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Work! work! work!
From weary chime to chime, Work! work! work!
As prisoners work for crime ! Band and gusset and seam,
Seam and gusset and band,
Till the heart is sick, and the brain benumbed, As well as the weary hand.
Work! work! work!
In the dull December light; And work! work! work!
When the weather is warm and bright!
The brooding swallows cling,
Oh! but to breathe the breath
Of the cowslip and primrose sweet !
To feel as I used to feel,
Stitch! stitch! stitch!
In poverty, hunger, and dirt,
FIRST NOTIONS OF GEOLOGY.
Agglomerate, (ad, glomus, L.) to collect Petrified, (petros, G.) turned into into a mass. Aqueous, (aqua, L.) Detritus, (de, tero, L.) the waste of rocks, &c., washed down by streams. Fossil, (fodio, L.) Lit. anything dug out of the earth.
Fusion, (fundo, L.) the state of being melted.
Geology, (ge, logos, G.)
Igneous, (ignis, L.)
Oolite, (oon, lithos, G.) egg-stone-so called from its resemblance to the roes of fishes.
Phenomenon; Plur. Phenomena, (phai-
Secondary, (secundus, sequor, L.) next
Stratum, (sterno, L.) a bed or layer. Hence stratified, unstratified, stratification.
Tertiary, (tertius, L.) next to the secondary.
Transition, (trans, eo, L.)
HOW ROCKS ARE FORMED.
THE crust of the earth is that portion of it, from the surface downwards, which man has been able to explore. It is the business of geology to inquire of what materials this crust is composed, and how they have come to assume the forms in which we now find them. These materials are all included under the general name of rocks. It is not necessary that a substance be hard and stony, in order to be called by geologists a rock, for they apply the name to sand, clay, and mud, as well as to granite and limestone.
As the earth has a diameter of nearly 8000 miles, it is obvious that only a very small portion of its whole mass is accessible to us. Of its vast interior we know nothing with certainty. There are, indeed, plausible grounds for conjecturing that, beyond a certain depth, stones, metals, and all other substances, are in a state of fusion, and that the
centre of this our fair world is nothing else than a huge cauldron of liquid fire. Though this is by no means certain, it cannot be doubted that there are in its interior more or less extensive reservoirs of melted matter, which now and again finds its way to the surface. It is by the action of these internal fires that such phenomena as volcanoes and earthquakes are accounted for.
Volcanoes throw out immense quantities of dust, mud, and liquid matter called lava, which spread over the surrounding country, and solidify into rocks. By these substances the surface of a large district is often completely changed. The courses of streams are diverted, and sometimes so obstructed that the water accumulates and forms lakes. Valleys are filled up, trees and fields buried, and whole towns submerged beneath the fiery torrent. Such is one of the causes that contribute to the formation of rocks.
The rocks which owe their origin to the agency of fire are called igneous, and are found in many places where no volcanoes are known to have been in actual operation within the period embraced by historic records. They are usually hard, of rugged and irregular outline, and more or less. crystalline in structure. The granite, porphyry, whinstone, and basalt, of which our sublimest and most picturesque hills, cliffs, and caverns are formed, bear evident marks of igneous origin, whether they were produced by volcanic fires, or by the action of the same element on a still grander and more extensive scale.
But there is another and quieter agency by which a great proportion of the rocks of the earth have been produced. We are wont to speak of the "everlasting hills," without thinking that every one of our hills is constantly wearing away. But we cannot help seeing, if we will take the trouble to consider the matter, that this is the case. The streams which run down their sides have hollowed out for themselves channels that are ever deepening. When swollen by rains, the quantity of detritus which they carry down is often astonishingly large. But, even in their ordinary state, there is always more or less waste of the rocks
and stones over which they flow, an unceasing transportation of matter towards the sea. Again, the moisture of the atmosphere penetrates many hard and solid rocks, and, when frost sets in, expands (as water in freezing always does) with a force sufficient to loosen little fragments, which soon fall off, and crumble into sand. Slowly, yet surely, this sand is washed down by rains, first into the nearest stream, and thence onwards to the sea.
The sea itself, too, is constantly eating up the land. Where the coast is low and sandy, this process goes on rapidly, but it is distinctly visible even on the rockiest shores. The waves, breaking against the bottom of the cliffs, gradually undermine them, so that fragments from time to time tumble down from above. These are exposed to the action of the ever-returning waters, the smaller picces being dashed backwards and forwards till every corner is rubbed off, and they become as smooth and round as art itself could make them. The sandy matter which this constant wear produces, is deposited, like the detritus of rivers, in the bottom of the sea. There, in the course of long ages, are formed thick layers of sand, mud, stones, and other substances, which gradually consolidate into rocks. Such rocks, being formed by the action of water, are called aqueous.
This process of disintegration, to which the surface of the earth is everywhere exposed, is slow indeed, but it is unceasing. The dry land is daily crumbling away; and were there no counteracting influence, every continent and island would at length disappear, and again, as of old, when the fountains of the great deep were broken up,
"A shoreless ocean tumble round the globe."
ARRANGEMENT OF ROCKS.
Ir is to the carthquake and similar agencies, the result of subterranean forces, that we are indebted for counteracting
those disintegrating processes, which tend to reduce the earth's surface to one common level. The influence of earthquakes on the general configuration of a country is prodigious, the whole slope and drainage being sometimes changed. Large tracts of ground are often elevated by these terrible phenomena above their former level, and often depressed below it. Even when there is no sudden or violent convulsion, such elevations and depressions frequently go on gradually and in silence, till what was once the bottom of the sea comes to be the mountain top. So extensive have such changes been, that there is probably no part of the earth's surface which has not been long under water, and no part of it which has not at some time or other been dry land. Thus it is that aqueous rocks are found at great distances from the sea.
It is believed that nearly all the rocks of the earth's crust have been produced by such causes as were described in last lesson, acting through cycles of immense duration, too vast for human minds to grasp. If we keep this in view, and remember also how the earthquake and kindred forces suddenly or gradually disturb levels, and alter the boundaries of land and sea, we shall the more easily comprehend the order in which the various kinds of rock are now actually found to occur.
Lowest and most ancient are igneous rocks, forming, as it were, the groundwork or basis on which the superstructure of the earth's crust is built. Of these the chief varieties have already been mentioned. The aqueous rocks are piled above them in layers or strata, originally horizontal, like courses of stupendous masonry. Hence the aqueous rocks are also called stratified, whilst the igneous, consisting of matter agglomerated without any semblance of order, are said to be unstratified.
The difference in composition and appearance between the successive strata, prove that they have been deposited at different times, and under different circumstances. The lowest are usually known as transition or metamorphic rocks, inasmuch as they correspond in character partly with the