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ON PLUTONIC CHANGES IN THE STRATIFIED SURFACE OF THE EARTH.

You have become acquainted with three causes which have contributed to the production of the earth's crust. These are-1, the first hardening of the surface by cooling; 2, the action of subterranean heat in throwing up eruptive rocks through fissures to the surface, and also consolidating "nether-formed" rocks below the crust; and 3, the action of water in dissolving, wearing away, or disintegrating, portions of upper rocks, and carrying down the sand, or detritus, to deposit it at a lower level.

Upon an examination of sedimentary rocks, there are two inferences which you cannot avoid making. The first is, that the rock which has been worn or abraded by the water, must have been older than the rock formed by disposition. The second is, that the rocks thus worn by running water must, at the time of disintegration, have been at a higher level than the ! place where they are deposited. To this second inference, there is one exception. Water, hot or boiling, has a greater disintegrating power to act upon rocks, chemically, than when it is cold. When the earth's crust, therefore, had only just become cool enough to allow water to exist upon it, in a fluid state, and not in one of vapour, the heated, boiling, agitated waters must have worn away the granite at their bottom very deeply and extensively. These abraded materials which the waters held in solution or suspension, they would deposit, either in deeper hollows, or along surfaces, that were of a lower temperature.

There are some phenomena developed in the condition of some of these sedimentary rocks that will greatly puzzle a young inquirer when he meets them for the first time. They are sometimes on a higher level than the rock from which their sands or clays have been derived. In other cases, they are so altered in general aspect and mineral character, that he would hardly recognise them as stratified deposits. In other places, they are so disjointed, dislocated, and separated from the series, of which they formerly constituted a continuous part, that their stratification appears almost reversed.

All these changes are owing to the action and force of subterranean heat, as will be shown in the following illustrations. Fig. 6.

are on a higher level than the crust A, from which the materials were originally worn down; or of which A has been denuded. Since the laws of Hydrostatics would prevent water from depositing matter at this high level, the elevation of the beds must be ascribed to the action of the heat from below.

This elevation would take place gradually and tranquilly, in consequence of the slow expansion of the crust A B. This elevating expansion of the crust is not represented in fig. 5, which is only designed to show the action of heat in altering rocks.

Before the sedimentary rocks had been deposited, the crust heat very slowly, and the consequence would be that the temA B parted with its heat freely: but deposits of clay conduct perature of the stratum, below such beds of clay, would increase to a higher degree. The increase of heat in the stratum below, would enlarge its bulk by expansion; which, in its turn, would elevate the newly-formed deposits, above their former level; so that what was once the bottom of the sea may become a large island or small continent. This you will more easily understand, if you imagine that, previous to the elevation of F D G, a sea existed on the line FG.

It is not the science of geology only which asserts and proves that such elevations have taken place in very remote ages; for our own observation can demonstrate that they take place in our day. The changes of level which take place along seacoasts, are ascribed, by the common people, to the sea receding; but geologists can show that the change is the result of the earth rising.

Even so late as the year 1822, in the neighbourhood of ValSouth America, was raised three or four feet above its usua paraiso, the whole coast of Chili, on the western side of level along a line of more than a hundred miles in length. There could be no doubt of this elevation, for, after a tremendous earthquake, an old ship that lay as a wreck at some distance in the water, could, after Nov. 20th of that year, be safely visited dryshod: and an extensive bed of oysters and mussels, of whose existence the inhabitants of the city knew nothing, was now exposed, which with the dead fish contaminated the air with their bad odour. At this moment, the coast of Sweden, from Frederickshall to Abo in Finland, is gradually, but visibly, rising at the rate of about three feet in every hundred years; but the rate varies in different parts of the coast. This elevation is proved by the fact, not only that shores are now dry which used to be covered at low water, but, that the shells of fish which now live in the Baltic abound in the soil which is about four feet higher than the water, and that at the distance of about seventy miles from the present margin of the sea. It is also a fact that barnacles, shellfish which attach themselves only to rocks or walls washed by the sea, are now found fixed on high parts of the cliffs; which proves that these cliffs with their barnacles were once at a level which could be washed by the sea. You therefore see, that wherever the sea is receding, it is occasioned by the earth rising, and that this rising is caused by the expansive power of heat below.

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The elevation and alteration of sedimentary portions of the earth's crust by subterranean heat.

In fig. 6, is represented a large portion of the earth's crust, covered by sedimentary rocks, which have been deposited by the action of water. A B represents the original crust now resting on the nether-formed rock c, to which reference was made in Lesson III. DE are sedimentary beds, deposited on the crust in its primitive state along the line F B. The deposits VOL. I

E

B

C

While heat is, by expansion, affecting and elevating rocks that are remote from it, it is acting with greater intensity upon the rocks which lie nearest to it. It is consequently found, that, when the lower beds of the sedimentary rocks lie near enough to the fusing power of heat, they are the most altered by it, both in appearance and even in mineral, or lithological character. This is represented above in the darkened portion of the beds FDE, fig. 5.

This operation of subterranean heat in altering sedimentary 15

rocks is not, in this lesson, to be mistaken for the action of volcanic intrusions, whether of granite, of basalt, or of trap, to which future lessons will refer. Both actions are analogous to each other: but this lesson refers to very early changes which have taken place in the earth's crust, and which might have been expected from the influence of intense melted matter, and from the effort of disengaged gases struggling to make their way through the porous rocks that overlay them.

The alteration which intense heat produces in a sedimentary rock, will always be according to the nature of the deposit of which it is formed. Shale, a laminated clay, will become so indurated and compact as almost to lose its slaty peculiarity, Argillaceous, or earthy limestone, will become granular and crystalline, like the white marble of the statuary. The clays of the coal formations will appear like flinty or jaspery slate. Coal is turned into anthracite, or stone-coal; and anthracite into coke. Chalk becomes crystallised marble; which has been verified by a chemist who applied intense heat to chalk, sealed in a gun-barrel. Thus, then, it is seen that the clayslate used in roofing houses, is nothing but clay that has been subjected to strong heat under great pressure.

thick beds of stratified gneiss, which is only granite worn away by water, to be deposited on a bottom of granite, you can imagine that the subterranean heat might acquire such intensity as to melt the granite crust under the gneiss afresh. This fresh fusion would rise to reach the lower beds of the overlying gneiss, and to penetrate them so thoroughly, as almost to destroy completely, all trace of the original lines of their stratification, and make them to appear as if they had never been under the action of water.

Keep in mind that these changes in the character of altered rocks is not produced by heat alone. Volcanic action, in what may be called recent and modern epochs of geological time, assists us in studying the character of Plutonic action in more remote ages. It is well known that volcanoes send forth immense volumes of heated gases, which disengage themselves from melted matter, and struggle to make their way from the enormous pressure which overlies them. They maintain this effort for weeks, months, and years. When, therefore, fused granite or porphyry is burning, boiling, and heaving under great pressure, and containing powerful gases which cannot escape, these gases will act upon the crust above; and, when they are near porous rocks, they will pass through them with great facility, and, in passing, greatly modify them.

It is true that we can study these phenomena only as they are observed on the surface of the earth; but it is clear that as gaseous fluids have altered the upper surface of the rocks, and as these fluids could only come from subterranean sources, they

Though these kinds of alteration are remarkable, still greater ones may have been produced in proportion to the greater intensity of the fusing heat; or according to the length of time in which the action of heat continued. There are, for instance, in the extreme south of Norway, sedimentary rocks penetrated by a large mass of granite, which must have protruded itself in a state of fusion. All Fig. 7. about the mass of granite, the sedimentary beds are altered to the distance, from the once melted matter, of from fifty to four hundred yards. Before this protrusion took place, the shale or the schist consisted of green and chocolatecoloured layers of sediments; but the fused granite has changed these into ribboned jasper, like those which are found in the pebbles at Aberystwith, in South Wales,-specimens in which each stripe faithfully repre

The dislocation of sedimentary strata by eruptive rocks.

sents the original lines in which their various clays were deposited. The limestone of the neighbourhood, which was originally of an earthy texture, and of blue colour, as it is still found at a distance from the granite, is become white granular marble. It is also remarkable that both the slate and the limestone of that rock contain garnets, and ores of iron, copper, lead, and silver.

In Cornwall, also, the fused granite has protruded veins into a rock, which the Cornish miners call "killas," a coarse argillaceous or earthy schist or slate,-a rock which has been altered by the heat of the fused matter, into hornblende schist. This operation is well developed both at St. Agnes, and St. Michael's Mount in the Bay of Penzance. These and a thousand similar instances prove that powers exist in nature which are capable of transforming sedimentary and fossiliferous rocks into crystalline strata.

It has been intimated that in altering rocks, heat not only changes their appearance or aspect, but also gives them a new mineral character, and causes them, in some instances, to become identical with the melted rock which has changed them, though they themselves have not been meited. Chemists have proved by experiment, that a rock need not be perfectly melted before its component parts will re-arrange themselves, that is before they crystallise, or take a new mineral character. Sedimentary rocks, therefore, may be completely altered, without having the lines of their stratification obliterated.

This theory will help you to understand a phrase often used by geologists, when they speak of "one rock passing into another," and that by imperceptible gradation. If you imagine

must have made their way through the entire crust, from the deep reservoirs below into the open air.

Other alterations of strata will be more fully considered when we D come to the subject of

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E

metamorphic

rocks,

and to the influence of volcanic action in the B protrusion of trap and basalt. The Plutonic changes, just alluded to, are mentioned now, only to illustrate one of the operations of heat on the early crust of the earth.

In fig. 6, while the lower portions of the sedimentary beds DE are represented, by darkened lines, as having been altered either by heat or by gases, the altered strata still retain their original relation to the beds that have not been altered. There are, however, innumerable instances in which stratified beds, whether altered or not, have been completely disturbed and dislocated, as represented in fig. 7. A thousand instances are found, in which the strata have been broken through and tilted up, so that what was deposited horizontally appears now with their lines of stratification highly inclined; sometimes, almost perpendicular; at other times perfectly vertical; and, in some instances, quite inverted. Sections of vertical position you may find at Alum Bay, in the western end of the Isle of Wight; and, at Whitecliff Bay, in the eastern end of it. The same also may be seen near Welshpool, in North Wales, where Powis CASTLE is built upon Silurian strata almost perfectly vertical. In fig. 7, A B is the earth's crust. CD, the sedimentary rocks resting on it. F, a dislocated portion of the altered beds ε, and separated from them by the eruptive rock &, which has been thrown up to the earth's surface by the subterranean heat H.

The study of fig. 7, will help you to apprehend the nature of geological reasoning. Suppose that a geological student travels from c to a, along a sedimentary rock. At a he comes to a rock of a different mineral character, and may be in difficulty to account for it. As he walks over F, or passes alongside of it, and has the face or section of F on his left hand as he walks towards d, he may not understand the new rock, till he comes to b. Here he finds the Plutonic rock G, say granite or porphyry, evidently of igneous origin. He goes over, or by

the side of o, till he comes to c, where he finds the same rock over which he travelled from c to a. He now conjectures, and then reasons out, the conclusion that the rock a Fb is a portion of the beds CD, first altered by heat, and then tilted up by the eruptive rock bac. He also argues with perfect certainty; first, that if he could follow a down to its depth or origin, he would find that eruptive rock to be eontinuous to the heated reservoir at H; and secondly, that if, between c and d he could sink a pit to the lowest line of CE, he would be sure to come to the altered beds of which he had a specimen in a F b. In the few lessons already given you, I have endeavoured to place in your mind the two great principles of geology: first, that the earth's crust is a fabricated article, produced in the laboratory of a stupendous chemistry, according to the fixed laws of the supreme Contriver and Intelligent Maker of the whole; and secondly, that the article thus fabricated has been from the beginning, and at successive periods, disturbed, altered, and dislocated by agencies from within itself. In the course of the lessons on which you are next to enter, you will find how the crust of the earth has been affected and modified by volcanoes, by the waters of seas and rivers, by organic life, by vegetation, by ice and snow, and by other means and agencies.

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Que pensez vous de cela?

That which you learn is useful. Do you find what you seek? pronoun what, used absolutely

What do you think of that?

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Arriv-er, 1to arrive.
Avec, with.
Coffre, m. trunk.
Command-er,1, toorder. Linge, m. linen.
Ecossais, e, Scotch.
Enfant, m. child.

Presque, almost.

Rien, nothing.

Soulier, m. shoe.
Monsieur, m. gentleman. Vrai, e, true.
Nom, m. name.

1. Qui connaissez vous? 2. Nous connaissons les Hollandais dont vous nous parlez. 3. Quelles leçons apprenez vous? 4. Nous apprenons les leçons que vous nous recommandez. 5. Ce que je vous dis est il vrai. 6. Ce que vous nous dites est vrai. 7. De qui nous parlez vous? 8. Nous vous parlons des Ecossais qui viennent d'arriver. 9. Savez vous qui vient d'arriver? 10. Je sais que le monsieur que votre frère connait vient d'arriver. 11. Vos sœurs que font elles? 12. Elles ne font presque rien, elles n'ont presque rien à faire. 13. Que mettez vous dans votre coffre? 14. Nous y mettons ce que nous avons, nos habillements et notre linge. 15. N'y mettez vous pas vos souliers? 16. Nous y mettons les souliers dont nous avons besoin. 17. De quoi avez vous besoin? 18. Nous avons besoin de ce que nous avons. 19. Cet enfant sait il ce qu'il fait? 20. Il sait ce qu'il fait et ce qu'il dit. 21. Ne voulez vous pas le leur dire? 22. Avec beaucoup de plaisir. 23. Faites vous ce que le marchand vous commande? 24. Nous 25. Il parle de ce dont vous parlez. faisons ce qu'il nous dit. EXERCISE 60.

we want.

1. Have you what (ce dont) you want? 2. We have what 3. Is the gentleman whom you know here? 4. The lady of whom you speak is here. 5. Is she just arrived? [Sect. 25. 2.] 6. She is just arrived. 7. Do you know that gentleman? 8. I know the gentleman who is speaking with your father. 9. Do you know his name? 10. I do not know his name, but I know where he lives (demeure). 11. What do you do every morning? 12. We do almost nothing; we have very little to do. 13. Does the tailor make your clothes? 14. He makes my clothes, my brother's, and my cousin's. 15.

6. Quoi, when not used as an exclamation, is generally pre- Do you know what you say? 16. I know what I say, and ceded by a preposition, and relates only to things:

De quoi voulez vous parler ? A quoi pensez vous ?

Of what do you wish to speak? Of what do you think!

7. Lequel, m. laquelle, f. lesquels, m.p. lesquelles, f.p. which, or which one [Seet. 17. 6], or which ones, relate to persons or things. They may be preceded by a preposition :Lequel avez vous apporté ? Duquel parlez vous?

Which one have you brought Of which one do you speak?

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what I do. 17. Do you know the Scotchman of whom your brother speaks? 18. I know him well. 19. What does he put into his trunk? 20. He puts his clothes. 21. Is that which you say true? 22. What I say is true. 23. Do you understand that which I say to you? 24. I understand all that you say. 25. Of whom does your brother speak? 26. He speaks of the gentleman whose sister is here. 27. Is your brother wrong to do what he does? 28. He cannot be wrong to do it. 29. What are you doing? 30. I am doing that which you do. 31. Where do you put my books? 32. Into (dans) your brother's trunk. 33. Is your brother here? 34. He is not here. 35. He is at my brother's, or at my father's.

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in the sense

vefter have a house built.?

in one built.

seuse before its own infini

I have a cloth coat made. You have leather shoes made.

coat made. 13. I am going to have a coat and a vest made. 14. Does your brother have his boots mended? 15. He has them mended. 16. What does your son mean? 17. I do not know what he means. 18. Is he angry with me or with my brother? 19. He is neither angry with you nor with your brother. 20. Is he afraid to spoil his coat? 21. He is not afraid to spoil it. 22. Does the druggist want money? 23. He does not want money. 24. Has your sister taken my book

...u followed by dire is used in the sense from the table? 25. She has not taken it away. 26. Why

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Gilet, m. waistcoat. Grand, e, large, very. Manteau, m. cloak. Noir, e, black. Pantoufle, f. slipper. Pourquoi, why.

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Prêt, e, ready.

Raccommod-er, 1, to mend.

Tout-à-l'heure, immediately.

Uniforme, m. uniform. Velours, m. velvet.

Dimanche, m. Sunday. Dîner, m. dinner. Fâché, e, sorry, angry. 1. Le général N. met il son uniforme? 2. Il ne le met point. 3. Pourquoi ne portez vous point votre manteau noir? 4. J'ai pour de le gâter. 5. Mettez vous vos souliers de satin tous les matins 6. Je ne les mets que les dimanches. 7. Il est midi; le domestique met il le couvert? 8. Il ne le met pas encore; il va le mettre tout-à-l'heure. 9. Le dîner n'est il pas prêt? 10. Le domestique ôte-t-il le couvert? 11. Il ne l'ôte pas encore, il n'a pas le temps de l'ôter. 12. Otez vous votre habit quand vous avez chaud? 13. Je l'ôte quand j'ai trop chaud. 14. Faites vous faire un habit de drap? 15. Je fais faire un habit de drap et un gilet de satin noir. 16. Ne faites vous point raccommoder vos pantoufles de velours? 17. Ne faites vous pas creuser une cave? 18. Je fais creuser une grande cave. 19. L'apothicaire que veut il dire? 20. Il veut dire qu'il a besoin d'argent. 21. Savez vous ce que cela veut dire? 22. Cela veut dire que votre frère est fâché contre vous. 23. Avez vous envie de mettre votre manteau? 24. J'ai l'intention de la mettre, car j'ai grand froid. 25. Je vais l'ôter, car j'ai chaud.

EXERCISE 62.

1. Do you take off your coat? 2. I do not take off my coat, I put it on. 3. Do you take off your cloak when you are cold? 4. When I am cold I put it on. 5. Does your little boy take off his shoes and stockings? [§ 21 (4).] 6. He takes them off, but he is going to put them on again (remettre). 7. Does that little girl lay the cloth? 8. She lays the cloth every day at noon (midi). 9. Does she take away the things after dinner? 10. She takes away the things every day. 11. Do you intend to have a coat made? 12. I intend to have a

do you take off your shoes? 27. I take them off because they hurt me (gênent). 28. Do you intend to have a house built? 29. I intend to have one built. 30. Does the tailor spoil your coat? 31. He does not spoil it. 32. Who spoils your clothes? 33. No person spoils them. 34. What hat do you wear? 35. I wear a black hat.

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tion.

D

LESSONS IN GEOMETRY.-No. VII.

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HAVING, in the preceding lesson, given some account of the nature of the apparatus and instruments used in surveying, we now proceed to explain more particularly the nature of their application to actual practice. Let us begin with the most simple,—namely, the chain and surveying cross. ABCDEFGHI is the representation of a field, and of the manner of measuring a base line within it, and the perpendiculars drawn to it from every corner. This figure is divided into several triangles and trapezoids, and their sides are taken parallel to each other, and perpendicular to the base-line, on each side. The method of measuring in the field is as follows:-Set up a picket or station-staff at each end of the base-line to be measured that is, at A and E, and beginning at A, measure with the chain in the direction from A to E, using the sights of the cross for the purpose of preserving the measurement constantly in that direcWhile this process advances, find, by the use of the cross, the different places along the base-line where perpendiculars would be drawn to it from the several corners or bends in the boundary of the field on both sides,-viz., from 1, H, G, and F, on the one side; and from B, C, and D, on the other side. These perpendiculars are to be measured at once by the chain as soon as their places are found, by using the sights of the cross, before the rest of the base-line is measured, in order to save time and ensure accuracy. The proper places from which they are to be measured, will be found by the cross after a few trials, by viewing both ends of the line through one pair of sights, and the corners or bends in the boundary of the field, through the other pair of sights; for it will be impossible to see the extremities of the base-line A and E, and any corner such as G, to which the measurement is to be made, or the picket placed there, unless the exact spot as d, of the perpendicular a d is found. In measuring these perpendiculars a 1, CH, d G, and ƒ F, on the one side; and b B, g C, and e D, on the other; one of the assistants keeps a book to record the observations as they proceed. Sometimes a rough sketch is made of the field as it appears to the eye, or as it is suggested by the measurements, and the measurements are marked on the corresponding lines drawn on the sketch. Both are useful, and both should be practised. The following is the form of the field-book in the present instance, where the measurements are marked in links of a chain.

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Of the triangle a a 1

106000

Of the trapezium a 1 H c

799500

Of the trapezium c H G d

946000

Of the trapezium d Grƒ

907200

Of the triangle fr E

162000

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20000

Square yards 24,20000

Area of the field A B C D E F GI, 23 ac., 3 ro., 24 po., 24 sq. yds.

LESSONS IN LATIN.-No. XIV.

By JOHN R. BEARD, D.D.

THE LATIN VERB.

IN form, the Latin verb has two chief divisions-1, active; 2, passive. Thus laudo is I praise, in the active voice, and laudor, I am praised, in the passive voice. There are some verbs which, though passive in form, are active in signification; as, hortor, 1 encourage. The ending in shows that hortor is of the passive form. This form, the verb, so to say, lays down, or lays aside, and hence it is called deponent (from de, down, and pono, I put). Deponent verbs, then, are words which, disregarding the claims of their form, have an active import, just as if they were active in form. As these verbs have an active meaning, their past participle has an active meaning; e. g.-hortatus, the past participle of hortor, is not being encouraged, but having encouraged. This past participle joins with parts of the verb sum I am, to form the perfect tense; thus, hortatus sum, means I have encouraged. There are deponent verbs in all four conjugations.

The tenses of the verb in Latin are pretty much the same as in other languages. Thus we have PRESENT, amo, I love, or I am loving; IMPERFECT, amabam, I was loving, or I did love; PERFECT, amavi, I loved, or I have loved; PLUPERFECT, amaveram, I had loved; FIRST FUTURE, amabo, I shall or will love; SECOND FUTURE, amavero, I shall have loved.

The present tense denotes either an action continued in the present time, or an habitual action. The imperfect tense denotes an action continued in past time. The perfect tense has two meanings; first, it signifies an action done and completed in past time indefinitely, and from the period in past time being indefinite or undefined, it is called an aorist, or is said to have an aorist import; (aorist is a Greek word, denotes a tense of. the Greek verb, and signifies undefined, or indeterminate;) in the second place, the perfect tense indicates an action which, in itself, or in its consequences, continues from the past to the

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