1. Qui vous a dit cela? 2. L'avocat me l'a dit. 3. Lui avez vous parlé de cette affaire? 4. Je ne lui en ai pas encore parlé. 5. L'avez vous vu dernièrement? 6. Je l'ai vu il y a quelques jours. 7. N'avez vous pas écrit hier? 8. Nous avons lu et écrit toute la journée. [Sect. 25 (9).] 9. N'avez vous pas ôté vos gants et vos souliers? 10. Je n'ai pas ôté mes gants, mais j'ai ôté mon chapeau? 11. Le tailleur n'a-t-il pas mis son chapeau? 12. Oui, Monsieur, il a mis son chapeau. 13. Qu'avez vous fait à ce petit garçon? 14. Je ne lui ai rien fait. 15. Ne lui avez avous point dit que je suis ici? 16. Je ne le lui ai pas encore dit. 17. Qu'avez vous étudié ce matin ? 18. Nous avons étudié nos leçons et nous avons lu nos livres. 19. Le jardinier du ministre a-t-il plante le poirier? 20. Ill'a planté il y a plus de huit jours. 21. Avez vous acheté un habit de drap noir? 22. J'en ai acheté un. 23. L'avez vous porté aujourd'hui ? 24. Je ne l'ai pas encore porté. 25. Nous avons mis nos souliers et nos bas ce matin. EXERCISE 80. 1. Have you studied to-day? 2. We have no time to study, we have read a page. 3. Have you not written to my brother? 4. I have not yet written to him. 5. Has not the German written to my mother? 6. He has not yet written to her. 7. Have you told (à) my mother that I have taken (pris) this book? 8. I have not yet seen your mother. 9. What have you done this morning? 10. We have done nothing. 11. Have you taken off your coat? 12. I have not taken off my coat, it is too cold. 13. Has the bookseller written to your brother? 14. He wrote to him a long time ago. 15. Did he write to him a month ago? 16. He wrote to him more than a year ago. 17. Have you planted a pear-tree? 18. We have planted several. 19. Is it too cold to (pour) plant trees? 20. It is too warm. 21. What has the gardener done to your little boy? 22. He has done nothing to him. 23. Has any one done any thing to him? 24. No one has done anything to him. 25. Is anything the matter with him? 26. Nothing is the matter with him. 27. Has your father put on his black hat? 28. No, Sir, he has not put on his black hat. 29. What has your brother said? 30. He has said nothing. 31. Has your sister told you that? 32. She told it me. 33. Did you not work yesterday? 34. We did not work yesterday, we had nothing to do. 35. Your little boy has done nothing to-day. 8. When the régime direct or objective (accusative) follows the participle, no agreement takes place [§ 134 (5)]: Vos sœurs ont elles écrit ? Nous ne leur avons pas parlé. Avez vous acheté des pommes ? Nous en avons acheté. Achet-er, 1. to buy. [§ 49 (5).] Apport-er, 1. to bring; Appel-er, 1. to call. [49 (4).] Broch-er, 1. to stitch; Have your sisters written? The letters which we have written. I have read them, I have written them. Have you brought them? Fhave not brought them. Have you called those ladies? Whom have you seen this morning? We have not spoken to them. I have unbound (stitched, in paper covers,) books. Have you bought apples? I have bought some. We have bought some. We have persuaded them of it. 1. Nous avez vous apporté nos habits? 2. Nous ne les avons pas encore apportés. 3. Les avez vous oubliés? 4. Nous les apporter. 5. Pourquoi n'avez vous pas appelé les marne les avons pas oubliés, mais nous n'avons pas eu le temps de chands? 6. Je les ai appelés, mais ils ne m'ont pas entendu. 7. Avez vous entendu cette musique? 8. Je l'ai entendue. 9. N'avez vous pas vu les jolies fleurs que j'ai apportées? 10. Je les ai vues; à qui les avez vous données? 11. Je ne les ai données à personne, je les ai gardées pour vous. vous bien examiné ces gravures 13. Je les ai bien examinées. 14. Les avez vous achetées. 16. Je ne les ai point achetées. 16. N'avez vous point reçu vos revenus? 17. Je ne les ai point encore_reçus. 18. La domestique a-t-elle cassé ces tasses? 19. Elles les a cassées. 20. A-t-elle cassé des tasses exprès. 21. Elle n'en a pas ca ssé exprès. 22. Avez vous acheté des livres reliés ou brochés.. 23. J'ai acheté des livres 12. Avez reliés. 24. Nous avez vous dit ces paroles? 25, Nous vous les avons dites, mais vous les avez oubliées. 26. Je n'ai pas | called a line, and has no breadth. For, if it have any, this breadth oublié votre commission. EXERCISE 82. 1. Have you seen my cups? 2. I have not yet seen them. 3. Have you brought me my books? 4. I have not forgotten them, I have left them (laiss-er, 1.) at my brother's. 5. Has your mother called your sisters? 6. She has not yet called them. 7. Has the servant told you this news? (nouvelle.) 8. She has told me this news. 9. She has told it me. 10. Have you forgotten my errand? 11. We have not forgotten it, we have forgotten your money. 12. Where have you left your purse? 13. We left it at the merchant's. 14. Have you bought the beautiful (belles) engravings which I saw at your booksellers? 15. I have not seen them. 16. Has your mother bought them? 17. She has bought books, but she has bought no engravings. 18. Has that little girl broken my cups? 19. She has broken them on purpose. 20. Does that lady receive her income every month? 21. She receives it every six months. 22. Is the house which you have bought large? 23. I have bought no house. 24. Did you receive a letter from your father yesterday? 25. I received a letter from him four days ago. 26. Have you spoken to those ladies? 27. I have spoken to them. 28. Have you given them flowers? 29. I have given them some (en). 30. Are the books which you have bought bound? 31. No, Sir, they are in paper covers. 32. Have you examined that house? 33. I have not examined it. 34. Your brother (en) has examined several (plusieurs). LESSONS IN GEOMETRY.-No. IX. must be part either of the breadth of the superficies A B CD, or of the superficies KBC L, or part of each of them. It is not part of the superficies KBCL; for, if this superficies be removed from the superficies A B CD, the line B C, which is the boundary of the superficies A B CD, remains the same as it was; nor can the breadth that BC is supposed to have be a part of the superficies ABCD; because, if this superficies be removed from the superficies KBCL, the line BC, which is the boundary of the superficies KBC L, does nevertheless remain. Therefore the line BC has no breadth. And, because the line B C is in a superficies, and that a superficies has no thickness, as was shown, therefore a line has neither breadth nor thickness, but only length. The boundary of a line is called a point, or a point is the common boundary or extremity of two lines that are contiguous. Thus, if B be the extremity of the line A B, or the common extremity of the two lines AB and K B, this extremity is called a point, and has no length. For, if it have any, this length must either be part of the length of the line A B, or of the line K B. It is not a part of the length of KB; for if the line KB be removed from the line A B, the point B, which is the extremity of the line AB, remains the same as it was; nor is it a part of the length of the line A B; for, if the line AB be removed from the line KB, the point B, which is the extremity of the line K B, does nevertheless remain. Therefore the point B has no length. And, because a point is in a line, and that a line has no length, breadth, or thickness; therefore a point has no length, breadth, or thickness. And in this manner the definitions of a point, a line, and a superficies are to be understood." This explanation of Dr. Simson is so complete that nothing can be added to it. He who does not understand in what sense the terms, point, line, superficies or surface, and solid are to be taken in the Greek Geometry, after what has been said above, must be unacquainted with the meaning of the simple words that IN our last lecture, we stopped just at the point when every one are employed, or else deficient in the ordinary gift of human wished most anxiously to know what we had to say about a point; intellect. we mean a geometrical point. Well, we have often given the sub-in either of these predicaments; and therefore we shall conWe shall not suppose that any of our readers are stance of Dr. Simson's explanation, when lecturing to a class without book; but here we must present our students with the ipsissima verba, the very words themselves written by that learned man. H G F N M "It is necessary to consider a solid, that is, a magnitude which has length, breadth, and thickness, in order to understand aright the definitions of a point, a line, and a superficies; for all these arise from a solid and exist in it. The boundary, or boundaries, which contain a solid, are called superficies, or the boundary which is common to two solids which are contiguous (adjacent), or which divides one solid into two contiguous parts, is called a superficies. Thus, if BCGF be one of the boundaries which contain the solid ABCDEFGH,† or which is the common boundary of this solid, and the solid BK LCFNMG, and is there- E fore in the one, as well as in the other, solid; it is called a superficies and has no thickness. For, if it have any, this thickness must either be a part of the thickness of the solid AG, or of the solid BM, or a part of the thickness of each of them. It cannot be a part of the thickness of the solid B M; because if this solid be removed from the solid A G, the superficies BCG F, the boundary of the solid A G, remains still the same as it was. Nor can it be a part of the thickness of the solid AG, because if this [thickness] be removed from the solid BM, the superficies BCGF, the boundary of the solid B M, does nevertheless remain. Therefore the superficies has no thickness, but only length and A D C L B K come We sider further explanation of these terms unnecessary. line. This Dr. Simson has not considered it requisite to explain. now to consider the important definition of a straight without justice. Of course, we take it as the Dr. has given it to Yet great fault has been found with Euclid's definition, and not us; for, to enter into the question of the meaning of the Greek our chief object, and could not be expected to interest every reader. terms, which he has translated, would lead us too far away from The principal fault of the definition of a straight line is, that in the explanation, no very definite property of a straight line is involved. The word evenly, on which it hinges, is in its application here, nearly synonymous with straight; and therefore the definition almost amounts to this: a straight line is a straight line. Seeing this, it has been declared, by some geometers, that the idea of a straight line is so simple and self-evident, that it is incapable of logical definition. However this may be, all writers on geometry, and all editors of Euclid, have considered it necessary to give some definition of a straight line. Our esteemed friend Dr. Thomson, in his edition, adopts the definition given by Professor Playfair, as a substitute for Euclid's; viz., "If two lines be such that they canthem is called a straight line." This definition is manifestly imnot coincide in two points without coinciding altogether, each of perfect, because two arcs of the same circle, are two lines such that inciding altogether, and yet neither of them is a straight line. Dr. in a certain position they cannot coincide in two points without coThomson felt this, and therefore in his notes, he added an explanation or illustration to the effect that it was necessary to consider the two lines in all positions, like two rulers placed alongside each other, and made to turn round and round on their axes, or The boundary of a superficies is called a line, or a line is the lengthwise upon one another. In an edition referred to in our common boundary of two superficies that are contiguous, or which last lesson, an attempt is made to convey the idea of a straight divides one superficies into two contiguous parts. Thus, if BC be line in the following manner:-"If a perfectly flexible string one of the boundaries which contain the superficies ABCD, or be pulled by its extremities in opposite directions, it will aswhich is the common boundary of this superficies and of the super-sume, between the two points of tension, a certain position. ficies KBCL, which is contiguous to it, this boundary BC is Were we to speak without the rigorous exactitude of geometry we should say that it formed a straight line. But upon consideration, it is plain that the string has weight, and that its weight produces a flexure in it, the convexity of which will be turned towards the surface of the earth. If we conceive the weight of the string to be extremely small, that flexure will be proportionably small; and if, by the process of abstraction, we conceive the string to have no breadth. This is a Latin word of the fifth declension like res, and it is the same both in the nominative singular and the nominative plural; this is also retained in its English use; in the present case it is plural. The letters here which represent the solid are those at each of its eight corners; afterwards the same solid is represented by two letters at opposite corners, the line joining which would pass right through the middle of the solid. weight, the flexure will altogether disappear, and the string will be accurately a straight line." In this extract, it is plainly supposed that the two points between which the "flexible string" is pulled in opposite directions, are placed in a horizontal position; if at these points, pulleys were placed and the string made to pass over both with heavy weights balanced at each extremity, it can be shown by the laws of mechanics, that the string could never be made to assume the horizontal position, until the weights were increased to infinity; indeed, Dr. Whewell, in an early edition of his "Elementary Treatise on Mechanics," has added the following curiously-worded corollary to a problem of this kind : "For no force, however great, Can stretch a cord, however fine, Into horizontal line, That is exactly straight." But what learner is able to enter into the spirit of this illustration, without a much greater knowledge both of geometry and mechanics, than he can be supposed to have at the commencement of his studies? Is it necessary to go thus far for an explanation of a straight line? With all the above learned discussion, the said "flexible string," would not be, as the writer strangely says, "accurately a straight line;" it would not in fact, be a geometrical line at all, however straight. Several other definitions of a straight line have been proposed, all of them more physical than metaphysical, that is, more dependant upon our notions of sensible objects, than upon our mental conceptions or abstractions. Plato, and long after him, Proclus, a commentator on Euclid, defines a straight line as that which viewed throughout its whole length from one extremity to the other, appears simply as a point. This is a very clever and ingenious definition; but here, you fancy you see a fellow taking up a straight line in his hand and looking at one end of it, in order to see along the whole of it to the other end of it, as if it were a ruler, or straight piece of iron. The definition of Archimedes, the prince of ancient mathematicians, is generally considered the best; viz., "A straight line is the shortest way or distance between two points." Every one knows and understands this definition; it is the metaphysical reason of the practical fact which occasions the formation of so many footpaths across our fields from one place to another. Men reason and ac geometrically, without giving their actions the name of geometry. So do bees, as we shall see further on; but these do it by instinct; those by reason. Still, even this definition is defective, great as its author really was, both as a mathematician and a philosopher. The defect is, that it does not apply to an indefinite straight line, any more than Euclid's; it is fixed between two points. Hence the necessity of Euclid's first postulate. This defect was removed by an ingenious friend of ours, whose original views of many subjects shine forth more fully developed in those of the well-known and eminent sons he has left behind him; we mean the late Thomas Wright Hill, Esq. of Birmingham. To him are we indebted for the complete definition of a straight line which we have added to Euclid's; viz., "A straight line is that in which, if | any two points be taken, the part intercepted between them, is the shortest line that can be drawn between those points." The definition of a plane superficies is due to Dr. Simson; for he says, "instead of the definition as it is in the Greek copies, a more distinct one is given from a property of a plane superficies, which is manifestly supposed in the Elements, viz., that a straight line drawn from any point in a plane to any other point in it, is wholly in that plane." In the edition of Euclid above referred to, this definition is ascribed to Hero of Alexandria, and it is added that Plato defined a plane surface to be one whose extremities hide all the intermediate parts, the eye being placed in its continuation. Euclid's definition of a plane superficies was similar to that of a straight line given by him,-viz., that which lies evenly between its lines or boundaries. This, of course, is more objectionable even than that of a straight line. Why it is so we leave to our ingenious students to find out. In conclusion, we add that a plane superficies may be more correctly defined as that in which, if any two straight lines be taken, the part intercepted between them, is the least surface that can exist or can be supposed to exist between those lines. The distinction between a plane and a curve surface is this, that a The father of Rowland H, Esq., the inventor of the Penny Postage scheme; of M. D. Hill, Esq., Q.C., and Recorder of Birmingham; of Frederick Hill, Esq, Government Inspector of Prisons; of Edwin Hill, Esq., Superintendent of the Postage Stamp Department; and of Arthur Hill, Esq., Conductor of Bruce Castle School, Tottenham. straight line cannot be drawn in the latter in every possible direction, whereas in the former it can. A straight line cannot be drawn on the surface of a sphere; it may be drawn on the surface of a cylinder or cone in one direction, but not in every possible direction. QUESTIONS ON THE PRECEDING LESSON. Give Dr. Simson's explanation of a point; of a line; of a surface; and of a solid. What is defective in Euclid's definition of a straight line? What is Playfair's definition of a straight line, adopted in Dr. Thomson's edition? Give some idea of the attempts to deduce the definition of a straight line from physical notions. Why does a flexible string over pulleys placed in a horizontal line, and stretched by equal weights at each end, fail to represent a straight line? What is the definition of a straight line given by Plato and Proclus? What is the definition of it given by Archimedes? What is the improvement made in this definition by Mr. Hill? (To be continued.) These departures from exact correspondence, precision, and Present Participle. uniformity are certainly drawbacks; but, notwithstanding these drawbacks, great aid may be derived from a careful and systematic attention to the system here set forth. GER. The Gerund. Having in the above corresponding parts given the Latin as well as the English of several members of the verb, I need not repeat them. I supply in full what remains. As I write for young men and women rather than for children, I omit adding the English in all the detail of the persons; for when you know what is the first person, you will readily supply the rest; thus, if the English of amaveram, the first person, is I had loved, you know that the English of amaveras, the second person, is thou hadst loved, and of amaverat, the third person, he hut loved; so also in the plural, Instead of I might have loved, the sub. pluperf. may sometimes be rendered (put into English) by I would, I should, or I could have loved. In the corresponding English words, I have given the nearest approach to the several Latin parts. The student will do well to adhere strictly to these meanings at the first, though, as the correspondence between the several Latin and the several English parts is not entirely complete and constant, he will find occasions when his English will appear scarcely idiomatic, or strictly proper. He cannot, however, learn too soon, that in few particulars are any two languages exactly correspondent. Accordingly, for amo, I have set down what may be termed three meanings,-namely, I love, I do love, and I am loving. Here, it is obvious that the English is more rich than the Latin, inasmuch as it has three forms of the present tense indicative mood, while the Latin has but one form. Having but one form, the Latin cannot by a form indicate the variations of the English present tense. Consequently here is a want of strict correspondence; and here also is a source of doubt; for we may ask, what is the English equivalent of amo is it, I love, or I do love, or I am loving? After these remarks the student will know that it is with some latitude that he is to take these CORRESPONDING LATIN AND ENGLISH SIGNS. I have said that these signs are applicable to all verbs. If so, they need not be repeated. And in general the statement is correct. You will, however, bear in mind what you have previously learnt as to the tense-endings, and the mood-endings; and then you will remember that instead of bo,-am, (es, &c.) is the ending, and as the ending so the sign of the first future of the third and the fourth conjugations. One or two other deviations will occur to you. FUTURE. Sing. Plural. IMPERFECT. Sing. Plural INF. PERF.-Latin. isse IMP. I. SUP. II. SUP. PART. PRES. FUT. PART. ACT. INF. FUT. Lat. rum esse ama do Eng. about to Give yourself a thorough practice in these signs. Again and again ask, until you are perfect, what is the English sign of the indicative mood present tense? what the Latin sign? what is the Latin sign of the sub. pluperf.? what the English sign of the same? So go through all the parts. I hope you understand what I mean by these signs. Your understanding of them is the more important because they pertain not merely to the verb amo, or to the first conjugation, but to all the verbs; and because, when you are perfect in your knowledge of them as just given, you will easily put Latin into English and English into Latin. On the account of this importance, I will subjoin a few explanations. These signs, then, might be called a set of equivalents, and I might have indicated them after this manner : ama-(vi)ssétis ama-(ve)rátis ama-(ve)ránt ama-(vi)ssint amá-(ve)ro amá (ve)ris amá-(ve)rit [amá-(vé)rimus ama-(vé)rītis amá-(ve)rint GERUNDS. EXAMPLES.-Like this model, conjugate laudo 1, I praise; curo 1, I take care of; voco 1, I call. Compare together the II. Fut. with the Sub. Pres. You will find that the endings are the same, except in the first person, which in the former is ro, in the latter rim. In other words, the Latin language has no distinctive form beyond the first person for one or the other of these tenses. A distinction is attempted with the aid of the accent or the quantity. Thus the first person plural of the second future is sometimes pronounced long, as amaverimus. But the authority for this is not uniform, and consequently you find the sign of the long and the sign of the short vowel thus over the i; denoting that the vowel is sometimes pronounced with and sometimes without the accent. There is a difference between the first future, amabo, and I like two walls; and its upper surface also hardens, so as, with the future formed with the aid of the future participle, thus, the two sides, to form a kind of tunnel through which the amaturus sum. Amabo means I will or shall love, simply in- burning or incandescent matter flows. dicating a future act, without determining when, or the precise point in the future when the act will take place. Amaturus sum signifies I am about to love, that is, I shall shortly love; intimating that the action signified in the verb is near at hand, is in the immediate future. Of the first future there is properly no subjunctive tense; the import, however, is expressed by combination, thus, amaturus sim (sis, sit, &c.), I may be about to love; amaturus essem, I might be about to love. The second future also is without a subjunctive mood. EXERCISES.-Form according to the model now given, that is, write them out in full, with all the parts in both Latin and English, these verbs,-laudo 1, I praise; vigilo 1, I watch; compăro 1, I procure. LESSONS IN GEOLOG Y.-No. IX. By THOMAS W. JENKYN, D.D., F.G.S. CHAPTER I. This peculiarity of the walls of a lava current is well known in Italy, and by this knowledge men are able to deflect the burning stream, and to turn it aside from its intended course. The people make a gash in one of the hardened sides of the current. At this gash the lava will issue out, and discontinue the course which it threatened to take. By this method many villages and towns have been saved from the destruction which menaced them. An instance of this took place in Italy a few years ago. The people of Campania saw a current of lava descending from Vesuvius which was likely to overwhelm their hamlet. They immediately went up to meet the fiery stream, attacked it on the side farthest from their direction, and turned the current towards Paterno. When the inhabitants of Paterno heard of this manœuvre, they took up arms, arrested the operation, and caused the burning tide to take its own course. As such a hardened crust is a good non-conductor of heat, the melted matter within it takes a long time to cool. The lava which flowed from Etna in 1819, was, nine months after the eruption, in a state sufficiently fluid or molten, to move at the rate of a yard a day. There is an instance, in the same after the eruption. This deserves your notice, on account of a very remarkable fact, and a fact which may help to resolve some difficult problems in the examination of ancient rocks. ON THE ACTION OF VOLCANOES ON THE EARTH'S CRUST mountain, of lava being in perceptible motion even ten years SECTION V. ON VOLCANIC PRODUCTS, OR THE MATERIALS ERUPTED FROM VOLCANOES. THE quantity of matter which volcanic fires abstract from the bowels of the earth, and throw up to the surface is enormous. It has been scientifically calculated, that a volcano has, in some instances, thrown up, even at a single eruption, more matter than if the entire mountain had been melted down to yield the supply. The question which must interest every geologist is, "Where does all this mass of matter come from?" Among the various productions of volcanoes may be enumerated, gases, aqueous vapours, lava, minerals, scorise, stones, ashes, sand, water, and mud. It is well known that volcanoes emit different kinds of gases, such as muriatic gas, sulphur combined with oxygen or with hydrogen, carbonic acid gas, and nitrogen, besides aqueous vapours. Several of the simple minerals, and some of the metals are found in the melted materials ejected by volcanoes, such as common salt, chloride of iron, sulphate of soda, muriate and sulphate of potassa, iron, copper, lead, arsenic, and selenium. The examination of these gases and minerals belong rather to chemistry than to geology. They are related to geology only as they give aid in the study of the mineral character of rocks. From the very nature of such mineral productions it was to be expected that volcanic substances should greatly vary in lithological character, from that of light ashes to that of compact and heavy crystalline rock. Nor is it a wonder that the quantity of mineral matter ejected is so great as it is, especially when you consider what a multiplicity of elementary substances are acted upon by the fires below, and how these elements in their fused state, strive to combine with each other in different ways and proportions. It has been ascertained that, within three square miles around Vesuvius, more specimens of the simple minerals have been found than on any other spot of the same dimensions. Of the 380 different species of minerals known to the celebrated Haüy, 82 had been found on Vesuvius alone. LAVA is a name given to any mineral matter melted in a volcano, and ejected in a stream over the rim of the crater. When the molten lava is consolidated by cooling, it receives fresh names, partly according to its mineral composition, and partly according to the slowness or rapidity of its refrigeration. Hence such names as scoriæ, cinders, pumice, basalt, trachyte, obsidian, &c. The melted lava may be boiling for years within the walls or cliffs of a crater, as has been represented in fig. 11 and fig. 15, without flowing over its edges. When lava swells above the edges of a crater, and flows down the declivities of the hill, it does not spread itself on all sides as a flood of water would, but it moves in a tall half-rounded mass, not very unlike the engravings that you have seen of a tubular bridge. The sides of this moving body of lava harden so as to form something In 1828 a large mass of ice, several hundred square yards in extent, was found in Mount Etna lying under a bed of lava, which had covered it while flowing in a melted state. How could this be? You can imagine that rain-water, or drifted snow, might freeze into a glacier at the elevation of ten thousand feet, which was the height at which this ice was found. This bed of ice was formed in a large hollow, while the volcano was in a state of rest. But, when the burning lava flowed over the ice, how is it that the ice did not melt? It is probable that the bed of ice had been previously covered by a thick shower of volcanic ashes. As such a layer of ashes is also a good non-conductor of heat, it prevented the ice from melting: and after the bed of lava had cooled over it, it continued to preserve the ice in an unmelted state. The truth of this theory is established by facts which occur about Etna in the present day. In the higher regions of that mountain, the shepherds, in order to provide a supply of water for their flocks during summer, are in the habit of sprinkling beds of snow with a layer of volcanic sand, a few inches thick, and this is found to be an effectual means of preventing the sun from melting until it is wanted. The term SCORIA or cinders, is applied to the fragmentary slags of lava which are ejected into the air, and then settle around the volcano. The structure of these cinders is owing entirely to the influence of the external air, and not to any special difference of material in composition. Whether lava flows like a stream, or is thrown up in jets, it cracks and becomes porous, as soon as it is acted upon by the atmospheric gases. The result is, that the pieces or fragments become cellular or vesicular, that is, a mass full of small rounded holes, as may be seen in any specimens of pumice and lava. If lava is cooled under great pressure, it becomes compact, and even crystalline as in trap, trachyte, &c. During an eruption, masses of STONE are frequently thrown up into the air. Where do these stones come from, and come unmelted? When the little islet, called Graham's Island, rose in the Mediterranean, near the coast of Sicily, in 1831, its crater ejected pieces of dolomite rock, and fragments of limestone; and also masses of some pounds weight of Silurian 10ck. In the awful eruption of Tomboro, in Sumbawa, an island in the Molucca group, which took place in 1815, stones fell very thick-some of them as large as two fists, but most of them only of the size of a walnut. In a museum at Naples, are exhibited specimens of the various stones which have been ejected from the crater of Vesuvius. Several of these specimens are fragments of the limestone which prevails in the district, and these limestone specimens contain organic remains in them. These specimens prove that the vent of the volcano goes lower down than the limestone bed, and that the melted matter thrown up rubs against the sides of this rock, rends and tears portions of it off, and throws them up into the surface. These |