bola, any ray falling on the mirror parallel to the axis is reflected so as to pass exactly through the focus. For other mirrors it is approximately true only when the breadth of the mirror is very small in comparison with its radius of curvature. When the breadth of the mirror is large in comparison with its radius of curvature there is no definite image, even of a luminous point. In such cases the image is spread over what is called a Caustic, or sometimes a Catacaustic.

Р

B

An example of the caustic is given in the annexed figure for the simplest case-namely, that of rays falling directly on a concave spherical mirror, BAB', from a point so distant as to be practically parallel. Two very near rays, P and Q, will after reflection intersect at C. By finding in this way all the points of intersection of the reflected rays, we get a continuous curve, BCFB', which is the section of the caustic surface by a plane passing through its axis. The curve BCFB' varies of course with the form of the reflecting surface. In the case under consideration it is known as an epicycloid.

B'

F

The reader may see a catacaustic on the surface of tea in a tea-cup half full by holding the circular rim to the sun's light. The space within the caustic curve is all brighter than that without, as it clearly should be, as all the light reflected affects that space, while no point without the curve is affected by more than the light reflected from half of the surface. The rainbow, it may be mentioned, forms one of the most interesting of the whole family of caustics.

When a caustic is produced by refraction, it is sometimes called a Diacaustic. No such simple example can be given of the diacaustic curve as that above given of the catacaustic. It is only in the simplest cases that the curve takes a recognisable form. In the case of refraction at a plane surface, it can be shown that the diacaustic curve is the evolute either of the hyperbola or ellipse, according as the refractive index of the medium is greater or less than unity.

Cauterets, a fashionable French wateringplace in the department of Hautes-Pyrénées, lies 3250 feet above sea-level, in the valley of the Laverdan, 5 miles S. of Pierrefitte, the nearest railway station, and 42 SSE. of Pau. The stationary population was (1886) only 1468, but it is annually swelled in summer by 15,000 to 20,000 visitors, for whose accommodation numerous sumptuous hotels and bathing-establishments have been built. It is a good centre and guide station for ascents among the Pyrenees. The sulphurous springs, twenty-five in number, and varying in temperature from 60° to 131° F., are the most abundant in the Pyrenees (330,000 gallons per day), and have been known from Roman times; though their modern reputation dates from the 16th century, when Margaret, sister of Francis I., held her literary court and wrote much of her Heptameron at Cauterets.

Cautery (Gr. kaio, 'I burn'), in Medicine, is used of any substance which burns the tissues. (The term 'potential cautery,' as applied to caustic substances, is becoming obsolete.) The actual cautery is an instrument with a head or blade of steel, iron, or platinum, which is heated in a fire or spirit-lamp. In the thermo-cautery (or Paquelin's cautery, from its inventor), the head or blade is

CAUTION

made of hollow platinum, so arranged that a flame of benzole can be kept burning in its interior. The galvano-cautery consists essentially of a platinum wire which can be heated to any required degree by passing a strong galvanic current through it. The cautery is used for three main purposes in surgery: to produce counter-irritation over an inflamed part (see BLISTER) (actual cautery); to check bleeding (actual or thermo-cautery), by slowly destroying the tissues at the bleeding point or surface; to perform operations, where the tissues to be divided are either very vascular (thermocautery), or very difficult of access (galvanocautery). See CAUSTIC.

Caution, in the Law of Scotland, like Guaranty (q.v.) in England, is an obligation undertaken by a second party, whereby he binds himself, failing the primary obligant, to fulfil his obligation, whether it be of a pecuniary nature or otherwise. Cautionary obligations are thus essentially of an accessory nature, and cannot subsist apart from the principal obligation. The law of this subject is now largely founded on the Mercantile Law Amendment Acts, 1856, which assimilate the laws of England and Scotland, and according to which the creditor may proceed at once against the cautioner, just as if he were a joint obligant, without suing the primary debtor, unless the cautioner has expressly stipulated that this shall be done. The creditor, however, is in every case bound to use proper precaution in retaining and making available securities. He is not, however, bound to make the same full disclosure of material facts as in insurance, and therefore a cautioner should make careful inquiry for himself. Cautionary obligations are generally gratuitous, being, for the most part, undertaken from motives of friendship; but it is by no means uncommon for them to be entered into in consideration of a premium paid by the person guaranteed, or by those interested in his fortunes. Where a premium is paid, the transaction becomes a mere insurance of solvency, honesty, or efficiency; and associations of great public utility (see GUARANTEE) have been formed, both in England and Scotland, for the purpose of undertaking to guarantee the fidelity of persons employed either in public or private offices of trust. The tendency of judicial decisions, both in England and Scotland, for many years past, has been to require greater strictness than formerly in the constitution of cautionary obligations; and under the statutes already mentioned all such engagements must be in writing, subscribed by the person undertaking or making them, or by some person duly authorised by him, otherwise they shall have no effect. cautionary obligation is dependent on a condition, it will, of course, be ineffectual unless the condi tion be complied with. The cautioner may, in to the principal debtor, and the extinction of the general, plead every defence which was competent primary obligation extinguishes the secondary one. The cautioner is discharged by any essential charge being made on the obligation of the debtor, or in respect of the person relied on, without his assent. The statute expressly provides that changes of partnership either of creditor or debtor will extinguish the guarantee. If the creditor gives time -e.g. takes bills from the debtor of an unusual currency-that will also operate discharge. discharge of one cautioner, moreover, unless consented to by the rest, is a discharge to all. The cautioner is entitled, on full payment, though not on payment by a dividend, to an assignation of the debt and diligence, by which means he comes, in all respects, into the creditor's place; and moreover, if the solvency or other conditions of the principal debtor should seem precarious, he may

If a

The

CAUVERY

adopt legal measures for his relief. Co-cautioners, or persons bound together, whether their obligations be embodied in one or several deeds, are entitled to mutual relief. But where a co-cautioner obtains relief from the others, he must communicate to them the benefit of any deduction or ease which may have been allowed him in paying the debt. Letters of credit and recommendation raise much the same relation of parties as a formal cautionary obligation, but since 1856 a mere verbal introduction cannot have that effect. For the forms and effects of ordinary mercantile guarantees, and for the forms of guarantee insurance of fidelity, see GUARANTEE. For the Scottish cautionary obligation in cash-credit bond, see BANKING, II. 713.

JUDICIAL CAUTION, in the Law of Scotland, is of two kinds-for appearance, and for payment. If a creditor makes oath before a magistrate, that he believes his debtor to be meditating flight (in meditatione fuga), he may obtain a warrant for his apprehension; and should he succeed in proving the alleged intention to flee, he may compel him to find caution to abide the judgment of a court (judicio sisti). The cautioner, or surety, undertakes that the defender shall appear to answer any action that may be brought within six months. The old Bond of Presentation, by which in order to gain time the surety undertook to produce the debtor or pay the debt at a future date, is now superseded by the abolition of imprisonment for debt. There is also a form of judicial caution called judicatum solvi, given in cases of general loosing of arrestment of ships, in which the surety becomes liable for the whole debt. The commonest form of judicial caution, however, is the security usually given in the Bill Chamber (q.v.), when a bill or bond is brought under suspension; the security is for the principal sum and expenses, if the suspension should be refused. Interdict is also frequently granted upon caution for the damages that may result from the interdict, should it turn out to have been wrongly obtained.

Cauvery. See KAVERI.

Cava del Tirreni, a town of Italy, in a lovely valley, 5 miles NW. of Salerno by rail, with a cathedral, and manufactures of silk, woollens, cotton, and linen. Pop. 6339. About a mile distant is the Benedictine monastery of the Trinity,

celebrated for its archives.

Cavagnari, SIR LOUIS, born in France in 1841, was educated at Christ's Hospital, London, and in 1857 was naturalised as a British subject. He had seen twenty-one years' military and political service in India, when on 3d September 1879 he was murdered at Kabul. See AFGHANISTAN.

to his generalship. His task being done, he resigned his power into the hands of the National Assembly, which appointed him President of the Council. As a candidate for the presidency of the republic, when Louis Napoleon was elected, he received nearly a million and a half of votes out of 7,327,345. On the coup d'état of December 1851, Cavaignac was arrested, but released after a short detention; and though he consistently refused to give in his adhesion to the Empire, he was permitted to reside in France without molestation. He died, 28th October 1857, at his country house near Tours. Cavaignac was an able soldier, a zealous republican, and in every way an honourable man. See his Life by Deschamps (2 vols. Paris, 1870).

Cavaillon (ancient Cabellio), a town of the Avignon by rail, with a cathedral, and some French department of Vaucluse, 18 miles SE. of Roman remains. Pop. 5164.

1300.

Cavalcanti, GUIDO, Italian poet, born in 1230, Guelph, by the Ghibellines, a daughter of one of was banished, for mercantile transactions with a broken health to Florence only to die there, about whose chiefs he had married, and returned in His works sonnets, ballads, and canzoniare remarkable alike from their language and depth of thought, although his epicurean philosophy gained him, among his contemporaries, the reputation of an atheist. See Ercole, Guido Cavalcanti BARTOLOMMEO (1503-62), a noble and eloquent e le sue Rime (Milan, 1885).—Another of the name, Florentine, led a revolt against the Medici, and was afterwards employed by Pope Paul III.

Cavalcaselle, GIOVANNI BATTISTA, Italian art writer, born 22d January 1820, at Legnago, early visited the art centres of Italy, and in 1846 proceeded to Germany, where he met J. A. Crowe (q.v.), with whom he returned to Italy. Banished for his share in the revolution of 1848, he accompanied Crowe to London, and there their first joint work, Early Flemish Painters (1857; 3d ed. 1879), 1858, and in 1861 commenced with Crowe the History was published. Cavalcaselle returned to Italy in

Painting in Italy (Lond. 5 vols. 1864-71). Other joint works are Titian (1876) and Raphael (1883); importance. He is head of the art department in Cavalcaselle's independent writings are of less the ministry of Public Instruction at Rome.

Cavalier (Fr., from Lat. caballus, a nag'), from 'horseman' acquired the meaning of 'knight' or 'gallant,' in which sense it is used by ShakeIV., Part II., V. iii. 62. In 1641 Cavaliers' was speare (Henry V., III. 24), like cavalero, in Henry applied as a nickname to Charles's partisans in opposition to the Roundheads, or friends of the Parliament; and from a term of reproach it came to be adopted as a title of honour, until, after 1679, it was superseded by Tory.' For the 'Cavalier Parliament' (1661-79), see CHARLES II.

Cavalier, JEAN, a journeyman baker, from Ribaute, near Anduze, who, born in 1681, in 1702 became a famous leader of the Camisards (q.v.), withal a prophet and preacher. He surrendered to Villars in 1704, and entered the service of Savoy; but in 1711 we find him settled with a

British pension in England, and he died at Chelsea, governor of Jersey, 17th May 1740. See a long article in vol. ix. of the Dict. of National Bio

Cavaliere Servente. See CICISBEO. Cavalry is a general name for horse-soldiers or troopers trained to act in a body. In the British army there are 31 regiments of European, and 30 of native Indian cavalry. The former comprise 2 regiments of Life Guards (red), 1 of Horse Guards

(blue), and 7 of Dragoon Guards, classified as heavy cavalry; 3 regiments of Dragoons, and 5 of Lancers, classified as medium; and 13 Hussar regiments or light cavalry-all carrying carbines and swords. The war strength of each is 1 lieutenant-colonel, 1 major, 8 captains, 9 lieutenants, 7 sub-lieutenants, 1 adjutant, 1 paymaster, quartermaster, 1 medical officer, 1 veterinary surgeon, 75 non-commissioned officers, 8 farriers, 8 shoeing-smiths, 8 trumpeters, 4 saddlers, 2 wheelers, 15 bandsmen, 480 troopers, and 22 drivers, 559 riding and 44 draught horses, and 11 wagons.

The native Indian cavalry are all light, and some have the front ranks armed with lances, the rear with sabres. Bengal has 19 regiments, each of 8 troops, consisting of 10 European officers (1 in command and 1 surgeon), 17 native officers, and 536 native non-commissioned officers and troopers. Madras has 4 regiments of only 6 troops each, the same number of European, but 12 native officers and 396 of other ranks. Bombay has 7 regiments with the same organisation and numbers as Bengal, but only 518 native non-commissioned officers and troopers. Besides these regiments there is a troop of native cavalry at Aden, and one as a body-guard for each lieutenant-governor, and the governorgeneral of India.

The auxiliary cavalry in Great Britain comprises 39 regiments of Yeomanry, 2 of Volunteer Light Horse, and 1 of Volunteer Mounted Rifles, of various strengths. There is a cavalry depôt at Canterbury, and a school of instruction for auxiliary cavalry at Aldershot.

After the American civil war, the United States' cavalry was reduced to 10 regiments of 936 privates each. The commissioned officers of a regiment consist of 1 colonel, 1 lieutenantcolonel, 3 majors, 12 captains, 14 first lieutenants, and 12 second lieutenants.

History.-For the place of cavalry in the ancient armies, see ARMY. In the middle ages horsemen -knights, esquires, and their attendants-formed the most important part of the great armies; but after the disappearance of the Roman cohort with its 132 highly trained horsemen, the organisation of cavalry, as we now understand the word, was neglected until 1445, when Charles VII. of France grouped his men-at-arms into companies 100 strong. The method of fighting, from 1645 until Frederick the Great introduced the charge or shock tactics, was to advance to close quarters, fire pistols from the saddle, and then commence cutting with the sword. The value of dismounted cavalry able to act as infantry was then recognised, and dragoons armed with muskets were much in vogue until the beginning of the 19th century. They then lost favour, and though all European nations continued to train their troopers to dismount and use their carbines to hold some important point until the arrival of infantry, it was taught that the sword was their proper weapon, and the saddle their proper place. But Russia has lately armed all her cavalry, except the Cossacks, with long rifles, thus turning them into dragoons, and it is now generally felt that the dismounted service of cavalry must be developed to a greater extent than has hitherto been the case. Mounted infantry too, using their horses merely as a means of rapidly covering the ground, have been found so useful in the British army, that in 1887 a school for this arm was formed at Aldershot; and it has been decided that a force 900 strong shall accompany the cavalry division on

active service.

Formation.--A cavalry regiment in the field is divided into 4 squadrons, each of 2 troops. The men of each squadron when in line are 6 inches from knee to knee, and formed in two ranks, a horse's length apart. The officers are at a similar distance

CAVAN

in front, and the 'serrefiles,' or supernumerary noncommissioned officers, in rear. There is an interval of 12 yards between squadrons. The pace is, walk 4 miles an hour, trot 8, gallop 12. The maximum distance covered by cavalry is 68 miles by day (6 A.M. to 10 P.M.) and 18 by night-86 for the 24 hours; but after such a march there must be a rest all next day. For a continuous march 35 miles a day, at 5 miles an hour, is a good rate. Duties on Service. In large armies, from oneeighth to one quarter of the whole force should be cavalry. Their duties are to cover the movements of their own army, and to find out those of the enemy-besides taking part in the actual battles by guarding the flanks, seizing all opportunities of charging, completing success by an active pursuit, or covering defeat. The screening and reconnoitring duties are performed by the cavalry divisions, each of two or more brigades, one or two days' march in front of the main body. The light Brigades (q.v.) are perhaps best for the actual scouting, but must be supported by heavy cavalry in order to meet that of the enemy, which would otherwise have the advantage of greater weight in the charge. Each brigade of two or more regiments is accompanied by a battery of Horse Artillery.

The battle of Mars la Tour in the Franco-German war of 1870, supplies the best examples of a cavalry fight on a large scale, and of a charge (that of Barby and Bredows' brigades) directed against infantry. The action of the German cavalry throughout the same campaign illustrates the screening and reconnoitring duties of the arm. The capture of Cairo by the rapid advance of the British cavalry after the battle of Tel-el-Kebir (1882), shows its value after a successful engagement.

Tactics. Unless acting dismounted, cavalry must either attack or retire; it cannot otherwise defend itself. Against cavalry it must therefore manœuvre with its first line, so as to attack to the best advantage-i.e. against the adversary's flank. Its second line following, en échelon, in order to have a clear front, protects the flanks of the first from counter attack, and supports its movement, completing its victory, or covering its retreat. Horse artillery on the protected flank fire upon the enemy up to the last moment before the charge. A third portion, formed into a reserve, follows, and behind it the other two can rally after the charge, which, even when successful, creates great confusion. Cavalry attacks artillery in two bodies-one in line formation charges the escort, and the other in extended order, the men a horse's length apart, converges upon the guns. Infantry can defend itself from a cavalry charge, unless surprised by a flank attack, which would generally be delivered by comparatively small bodies in successive lines, but such an opportunity rarely occurs on a modern battlefield.

Cav'an, an inland county in the south of Ulster. It lies in the narrowest part of Ireland, 18 miles from the Atlantic, and 20 from the Irish Sea. Area, 746 sq. m., of which less than a third is under crops. Bogs and hills, with many small lakes, are found in the north-west, where Cuilcagh attains a maximum altitude of 2188 feet. The chief rivers are the Erne, the Woodford, and the Annalee. The eastern half of Cavan rests on clay-slate and graywacke; the mountain district in the west is carboniferous formation.

Of minerals, Cavan affords coal, iron, lead, and copper, with many mineral springs. The climate is cold and damp; and the soil is poor, wet, and clayey, except along the streams. The chief crops are oats and potatoes, the cultivation of flax having greatly decreased since 1850. The farms are small. Agriculture forms the staple industry, but linen is manufactured to a considerable extent. The chief towns are Cavan, Cootehill, and Belturbet. Cavan returns two members to parliament. Pop. (1851)

CAVATINA

174,064; (1881) 129,476; (1891) 111,679, of whom 90,329 were Catholics, and 16,325 Episcopalians.CAVAN, the county town, stands on a branch of the Annalee, 85 miles NW. of Dublin by rail. It has a court-house and a grammar-school; and the beautiful demesne of Lord Farnham lies between Cavan and Lough Oughter, which is about 5 miles west. Pop. about 3000.

Cavati'na, a short form of operatic air, of a smooth and melodious character, differing from the ordinary aria in consisting only of one part, and frequently appearing as part of a grand scena. Examples of cavatina are found in many wellknown operas, as Sonnambula and Les Huguenots. The term is also often used for a complete air or song, such as the 'Salve dimora' in Faust.

Cave, or CAVERN (Lat. cavus, 'hollow'). The natural hollows which occur in and underneath rocks have originated in various ways-some being due to the chemical and mechanical action of water, others to dislocations and disruptions produced by movements of the crust, or by superficial rock-falls and landslips, while yet others are tunnels which now and again occur in or under thick sheets of lava. Caves formed by marine erosion are frequently met with along the coast-line of Britain and other countries, Fingal's Cave at Staffa (q.v.) being a splendid example. They are not confined to any particular kind of rock-although, other things being equal, they are of course more easily formed in readily yielding rocks than in more durable kinds. It is rather the character of their natural divisionplanes or beds and joints than their composition and texture that determines whether the rocks at the base of a sea-cliff shall be hollowed out or not by the action of the waves. If the rocks are thinbedded and abundantly and regularly jointed, it is obvious that as soon as any portion is undermined by the sea, the overlying masses will immediately yield along their division-planes and topple down. If, on the other hand, the rocks are meagrely and irregularly jointed, and occur in massive beds, then they will not so readily collapse when undermined, and caves will tend to be formed. Caves which have had this origin are not uncommonly met with along the line of old sea-margins in many regions which have been elevated in recent geological times. Most frequently, however, the entrances to such caves are concealed by the rock-rubbish which has been detached from time to time by the action of the weather from the cliffs above. Caves of erosion are also formed by river-action at the base of crags and cliffs in many valleys. And now and again such hollows may be detected at various levels in river-cliffs, as if they had been formed during the gradual excavation of the ravines in which they occur.

In Britain and other countries long occupied by man most of such river-cliff caves or rock-shelters have been artificially deepened and widened, and this to such an extent that it is often hard to say how much of the work can be attributed to nature. By far the most important caves, however, are those which owe their origin to the action of underground water. But before these are described, mention may be made of the hollows which occur now and again in and under lavaflows. Where lava has flowed over and solidified above a mass of snow and ice, the subsequent melting of the latter will leave a hollow behind. Near the Casa Inglese, on the south-east side of the highest cone of Etna, a mass of ice of unknown extent and thickness, covered by lava, was seen by Lyell in 1828 and again in 1858. But this, it must be remembered, is at a height of 10,000 feet above the sea. In lava itself, however, caves of considerable extent occur. Many of

these are simply great blisters or hollows formed by the expansive power of the highly heated vapours contained in the lava at the time of its eruption. Others again may have been caused by the sudden conversion into steam of the water of lakes or streams suddenly overwhelmed by a lavaflow-the steam thus generated might either violently rupture the lava by its explosive force, or produce great tunnels and irregular cavities under the liquid lava, already inclosed in its solid crust, by pressing it upwards. The extensive Fossa della Palomba of Etna is supposed by some to have had such an origin. But probably the greater formed by the escape of the lava itself from its own number of the larger caves under lava have been solidified envelope. When lava pours out from a volcanic orifice it very rapidly coagulates above and below, so that the liquid rock becomes imprisoned in a hardened crust of its own material. The great pressure of the inclosed lava, however, upon the crust at the terminal point of the flow suffices again and again to rupture it, and the lava then flows out freely until it is again imprisoned in the same manner. In the case of very liquid lavas this escape is often completed in a perfect manner -and a long underground tunnel is left behind, from the roof of which depend long stalactites of black glassy lava. Extensive caves formed in this way-some of them measuring over 100 feet in width-occur in the Azores, the Canary Islands, Iceland, and other volcanic regions.

Another class of caves embraces such hollows as have originated during earthquakes or other movements in the crust of the earth. At such times rocks are rent asunder, and when they fall rudely together irregular cavities are left between the disjointed masses, and similar results often take place when great landslips occur. But the most extensive caves and underground galleries have been excavated by the chemical and mechanical action of underground water. Sometimes these hollows continue more or less persistently in one direction, but most usually they wind tortuously about, and often open into similar intricate galleries, which, in like manner, communicate with lateral extensions of the same character. There can be no doubt that caves of this kind are the channels of underground streams and rivers, and that they have been excavated, in the first place, by the chemical action of acidulated water making its way downwards from the surface along the natural division-planes of the rocks, until eventually space has been licked out for the passage of a subterranean stream. The cavities would then tend to be enlarged by the filing action of the sand and gravel which the underground stream and its numerous feeders might sweep along. Many such underground watercourses are well known at the present day, and the direction of some of them can be traced by the swallow-holes, chasms, and sinks,' which indicate places where the roofs of the cavities have given way, or have been pierced by the action of acidulated water. In certain regions almost all the drainage is thus conducted underground-rivers after flowing for a considerable distance at the surface suddenly disappear, and follow a hidden course, for it may be many miles, before they emerge again to the light of day. Sometimes, indeed, they never come to the surface again, but enter the sea by subterranean channels. Should anything occur (such as earthquakes, &c.) to interrupt such a system of underground drainage, and the streams and rivers be compelled into new channels, the old subterranean courses will then become galleries more or less dry, which may be accessible by one or even by several openings.

As it cannot be doubted that all such great

underground galleries owe their inception entirely to the chemical action of water seeking its way downwards from the surface, and following the lines of natural division-planes in the rocks, it is obvious that caves will be of most common occurrence in regions where the rocks yield most readily to such chemical action. Among the more soluble rocks are rock-salt and gypsum, but these are only locally developed in such quantities as to give rise on their removal to underground cavities of any extent. Calcareous rocks, more especially limestone, have not only an almost world-wide distribution, but they also occur in greater mass than either gypsum or rock-salt, and hence, although not so readily acted upon by water as the latter two, it is in limestones that nearly all the most renowned caves and subterranean galleries appear.

Many caverns have a calcareous incrustation lining their interior. Sometimes this deposit is pure white; it is, however, more generally coloured by the impurities which the water, percolating downwards from the surface, has taken up from the superincumbent rocks. To the incrustations which are suspended from the roof like icicles, the name stalactites is given, while those rising from the floor are called stalagmites. The origin of these is as follows: Water which has percolated down from the surface always contains a certain proportion of carbonic acid-it is acidulated water-the acid being derived from the atmosphere and the decaying organic matter of the soil, &c. Water thus charged with carbonic acid has the power of dissolving limestone-i.e. it takes up a certain proportion of carbonate of lime and converts it into the soluble bicarbonate. Arrived at the roof of a cave it oozes out and is there subject to evaporation, the excess of carbonic acid is parted with, and a thin pellicle of carbonate of lime is deposited as an incrustation. When the drops fall to the floor they are subject there in the same way to evaporation, and are thus compelled to give up the remainder of the calcareous matter held in solution. By this constant dropping and falling, icicle-like pendants grow downwards from the roof, while sheets, bosses, and domes gradually accumulate upon the floor-until, not infrequently, these stalagmites come at last to unite with the gradually lengthening stalactites, and so to form, as it were, pillars which look as if they had been placed to support the roof. See the articles on ADELSBERG, AGTELEK, Kent's CAVE, MAMMOTH CAVE, &c.

BONE-CAVES.-Caves are of interest to geologists not only because they testify to the potency of the chemical and mechanical action of underground water, but on account of the remarkable evidence they have yielded as to the contemporaneity of man with many extinct and no longer indigenous mammals. This evidence is furnished by the accumulations which so frequently cover the floors of caverns to a greater or less depth. The accumulations in question consist partly of clay, sand, gravel, and shingle, and partly of red earth and sheets of stalagmite. Some of these are doubtless the alluvial detritus carried forward by underground streams. This detritus often consists largely of angular, subangular, and water-worn fragments of limestone, which have doubtless been derived from the roof and walls of the underground galleries, but not infrequently the presence of other kinds of rock-fragments shows that no inconsiderable amount of material has been introduced from the outside by the streams as they plunged into their subterranean courses. Much debris also may have been swept in by heavy rain or flooded torrents washing down through the sinks and swallow-holes that so frequently pierce the roofs of subterranean watercourses. These sinks often become pitfalls to unfortunate cattle in our own day, and in former

times many animals may have been entrapped in the same way-for broken and rubbed bones often occur, sometimes very abundantly, in the old torrential accumulations of deserted subterranean watercourses. When the galleries ceased to be traversed by streams, stalagmitic accretions would then begin to accumulate over the shingle and debris beds. In course of time many of these subterranean hollows, becoming more or less accessible from the outside, were occupied by carnivorous animals, who carried thither their prey, and thus by and by accumulations of bones were formed, which the drip of water from above gradually inclosed in calcareous matter, and eventually covered up under a sheet of stalagmite. Now and again the caves were occupied for shorter or longer periods by man-his presence being still evidenced by his implements and weapons, by charred and split bones, &c., and occasionally by portions of his own skeleton-and these relics, in like manner, subsequently became sealed up in a more or less thick accumulation of stalagmite. Some of these bone-caves contain the record of many physical changes. Thus, we have evidence to show that after having been the haunt of wild beasts or the abode of man for some indefinite but often prolonged period, the cave again gave passage to a flow of water, and deposits of loam, clay, or gravel, &c. were laid down upon the stalagmitic pavement and bone-breccia. Or, as in some cases, the stalagmite, together with bones covered by and inclosed within it, was broken up and partially or wholly removed. Then, at a subsequent date the stream once more deserted its channel, while carnivores or man again returned, and newer heaps of bones and stalagmite accumulated. Commingled with these stalagmites of the bone-caves there is almost always more or less of a reddish earth or clay, which is the insoluble residue of the limestone from the dissolution of which the stalactites and stalagmites are formed. Some of the more remarkable bone-caves which have yielded testimony as to the contemporaneity of man with extinct mammalia, are Kent's Cave (q.v.) and Brixham Cave in England, the caves in the valley of the Lesse in Belgium, the caves of Perigord and the Pyrenees in France, and the Kesserloch near Thäingen in Switzerland. Bone-caves containing the remains of post-tertiary mammals are rare in North America; those of Brazil have many bones of large rodents and edentates. For caves at Wick, in Scotland, still occupied by tinkers, see Sir Arthur Mitchell, The Past in the Present (1880). For accounts of special caves, see the British Association Reports (for Kent's Cave) and the Philosophical Transactions (1822-73). For general descriptions, see Buckland's Reliquiæ Diluviance, Dupont's L'Homme pendant les Ages de la Pierre, Lartet's and Christy's Reliquiæ Aquitanica, Lubbock's Prehistoric Times, Dawkins' Cave-hunting, J. Geikie's Prehistoric Europe. For further information as to the European_cavedwellers of prehistoric times, see MAN, FLINT IMPLEMENTS, PLEISTOCENE.

ARTIFICIAL CAVES.-The primitive inhabitants of most civilised countries and many primitive tribes at the present day have been troglodytes or cave-dwellers. In many countries where natural caves are either of rare occurrence or do not occur at all, certain rock-exposures have been artificially excavated, and occupied either permanently as dwelling-places or occasionally as retreats in times of danger, while others have been used as cells, hermitages, or burial-places. Such caves are not uncommon in the cliffs of Scottish river ravines, as at Hawthornden near Edinburgh, and in the valley of the Jed, Roxburghshire. Caves of this kind occur usually in rocks that are readily dug into, such as soft sandstone. Now and again,