may have been periods of comparative rest and quiescene, but none of perfect stagnation and stability; so that the present condition and configuration of the earth's surface may be considered as the last result of a series of cosmical changes, which commenced with the dawn of creation, and are continuing on into the future.

"Had the exterior crust of the earth been subjected to no modifying causes, the world would have presented the same appearance now as at the time of its creation. The distribution of land and sea would have remained the same; there would have been the same surface arrangement of hill, valley and plain, and the same unvarying aspects of animal and vegetable existence. Under such circumstances, geology, instead of striving to present a consecutive history of change and progress, would have been limited to a mere description of permanently enduring appearances. The case. however, is widely different." There is no part of the present land-surface of the globe which has not at some time been covered by the ocean, while much of the present sea bottom has been in turn dry land. Many of the loftiest and most extensive ranges of mountains upon the globe-the Alps, the Andes, and the Himalayas-are of comparatively recent elevation (recent as compared with the White Mountains of New England, or the Appallachian chain of the Atlantic States); while the commencement of the existence of every animal and vegetable species at present found upon the earth was long subsequent to the existence of the myriad organisms, whose remains are now found fossil beneath its surface.

The agencies which have produced, and are still tending to produce, changes in the constitution and structure of our planet, may be classified as follows: 1. Igneous agencies, or such as manifest themselves in connection with some deepseated source of heat in the interior of the globe. 2. Aqueous, or those arising from the action of the water. 3. Atmospheric, or those operating through the medium of the atmos phere. 4. Organic, or those depending on animal and vegetable growth. 5. Chemical, or those resulting from the chemical action of substances on each other. Wells' Illus trated Geology.

THE TEMPERATURE OF THE EARTH.

The following are some of the observations made most recently on this subject: In England, observations have been made in the vertical shafts of two very deep coal mines, viz., at Monkwearmouth, which is 1800 feet deep, and Dunkinfield, which is upwards of 2000 feet deep, and in both cases the observations were made while the workmen were sinking the shafts, and with every precaution against the influence of any extraneous causes. The former gave an increase of 1 deg. of Fahrenheit for every sixty feet of depth, and the latter 1 deg. for about every seventy feet. The artesian well of Grenelle (Paris), is 1800 feet deep; observations made by Arago, during the boring, showed that the average increase of temperature in this was 1 deg. for sixty feet. At Mordorff, Luxemburg, the depth of the artesian well is 2400 feet, and the increase in temperature 1 deg. for every fifty-seven feet. At the artesian well of New Seltzwork, in Westphalia, the depth is 2100 feet, and the increase 1 deg. for every fifty-five feet. At Louisville, Ky., the depth of an artesian well, finished in 1859, is 2086 feet deep, and the average increase is 1 deg. for every sixty-seven feet below the first ninety feet from the surface. In the silver mine of Guanaxato, Mexico, 1713 feet deep, the increase is 1 deg. for every forty-five feet. In the coal mines of Eastern Virginia, the increase is about 1 deg. for every sixty feet.

VOLCANIC ERUPTIONS.

One or two remarkable instances of volcanic eruptions may be briefly noticed. First, for duration and force we may refer to that which took place in the island of Sumbawa (one of the Sunda Islands lying east of Java), in the year 1815. It commenced on the 5th of April, and did not entirely cease until July. Its influence (i. e. shocks, and the noise of the explosions) was perceptible over an area 1,800 miles in diameter, while within the range of its more immediate vicinity, embracing a space of 400 miles, its effects were most terrific. In Java, 300 miles distant, it seemed to be awfully present. The sky was overcast at noon day with clouds of ashes, which the light of the sun was unable to penetrate, and fields, streets, and houses were covered with ashes to the depth of several inches. At Sumbawa itself, immense columns of flame appeared to burst forth from the top of the volcano, Tombora, and in a

short time the whole mountain appeared like a mass of liquid fire, which gradually extended in every direction. As the eruption continued, a darkness supervened, so profound as to obscure even the light of the flames; showers of stones and ashes fell continuously over the whole island; the sea rose twelve feet higher than it had ever been known to do before; and finally a whirlwind ensued, which tore up the largest trees, and carried them into the air, together with men, horses, cattle, and whatever else came within its influence. Of 12,000 inhabitants in the vicinity only six are believed to have escaped, and of some entire villages not even a vestige remained.

In 1772, the Papandayang, one of the loftiest volcanic mountains in Java, after a short but severe eruption, suddenly fell in and disappeared in the earth, carrying with it about ninety square miles of territory. Forty villages were engulfed, or covered with ejected matter, at the same time, and nearly 3,000 persons perished.— Wells' Illustrated Geology.

DESCRIPTIONS OF AN EARTHQUAKE.

"A powerful eathquake," says Mr. Darwin, "at once destroys the oldest associations; the world, the very emblem of all that is solid, has moved beneath our feet like a crust over a fluid; one second of time has conveyed to the mind a strange idea of insecurity, which hours of reflection would never have created."

"To man," says Humbolt, "the earthquake conveys an idea of some universal and unlimited danger. We may flee from the crater of a volcano in active eruption, or from a locality threatened by the approach of a lava stream; but in an earthquake, direct our flight whithersoever we will, we still feel as though we trod upon the very focus of destruction. Every sound-the faintest motion in the air-arrests our attention, and we no longer trust the ground on which we stand. Animals, especially dogs and swine, participate in the same anxious disquietude; and even crocodiles, in the rivers of South America, which at other times are dumb, have been observed to quit the water and run, with loud cries, into the adjacent forests."

AQUEOUS AND ATMOSPHERIC AGENCIES.

The aqueous and atmospheric agencies most prominently concerned in producing geological changes, are rains, and the

gasses and moisture of the atmosphere, winds, ice, and snow, springs, rivers, waves, tides, and oceanic currents.

The operation of water, acting mechanically, is, under all circumstances, to wear down the higher portions of the earth's crust, and transport the materials to lower localities-an ac tion which obviously tends to reduce the whole surface to a smooth and uniform level. On the other hand, the operations of igneous agents-volcanoes, earthquakes, etc.-by breaking up and elevating the crust of the earth, tend to counteract the equalizing action of water and to produce that diversity of surface which is indispensable to variety in both the vegetable and animal kingdoms. These two forces, therefore-the aqueous and the igneous-may be considered as antagonistic to each other, and to them may be ascribed the principal modifications which have taken place, and are still taking place, in the crust of the globe.- Well's Illustrated Geology

CORAL REEFS.

"The ocean," says Mr. Darwin, "throwing its breakers on the outer shore, appears an invincible enemy, yet we see it resisted, and even conquered, by means which at first seem weak and inefficient. No periods of repose are granted, and the heavy swell caused by the steady action of the trade wind never ceases. The breakers exceed in violence those of our temperate regions; and it is impossible to behold them without feeling a conviction that rocks of granite or quartz would ultimately be demolished by such irresistable forces. Yet these low coral islands stand and are victorious, for here another power, antagonistic to the former, takes part in the contest. The organic forces separate the atoms of carbonate of lime, one by one, from the foaming breakers, and unite them into a symmetrical structure; myriads of architects are at work day and night, month after month, and we see their soft and gelatinous bodies, through the agency of the vital laws, conquering the great mechanical power of the waves of the ocean, which neither the art of man nor the mechanical works of nature could successfully resist." The animals which produce coral are very simple, and resemble plants both in their figures and colors.

THE FIRST FORMED STRATIFIED ROCKS.

The adoption of the theory, that our earth was once in a state of entire molten fluidity, involves the existence of a subsequent period, when its primeval crust had sufficiently cooled down to allow of the condensation of watery vapor and of the existence of a sea upon its surface. Whenever this happened, the eroding and destructive action of water must have immediately manifested itself, while the particles of the consolidated igneous crust, worn off by the action of waves, tides, and currents, and deposited as sediments, would naturally produce stratified formations.

The internal heat of the earth at that period, however, must have continued to act with great intensity near the surface, and the strata first deposited, consequently, were, in all probability, soon greatly metamorphosed, i. e., remelted down to form igneous rocks, or converted into hard crystalline semiigneous rocks, that retained, in part, their original lines of stratification.

Whether any of these first formed stratified rocks are in existence, and open to our inspection, it is impossible to affirm. Some geologists incline to the opinion that they were entirely remelted, and are now represented by the older or fundamental granites, which, in some instances, appear to have an obscurely stratified structure.

Be this as it may, it is, however, a matter of fact, that the oldest rocks of which we have any knowledge, which exhibit evidence of a sedimentary origin, appear to have been formed under conditions analogous to those above supposed. Thus, they are all more or less crystalline and indurated; their lines of stratification are indistinct, and often altogether obliterated; and their whole aspect is very different from what is usually ascribed to rocks deposited in water.- Wells' Illustrated Geology.

FORMATION OF COAL.

It is now universally admitted by geologists, that coal is a mass of compressed, altered, and mineralized vegetation, just as sandstone is consolidated sand, and the slate and shale con. solidated clay or mud.

The evidence upon which the belief is founded may be briefly stated, as follows:

1st. The enormous profusion of fossil plants, in the form of