LESSONS IN GEOLOGY.-No. XLVIII.

BY THOS. W. JENKYN, D.D., F.R.G.S., F.G.S., &c.

CHAPTER V.

ON THE CLASSIFICATION OF ROCKS.

SECTION II.

ON THE RELATIVE POSITION OF ROCKS IN THEIR VERTICAL
ORDER.

2. You are aware that, in very many districts, some one of the different strata marked from a to w forms the surface rock of the country; therefore it would be in vain for you, in digging your shaft, to expect below that surface the rocks which are arranged above it.

3. The geological doctrine about the superposition of rocks is, that the different beds or formations lie in order, according to the later or earlier epochs in which they were formed, or according to the more ancient rock on which they were deposited,

4. Suppose that you live in any part of England along a straight line from Devizes to Norwich or to Dover. There the surface rock is the chalk formation, the G of your diagram. The meanthese lines you dig a shaft to the centre of the earth, you would never meet any of the strata that are represented as lying between G and A. If you live on the line from Bath to Lincoln, you would dwell on K, the oolite formation; and your shaft would never meet with either of the strata that lie between K and A. The same reasoning would be true if you lived on the coal measures; or on 1, the old red sandstone, &c.

EVERY beginner in geology ought to make himself as much master of the order of rocks in the crust of the earth as he is of the let-ing, then, of the geological doctrine is, that, if along either of ters of the alphabet. Indeed the knowledge of this order of vertical position is of more importance to him than accuracy in the order of the alphabet; for if A took the place of K, or if v stood in the position of B, the arrangement would not in the least embarrass the learner of a language.

The accurate and certain knowledge of the order of the sedimentary rocks, is as essential to the geological student as a knowledge of the distribution of letters is to the compositor; or a knowledge of the shelves of laces, ribbons, silks, and cloths to the draper; or the order of folios, quartos, octavos, and duodecimos to the keeper of a library.

This order must be learnt. You may learn it in your own way; but learn it you must. It will cost you no more trouble than did your learning the multiplication table; and this order, like that table, when once completely mastered, will be useful to you through life.

You had better learn this vertical order from some ONE approved writer, and then make corrections according to the progress which you make, either in geological reading or in scientific observation. The order which was presented to you in the last lesson, and founded upon the enlarged science of Sir Charles Lyell, you may depend upon as being one of the best. All geological writers agree as to the order in which the rocks lie on, or under, one another. The subject on which they vary is the grouping of different beds into what is called a FORMATION; that is, whether such beds ought to be grouped with the series above them or with the beds ought to be grouped with the series above them or with the series below them. It is true that there are many cases in which certain beds are found in anomalous and perplexing positions, for which geologists find it difficult to account; but such anomalies are only exceptions, which do not disturb the regularity of the order of position as a whole.

To the well-sinker, the practical miner, the civil engineer, and the field geologist, an accurate familiarity with the superposition, the structure, the fossil contents, and the relative dates of the different beds in a rock is an indispensable acquirement. Some rocks, though formed in the same age, differ exceedingly, both in litho logical character and in fossil remains; and other rocks, formed under similar circumstances, but at epochs very remote from each other, may very much resemble one another, and may therefore be placed by the geologist in the wrong order of position. The study of this order of strata, and the knowledge of the mineral peculiarities of each bed, form what is called descriptive geology. The great mistake made by the majority of beginners, in commencing the study of geology, is the supposition, that, were a quarry or a section of immense depth to be exposed to their view, or were they to dig a shaft from the surface of the earth down to its centre, they would behold every one of these strata lying regularly in the order presented in geological treatises. This is a great mistake, and you must at once either avoid it or correct it; for the geological doctrine of the regular position of strata is far from involving any such idea. I will therefore try to explain the principles of this doctrine to you; and will take for granted that, while reading my explanation, you will constantly refer to the diagram presented to you in our last lesson. Observe particularly, however, that under the Cambrian ought to be placed the Granite Rocks, and these being lowest, we denote them by w. The ideal section will then be complete from A to w; and the lowest stratum can easily be filled up in the mind of the student.

1. It is barely possible that there may be certain localities on the earth's surface where, if a shaft were made to the centre, the workings might pass through the whole series from A to w as represented in the diagram referred to. Such a circumstance, however, is scarcely probable.

a

5. Still the order of superposition does not imply that, if you digged your shaft downwards from G, for example, you would meet ALL the strata that are represented between G and w, for many of them might be missing. It is possible that G. might be found to rest on K, and even on Q, without any of the intervening strata being present; and E, the coal, might be found to rest, not on s, but immediately on the granite, w.

be found above G, and that R will never be found below U. 6. The meaning of the doctrine is, that K or L will never it is never, except in easily explained cases, inverted. As you This order may frequently be found imperfect or defective; but would dig your shaft downwards, you would often miss one or more beds, or strata, and even formations, in the series; & or having been swept away by denudation; and even several rocks J might be missing, as having never been deposited, or perhaps in succession, such as I, J, K, L, M, &c., might be altogether absent. Fix it therefore in your mind, that all that the doctrine of superposition teaches is, that F will never be found taking the place of c, or that in the vertical order R may come before K. To sum it up in a sentence, I may say, that you will never find the entire series in any one district; but the members of any series that are found to occur are always found to follow the ver◄ series that are found to occur are always found to follow the vertical order of sequence.

7. These statements about the regular order of superposition are in harmony with processes of deposition which are now going on around our own country. All the sediments, which our numerous rivers are carrying in all directions to the sea, must be deposited somewhere, and must therefore form a sedimentary rock. Let us call this rock, wherever it is deposited, by the designation A, which represents a new sandstone or a shaly clay. Between Kent and France, A, like the Goodwin Sands, rests on &; about Cornwall on w orT; in the Bristol Channel upon T or R; in the Irish Sea on u or v; around the north of Scotland on T or v; and along the east coast of England on c or F or G.

8. The exceptions which the practical miner and field geologist find to this regularity of vertical sequence, and the anomalous position in which some rocks are discovered, do not disturb the stability of this geological doctrine. For instance, there may be cases in which the rocks T, S, R, Q, and even K or G, formed at one time the bottom of the ocean, at which epoch some plutonic action from below w might impel upward a stream of melted trap or porphyritic granite, which would rise to the surface and spread over the bed T or s, or any other superior stratum. If you commenced our supposed shaft in such a mass of granite, you might infer, from the reasoning of our diagram, that, lower down, you would not meet any sedimentary rocks; and yet the facts of the case would be otherwise. Again, there are cases, as in the Alps, and in the Apalachians of North America, in which certain beds have, by a tremendous power from below, been thrown completely topsy-turvy; so that, instead of the beds lying in the regular sequence of A, B, C, D, they lie vertically in the order of D, C, B, A, the upper beds being the lowest. This fact disturbs the regular order of superposition no more than when an earthquake power would hurl up a tower, and cause it to fall with its turrets and pinnacles downward.

9. You are not to imagine that this geological arrangement

rocks is a fanciful one, made for the convenience of inquirers. The order of vertical sequence is what has been found to be strictly true in many localities, as they have been observed and recorded by quarrymen, by well-sinkers, by miners, and by civil engineers, as well as by field geologists, who have marked the relation of rocks as they have found them exposed in ravines, in cliffs, in mountain slopes, in quarries, in railway cuttings, and in mines and collieries.

The geological beginner is often puzzled with the questionthat, since no man has ever seen a quarry half a mile deep, and as no one has sunk a shaft to the depth of ten miles, how can it be possible for geologists to know the order of sequence in the rocks that constitute the earth's crust?

The way in which they attain certainty in such knowledge is this. They collect together the results of the examinations which have been independently made by separate geologists in different districts, and then they apply such results to the appearances or sections of rocks presented to them in any given countries. One geologist may live in Norfolk or Suffolk, and he verifies all the rocks in sequence from A to D; another lives about London, and

he ascertains the order of all the beds between D and G; another
resides between London and Brighton, and he demonstrates the
order of rocks from a to K; another makes his inquiries in Glou-
cestershire or Northamptonshire, and he gives all the rocks
which he has observed between K and Q. A practical miner in
South Wales, Staffordshire, or Northumberland, makes a sec-
tion of all the strata between a and s.
An able quarryman in
Scotland, in Breconshire, or in Devonshire, ascertains minutely all
the beds between 8 and u. A field geologist traverses North
Wales and Cumberland, and exhibits the regular system of forma-
tions that lie between T and w. By this division of labour, the
theoretical geologist finds that, for all the purposes of scientific
induction, he has a section of the earth's crust that is about ten
miles deep.

il cap-pêl-lo che mí-a má-dre ha com-prá-to? Ab-biá-mo tro-vá-to un lib-ro. A-vé-te vói per-dú-to un lí-bro? Dó-ve hai tu com-prá-to la tú-a pen-na? Vô-stro zí-o ha un buôn ca-vál-lo. Nô-stro pá-dre ha án-che com-prá-to un ca-vál-lo. Ab-biá-mo ve-dú-to il ca-vál-lo che vô-stro pá-dre ha comprá-to. Mí-o fra-têl-lo è un buôn fan-ciúl-lo; é-gli è môl-to pic-co-lo.

ENGLISH-ITAlian.

The tailor asks for nine yards of cloth, two dozen of buttons, and half an ounce of silk. Send for a loaf of sugar and two pounds of coffee. I shall return in a quarter of an hour. Finish this glass of wine, and eat this small crust of bread. London. I come by order of the master to tell you that Take the map and find me the city of Paris and the city of the preparations for to-morrow are to be made. The month of London. I come by order of the master to tell April is changeable, the month of May, on the contrary, is very pleasant. The months of December and January are the roughest in the year. What dress will you put on for the ball of to-morrow? Were you at the performance of yesterday? He had given him the lower rooms.

Dozen, doz-zí-na (ds), f.
Button, bot-tó-ne

Half an ounce, mêz-za ón-
cia, f.

Send for, man-dá-te a prên-
de-re

Loaf. pá-ne, m.

Sugar, zúc-che-ro (ts), m.
Pound, lib-bra, f.
Coffee, caf-fè, m.

I shall return, ri-tor-ne-rò

(pron. ri-tor-ne-ró)

Quarter, quár-to

Hour, ó-ra, f.

cia-no

Preparation, pre-pa-ra-ti-vo,

or Finish drinking, fi-ni-te di Year, ón-no (with the genit.)

bé-re

Glass, bic-chiê-re, m.

Wine, ví-no, m.

Eat, man-gia-te

Small crust, cro-stí-no, m.

B ead, pá-ne, m.
Take, pren-dé-te

Map, cár-ta geo-grá-fi-ca, f.
ind m.
cer-eá-te-mi
ity, cit-tà
Paris, Pa-ri-gi
London, Lôn-dra
! come, vên-go

What, che

Dress, á-bi-to

Will you put on, met-te-ré-te
Ball, bál-lo

To-morrow, do-má-ni
Were you, siê-te stá-to
Performance (i.e., comedy),
com-mê-dia, f.

Yesterday, jê-ri

He had given him, gli fu-rono as-se gná-te

Room, cá-me-ra, f., sót-to, below, underneath

ITALIAN-ENGLISH.

Ta-bac-chiê-ra d’ô-ro.

Ve-sti-to
Il

Mi-o pa-dre è buô-no; é-gli ha án-che un buôn fra-têl-lo. Mi-a má-dre è buô-na; él-la ha án-che ú-na buô-na so-rêl-la. Ab-biá-mo ve-dú-to vô-stro zí-o; é-gli ha com-prá-to un gran lí-bro. A-vé-te vói ve-dú-to il nô-stro giar-dí-no? és-so è mól-to grán-de. Hô com-prá-to ú-na pén-na; és-sa è mól-to buô-na. In tú-o lí-bro è píc-co-lo, ma és-so è buô-no. AbUn vá-so d’ar-gên-to. biá-mo un pá-dre che è buô-no. A-vé-te ú-na má-dre che è | di vel-lú-to. Ví-no d’I-tá-lia. Un cuôr di ma-ci-gno. buô-na. Hô un lí-bro che è mól-to píc-co-lo. Mí-a so-rêl-la | fí-lo di fêr-ro. Guán-ti di pêl-le fí-na. Cap-pêl-lo di pá-glia. ha ú-na pén-na che è mól-to gran-de. Il lí-bro che a-ré-te U'-na mi-niê-ra d' ô-ro, d'ar-gên-to. Ac-ciá-jo d' In-ghil-têr-ra. com-pra-to è buô-no. Il giar-dí-no che ab-bia-mo ve-dú-to è | Fêr-ro di Stí-ria. Fiê-ra di Fran-co-fôr-te. La fe-sta di ảo-mámo-to grán-de. Hai tu ve-dú-to il lí-bro che mí-o z1-o hani. Il giór-no d’ôg-gi. La com-mê-dia di jê-ri. Il teá-tro d’ôg-gi com-pra-to? Il lí-bro che vô-stro zi-o ha com-prá-to è mól- | giór-no. U’-nama lat-ti-a di quát-tro set-ti-ma-ne. Il ví-no di to píc-co-lo, ma és-so è buô-no. Hô án-che com-pra-to unốt-to, di vén-ti án-ni. Laguêr-ra di sêt-te án-ni. Un bên cól-po lí-bro, ma és-so è grán-de. Vô-stro fra-têl-lo ha il lí-bro che d'ôc-chio. Lo squil-lo dél-la tróm-ba. U'-na per-só-na di vói a-vé-te ve-dú-to. Ho un pic-co-lo cap-pêl-lo. Il tú o fé-de. E'-gli è di tê-sta dú-ra. Uô-mo di cór-te, di món-do. eap-pel-lo è grán-de. Mí-o fra-têl-lo ha un buôn’o-ro-lô-gio. | Uô-mo di lêt-te-re, di dól-ce têm-pra. Uô-mo di grand’afHai tí án-che un o-ro-lô-gio? I mí-o o-ro-lô-gio è píc-co-lo, | fá-re, di gár-bo. Uô-mo di cat-ti-va con-đót-ta. Uô-mo di és-so è mól-to buô-no. Ho per-dú-to il mí-o tem-pe-rí-no.grán-de a-bi-li-tà, di gran re-pu-ta-zió-ne. Uô-mo di mêz-za A-vé-te vói tro-vá-to un tem-pe-rí-no? Nô-stra má-dre ha tá-glia. Uô-mo di mal ta-lên-to, di spá-da, di guêr-ra. Uôcom-prá-to un cap-pel-io per mi-a so-rel-la. Hai tu ve-du-to mo di b s-sa e-stra-zió-ne. Uô-mo di pô-ca sa-lu-te. La côn

Barca, barge, boat (ponte di
barche, pontoon).
Inspettore, inspector.

Duro, m., dura, f., hard, ob- Cannone, cannon.†

la. Ab-biá-mo ri-ce-vú-to un re-gá-lo. A-vé-te vói scrít-to Gelatine possesses but a very feeble power of endosmose. In ú-na lêt-te-ra Mi-a so-rêl-la ha ri-ce-vú-to ú-na bêl-la cúf-general, the current of endosmose is towards the denser liquid. fia. Hô ven-dú-to la mí-a car-rôz-za. Hai tu án-che ven- Alcohol and ether, however, are exceptions; for these liquids dú-to la tú-a car-rôz-za?? Qué-sto re-gá-lo è per vô-stra zí-a. act upon water like denser liquids. With regard to acids, it Vô-stro fi-glio è mól-to píc-co-lo, ma é-gli è buô-no. Mi-a is found that, according as they are more or less concentrated, fi-glia è gran-dis-si-ma. Qué-sto pá-dre ha ú-na bêl-la fi-glia. endosmose takes place from the water to the acid, or conQué-sto fan-ciul-lo è mí-o fi-glio. Il giar-dí-no che ho ve-dú-versely. to è gran-dís-si-mo. Mi-o pá-dre ha per-dú-to il sú-o cappêl-lo e la sú-a om-brêl-la. Nô-stro zî-o ha ven-dú-to la sú-a bêl-la car-rôz-za. Mi-a so-rêl-la ha tro-vá-to il sú-o a-nêl-lo, Qué-sto pá-dre ha per-dú-to sú-a fi-glia. Qué-sta má-dre ha per-dú-to sú-o fi-glio. Mi-o zi-o ha com-prá-to ú-na cúf-fia per la sú-a píc-co-la fi-glia. Qué-sto re-gá-lo è per mí-a sorêl-la. Qué-sto fan-ciúl-lo ha scrít-to ú-na gran-dis-si-ma lête-ra per sú-a má-dre. Nô-stra zí-a ha com-prá-to un bel-lissimo man-têl-lo per sú-o fi-glio. A-vé-te või tro-vá-to un' anêl-lo? Mi-o zí-o ha per-dú-to il sú-o man-têl-lo.

ENGLISH-ITALIAN.

The present times are not the best. He had hidden himself in the back room. Our town has a stone bridge; yours has only one of wood. Edward has received from London a gold watch, a silver sword, and a pair of steel shoe-buckles. Once they wore cloth dresses and velvet waistcoats. The use of copper vessels has been prohibited in Sweden. Beef, veal, and mutton, are for sale in the shambles. What means this ringing of bells"? What do you say of the cloth which I have bought? It is good and fine. And of the colour? It is beautiful. What do you think of the man whom you see, of the boy whom he carries along with him, and of the beggar who follows him? Here are ten yards of the taffeta, some of which you wanted, and twelve yards of the cambric which you have demanded. Send me a dozen of the lemons, and two pounds of the figs which you have received from Smyrna. Spare me a bottle of the eau de Cologne which has been sent

to you.

M. Dutrochet has demonstrated by his experiments, that the phenomena of endosmose can take place only when 1st, the liquids are heterogeneous and miscible, as water and alcohol; 2nd, when the liquids are of different densities; and 3rd, when the membrane which separates them is permeable, at least, by one of them.

All vegetable and animal substances are permeable; as to inorganic substances, such as slates, stone, porcelain and pipeclay in certain states, they are less permeable in proportion as they contain more silica. Pipe-clay, which is more aluminous than porcelain, is more permeable; it is this property which makes it catch the tongue. Through thin inorganic laminæ the current is feeble, but it may be indefinitely continued. Organic membranes, on the contrary, are speedily disorganised, and endosmose ceases.

Several theories of endosmose have been proposed. Some attribute it to an electric current which takes the same direction as the endosmose. Beef, veal, tion as the endosmose. Others suppose that the cause of the phenomenon is a capillary action which is united to the affinity of the two liquids. Others again suppose that endosmose is the result of the unequal viscosity of the liquids. Lastly, this phenomenon has been ascribed to the greater or less permeability of the membranes by the different liquids. Of all these hypotheses, not one explains endosmose in a satisfactory manner. Whatever the cause may be, the phenomenon appears to be intimately connected with the causes which produce capillary action; yet it is observed that an elevation of temperature which increases endosmose, on the contrary weakens capillary action.

ON PHYSICS OR NATURAL PHILOSOPHY.
No. XVI.

(Continued from page 214).

ENDOSMOSE, ABSORPTION AND IMBIBITION, Endosmose and Exosmose.-These words, which are taken from the Greek, signify respectively a forcing inwards and a forcing outwards, and are applied to the action of two liquids of different kinds, which are separated from each other by a thin and porous membrane, whether organic or inorganic. They were first adopted by M. Dutrochet, who, in 1826, gave a complete explanation of the phenomenon of one liquid flowing into a vessel or out of it, through a membraneous substance, and mixing with another liquid of a nature different from itself. This phenomenon was proved by means of the endosmometer, an apparatus composed of a membraneous bag, fastened to a long glass tube and made both air-tight and water-tight. This bag being filled with a mucilaginous or gummy solution thicker than water, as milk, albumen, syrup, is immersed in a vessel full of water. In a little time the liquid in the tube rises to the height of some parts of an inch, and the liquid in the vessel sensibly sinks; from which it is concluded that a part of the pure water has passed through the membraneous bag and has mixed with the liquid within it. It is also found that, after a certain time, the water in which the endosmometer is immersed contains some of the mucilaginous or gummy solution; a current is therefore produced in two opposite directions; and the process by which the mucilaginous liquid is increased, is called endosmose; while that by which the water is diminished, is called exosmose. If pure water be put in the membraneous bag, and it be immersed in a gummy solution, endosmose takes place from the pure water to the solution, that is, the level of the exterior liquid is elevated. The height to which the liquid in the endosmometer rises varies in different liquids. Of all vegetable substances, sugar in solution is that which, under equal density, possesses the greatest power of endosmose; of all animal substances, it is albumen.

Gaseous Endosmose.-The gases also present the phenomena of endosmose. If two gases of a different nature are separated by a dry membrane, there is a simple mixture of them, that is,' the currents are equal on both sides of it; but if the membrane be wet, endosmose takes place, that is, the currents are unequal. This is proved by the following experiment: a bladder filled with carbonic acid is inclosed in another bladder larger than it, and containing oxygen. The latter bladder is soon filled with the carbonic acid, which shows that the endosmose is from the carbonic acid to the oxygen. In like manner, if a soap-bubble be blown under a glass vessel full of carbonic acid, it will become larger and larger.

In the

Absorption and Imbibition.-The words absorption and imbibition in physics are nearly synonymous; both equally indicate the penetration of a foreign substance into a porous body. Absorption, however, is used indiscriminately in speaking of liquids and gases, while imbibition is restricted to liquids. In physiology, absorption is distinguished from imbibition. former case, there is the penetration of a foreign substance into the tissues of a living being, while in the latter there is only penetration into the pores of a body destitute of life, whether organic or inorganic. In short, in absorption the vital forces are put in action; in imbibition they are not.

Absorption of Gases.-The property of absorbing gases, in the physical sense, belongs to all bodies possessed of sensible pores, but in very variable degrees. This property is particularly evident in oak charcoal; extinguished under a vessel filled with a given gas, this body absorbs, under the ordinary pressure, 90 times its volume of ammonia, 35 times its volume of1 carbonic acid, and 9 times its volume of oxygen. In a humid state, this charcoal absorbs only half as much, which proves that its absorbing power is due to its porosity, and consequently to capillary action. The absorbing power of fir-charcoal is only half that of oak-charcoal. The charcoal of the cork-tree has no absorbing power; neither has the very compact natural charcoal called graphite. Hence it is inferred that, while porosity is a condition essential to the absorption of gases, yet the pores of bodies which have this power are comprised within certain limits.

Absorption in Plants.—In the vegetable kingdom, absorption takes place in all parts of plants, but especially in the spon