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. measures; or on 1, the old red sandstone, &c. the coal The same reasoning would be true if you lived on

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 correctious 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 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 lithological 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.

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 & and w, for many of them might be missing. It is possible that G. might be found to rest on K, and even on a, without any of the intervening strata being present; and R, the coal, might be found to rest, not on s, but immediately on the granite, w.

be found above 9, 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; E or I might be missing, as having never been deposited, or perhaps having been swept away by denudation; and even several rocks 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. the entire series in any one district; but the members of any To sum it up in a sentence, I may say, that you will never find 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 G; about Cornwall on worT; 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 r 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 1. It is barely possible that there may be certain localities on of D, C, E, A, the upper beds being the lowest. This tact disthe earth's surface where, it a shaft were made to the centre, the turbs the regular order of superposition no more than when an workings might pass through the whole series from A to Wearthquake power would hurl up a tower, and cause it to fall with as represented in the diagram referred to. Such a circumstance, its turrets and pinnacles downward. however, is searcely probable.

9. You are not to imagine that this geological arrangement of

rocks is a fanciful one, made for the convenience of inquirers. il cap-pêl-lo che mi-a má-dre ha com-prá-to? Ab-biá-mo 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 G to K; another makes his inquiries in Gloucestershire 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 & and s. An able quarryman in Scotland, in Breconshire, or in Devonshire, ascertains minutely all the beds between s and u. A field geologist traverses North Wales and Cumberland, and exhibits the regular system of formations 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.

tro-vá-to un lib-ro. A-vé-te vói per-dú-to un lí-bro? Dé-ve hai tu com-prá-to la tú-a pen-na? Vô-stro zi-o ha un buôn ca-vál-lo. Nô-stro pá-dre ha an-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 mil-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. 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 you that 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 IIe had given him the lower rooms. of to-morrow? Were you at the performance of yesterday?

Send for, man-da-te a prèn

de-re

Loaf. pú-ne, m.

Sugar, zuc-che.ro (is), m.
Pound, lib-bra, f.

Coffee, caf-fè, m.

I shall return, ri-tor-ne-rò

(pron. ri-tor-ne-rô)

Quarter, quar-to

Hour, ó-ra, f.

By, per

Order, ór-di-ne, m.
Master, pa-dró-ne, m.
To tell you, a dir-vi

That are to be made, che si fác

cia-no

Preparation, pre-pa-ra-ti-co,

m.

To-morrow (gior-no, day, anl

do-ma-ni, to-morrow)
Month, mé-se, m.
April, A-pri-le

Changeable, va-rid-bi-le
May, Mag-gio

On the contrary, all' in-cón

tro

Very, mol-to

Pleasant, a-me-no

December, De-cembre

January, Gen-na-jo
Roughest, il più ri-gi-do

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

be-re

Glass, bic-chic-re, m.

Wine, vi-no, m.

Eat, man-gia-te

Small crust, cro-sti-no, m.

B ead, pa-ne, m.
Take, pren-dé-te

Map, car-ta geo-grú-fi-ca, f.
ind m, cer-ed-te-mi
ity, eta
Paris, Pa-ri-gi
London, Lon-dra
come, vên-go

What, che

Dress, d-bi-to

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

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

Yesterday, je-ri

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

Room, ca-me-ra, f, sót-to, below, underneath

ITALIAN-ENGLISH.

Mí-o pa-dre è buô-no; é-gli ha án-che un buôn fra-tel-lo Mi-a mà-dre è buô-na ; él-la ha án-che ú-na buô-na so-rêl-la. Ab-bia-mo ve-dứ-to vô-stro z-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-80 è mól-to grán-de. Hô com-prá-to ú-na pén-na; és-sa è mól-to buô-na. I1 tú-o lí-bro è píc-co-lo, mà és-so è buô-no. Ab- Ta-bac-thiê-ra d’ô-ro. Un vá-so dar-gên-to. Ve-sti-to biá-mo un pá-dre che è buồ-no. A-vé-te ú-na ma-dre che è | di vel-lú-to. Ví-no d'I-tá-lia, Un cuor di ma-cí-gno. Il buô-na. Hô un lí-bro che è mól-to píc-co-lo. Mí-a so-rêl-la | fi-lo di fer-ro. Guan-ti di pêl-le fi-na. Cap-pêl-lo di pá-glia. ha ú-na pén-na che è mól-to gran-de. Il lí-bro che a-vé-te U-na mi-niê-ra d' ô-ro, d' ar-gen-to. Ac-ciá-jo d' In-ghil-têr-ra. com-prá-to è buô-no. II giar-di-no che ab-bia-mo ve-dú-to è | Fer-ro di Su-ria. Fiê-ra di Fran-co-for-te, La fe-sta di do-mámól-to grán-de. Hai tu ve-dú-to il li-bro che mí-o zí-o ha ni. Il giór-no d'ôg-gi. La com-mê-dia di jê-ri. Il teá-tro d'ôg-gi com-pra-to? Il li-bro che vô-stro zí-o ha com-prá-to è mól- | giór-no. U’-nama lat-ti-a di quát-tro set-ti-ma-ne. II ví-no di to píc-co-lo, ma és so è buô-no. Hồ án-che com-prá-to unit-to, di vén-ti án-ni. La guêr-ra di sét-te an-ni. Un bên có!-po lí-bro, ma és-so è grán-de. Vô-stro fra-têl-lo ha il li-bro che d'ôc-chio. Lo squil-lo dél-la tróm-ba. U'-na per-só-na di với a-vé-te ve-du-to. Hô un pic-co-la cap-pêl-lo. II tú o | fé-de. E’-gli è di tê-sta dú-ra. Uô-mo di cór-te, di món-do. cap-pêl-lo è grán-de. Mi-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 tn-che un o-ro-lô-gio? Il mi-o o-ro-lô-gio è fíc-co-lo, fá-re, di gár-bo. Uô-mo di cat-tí-va con-dót-ta. Uô-mo di é3-so è mol-to buô-no. Hô per-du-to il mí-o tem-pe-rí-no. gián-de a-bi-li-tà, di gran re-pu-ta-zió-ne. Uô-mo di mê -za A-vé-te với tro-vá-to un tem-pe-ri-no? Nô-stra ma-dre ha tủ-glia. Uô-mo di mal ta-lên-o, di sph-da, di guêr-ra. Uộ com-prá-to un cap-pêl-lo per mi-a so-rêl-la. Hai tu ve-dú-to mo di b s-sa e-stra-zió-ne. Uô-mo di pô-ca sa-lú-te. La cô

Cotone, cotton (filatojo
cotone, cotton-mill or manu-
factory).
Ponte, bridge.

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

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