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hardens again into rock, which may again turn to sand, and so repeat the process-from rock to sand, and from sand to rock.

It is found too that, while mountains are worn down in one place, they are thrown up in another. This wearing down and heaving up has been going on for many, many ages, long before mankind were upon the earth, and it will no doubt continue as long as the earth endures.

A journey by rail will often afford a very valuable opportunity for gaining an insight into the more important truths of geology, as there are few lines which do not, in some part of their course, dip more or less into the crust of the earth. Let us imagine ourselves taking such a journey. We see all manner of surface, pretty woodland with leafy trees, arable land with its wavy corn, pasture land dotted over with nodding kine and frisking lambs; now we come to the bleak moorland, and anon we are rattling along amongst hills and mountains. Suddenly we enter a tunnel. As we emerge, we examine its sides, and find them to consist of one solid mass of dull, heavy-looking matter, which is called unstratified rock. This is the foundation or original of almost all rock. It was produced by the agency of fire, in the interior of the earth, whence it has been thrown up. It is therefore called igneous rock, from the Latin ignis, fire. There are three varieties of igneous, or unstratified rock: the granitic, trappean, and volcanic.

Proceeding on our way, we presently arrive at a cutting through rocks which are formed by the agency of water. Observe the difference. The unstratified rock was one solid mass, or nearly so; but here the rock lies in layers piled one above the other, like a pile of books on a table, or the courses of bricks in the wall of a house. These are called stratified rocks, from the fact of their lying in strata or layers; and because they are formed by the action of water, they are also termed aqueous rocks, from the Latin aqua,

water.

In this instance the layers are, perhaps, perfectly horizontal; but as we pass along, we shall come to a part where they are displayed in a sloping position. The cause of this

is, that at some period or other a lumbering mass of unstratified rock has been thrown up against them from below. Further on, they will be found to slope downwards in the opposite direction. In some instances they are found to stand on end; in others, only one part of the strata will be found to be out of the level, the adjoining strata not having apparently been affected by the shock. Those varieties of appearance result from the various degrees of violence or suddenness of the disturbing forces by which they are all produced.

GRANITE

Of the unstratified rocks, granite is the prettiest. It consists of numerous varieties, and is found in many places. Its beauty and durability render it a favourite building material, where these qualities are requisite. Peterhead granite has long been famous. Aberdeen is noted in all parts for its fine specimens. That town is almost entirely built of it, so abundant is it there. Pompey's pillar, in Egypt, is a very good specimen of fined grained granite; and so is the statue of Memnon in the same country.

The Giant's Causeway, in Ireland, and the Islandof Staffa, in which is the world-famed Fingal's Cave, afford fine specimens of the trap rocks. The hard, durable greenstone, or whinstone, as the Scotch call it, is largely used for causeways in our streets; and basalt, or any of the harder traps, is useful for breaking into small pieces for our macadamised roads.

The various stratified rocks invariably appear in one order. Certain of the rocks may be wanting in any particular spot, but the order of those which remain is never, on any account, reversed or changed. For the purpose of obtaining an idea of the varieties of stratified rocks

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and of the order in which they are
found, we will imagine ourselves to be
descending a pit sunk at a place where
they all appear. We will get into the
bucket, for the cage is not yet placed. q
Be careful now; keep clear of the chain. P
Down we go, and how smoothly and 0
pleasantly! Do not be afraid; for
when fear comes here, danger is nigh. n
We are at the bottom, and after a rest m
we will ascend. We are supposed to 1
be standing upon granite or some other
of the unstratified family of rocks. We k
are ready. Up we go. Shade the light,
and we shall see all the rocks nicely.
This is gneiss, the first of the stratified
series, very like its parent, granite; but
with a washed, watery look, unlike the
sharp, well-defined fracture of any of the
igneous rocks, Mica and tale schist are
the next, then clay slates, so useful for
roofing and other purposes. These
formed the PRIMARY ROCKS of the early
works on geology; but the name is now g
disused.

h

Next are greywacke, sandy slates, f and the old red sandstone. These used to be called the TRANSITION ROCKS.

Now we are at the mountain-lime e stone, and next come the coal measures with their abundant stores of fuel, ironstone, shale, etc., the most profitable d and important of all. These form the chief source of our greatness, being the mainspring of our enormous commerce. Fears are entertained that these important measures will soon become ex- b hausted in Britain, and that, with these gone our power must decline. Let us hope not, but meanwhile exercise all care in

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getting and using our coal. After the coal and its attendant shale, so useful in the manufacture of paraffin, we have the magnesian limestone, and new red sandstone, then shell limestone, and marls." Lias limestone" and shale follow, then the oolite, or egg-shaped particled limestone. The chalk and greensand next appear. On strata of this sort the city of London stands. All these were called the

SECONDARY FORMATION.

We have now clays, marls, gypsum, or plaster of Paris, so useful in the arts, and called stucco after it is formed into figures. Sandstone and calcareous grits1 complete the old TERTIARY SERIES.

We must now step out of the bucket, for we are near the surface. The rest of the pit-shaft must be solid masonry, founded upon the rock. Behind the building is drift clay with boulders, or huge round stones like enormous pebbles, some weighing several tons. Alluvial sand and gravel lie above, and then we have vegetable soil,* on which we depend for our food and raiment, and which makes our earth so fair and beautiful by its numberless products and the various trees and plants that grow in such rich luxuriance in the tropics and temperate zones.

Had we leisure to examine closely the stratified rocks noted in our ascent of the pit, we should find in them petrified remains of animals and plants, many of which are of most extraordinary forms. To these the name of Fossils has been given. No fossils have yet been discovered in gneiss, mica, and talc slates; hence these rocks have been classed as Azoic (A) or void of life. From greywacke to mountain limestone are found the oldest fossils, and these are classed as PALEOZOIC (B) or ancient life. The remaining rocks are classed as MESOZOIC (C) or middle life, and CAINOZOIC (D) or recent life.

EXERCISE.-64. MEANINGS OF WORDS.

1. Give the meaning of the following:-probably, geology, tunnel, considerable, characteristic, enormous, excavate, seething, homogeneous, macadamised, calcareous.

2. Distinguish between:-thrown, throne; due, dew; new, knew; which, witch; basalt, baysalt; gneiss, nice.

3. Illustrate the different meanings of :-trap, foundation, order, pit, pile, fair, coal-measure.

TO A SKYLARK.

PERCY BYSSHE SHELLEY.*

un-pre-med-i-ta-ted [L. in, rot; præ, before; meditor, to think], not previously thought of, not done purposely or by design. pro-fuse [L. profusus, from pro, forward; fundo, to pour], exuberant, lavish, liberal to excess. pres-ence [L. præ, before; sum, I am], the state of being in view of, or near any one, approach face to face, nearness. po-et [L. poeta, from Gk. poieo, to make], the writer of a poem, one skilled in making verses.

HAIL to thee, blithe spirit!
Bird thou never wert,
That from heaven, or near it,
Pourest thy full heart

In profuse strains of unpremeditated art.

Higher still, and higher,

From the earth thou springest

Like a cloud of fire;

The blue deep thou wingest,

And singing still dost soar, and soaring ever singest.

In the golden lightning

Of the sunken sun,

O'er which clouds are brightening,
Thou dost float and run,

Like an unbodied joy whose race is just begun.

The pale purple even
Melts around thy flight;
Like a star of heaven,

In the broad daylight

Thou art unseen, but yet I hear thy shrill delight.

* PERCY BYSSHE SHELLEY was born at Field Place, near Horsham, Surrey, August 4, 1792, and was drowned by the upsetting of a boat in the Gulf of Spezzia, a bay on the coast of Italy near Genoa, July 8, 1822. It has been justly remarked that "the remote abstract character of Shelley's poetry, and its general want of anything real or tangible, by which the sympathies of the heart are awakened, must always prevent its becoming popular." His odes "To a Skylark," and "The Cloud," bear a purer poetical stamp than any other of his poetical productions, and, being more readily comprehended, will be better appreciated by the general reader than his more ambitious works.

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