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FOR A PENSIONER.

We pass now to the University fees. These are paid to per week being compulsory. The charge for this varies in the the common chest (1) on matriculation, (2) on attending profes- different colleges from 1s. 6d. to 28. 6d. per day. This comprises sors' lectures, (3) for the previous examination, and (4) on taking a certain dinner, and anything had which is not comprised in a degree. On matriculation, a sizar pays 158.; a pensioner, £5; the college provision is supplied from the kitchen and charged a fellow-commoner, £10 10s.; a nobleman, £15 108. The total for separately. As regards breakfast and tea, the student may fees on going into residence, therefore, are-for a sizar, £13 15s.; supply himself if he pleases from shops in the town, but more for a pensioner, £23; for a fellow-commoner, £45 10s.; for a usually bread, butter, and milk are dealt out from the college nobleman, £70. On passing the previous examination, every butteries every morning to the various gyps for their respective student pays £2 10s., and for every series of professors' lectures masters. Other things will be kept in stock by the student himself. (one series of which is required from the candidates for the ordi- To sum up briefly the annual expenses while at Cambridge, and pary degree) the fee is £3 3s. On taking the degree of B.A., taking rather a low estimate, we may compute them as follows :which is the only one of which we shall speak, every student pays £7 to the University, and a sum varying from £3 to £6

8. d.

Tuition. to his college.

0 0

Rooms At present we have mentioned only the tuition afforded by

Attendance, Gyp and Wife the college to all students alike. This, as we have pointed

Coals, about out in our former article, is in most cases insufficient for Cost of living for 25 weeks, at 25s. per week. those who are desirous of taking a good place in any of the Sundries, about honour triposes. It is, of course, almost impossible that a Shoe-cleaning lecturer, who has to deal with perhaps forty or fifty men in

Extras

3 00 the course of an hour, can devote much attention to individuals,

£73 16 0 however much he may exert himself in his endeavours to do so. Moreover, the course of reading which will be most suitable Under the heading “extras" are included all fines, library pay. will vary according to the powers or previous reading of the ments, etc. A sizar's expenditure will be diminished by £12 in various students, and a course of lectures cannot therefore be the tuition, by £1 10s. in the gyp, and possibly by £3 in the made to suit every one. Hence the necessity for obtaining the rooms, making the total about £57 6s. This, again, is a very assistance of a private tutor in addition to the lectures provided low estimate, and does not include private tuition, clothing, by the college. The ordinary charge per term is £8, and for pocket-money, the cook's bill, or any expenses except those the long vacation £12. An addition of £36 to the year's which are absolutely necessary during a residence of twenty-five expenses is a very important item, and weighs considerably weeks at the University. Taking everything into consideration, with the poorer class of students in their choice of reading. except the expenses of living while away from Cambridge, we The above charges are considered to entitle the pupil to one should say that the lowest amount upon which a man can live hour's private tuition every other day. But those tutors who with anything like comfort is £140 for a pensioner, and £120 take a large number of pupils, usually read with them in for a sizar. A syndicate of the University have just presented classes, which has, at all events, one beneficial effect in exciting a report on a scheme for enabling students to be members of the a feeling of competition. The professors' lectores and other University and obtain a degree without being members of a sources of instruction remain to be mentioned. Our space college. This will probably materially diminish the expenses of would fail us if we attempted to speak of these individually, residence. and we therefore content ourselves with remarking that it is We have now to consider the various means by which a by means of these that the University proper—that is, as dis- student may partially, and in some cases wholly, defray the tinct from the colleges—gives its instruction. One course, at expenses of his University course. We have said sufficient least, is required of every candidate for the poll degree or the on the subject of sizarships. We shall therefore pass on at theological examination. In the latter case, the course must once to scholarships and exhibitions, whether from the school, be that of one of the divinity professors. Many of the lectures the college, the University, or from some mercantile company. given are of a very high order, and in the mathematical branches To take first the mercantile scholarships. These are given by they are of little practical use, so far as regards the tripos ex some of the great City companies to young men, generally song aminations, except to men of the highest ability.

of freedmen, on their going up to the University, and a prior These, then, are the three methods of acquiring knowledge claim is usually given to those who ask for them on the ground while residing at Cambridge :—by college lectures, which are of poverty. They range from £30 to £50 a-year. compulsory, and paid for in the terminal payment to the college All the large public schools, and many private ones also, are tator; by private tuition, which is voluntary, and ought not to endowed with exhibitions for the benefit of their elder boys on be required by any but candidates for high honours; and by uni- leaving school. They are given for proficiency in various versity lectures, which are voluntary, except in the case of poll branches of education, mostly in classics or mathematics. They men, for whom one course is compulsory.

are the means of sending to the University many boys who, but We pass on now to the question of general expense, apart for the assistance thus given, would be debarred from the from fees and tuition. On going into residence, the first question privilege. They range from £30 to £70, and some even as which arises is that of obtaining rooms, the second that of fur- high as £100 a-year. nishing them. The question is often raised as to the compara The pecuniary rewards given by the colleges to undergradutive economy of living in college or in lodgings in the town. So ates are of three kinds : minor scholarships, scholarships, and many collateral influences affect the matter that it cannot be exhibitions. Of these, the first are of recent establishment. satisfactorily settled in a genoral answer. The rent of lodgings They are offered for public competition amongst intending is undoubtedly higher, but the outlay in furnishing is avoided, students before going into residence, and are really probationary and a man of quiet tastes may certainly lead a more retired scholarships, usually lasting for two years, and varying in value life in lodgings than he can in college. But the student must from £50 to £70 a-year. The holders of them enjoy all the remember that out of college he never really tastes the true privileges of scholars. Scholarships are usually given by the flavour of university life.

colleges for competition amongst their own members. A scholar The rent of lodgings varies from £5 to £15 per term; the differs from an exhibitioner in that he is on the foundation of rent of rooms in college from £4 to £10 per annum, the average the college. His position is higher than that of the ordinary being about £6. In addition to this there is in college the charge undergraduate, and he receives a certain amount of income, for attendance, £1 per term for a bedmaker only, £1 109. for a generally £50 a year, from the college revenues. An exhibitioner, gpp and his wife who will act as bedmaker. Furniture is gene- on the other hand, even though he may receive more money from rally taken on valuation from the preceding occupant of the the college, is not on the foundation, and his exhibition is only rooms, but the new-comer is not obliged to take any article given at the option of the master and seniors. A scholarship which he may not wish for. In this way the expense of furnish is usually tenable till the student is of standing to take the ing is sometimes exceedingly small, £15 being sufficient to fit degree of M.A. op, scantily of course, a sitting-room, a bed-room, and a gyp The highest honour which a student can gain during his room. This will not include linen or plate.

undergraduate course is that of obtaining one of the University All students dine in hall

, a certain number of dinners there scholarships. These vary very much in value, and are given

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for proficiency in various subjects, among which mathematics, with lead oxide in several proportions ; with 7 molecules of the classics, Hebrew, theology, law, and poetry are included. They oxide it forms Turner's yellow; with one molecule a white paint are competed for by the best men of all years, and their value is produced, whieh is prepared by Bell of Newcastle, Cassel's to the successful candidate consists rather in the distinction yellow is still more basic. which they confer than in the pecuniary emolument which they Iodide of Lead (PbI,) falls as a beautiful yellow precipitate bring.

when an iodide is added to a lead solution. We have thus endeavoured to give our readers some slight The other salts of lead afford nothing of peculiar interest, sketch of the University and of its internal dealings with its The oxalate is the most insoluble, and therefore its precipitate own members. We shall consider in another article the local offers a good test for the presence of the metal. examinations which it holds, both for youths and young women, Besides the characteristics of these salts, already mentioned, in various parts of the country.

lead may be reduced with ease on charcoal, thus its presence is

by no means difficult to ascertain. LESSONS IN CHEMISTRY.-XXV.

The Noble Metals have already been defined to be those which LEAD (continued)-MERCURY-SILVER.

are capable of being reduced from their oxides by heat. They

are nine in number : Mercury, silver, platinum, gold, palladium, Dry air has no action on lead; but if moisture be present, the rhodium, ruthenium, osmium, and iridium. bright surface of the metal is soon tarnished by a closely-adhering film of oxide. Lead, on account of its pliability, is much

MERCURY OR QUICKSILVER. used for water-pipes and cisterns; but it should never be used SYMBOL, Hg - COMBINING WEIGHT, 200 — SPECIFIC GRAVITY, 13 59 for storing rain-water, for this is pure water containing air, and

– DENSITY OF VAPOUR, 100. in such water the oxide of lead is soluble, rendering the liquid Occasionally mercury is found native, disseminated in sma!? poisonous. Well-waters, containing nitrates and chlorides, act globules through the rock. Its chief ore is cinnabar (mercuric on lead, forming soluble salts, therefore they should not be sulphide). The extraction of the metal is simple, and is effected brought in contact with it; but hard waters have little or no either by heating the ore in retorts, burning off the sulphur, and action on lead, for a thin deposit of sulphate or carbonate is distilling the mercury; or by mixing the ore with some body formed on its surface, preserving it from further action. How- like quicklime, with which the sulphur combines, the metal as ever, water charged with carbonic acid gas is capable of dissolv- before distilling off. ing the lead carbonate to a dangerous extent.

Cinnabar is mined in many parts of the world : Almaden, in Lead is used in several alloys: shot is composed of lead, which Spain, and Idria, in Carniola, are the most important European is alloyed with a little arsenic, to render it hard and more easily mines. granulated. The other important alloys have been mentioned. The metal is imported into England in iron bottles. With most There are three oxides of lead.

metals it forms amalgams; but the film of oxide, ever present Plumbic oxide, or litharge (PbO), is a yellow powder formed on the surface of iron, prevents the amalgamation of the metals

. when lead is heated in a current of air. It is soluble in caustic, At -- 40° it becomes a solid, crystallising in octahedra ; at 3500 potash, or soda ; and if the solution be allowed to stand, car it boils; but at all temperatures it seems to give off vapour, bonic acid is gradually absorbed from the air, the alkali rendered In the Torricellian vacuum, the space above the mercurial a carbonate, and the lead oxide deposited in transparent dode-column in a barometer, globules of mercury may often be found cahedral crystals. Litharge is capable of fusion, and then com condensed on the tube. bines with glass, etc., forming fusible plumbic silicates. It is Hydrochloric acid has no action upon it; with sulphuric acid a largely used as a fux, and for glazing earthenware. A solution sulphate is formed, sulphurous acid coming of. The action with of it in lime-water is prepared for a hair-dye. The lime par- nitric acid is violent, nitrous acid gas being copiously evolved; tially decomposes the hair, when the lead with the sulphur in when triturated with sulphur or iodine, it will unite with them. the hair forms lead sulphide, staining the hair black.

Its action on the human frame is serious, producing salivaPerowide of Lead, or Plumbic Dioxide (PbO2), is a brown tion; and the workmen are subject to "mercurial palsy," : powder obtained by digesting red-lead in nitric acid. It can peculiar form of nervous debility. be decomposed by a high heat, becoming litharge, and giving

Black Mercurous Occide (Hg,O) and the Red Mercuric Oxide off oxygen. With sulphuric acid a sulphate is formed, and (HgO) are the only oxides. The former is obtained by the oxygen comes off ; with hydrochloric acid chlorine is evolved, action of potash on mercuric nitrate or on calomel. It is a dark and a plumbic chloride is made.

grey powder, and when heated is decomposed into metallio Minium or Red Lead (PbO,Pb0,) is a compound of the other mercury and two oxides; it is obtained by heating plumbic oxide or massicot,

Red Mercuric Oxide.—This oxide may be prepared by heating but not sufficiently to fuse it into litharge; it absorbs oxygen, the metal in the air to a temperature of 300° ; but this process and becomes bright red. Its chief use is in the manufacture of is slow, and the one generally adopted is the decomposition of flint glass; it is also employed to colour inferior sealing-wax mercuric nitrate by cautiously heating. In a state of fine suband in paper-staining. At a high temperature it parts with division it is yellow; such is the case when it is precipitated by some of its oxygen and becomes litharge.

potash from a solution of the nitrate. Plumbic Carbonate, or White Lead (PbO,Co.), is the well

The sulphides correspond to the oxides. known paint; it may be obtained in a state of purity by pre

Mercurous Sulphide (Hg,S) is a black powder, and may be cipitation from a solution of a plumbic salt by an alkaline car. procured by the action of sulphuretted hydrogen, or a merourous bonate. To procure it in large quantities, sheets of lead are salt. exposed to the simultaneous action of acetic acid and carbonic Mercuric Sulphide (HgS) is the ore cinnabar, or vermilion. acid. This is effected by placing the sheets rolled into coils in It is prepared artificially by heating together sulphur and 6 earthenware pots, at the bottom of which is some crude vinegar times its weight of mercury; the black mass thus formed is (acetic acid); these pots are packed in manore, from the fer placed in tall earthen pots, the lower parts of which are redmentation of which the carbonic acid is supplied. The acetic hot. The top is then closed, and after thirty-two hours the vessel acid, volatilised by the heat of the fermentation, attacks the is opened; the sublimation being complete, the vermilion is metal oxidised by the air, forming acetate of lead (sugar of found deposited on the upper parts of the vessel. lead). The carbonic acid gradually displaces the acetic acid Mercurous Chloride, or Calomel (Hg,ci), is usually prepared by from its combination, and thus the plumbic carbonate is formed. triturating 17 parts of corrosive sublimate, moistened with 13

Lead Sulphide (PbS).—Galena has been noticed as the chief parts of mercury, and then subliming. It is a white powder ore of lead. Artificially, this compound may be produced by decomposed by the alkalies, but insoluble in water. It is passing a current of sulphuretted hydrogen through a solution largely used in medicize. of a lead salt. Dilute nitric acid causes this compound to Mercuric Chloride, or Corrosive Sublimate (HgC1), is formed deposit its sulphur ; but if the acid be strong, both the lead and when mercury burns in chlorine, or when mercurio oxide is disthe sulphar are oxidised, forming a lead sulphate.

solved in hydrochloric acid; it is usually prepared by subliming a Plumbic Chloride (PbC1,) is precipitated from a solution of The nitrate by the addition of sodium chloride. It combines * The density of its vapour is 100, being an exception to the rule:

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SILVER.

mixture of salt and mercuric sulphate. In this instance the Argentic Sulphide (Ag,S) is found as the mineral "silver action is

glance.” Sulphuretted hydrogen precipitates it from a silver 2NaCl + Hg50. = HgCl, + Na,so,

solution; it falls as a black powder. It is also decomposed by the alkalies, but is soluble in water; The presence of silver is easily detected by the precipitation it is a violent poison. The white of eggs (albumen) is the of the chloride. Copper, zinc, and iron precipitate metallic antidote, since with this substance an insoluble compound is silver from its solutions; mercury produces the crystalline deformed. The action of ammonia on these chlorides is peculiar, posit, which is an amalgam, and is known as “arbor Dianæ." a molecule of amidogen (NH) replacing an atom of chlorine :- Phosphorus also becomes coated with silver when suspended in (1.) Hg,Cl, + 2NH, = Hg,C1,NH, + NH,Cn.

an argentic solution. (2.) HgCl + 2NH, Hg,Cl,NH, + NH,Cl.

Mercury, lead, and silver are distinguishable by the action of

their chlorides with ammonia. Mercurous Iodide is a green powder, formed when any mercuroas salt is acted on by potassium iodide ; it easily decom- the chloride of mercury is blackened.

The chloride of silver is soluble—that of lead insoluble ; while poses, even by light, into

Mercuric Iodide, which is a brilliant red colour, formed with mercuric salts and potassium iodide ; it is soluble in an

LESSONS IN BOOKKEEPING.–XII. excess of the latter solution. The mercurous salts are distin. guished from the mercuric salts by the addition of a chloride,

COTTON BOOK. when calomel falls.

In the Day-Book, which was given in our last lesson, all the The salts of mercury are readily recognised by the appear- transactions relating to the purchase and sale of the different ance of the metal when they are submitted to heat.

kinds of Cotton have been entered as a primary record of these transactions; but if the merchant be desirous of keeping a dis

tinct and separate account of his dealings in Cotton, in order to SYMBOL, Ag - COMBINING WEIGHT, 108 -SPECIFIC GRAVITY, 10-5. be able to tell at a glance what is actually in his Warehouse, or

Silver, the most beautiful of the metals, is frequently, though in Stock, as the phrase is, he will have a book similar to the not plentifully, met with in a native state; it is often combined following specially made for the purpose. In this book, the with mercury, antimony, and gold; but usually is found as a transactions can be more clearly and distinctly arranged; for sulphide, with the sulphur ores of lead, antimony, copper, and he can have a separate account of each kind of cotton, with iron.

columns for the number of the bags, the net weight in pounds, The chief silver mines are those of Peru and Mexico ; Kongs- the rate per pound, the prime cost, and the selling price; and he berg, in Norway; and Schnuberg, in Saxony.

can appropriate the one side of the folio for the purchases, and Its extraction from lead has been already noticed.

the other side of the folio for the sales; so that the difference To liberate the metal from its ores the method of amalgama- between them can be found in a moment, if necessary. If any tion is often resorted to, which consists in reducing the silver particular kind of Cotton be all sold, then this book will show to the state of a chloride by roasting the crushed ore with salt; at once what has been gained or lost by the transactions in this then it is placed in barrels of water with pieces of iron, which kind; and as the same principle is applicable to all kinds, it are made to revolve by this means. The iron becomes a follows that if all the Cotton of every kind has been sold, this chloride, and the metallic silver is liberated. Mercury is now book will show, both individually and collectively, the gain or added, with which the silver amalgamates. The mercury is loss on each, and the gain or loss on the whole. This is a great then distilled off and the silver remains.

advantage where a merchant deals chiefly or wholly in any parThe metal is the best conductor of heat and electricity, and ticular kinds of goods, as he can form an idea of his gain or exhibits extraordinary ductility.

loss on the principal part or the whole of his business acSilver is largely used in the arts, but is then usually alloyed, cordingly without consulting his Ledger or striking a general to give it the requisite hardness for wear. Standard silver, of balance. which coins are made, contains 7.5 per cent. of copper. Since It is evident that in any trade, business, or mercantile proit is capable of receiving the highest polish, it is much used for fession, such a book as this for every separate species of goods reflectors. When melted it possesses the remarkable property bought and sold would be of immense advantage, and would of absorbing oxygen from the air ; this it liberates again on certainly be preferable to one book, such as the Day-Book, cooling, and hence the surface of a cooled mass is covered with where all kinds of goods are indiscriminately classed together bubbles, from which the oxygen has escaped.

according to the dates of the different transactions ; for the There is reason to believe that three oxides exist: the sub-oxide order of dates, though highly important, is not so useful to a (Ag,0), the silver oxide (Ag,0), and the neutral peroxide (Ag,02). merchant as the classification of his transactions; whilst even

The Silver Oxide (Ag,0) is precipitated as a brown powder when in that classification this order can be preserved. Hence a merpotash is added to a solution of argentine nitrate.

chant may have his Sugar-Book, his Indigo-Book, his Tea-Book, When this powder, freshly precipitated, is digested for some his Coffee-Book, etc., according to the nature of his business ; hours in ammonia, fulminating silver is the result, which must be and in keeping books by Single Entry, which many persons yet carefully dried in small quantities on pieces of blotting-paper. mistakenly follow, such books as these are indispensably neces

Argentic Nitrate (AgNO3) is produced when the metal is dis- sary, inasmuch as the Ledger kept by Single Entry gives them solved in nitric acid. It may be obtained in tabular crystals; no information whatever as to the actual state of their Assets it is soluble in its own weight of cold water. When fused it is and Liabilities. If the book, such as the following, be devoted sold as lanar caustic. With organic matter, in sunlight, it under to one or more classes of goods, and each be kept separate and goes decomposition, staining the body with black suboxide. This distinct, so that no confusion be introduced into the different property is the foundation of photography.

transactions, it may be called legitimately the Stock or WareArgentic Chloride (AgCl) falls as a white, curdy precipitate house Book, as the merchant can always tell his Stock of Goods whenever a chloride is added to a silver solution :

by consulting it, without actually going to the warehouse and AgNO, + Naci AgCl + Na.NO,

turning over the goods in order to see what he has got in hand. When heated strongly it melts; and when cool it is named horn the account of clear gain made by the purchase and sale of

The following is the state of the Profit and Loss account, or silver from its appearance. chloride, it is only necessary to moisten it with dilute sulphurie Cotton of different kinds from January to June, as per Cottonacid, and place a piece of zinc in contact with it; a gradual

Book :transfer of the chlorine from the silver to the zinc takes place. Gain on Berbice

£60 5 8 In sunlight it changes colour, becoming purple, with a loss of

Grenada

33 04 chlorine. It is readily soluble in ammonia.

Maranham

85 14 8 Argentic Iodide (AgI) is the most sensitive to light of the silver

West India

123 16 8 salts; for this purpose the collodion of the photographer is

Madras

355 4 10 iodised, so that when the plate is immersed in the bath of

Demerara

111 16 5 argentic nitrate, on its surface may be formed a film of iodide of

Whole gain

$769 18 7

silver.

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LESSONS IN GEOLOGY.-IX.

larger quantity were treated in the same manner, the basalt

returned to its former stony appearance; but in doing so, it LITHOLOGY-PETROLOGY-GEOLOGICAL TERMS.

was observed that the molten mass congregated into little balls, UNDER the general term Geognosy is included all that can be and these increased in size by the continuous addition of more said in relation to the structure of the matter composing the matter to their external coating. In due time these balls earth's crust. Such a description readily permits of a sub- touched each other; but as their increasing capacity still condivision.

tinued, they were squeezed together; and as the expansive force The rock-masses may be treated of as to their mineral, progressed, their curved surfaces were flattened. Presuming the their internal structure, and those characters which may be force in each ball to be exactly the same, by this process determined by handling specimens, such as texture, construction, hexagonal (six-sided) short prisms would be produced. This will hardness, etc. All this is Lithology,

be sufficiently evident from Fig. 15. Petrology describes the larger charac

For some reason or other these spheres teristics of rock; the relative positions they

arranged themselves one above the other, so occupy, and the disturbances they have

that a straight line would pass through their undergone.

centres. This explains the formation of the Neither of these sub-divisions treats of

columnar structure. rocks arranged in geological groups. Hence

Certain green stones are found which apthis forms a third part of the subject, and

pear in spherical masses. When exposed to to enable us to classify rocks chronologi

the weather they are liable to exfoliate ; cally—that is, to determine which rocks were

that is, one coat after the other peels off, deposited at or about the same time-we

thus demonstrating their concretionary chamust appeal to their organic contents. The

racter, or that they were made by successive mineral composition is of little service.

layers accumulating round a nucleus, proFor instance, two sandstones, identical in

bably in the same manner as the globules their composition, may be found, which we

of basalt, in which the columnar structure know must have been formed at two periods

Fig. 14,

originated. separated by vast intervening ages; and

All masses of rock are intersected by this we discover by their fossil contents. Hence a study of regular sets of cracks, which are termed joints. Without these fossils is of the greatest importance, and this has received the it would be difficult to quarry stratified rocks, and impossible to name of Palæontology.

hew out hard primary rocks. Mineralogy is a further sub-division of Lithology.

Joints generally traverse rocks at right angles to each other. Lithology, as we have said, treats of the mineral composition In granite quarries three sets frequently cut the stone into cubical of the rocks, but does not enter into the chemistry, etc., of these masses. mineral elements. Thus we find the remark we made in the Their existence can only be accounted for by supposing they opening lesson is true. To be a perfect geologist we must result from the shrinkage of the mass upon its consolidation. begin with Chemistry. This teaches us the elements whereof all When these joints are very close to each other, and pass bodies are composed, and the laws of their combination. A through the rock-mass in the same direction, the phenomenon step higher, and we reach Mineralogy, by which we are taught is termed cleavage, and the rock splits into slates. Some how those elements are arranged in bodies contained in the stratified rocks readily divide into horizontal slabs, the planes solid crust of the earth; the forms in which minerals appear, of division coinciding with those of stratification. Such slabs and their characteristics. Lithology groups these minerals into are called flags or flagstones. rocks, and forms the third division of our

When the rock exhibits a disposition to subject; Petrology tells how the rocks lie on

break up into thin leaves, it is said to be the surface, their contortions, interstratifi.

laminated. Shales are clayey deposits which cations, etc. ; while Palæontology, from the

were once soft and plastic, but upon drying fossils the rocks contain, groups them ac

became intersected by numerous joints, cording to their ages, and writes a history

which cause the mass to split up into small of the animal life of the globe. Minera

pieces. logy will be treated separately; and for a

Crystalline rocks are frequently found further description of the minerals we shall

possessing a laminated structure; they are have occasion to name, we refer the reader

then schists, or of a schistose structure. to the forthcoming lessons.

Occasionally the term foliated is applied to Technical Terms descriptive of the Struc.

rocks of this nature, from the leaf-like man. ture, and Internal Characters of Rocks.

ner in which the layers overlie each other. Although the particles of a mineral may be

Fissile is a general term which characterises arranged in a symmetrical order, forming a

all rocks which show any tendency to break crystal, this formation never extends to large

up into small parts. masses. No crystal has been discovered

Fig. 15.

When a layer of rock reposes on a stratum more than one or two feet long; but when

of different material, its under surface must a rock is composed of particles which are either crystals or frag- partake of smoothness or inequality of that stratum ; this is dements of crystals, it is said to be crystalline. Such is the struc- nominated bedding. A stratum of rook is sometimes called a bed, ture of loaf-sugar. The granites and many of the primary but the word is becoming geologically obsolete. Seam, unforrocks exhibit it. Occasionally a uniform structure is developed tunately, has two meanings; sometimes it is used to indicate the in large masses of rock ; this is always columnar (Fig. 14), as in line which marks in a section the junction of two strata, and the basaltic rocks of the Giant's Causeway, in the north of Ire- also it is applied to thin layers of mineral matter which traverse land, and in Fingal's Cave, on the opposite shore of the Isle of a series of strata. For example, thin beds of coal, a few inches Staffa.

or even feet thick, are frequently found at intervals in many The number of the sides of the columns varies from three to strata ; these would be called seams of coal. It is evident how ten. They fit so closely to each other that the blade of a knife the word has become applicable to each case. The thin bed was is with difficulty inserted between them. When broken hori- considered the line which divided the two layers of strata. zontally they exhibit a conchoidal fracture; that is, the surface The above terms are descriptive of the structure of rockof one piece is concave, the corresponding surface of the other masses. On examining a specimen in the hand, a closer inspecbeing of course convex-like a ball-and-socket joint.

tion reveals to us its internal characters. If it be made up of The origin of the columnar structure of rocks was proved ex- the same kind of matter, the rock is homogeneous ; when its perimentally by Mr. Gregory Watt. He caused a quantity of particles are in grains, perceptible to the touch or plainly visible, basaltic rock to be fused in a blast furnace. When a small the specimen is granular. Occasionally the material is arranged portion of this was removed and allowed to cool, it assumed a in fibres, as asbestos; it is then fibrous. When the fibres are eritreous character ; that is, like glass, but not transparent. If a distinct, long, fine crystals, it is said to be acicular (needle-like). TOL. III.

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