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5. Sometimes organic remains, such as bones, are found but partially decayed, and sometimes impregnated with mineral matter; sometimes, through chemical changes, the animal or vegetable matter has entirely disappeared, and the place. which it occupied, in what has since become rock, has been so entirely filled with mineral matter as to form a genuine petrifaction; sometimes, after the rock had become hardened, the animal or plant had decayed and escaped through the pores of the stone, so as to leave nothing but a perfect mould; while at other times the only evidence of the existence of an animal is its track in the clay or sand, since hardened into rock.

6. When Shakspeare made his charming Ariel sing

"Full fathom five thy father lies,

Of his bones are coral made,

Those are pearls that were his eyes;
Nothing of him that doth fade
But doth suffer a sea change

Into something rich and strange,"

he little thought how correctly he painted the chemical changes by which, during the ages past, decomposing animal matter has stamped its myriad forms upon what are now the "medals of creation."

7. The organic remains which have thus far been discovered are more abundant than is generally supposed. Fossil shells, in great quantities, have been found both on lofty mountains and below the beds of rivers. On mountains and in mines, hundreds of miles from the sea, are the remains of strange-looking fish; the skeleton of a whale has been found on a mountain three thousand feet high, and the skeleton of an elephant has been exhumed from the frozen sand and mud on the very confines of the Frozen Sea. But, what is more wonderful still, whole mountains, hundreds and even thousands of feet high, are essentially composed of organic remains.

8. Such is the character of the language which the geologist must learn before he can read the curious history of the earth, and of the animal and vegetable races that have lived upon it. A very accurate and extensive knowledge of zoology and botany will also be required, to enable him to ascertain whether the organic remains which he finds in the rocks belonged to extinct species, or are identical with those now living on the globe. That part of geology which gives the history of the remains of plants and animals is called Pal-eon-tol-o-gy, a Greek word which means "the science of ancient beings or creatures.'

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a a, Granite veins; b b, metalliferous veins; c c, dike of serpentine; d, dike of porphyry; e e, lava and volcano; f, dike of trap.

The above cut, designed to give a geological view of the earth's history, represents a vertical section of the earth, with the several classes of stratified formations resting upon the unstratified granite rocks, the latter being represented here as thrown up through the superincumbent mass by volcanic agency. By this tilting up of the stratified rocks in numerous localities, so that the edges of even the lowermost of the strata may be seen, both the relative position and the thickness of all the strata have been very accurately ascertained.

[blocks in formation]

1. The geological history of our globe, as gathered from its structure, begins far back-myriads of years beyond our powers of computation, but even then far removed from "the beginning"-in some unknown age of sterility and desolation. If plants and animals then existed, all traces of them were subsequently destroyed by a period of intense heat, which fused the earth's surface into a molten mass, and formed a vast layer, of unknown depth, of what are called the primary or unstratified rocks, of which the enduring granite, the low

est in the series, and the great frame-work of the earth's crust, is the most abundant.

2. It is granite rock chiefly which is now seen rising to the greatest heights, and stretching into those mountain chains which form the grand natural divisions of the globe. In these cases the granite has been thrown up by subterranean forces, breaking through the superincumbent strata, tilting them up on their edges, and thus affording to the geologist the opportunity of examining them in detail. It is chiefly in veins of the primary rocks that the ores of lead, tin, and the precious metals are found. The celebrated geologist Hugh Miller, in speaking of this primary period of the world's history, in which he supposes that the earth's crust had sufficiently cooled down to permit the existence of a sea, with waves and currents, draws the following imaginary picture: 3. "I dare not speak of the scenery of the period. We may imagine, however, a dark atmosphere of steam and vapor, which, age after age, conceals the face of the sun, and through which the light of moon or star never penetrates; oceans of thermal water, heated in a thousand centres to the boiling point; low, half-molten islands, dim through the fog, and scarce more fixed than the waves themselves, that heave and tremble under the impulsions of the igneous agencies; roaring geysers, that ever and anon throw up their intermittent jets of boiling fluid, vapor, and thick steam, from these tremulous lands; and, in the dim outskirts of the scene, the red gleam of fire, shot forth from yawning cracks and deep chasms, and bearing aloft fragments of molten rock and clouds of ashes. But, should we continue to linger amid a scene so featureless and wild, or venture adown some yawning opening into the abyss beneath, where all is fiery and yet dark-a solitary hell, without suffering or sin-we would do well to commit ourselves to the guidance of a living poet, and see with his eyes, and describe in his verse:

4.

The awful walls of shadows round might dusky mountains seem,
But never holy light hath touched an outline with its gleam;
'Tis but the eye's bewildered sense that fain would rest on form,
And make night's thick blind presence to created shapes conform.
No stone is moved on mountain here by creeping creature crossed,
No lonely harper comes to harp upon this fiery coast:
Here all is solemn idleness; no music here, no jars,
Where silence guards the coast ere thrill her everlasting bars;
No sun here shines on wanton isles; but o'er the burning sheet
A rim of restless halo shakes, which marks the internal heat;
As in the days of beauteous earth we see, with dazzled sight,

The red and setting sun o'erflow with rings of welling light.-THOMAS AIRD.

* Granite is composed chiefly of mica, quartz, and feldspar; but in some granite rocks talc and hornblende take the place of mica, and then the rock is called sienite. Porphyry is only another modification of granite. † See cut at the head of this lesson.

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GEOLOGICAL REMAINS OF ANIMALS OF THE TRANSITION PERIOD.

1, 6, and 8 are Coral Zoophytes of the Lower Silurian. 2, 10, and 12 are Lower Silurian Trilobites, from one to three inches in length. 3, 4, and 5 are the earliest Molluscs or Shellfish. 7, a Silurian Crinoidea-an animal having a radiated lily-shaped disk supported on a jointed stem. 9, a Placoid Fish of the Upper Silurian. 13 and 15 are Ammonites; and 14, a section of No. 13, showing the interior chambers. 16, a Star-fish. 17, one of the earliest Polypes, or plant-like Zoophytes.

1. IN entering upon the second age of the world's history, which is called the transition period, the evidences of stratification, which began to be dimly discerned in the uppermost of the primary rocks, are quite decisive, and layer follows upon layer, mostly of a slaty character, until the mass accumulates to the supposed average depth of five or six miles. All of these layers appear to have been gradually deposited at the bottom of the ocean during myriads of years by the slow wearing away of the mountains of the primary rocks by the action of water.

2. In this transition period, of incalculable vastness, we discern, in a few scattered fossils, the first faint traces of the beginnings of vegetable and animal life. In the lower, or Cambrian portion, a few sea-weeds have left their imprints in the rocks; and a few shells and corals, and a few trilobites -most singular species of Crustaceans-have been transformed into stone. In the upper, or Silurian portions, seaweeds are more numerous, and the fragmentary remains of a few terrestrial vegetables are discernible; but marine shells and corals abound, and the trilobites receive their fullest development, both in size and number. Here a few fishes first appear, of the Placoid order, as perfect in their kind as those of later ages, but their forms are not well known. In this period, myriads of ages ago, life appeared in fashions pecul

iarly antique, and nearly all of its types have long since become obsolete.

3. It is, however, interesting to notice here that shells of the family called Ammonites, which are among the earliest traces of the animal kingdom, appear in this early period; and it is a curious fact, that while all other families and orders of shells of this period-and, indeed, of many subsequent eras -have entirely died out, and now form vast layers of rocky strata of limestone and marble, some species allied to the ancient family of the Ammonites are found in every succeeding period of geological history, and kindred species exist in our seas at the present day. Among these is the Nautilus, whose geological history has been written in the following appropriate lines:

4.

5.

Thou didst laugh at sun and breeze
In the new created seas;

Thou wast with the reptile broods
In the old sea solitudes,

Sailing in the new-made light

With the curled-up ammonite.

Thou surviv'dst the awful shock

Which turned the ocean bed to rock,

And changed its myriad living swarms
To the marble's veined forms.
Thou wast there, thy little boat,
Airy voyager, kept afloat

O'er the waters wild and dismal,
O'er the yawning gulfs abysmal;
Amid wreck and overturning,

Rock-imbedding, heaving, burning.
Mid the tumult and the stir,

Thou, most ancient mariner,

In that pearly boat of thine,

Sail'dst upon the troubled brine.-MRS. HOWITT.

6. It should be remarked that thus far in the world's history no traces of any reptile, bird, or mammal have been discovered, which may be considered evidence conclusive that none of these animals were in existence at this epoch; but when, at length, after countless ages, fishes appeared, perfect in their kind, at the same time are presented the first evidences of a diminutive, yet highly organized tree vegetation. Vertebrated animals and land vegetation were new and distinct creations; and upward, from life's beginnings, through all its ascending stages, we constantly meet with evidences of new creations, but none whatever of any development of higher grades from lower. The first fiat of creation doubtless insured the perfect adaptation of animals to the surrounding media; and thus, while the geologist recognizes a beginning, he sees the same, evidences of Omniscience in the lower Crustaceans as in the completion of the higher Vertebrate form.

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