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STUDY OF GEOLOGY.

185

works of creation, and by imparting colour to other bodies, is made to minister in various ways to our gratification. How diversified are the means which the Creator hath adopted for the promotion of his benevolent designs!

Who, not content

With every food of life to nourish mạn,
By kind illusions of the wondering sense,
Has made all nature beauty to his eye,
Or music to his ear.

AKENSIDE.

2. Describe manga

QUESTIONS.-1. What is zinc and its uses? nese. 3. For what are its oxyds used? 4. What is antimony and its uses? 5. Describe arsenic. 6. Give a general account of the seven classes of metals. (See Appendix to Lesson 65.) [NOTE. The description of the metals properly belongs to the subject of Chemistry, (see Lesson 65) but for the sake of a little more variety it was thought best to insert a brief account of the most important ones after Mineralogy.]

LESSON 83.

Study of Geology.

Crude, unconnected, not well digested.

Intersection, the point where lines cross each other.

GEOLOGY has for its object the study of the earth in general, of its plains, hills, and mountains; and embraces the consideration of the materials of which it is composed, and the circumstances peculiar to its original formation, as well as the different states under which it has existed, and the various changes which it has undergone. Geology has now become an object of the attention and inquiries of many distinguished philosophers. The discoveries of chemists and mineralogists, and the observations of intelligent travellers, have all tended to facilitate these inquiries, and to render them more enlightened and satisfactory; and, although modern times have produced many visionary theories, and crude conjectures on this subject, they have also given birth to some important acquisitions, and much correct philosophy, which will be highly prized by all who study the history and structure of our globe. The science of geology, independently of the healthy employment it affords, is of great importance in a practical point of view. It very nearly concerns the miner, engineer, and drainer, and even the farmer

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and architect; and discloses a variety of indications highly useful in their respective pursuits: to the miner, the rocks containing metallic veins and coals; to the engineer, the association of hard rocks with soft; to the drainer, the intersection of a country by hard dykes, or veins impervious to water; to the farmer, the best places for finding lime-stone, marl, and clay; and to the architect, the most durable stones for buildings. The person who is attached to geological inquiries, can scarcely ever want objects of employment and of interest. The ground on which he treads

the country which surrounds him-and even the rocks and stones, removed from their natural position by art, are all capable of affording some degree of amusement. Every new mine or quarry that is opened, every new surface of the earth that is laid bare, and every new country that is discovered, offers to him novel sources of information. In travelling, he is interested in a pursuit which must constantly preserve the mind awake to the scenes presented to it; and the beauty, the majesty, and the sublimity of the great forms of nature, must necessarily be enhanced by the contemplation of their order, their mutual dependence, and their connexion as a whole.

QUESTIONS.-1. What is geology? 2. What is said of the discoveries of chemists and mineralogists? 3. Why is the science of geology important in a practical point of view? 4. What are the advantages of studying geology?

LESSON 84.

Geology.

Stratification, the division of a mass of rock into many parallel portions, whose length and breadth greatly exceed their thick

ness.

THE surface of the globe, considered with relation to its inequalities, is divided into highland, lowland, and the bottom of the sea. The highland comprises alpine land, composed of mountain groups or series of mountain chains; mountain chains, formed by a series of those still more simple inequalities, called mountains: in the former we consider their length, height, form, and connexion; the parts of the

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latter are the foot, the acclivity, and the summit. Lowland comprises those extensive flat tracts which are almost entirely destitute of small mountain groups. To the bottom of the sea belong the flat, the rocky bottom, shoals, reefs, and islands. It is only after a diligent study of the inequalities just pointed out, that we can with advantage undertake to explore the means employed by nature to produce them; and the first step is to proceed to the examination of the physical causes of the slow, but unceasing changes of the globe. Observation teaches us, that most of the elevations and hollows we meet with on the surface of the earth owe their origin to the action of the atmosphere, to that of the ocean, and to volcanic fire. These powerful agents may be considered with regard to their destroying, and, in consequence of this destruction, with regard to their forming effects.

All geologists are agreed that our present continents were once covered with water. This is proved by the remains of marine animals imbedded in the strata which lie on the summits of the highest mountains. The structure of the globe, as far as we are acquainted with it from the intersections made by rivers, by the action of the sea upon the coast, and by mining operations, consists of beds of different kinds of stone, which generally increase in thickness as we descend deeper. Stratification, in its simplest form, may easily be conceived, by placing a closed book with the back resting upon the table, and raising the opposite edges a little; the book may represent a thick mineral bed, and the leaves a series of strata. In nature we frequently find the strata much broken, and thrown out of the original position. Where any series of strata are wanting, a question naturally arises, have they been carried away by some sudden inundation, before the upper strata were deposited, or have they never extended to that place? In some instances it is certain that the strata have been carried away from particular situations, as in some of the excavations which have formed valleys, in which the strata that terminated on one side of the valley may be discovered again in the hills on the opposite side. The substances of which the strata are composed, are argillaceous, calcareous, or siliceous earth, which are generally more or less intermixed or combined. The strata of clay, or argillaceous strata, being water-tight, give rise to springs, as they arrest the water that runs through

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the porous strata, and convey it to other. situations. The inclinations of the strata, with the breaks and inequalities, render the globe habitable, by distributing the waters over the surface.

The strata to a great depth are generally characterized by the remains of animals or vegetables, in what is called a petrified state, the organic structure being distinctly visible, although the animal or vegetable matter is almost entirely removed, and its place generally supplied by calcareous or siliceous earth. These organic remains are more abundant in the upper than the lower strata; and in the lowest beds of rock which have yet been explored, no traces of organic existence have been found. These remains make us acquainted with the great changes which must have taken place in the condition of our planet in remote ages. The uppermost stratum in England and in various parts of Europe, is formed of alluvial soil. In this soil, the remains of quadrupeds of vast size, such as the elephant, the rhinoceros, and mammoth or mastodon, are frequently found. Many of these are different from any existing species, and they prove that dry land existed in the vicinity, and that Europe was then inhabited by species of animals at present unknown.

The researches of modern geologists have given abundant confirmation to the sacred history, not only with respect to the general deluge, but also with regard to the age of the earth. Until very lately several geological phenomena were considered, by superficial inquirers, as indicating that the creation of the globe we inhabit was an event much more remote than the sacred history represents. This opinion was kept in countenance only as long as geology was in its infancy. Every successive step which has been lately taken in the improvement of this science has served to show its fallacy. The investigations of the latest and most accurate philosophers have afforded the strongest proofs, that the earth, in its present form, cannot have existed longer than appears from the Mosaic account.

QUESTIONS.-1. How is the surface of the globe divided? 2. What does the highland comprise ?-lowland? bottom of the sea? 3. What does observation teach us? 4. In what are all geologists agreed? 5. How is this proved? 6. What is said of the structure of the globe? 7. How may stratification be conceived? 8. What are the substances of which the strata are composed? 9. What is said of organic remains? 10. What have modern geological researches confirmed?

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Relative Situation of Rocks.

Pseu'do, a prefix, which, put before words, signifies false, counterfeit.

Lichen, (pronounced Lik'en) a cryptogamous plant, growing on rocks; in Ireland, a species of Lichen is prepared and used as food.

Presented to the cultured eye of taste,

No rock is barren, and no wild is waste.

ROCKY masses, variously placed over each other, compose the whole crust of the earth, to the greatest depth that the industry of man has been able to penetrate. Now these rocks, with respect to each other, occupy a determinate situation, which holds invariably in every part of the earth. Thus limestone is no where found under granite, but always above it. Werner has chosen this relative situation as the basis of his classification of rocks. He divides them into five classes which are called formations; as primitive, transition, fletz, alluvial, and volcanic. The primitive formations are of course the lowest of all, and the alluvial constitute the very surface of the earth; for the volcanic, as is obvious, are confined to particular points. Not that the primitive are always at a great depth under the surface, very often they are at the surface and constitute mountains. In such cases the other classes of formations are wanting altogether. In like manner the transition and other formations may, each in its turn, occupy the surface, or constitute the mass of a mountain. In some cases all the subsequent formations which ought to cover them are wanting in that particular spot. Each of these grand classes of formations consists of a greater or smaller number of rocks, which occupy a determinate position with respect to each other, and which like the great formations may often be wanting in particular places.

The rocks which constitute the primitive formations are very numerous. They have been divided into several sets, such as granite, gniess, mica-slate, and others. It deserves attention, that the rocks constituting them are all chemical combinations, and generally crystallized; that they contain no petrifactions; and that the oldest formations contain no carbonaceous matter. Transition rocks are not so nu

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