consider the interior of the earth, at the present time, to be composed of elements in their simple and uncombined state. This being admitted, the earth at a certain depth consists of the bases of these earths, and alkalies in their uncombined and metallic forms; for, being excluded from any substance containing oxygen, there has been no opportunity since the creation, for these substances to combine and form compounds. It is well known to chemists, that the metallic bases of the alkalies may be kept in their elementary states for any length of time, by excluding them from the air, or by immersing them in naptha, a substance containing no oxygen. Hence, as combustion is excited when these metallic bases come in contact with water, (if the above suppositions be true,) there exists an analogy, by which it has been thought the phenomena of earthquakes might be accounted for, by the admission of water to these substances.

There are, however, insuperable difficulties in this hypothesis. Carbonate of lime is one of the most abundant materials of which the crust of our earth is composed. This, in the opinions of many geologists, had its origin in organized remains, being the product of sea shells, consolidated in a manner, which it is unnecessary here to explain. It is quite certain that a great portion of limestone is really the product of moluscous animals, of which the coral reefs, and the mountains of shells, are a sufficient proof. If, therefore, lime is the product of organized beings, it was not created in an elementary form, and therefore cannot produce the fire of volcanoes by the union of its elements, though calcium its base, may excite flame by contact with water.

Silex, or flint, another substance which enters largely into the compositon of the earth, and of which the primitive rocks are chiefly composed, does not possess an inflammable base, and therefore cannot be supposed to participate in causing any igneous phenomena.

The specific gravity of the earth, also, being at least five times that of water, shows that it is not composed, principally, of substances lighter than that fluid.

Besides, the phenomena of earthquakes and volcanoes, even admitting the interior of the earth to be composed of metallic elements, are not such as could be accounted for by the admission of water to these substances; nor are the products of volcanic action, in the form of lava, pumice,

and ashes, such as would result from the oxygentation of metallic elements. This theory, therefore, has not, even plausibility in its favor.

In the present state of geological knowledge, it is not to be expected that any theory which can be proposed, will account for every circumstance connected with earthquakes and volcanoes. But that which explains the greatest number of these phenomena, is founded on the hypothesis of a "central fire," that is, a mass, or masses of lava, or melted matter, deeply seated towards the centre of the earth. The two hundred volcanoes, existing in different parts of the globe, are the chimneys, or occasional outlets of this ocean of liquid fire.

When this mass is disturbed, as by the admission of water, an earthquake is the consequence, and this becomes more or less disastrous, according to the degree of internal commotion. When the pressure of the steam, into which the water is converted, becomes excessive, then the lava is forced up one of the chimneys, and poured forth on the surface of the earth, and thus a volcano is produced, and at the same time the internal pressure is relieved.

The hypothesis of a central fire, under various modifications, appears to be the prevailing doctrine of the geologists of the present day. "If," says Mr. Lyell, "we suppose a great number of large subterranean cavities, at the depth of several miles below the surface of the earth, wherein melted lava accumulates, and that water, penetrating into these, is converted into steam; this steam, together with the gasses generated by the decomposition of melted rocks, may press upon the lava, and force it up the duct of a volcano, in the same manner as it drives water up the pipe of a geyser. (The geyser is described under "Silicious Springs.") But the weight of the lava being immense, the hydrostatic pressure, exerted on the sides and roofs of such large cavities, and fissures, may well be supposed to occasion, not slight tremors, such as agitate the ground before an eruption of the geyser, but violent earthquakes. Sometimes the lateral pressure of the lower extremity of the high column of lava, may cause the more yielding strata to give way, and to fold themselves into numerous convolutions, so as to occupy less space, and thereby give relief for a time, to the fused, and dilated matter. Sometimes, on the contrary, a weight equal to that of the vertical column of lava, pressing on every part of the roof, may

heave up the superincumbent mass, and force lava into every fissure, which on consolidating, may support the arch, and cause the land above to be permanently elevated. On the other hand, subsidences may follow the condensation of vapor, when cold water descends through fissures, or when heat is lost by the cooling of the lava."

If this globe, towards its centre, is composed of an igneous fluid, then we might expect that the nearer we approach it, or the deeper we descend below the surface, the higher we should find the temperature, and many experiments tend to prove that this is actually the case.

Baron Fourier, who has investigated this subject with much attention, concludes, " that the rays of the sun penetrate the globe, and occasion annual and diurnal variations in its temperature, but that these periodical changes cease to be perceptible at a certain depth under the surface. Below that depth, the temperature caused by the sun has long ceased to have any influence. If, therefore, it is found that the temperature of the deep recesses of the earth become perceptibly greater, in proportion as we recede from its surface, it is impossible to ascribe this increase to the influence of the sun, and consequently it can proceed only from the primitive heat of the earth, and with which it was originally endued. It has long since been conjectured that the heat of the earth increased in some proportion to the distance of descent from its surface; but it is only within a short period, that experiments have been instituted, for the purpose of ascertaining whether this conjecture was well founded, and if so, to determine the ratio of increase. With this view, many mines have been accurately examined, and the fact of a gradual increase of temperature downwards, has been found general.

In the mines of Cornwall, England, Capt. Lean made the following experiments and observations, in the month of December.

At the surface the temperature of the air, was 50° Fahrenheit. At 120 feet below the surface, the air was 57°. At 600 feet below, temperature of the air 66o, of water 64°. At 962 feet below, air 70°, do. water 74°. At 1200 feet below the surface, air 78°, water do. 78°.

These, with other experiments in different mines, seemed to show that the increase of temperature downwards, was nearly in the ratio of one degree, for every sixty five. feet.

From M. Cordier, who has written a treatise on this subject, we learn that the number of mines in which experiments have been made is about forty. These mines are situated in France, England, Switzerland, Peru, Saxony, and Mexico. The whole number of experiments made are about 300, some being on the air of the mines, some on the water, and others upon the rocks, or earth.

From all these observations, made apparently with such caution as to prevent the possibility of any considerable error, M. Cordier derives the following conclusions.

1. "If we reject a certain number of observations as uncertain, all the rest indicate, in a manner more or less certain, that there exists a remarkable increase of temperature, as we descend from the surface of the earth towards the interior. It is reasonable then, to admit this increase."

2. The results collected at the observatory at Paris, are the only ones that can be depended upon with certainty, for obtaining a numerical expression of the law of this increase. This expression gives fifty one feet as the depth which corresponds to an increase of one degree, in the subterranean temperature. And we would remark in passing, that according to this result, the temperature of boiling water under the city of Paris, would be at the depth of 8,212 feet, or about a mile and a half."

3. "Among all the other results, a small number only afford numerical expressions of the law sought for, sufficiently approximate, to be taken into account. These ex

pressions vary from 104 to twenty four feet for one degree of increase; their average in general, indicates an increase more rapid than has generally been admitted. Their average has so much the more weight, as embracing the results of many series of long continued observations."

4. "Lastly, in grouping together by countries all the results, admissible on any principle, I am led to present a new and important idea, to wit, that the difference between the results collected at different places, are referable not solely to the imperfection of the experiments, but also to a certrin irregularity in the distribution of subterranean heat in different countries."

M. Cordier describes at length, the manner of making experiments on this subject, in order to prevent local errors, and from all that himself and others, have done and written, he draws the following inferences.

1. "Our experiments fully prove the existence of an internal heat, which is natural to the terrestrial globe; which depends not on the influence of the sun, and which increases rapidly with the depth."

2. "The increase of subterranean heat in proportion to the depth, does not follow the same law throughout the globe. It may be twice, or even thrice as great in one country as in another."

3. These differences are not in a constant ratio to the latitude or longitude."

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4. Finally, the increase is certainly much more rapid than has heretofore been supposed; it may be as great as twenty-seven, or even twenty-four feet for a degree, in some countries. Provisionally however, the mean must not be put lower than forty-six feet.”

We must therefore consider it as proved beyond all doubt, that below the crust of the earth, there exists either a mass of burning lava, or some other cause, by which there is perpetually maintained a considerable degree of heat; and there is reason to believe that a very high temperature exists towards its centre.

That this internal temperature is caused by a melted mass, such as we have supposed to exist, is not, it is believed, incompatible with any known phenomenon, but on the contrary, certainly accords with many of the effects already specified.

But there are other effects which are unaccountable, except on such a hypothesis; and one of these is the connection, which has often been observed to exist, between one volcano and another, and also between earthquakes and volcanoes. If there exists in the earth an extensive igneous fluid, communicating with the open air only by means of volcanic apertures, we should expect, that when this fluid by any means was set in motion, the surface of the ground would partake of such motion, and that in case this fluid should be pressed for want of room, it would be forced out at these apertures.

Now the wave-like motion of earthquakes is a phenomenon almost universally observed, and even where the shock is slight it produces nausea, like sea-sickness. This motion is inexplicable if the earth is composed of solid unyielding strata; but if we suppose its crust rests upon a fluid, liable to agitation, the solution becomes natural and easy. This motion may be strikingly illustrated by