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THE

POPULAR EDUCATOR.

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PHYSICAL MINERALOGY

GEOLOGY -THE GEOLOGICAL SYSTEMS AND LITHOLOGY-THE SOLAR SYSTEM, ETC. ETC. THE derivation of the word Geology (yn [ghee], the earth, and λóyos [log'os], a discourse, or a reasoning) indicates the main direction of the science. It confines its attention to a description of the solid crust of the earth, and to the elucidation of those forces and causes which have produced the changes the surface of our planet has undergone. To aid him in his investigation, the geologist needs the aid of the botanist, the zoologist, the chemist, the mineralogist, the physicist, and even of the mathematician. Although the subject looks formidable to the general reader, it is not only fraught with the deepest interest, but by far its greatest part may be traversed by common sense. Moreover, its study commends itself to all, since it requires no expensive apparatus, nor yet a preparation which all other sciences demand ere the student can enter on their practice. Young and old, gifted with observation, may at once become practical geologists; and by never passing a stone-heap without an examination, or never leaving a quarry or gravel-pit unsearched, they will soon lay the foundation of a geological cabinet, and be efficient labourers in the extension of geological research.

Every generation of our race has produced men of inquiring minds, and it is but natural that such men should turn their research to discover the origin of the world we inhabit, especially in the early times when but few channels were opened along which they were invited to expend the natural vigour of their intellect; hence, in the earliest records of eastern nations we find theories which attempt to account for the existence of our earth-these it is unnecessary to dwell upon.

It is evident that the only sound mode of procedure is to collect all the information which observation of the various existing phenomena of nature can give; to search the crust of the earth for any facts which the rocks, their position, their character, their fossil contents, can afford; to notice the arrangement of continents and seas, the position and directions of mountain chains, etc., and from these letters of the geological alphabet to spell out the history of our globe.

The history of the progress of geology, like that of any other science, can furnish many instances of theories built up without any facts for foundations; but as patient research gradually amassed information, these erroneous suppositions were abandoned, and geologists have, from so many warnings, become extremely careful of hazarding opinions. The experiences by which we have been taught not to speculate, though interesting and instructive, we cannot record in these pages, as our limited space requires us to attend to facts and the deductions which may be reasonably drawn from them.

The division of the subject we propose is the following:1. Physical Geology—that is, the geological agencies which have worked the various changes in the surface of our planet, both as to their present existence and as to the traces of their power which the rocks reveal.

2. The Geological Systems.-As we pass through these, we shall enumerate the fossils the rocks contain, the history of the animal and vegetable life of our globe, and the localities in which the members of these systems appear.

3. Mineralogy and Lithology.-In our last division we hope to describe the composition of the various kinds of rocks, as well as the physical and chemical properties of the minerals they contain.

Before we enter upon the immediate province of geology, it will be well to consider our position in the universe, and somewhat of the character of our world as a globe, noticing the most 53-N.E.

plausible of the theories yet produced to account for the construction of our system, and therefore of our earth.

The solar system, of which we are one of the members, consists of the sun and eight planets-four of which are very much larger. than the earth-and a number of very small planets, called asteroids, which revolve in the space separating the four exterior and larger planets from the interior and smaller ones. The position of the earth is the third from the sun. The earth is accompanied by a moon, which is not the case with any of the other interior planets, whilst the exterior planets are all attended by satellitesSaturn and Uranus by eight, Jupiter by four. All these bodies revolve round the sun in the same direction, and all move within a narrow belt. The exterior planets are much lighter than the interior. If the density of water be taken as 1, the density of the sun will be about 14; of Mercury, 9; of Venus, 5; of the Earth, 5; of the Moon, 34; of Mars, 34; of Jupiter, 14; of Saturn,; of Uranus, P.

The sun's magnitude is immense, as may be judged by the fact that if he were a hollow shell, and the earth placed at the centre, there would be sufficient room for the moon to revolve, as she now does, at 240,000 miles from the earth, and there would still be some 200,000 miles beyond the moon ere the shell of the sun were reached. The planets cannot be said strictly to revolve round the sun, but the sun and the planets revolve about the centre of gravity of the system; and, owing to the preponderating bulk of the sun, this centre of gravity lies not far from his own centre.

In searching for a record of the process of creation, we naturally turn our attention to that only Book the human library contains which did not emanate from the mind of man. But the Bible was not written as an instructor in physical science, hence we only find the sacred historian dedicating a few verses to the subject of "the creation of the world." Yet we may rest assured that, although the short notice only touches the prominent points, yet every word is true; and the more science has discovered, the more has she proved to be the com. mentator and unfolder of the great truths contained in those few words.

A generation since, geologists were looked upon as the opponents of revealed truth, the friends and abettors of infidels and atheists; but now we have learnt not to generalise from too few facts, but patiently to explore before pronouncing a definite judgment. The interesting questions, "the development of species" and "the antiquity of man," are to-day in the same position as the questions of "the universality of the deluge" and "the six periods of creation" at the close of the last century. But we know in these days nothing of the rancour with which the contest was then carried on. Explorers now in every part of the world collect information, and every right-minded man rests assured that in the end Scripture will not be eontradicted, but confirmed.

The chief points in the description of the creation given in Genesis will be found to be fairly explained by Laplace's nebular hypothesis, which has been extended to the explanation of the contour of the earth's surface. The first fiat of the creation was, "Let there be light." Now we are well aware that light is nothing more than the rapid vibration of an invisible existence called ether; so that our word "light" in the expression quoted must mean light-giving matter." This corresponds to the firecloud of the hypothesis. All bodies of our acquaintance are capable of existing in a state of vapour. The temperature at which this change of state takes place is so high that the vapours are luminous. Hence the first fiat of creative power called into existence all the matter of which the solar system is composed in a state of highly luminous vapour. In the expression that "the light was divided from the darkness," there seems to be an

indication that the law of gravitation was imposed upon this
vapour, and it began to revolve round its centre of gravity, thus
collecting itself into a fire-cloud, whose outmost edge stretched
beyond the orbit of our most distant planet. A moment's
thought will decide that the shape it would take would be that
of a watch, providing that the edges were somewhat thinner.
As this fire-cloud revolved in space, which is devoid of heat,
it would rapidly cool. Obedient to the great law, as it cooled
it would contract and become more dense, until its outward edge
had reached so low a temperature that, it could no longer
remain in its vapour condition, when it would condense into a
liquid.

The globe of red-hot matter thus produced has since lost all its heat, and forms the furthest planet of our system. So one after another the different planets condensed from the vapoury mass. As might be expected, they did so at intervals, regulated by a law, named, after its enunciator, "Bode's law." There are several points in our system which support this theory. The planets and their moons all move in the same direction. Their orbits are comprised in a narrow belt, which represents the thickness of the cloud. The exterior planets are light, and have many moonsboth which peculiarities are accounted for by the fact that the cloud would be denser near its centre, and gradually become more rare towards its outward edge, in the region where these planets condensed. There yet remains a further confirmation: the existence of Saturn's ring and the asteroids. It is well known that matter in rotation, if it be sufficiently pliable, will assume one of two shapes-either a sphere or a ring. The sphere will not be perfect, but will flatten at its poles and bulge out at its equator in proportion to the rapidity of its motion and the slight cohesion of its matter. The exterior planets are so elliptical in their shape that, looking at them through a telescope, the eye is at once struck with the fact.

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For many ages the surface of the earth was too hot to permit
water to rest upon it; but when the cooling had sufficiently pro-
ceeded to allow of this, then that vast quantity of fluid which
is the blood of the geological life of the world covered the
surface of hard bare rock from pole to pole.
But for long ere
this was effected, the water, in a state of condensed vapour,
which forms clouds, must have enwrapped the earth, and the
operation ascribed to the second period of creation was the
making of a firmament which should divide the waters which
were above the earth-the clouds-from the waters which were
on the surface: meaning to say that the cooling had sufficiently
proceeded to allow the water to remain on the surface, and
clouds to form.

With the dawn of the third era began the operation of a force
which still exists, and to which we shall frequently have to
allude: the heaving up, gradual and slow, of the northern
hemisphere, and the consequent draining off of the waters
towards the southern pole. The ridges, or the crests of the
wrinkles, which had a generally northern direction, being elevated
at their northern extremity, would form continents of a triangular
shape, the point of the triangle tending southwards.
This ap-
pearance is still perpetuated in North and South America,
Africa, India, etc. A glance at the map of the world will
afford many confirmations of this theory; making allowance for
the repeated elevations and immersions of the continents, which
would necessarily cause some alteration in their shapes. This
theory bears out the assertion of the sacred record, that the
sun was not made until the fourth day-that is, Mercury and
Venus were not until then separated from the mass, and that
luminary which we call the sun produced as he now appears to us.

From this time the various forces which are still existing date the commencement of their operations. The tides, the ocean currents, the rivers, the streams, the rain, the atmosphere, all The earth's equatorial diameter is twenty-six miles longer began their action on the Primary rocks, wearing them down, than its polar. It has been suggested that this shape may be and redistributing their particles in homogeneous order along due to the denudation of the poles by the continued evaporation the ocean bed; here forming stratified rocks which imbedded of water in the regions of the tropics and its condensation as the organic remains of that life which the Author of all life rain at the polar regions. By this means a thickness of thirteen had so abundantly shed upon the now habitable earth. Whether, miles was gradually transported from the poles, and deposited in after years, new facts discovered will cause another theory at the equator. But if this were the case, the earth would still to supersede this, remains to be seen. As yet, this is the only possess a spherical nucleus. This, however, is disproved by supposition at all tenable. And now, leaving theory, it is our certain astronomical considerations concerning the motion of duty to describe in turn these different agents, to notice their the moon. Hence, the earth must be elliptical from its centre-present action, and to discover traces of their handiwork in the that is, its shape is due to the action of its rotation when its rocky pages of Nature's book. mass was pliable.

The ring is the only other shape which fluid in revolution can assume to be in equilibrium; but it is remarkable that if a ring of oil which collects round a wire shape, immersed in a spirit of the same specific gravity as the oil, be made to revolve by turning the wire, when a certain speed is attained the ring suddenly breaks up into innumerable globules.

The existence of the ring of Saturn proves that that planet must once have been in a fluid condition. The asteroids seem to have been a ring of much larger dimensions, which, as in the instance quoted, broke up into many small planets. The view with which they used to be regarded-namely, that they were fragments of a planet which some internal convulsion had shattered-is now abandoned; for it can be proved that in this case the fragments must periodically return to the point from which they were hurled, which is not the case.

In the lapse of untold ages the various members of our system condensed from this vapour-cloud, and in process of time cooled down, until, losing their heat, they ceased to be luminous, and assumed the appearance with which we are familiar.

The sun is the remnant of this cloud, which was the result of the Great Being's first command, and no doubt the condensation and contraction are still going on.

But to return to our earth. After our globe had assumed the liquid condition, the process of cooling would still proceed, and the consequent contraction. The result of this would be that the vast ball of molten matter would be covered with a solid crust or skin. This crust, owing to the greater contraction of liquids than solids, would wrinkle, and, seeing the earth possessed a uniform motion, the wrinkles would take a uniform direction: this direction was from north to south. Whether water was existing in the atmosphere which enveloped the earth, as highly rarefied steam or as its constituent gases, oxygen and hydrogen, in an uncombined state, is a matter of little moment.

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2. Find the compound interest upon £555 10s. for 2 years at 41 per cent.

3. Find the difference between the simple and the compound interest upon £250 for 4 years at 6 per cent.

4. Find the difference between the simple and the compound interest upon £365 4s. 8d. for 3 years at 4 per cent.

5. Find the compound interest upon £250 for 3 years at 23 per cent.

6. Find the compound interest upon £1040 for 3 years at 4 per

cent.

7. Find the compound interest upon £625 for 2 years at 4 per cent. 8. The difference between the compound and simple interest of a sum for 3 years at 4 per cent. is 19s. ; find the sam.

[N.B. Find this difference for £100, and compare it with 19s.] 9. I buy a field for £1000, for which I receive £30 a year rent, which I invest as soon as received at 4 per cent. compound interest. At the end of 3 years I sell it again for £1030, What have I lost or gained by buying the field instead of investing the purchase-money on the same terms as I did the rent?

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The operation gives £10 15s. 8d., and therefore, rejecting one farthing, since the result only contains £10 once, we find the result correctly to a farthing to be

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5.

847 12

6

6.

4567

987 18 9 7. 7597 10 8

from July 8 to Dec. 26, at 5 per cent.
from April 21 to Sept. 24, at 5 cent.
per
from May 6 to Aug. 21, at 5 per cent.
COMPOUND INTEREST.

10. Where compound interest is reckoned, at the end of one year the interest is added to the principal. This amount becomes the principal for the second year, and the interest upon it for the second year must be calculated and then added to its principal, and so on. The difference between the final amount at the end of a number of years, and the original principal, is

the compound interest.

EXAMPLE. To find the compound interest for 3 years on £100 at 5 per cent.

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In finding the compound interest upon any sum, this is the process which must be followed. It will therefore readily be seen that, when the number of years is large, and the principal and rate per cent. complicated, the operation will be very laborious. All questions of compound interest are very much facilitated by the use of Logarithms, of which, however, we cannot treat here. Tables of the compound interest upon £1, at different rates per cent., and for different numbers of years, are constructed for practical use.

EXERCISE 56.

EXAMPLES IN COMPOUND INTEREST.

THE HISTORY OF ART.

XII. TITIAN AND THE ECLECTICS. FROM the days of Raffael and Michel Angelo onward, the history of art becomes mainly the history of the different national or sectional schools into which painting was divided. The general progress of all the fine arts grows too wide to follow in detail, and it is therefore necessary to confine ourselves to the great central art alone. Perfect technical mastery of the principles of painting had now been generally acquired. After Raffael and Michel Angelo, the mere handicraft of the artist could be taught almost mechanically, so that the veriest tyro could draw with a wooden accuracy and a fidelity to life which would have astonished the careful but undeveloped medieval painters. The varieties that could now arise were mainly those of a more delicate, intimate, and personal sort, dependent not so much upon differences of technical mastery as upon differences of taste or fancy. Every one could now learn the principles of perspective, of anatomy, and of chiaroscuro (or light and shade), but everybody had not the fancy, the feeling, and the power of touching our higher and finer chords which mark the really great painter; for the artist works with his brains and his heart as well as with his fingers. It was in these matters of feeling and taste that the greatest differences were henceforth to be noticed. Moreover, art now began to

split itself up into many classes or kinds. Hitherto we have heard nothing of landscape, nothing of any kind of art not religious; and we have dealt with Italy almost exclusively, leaving out of consideration Germany, France, the Low Countries, and England. Henceforth, however, we get, not a continuous stream of development in one country, but a divergence of art into many separate lines. During the Middle Ages, painting was all devotional in subject, and all given over to the delineation of the human figure. From the days of the Renais sance onward it has gone on multiplying its subjects and its aims in every direction. It has divided itself into historical, and each of these has been variously cultivated in various domestic, landscape, still life, and innumerable other branches, countries and by various schools. It is obvious that we can only glance very briefly here at the most important and most

characteristic of these.

This

Even during the lifetime of Michel Angelo and Raffael, a second great school of art, distinct from the Roman and the Florentine, was growing up in Italy itself at Venice. school dated back into the Middle Ages, but it attained ripeness at the same time as that of Florence. Tiziano Vecellio, whom we in England ordinarily call Titian, was two years the junior of Michel Angelo, being born in 1477; but, as he attained the

1. Find the compound interest upon £350 for 3 years at 5 per great age of ninety-nine years, he considerably outlived even

cent,

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