixs.

F. Middle Oolito. 6. Oxford Clay.

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II. THE MIDDLE OOLITE.

bituminous or pitchy as to be used for fuel, and it is, on that 15. Sandstone, containing clays and seams of coal, ard ironaccount

, called, in some places, Kimmeridge coal. It barns stone with vegetable remains. 6. A bed of limesione and dully, with a yellow smoky flame, having a strong emell of sand, corresponding with the interior oolite of the south of piteh. Some suppose that this mass of bituminvus matter England. results from the decomposition of vegetables ; but others, on Át Brora, also, on the east coast of Sutherlandshire, in the account of the bed abounding with marine shells, suppose it north oi Scoriand, are found shelly limestones with al: errations to be of animal origin,

of sands and shales, iron-stones with remains of plants, tertus In some places the beds contain the sulphate of lime and ginous or irony limestone with fossil wood and sheils, and iron pyrites (pronounced pee-ry-tes). This remarkable cirsandstones and shales with thin beds of coal. cumstance is accounted for by the supposition that the iron E. CORNBRASH.—The comhrash is an impezret limestone, pyrites, in decomposing, produces sulphuric acid, or oil of rough and rubbly, of a brown and earthy appeara.ce. This vitriol, which, by uniting with the calcareous or limy matter rock generally separates into thin layers. It is cnieily burned in the clay, forms the sulphate of lime.

for lime; tut occasionally, when masses of considerabile thick. In England these two oolitic beds, A and B, are found oniyness of it are found, it is used for builling, as about Malmes. in the southern courties of Wiltshire and Dorsetshire, where bury, in Wiltshire. It has immediately underneath it a bed they form beds of different thickness, averaging from 70 to of biue clay, which is sometimes of very great thickness, and 700 feet.

rests on a siliceous grit-stone.

F. FOREST MARBLE.-The forest marble consists of brownish

beds of argillaceous or clayey limestone, full of marine fossils. The strata of the middle oolite försists of gritty im nerfect | The more solid beds in this division furnish a stone of suffilimestone, forming a freestone-very perishable for building cient compaerness to receive a polish, and is hence called a materials, as may be seen in several of the older buildings oi maröle. Oxford. It is full of broken or comminued shells, and con

'The thir, beds afford coarse roofing tiles and rough flagstones, sists, in different places, of from one-tenth to one-third u1much used in West Wiltshire and in Somerset. The different sand, The middie ooliie is divided into three beds. i. The coral twelve inches in thickness.

layets are separated by thin seams of clay, from one inch to rag. 2. The calcareous gris. 3. The Oxford cing.

The whole rests on a deep bed of marly deposit called the c. The Coral Prag - The coral rag is a kind of Futbly Brailford clay, full of organic remains. limestor,e, formed chieily by the branchina vorul cailed mi

G. GREAT OOLITE.-The great oolite consists of calcareous
drepures. This store or rag is calied "corso", because its heds, having different degrees of compactness and consistency.
bed. consists of masses of patriard corais, who appear to The softer beds are perfectly oolitic, or consisting of egg-shaped
retain the very position in which they grew at the bottom of particles; but the harder and more compact beds have less of
the sea. These masses of coral rock are sortim's fitteen feet ihat roe-like appearance.
thick. It is used only for burring iime and mending roads. The best of ihree beds supply that beautiful building mate-

Between the coral rag and the Oxford clay, is found a bed rial called the Bath stone, which, on account of its softness
of calcareous or l.my grit, consistitg chiefly of siliceous of when taken from the quarry, is capable of every variety of
flinty sard of a yellowish colour, having in it about one-third artistical embellishtnent. St. Paul's Cathedral, in London, is
of calcareous matter.
These two beds form a rock of from 100 to 150 feet in thick - The hills around Bath are composed of it, and the city of Bath

built of this stone from a quarry at Burford, in Oxfordshire. ness; but at Whiteham-hill, in Berkshire, it attains an eleva- is built with it. When in the quarry, the Bath stone is soft tion of 576 feet.

and yellowish, but by exposure it becomes hard and white. D. The OxFORD CLAY.–The Oxford clay is very tenacious, H. Stox ESFIELD SLAT 19.-The Stonesfield slate is a bed of dark blue in colour, but brown on the surface. It forms a limestone of ouly six feet in thickness, and it is but very bed of great thickness, and contains masses of Septaria, or slightly bolitic. It was first known at Stonesfield, near Woodcement-stone. In some places these Septarin are called Turtle-stock, in Oxfordshire, and subsequently at Hinton, near Bath, stone ; in others, Melbury marble, from a district of that name Colly weston, in Northamptonshire, and the Cleveland Hills,

in Yorkshire. The bed, though thin and limited in extent, is In some places the Oxford clay is found combined with remarkable for the abundance and the variety of its fossils, bituminous matter, and forms an inflammable shale, like that buih vegetable and animals of the Kimmeridge clay, à circumstance which lias led to several abortive attempis at discovering coal. In the lower

'The quarries at Stonesfield exhibit different fossil beds of parts of this clay are remarkable beds of limestone, which is buff coloured politic Jinestones, called Pendle, each seam formed almost entirely of one mass of fussil shells. 'This sin- | about two feet in thicklites; separated by a bed of loose gular bed has been called Kelloway rock, on account vf its sard talleil Race of the same thickness. Imbedded in this being so well developed at kelloway-bridge, weat Chippenham, look like cakes, of limestone, from six inches to two feet

limestone are concretions called Whimstone, or Potlids. These The Oxford clay, like the Kimmeridge, contains iron pyrites into parallel' Hakes, and as they separate, their surfaces often

in diameter, and often blue in the centre.

This cake splits for when a mass of the clay is burned, it emits a very offensive expose impressions of shells. "The masses of the bed called snell. The well of Mulksham Spa, in Wiltshire, which is a l'endle are allowed to lie exposed to a winter's frostdy and suphureous chalybeate

, is sunk in this clayey stratum. The then, when struck hard on the edge, they also freely split into Kingsclifi

, in Northanptonshire; and Stansfield, in Lincolntime is the case with the springs at Cumhor, in Berkshire; nakes suficiently thin to be used for touring.

At Collyweston, the Stonesfield strata contain some fossil

ferns of a species common to the beds of the Yorkshire oolitek, The bed of the Oxford clay is very deep, and is estimated at where, on the castern coast, rocks of the bolitit age put on 700 feet. At Boston a well was sunk in' it to the depth of every aspect of a real coal field, and where thin stums of coal

have been actually worked, as in Brora in Sutherlandshire, II. THE LOWER OOLITE,

ny years.

1. Fuilers' Larti.- Under the Stoncsfield limestone is a The Power ovlites form a vety extensive group, consisting of deep bed of clay. In many places this bovi of clay is much like hard rocks with intervening beds of sands and clays. The Fullers' earth ; but ut Odd-down, near Bath, the bed is teally 2. Cornbrash. 2. Forest marble. 3. Great oolite. 4. Stones- stone of a blue colour. This bed is entirely wanting in the field slaze. 5. Fuilers' earth. 6. Inferior oolite,

oolites of Yorkshire and Sutherlandshire, In the northern parts of Great Britain the beds differ in 3. INFERIOR DOLITE.-The inferior volite, not to be con litholoyical character from those of the southern parts.

founded with the phrase "lower oblitus," is a calcareous In Vokshire, as developed on the eastern coast, the division (rock, coarse and gritty. It is distinguished from the great thin layers of coal. 4. Calcareous sand and shelly limestone. I and by being inore mixed with siliccous sand. In its midlani

in Dorsetshire.

in Wiltshire,

shire.

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and northern course, in England, it consists of siliceous and has no corals, but it has fossil Ammonites, No. 12, and Belem. ferruginous sandstone, supplying sometimes hard and gritty | nites,

No. 4, in great abundance. flagstones, but of very little use in building. In the south- 4. The Great Oolite, near Bath, contains various corais, western counties it is more calcareous, and more compact, especially the Eunomia rudiata. In the face of the quarry, á furnishing good building materials, which, though of darker single individual of this species of coral sometimes forms a colour than the Bath stone, is scarcely inferior to it. It is mass of several feet in diameter. That individual coral must sometimes called Cheltenham stone. Fine quarries of it have have taken many centuries to grow to that size. been opened in Dundry Hill, near Bristol, and at Doulting, In this bed are also found different species of Encrinites or near Shepton Mallet.

stone lilies, represented by No. 15. These must have had a

firm ground at the bottom of the sea, where their roots must II. THE ORGANIC REMAINS OF THE OOLITE.

have remained undisturbed for many centuries. No. 15 repreThe colitic series of rocks presents a good field for the study sents an Encrinite, called Enerinites moniliformis, as it grew on of Palæontology, for each subdivision in the system is distin. the surface of the Great Oolite. In the tall figure, the arms guished by its peculiar fossils. Our next illustration repre- of the coral are closed, but to the right, a young one has its sents some of the shells and other organic remains found in arms expanded.

5. The Stonesfield slate abounds in the fossil remains of

this group

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1. The Portland stone abounds with organic remains, tortoises, of two or three varieties of the crab and lobster tribes, especially of marine shells, such as the Trigoniæ, No. 8, and the backbones of fishes, marine shells, bones of birds, parts of ammonites, like No. 10 and No. 12, sometimes two or three insects, and especially the wings of a beetle. What has feet in diameter. Corals are rare in Portland stone, but in a rendered this slate so remarkable among geologists, is the fact quarry of it at Tisbury, in Wiltshire, one species of coral is that it contains seven specimens of the lower jaws of quadru. found very plentiful.

peds belonging to some animal of the Opossum family. The 2. The Kimmeridge clay abounds in organic remains, remarkableness of this circumstance is, that it is the first especially of Saurians, or lizards, and tortoises and fish. In instance of mammalian remains being

found under the ter; Bavaria, this clay has furnished many fossils of a species of tiaries. The animals to which these jaws belonged are called Aying lizard, or the Pterodactyl, mentioned in our last lesson. Amphitherium and Phascolotherium,

It abounds in shells of the Nautilus, No. 13, Ammonite, No. The Stonesfield slate, as represented by the flaggy sandstones 12, and Belemnite, No. 4. But the most characteristic shells of Collyweston, Northamptonshire, contain Trigoniæ like No. 8. are those of the Ostrea Deltoidea, and, in France, the Gryphæa 6. The Inferior Oolite, or Cheltenham stone, has for its Kirgula, a shell like No. 3,

characteristic shells, Terebratulæ, like No. 6 and No. 14, and, 3. The Coral Rag is so called because it abounds with the in Normandy, an Ammonite, very much like a Trochus, No. 9, remains of corals, belonging chiefly to the family of the Astræa, called Pleurotomaria ornata. No. 11, the Caryophyllia, and the Agaricia. It has also furnished many fossil remains of Saurian animals. In the calci.

III. SOME GEOLOGICAL PHENOMENA OF THE ferous grit connected with the Coral Rag, fossil wood, drifted

OOLITIC PERIOD. out to sea, is often found, The Oxford clay, underlying it, 1. The entire series of the colites are a marine formation,

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