certain variations.

It does not appear that our satellite is provided with an atmosphere of the kind found upon earth; neither is there any appearance of water upon the surface. Yet that surface is, like the face of our globe, marked by inequalities and the appearance of volcanic operations. These inequalities and volcanic operations are upon a scale far greater than any which now exist upon the earth's surface. The mountains are, in many instances, equal in height to nearly the highest of our Andes. They are generally of extreme steepness, and sharp of outline, peculiarities which might be looked for in a planet deficient in meteoric agencies, such as those which operate so powerfully in wearing down ruggedness on the surface of our

FIG. 1.

earth. The volcanic operations are on a stupendous scale. They are the cause of the bright spots of the moon, while the want of them is what distinguishes the duller portions, usually but erroneously called seas. In some parts, bright volcanic matter, besides covering one large patch, radiates out in large streams, which appear studded with subordinate foci of the same kind of energy. A large portion of the surface is covered with circular eminences, called Ring Mountains, of various diameters, from a quarter of a mile to several hundred miles, and in some places as close together as the circles on the surface of a boiling pot, which they in no small degree resemble. Some even intrude upon and obliterate portions of the neighbouring circles, thus leading to the idea of date, or a succession of events on the moon's surface. Generally, in the centre, there is a mount, which appears to be connected in the way of cause, with the annular eminence, beyond which again vast boulder-like masses are in some instances seen scattered. What, however, most strikes the senses

Quarter.

of an observer, is the vast profundity of some of the pits between the ring and the inner mount; in one case, this is reckoned to be not less than 22,000 feet, or twice the height of Ætna.

These characteristics of the moon forbid the idea that it can be at present a theatre of life like the earth, and almost seem to declare that it never can become so. But it is far from unlikely that the elements which seem wanting may be only in combinations different from those which exist here, and may yet be developed as we here find them. Seas may yet fill the profound hollows of the surface; an atmosphere may spread over the whole. Should these events take place, meteorological phenomena and all the phenomena of organic life, will commence, and the moon, like the earth, will become a green and inhabited world.'

It is unavoidably held as a strong proof in favour of any

1 Among the most extraordinary phenomena of natural science must be placed those relating to the fall of meteoric stones. The fact itself, so long doubted, has now been established by an accumulation of the most positive and unexceptionable evidence. The stones have been seen to fall, and taken up in a still heated state;-there can be no manner of doubt about the fact, although the explanation is extremely difficult. All these stones are found on examination to resemble each other in their general characters; they usually consist of an earthy material, having disseminated through its substance globules and small masses of metallic iron containing nickel in the state of alloy. The stones are often covered by a thin vitreous crust, as if partial fusion had commenced. It is well known, also, that large masses of soft malleable iron, also containing nickel, are found in several places far removed from each other, lying loose upon the earth, as in South America and in Siberia, and no doubt can exist of the meteoric origin of these masses. It has been conjectured that these meteoric stones proceed from the moon, having been shot out from volcanoes with such violence as to be brought within the reach of the earth's attraction. A view now more generally received supposes the existence in space of very numerous small bodies, moving in more or less regular orbits around the sun and larger planets, which at certain periods undergo such perturbation, that their motion becomes completely deranged, and they at length fall upon the surface of the earth or other planet, whose attraction has been the exciting canse of the derangement of their orbits. Whatever may be their real origin, they are by common consent looked upon as foreign to the earth: their physical constitution is completely different from any known minerals. But what is exceedingly remarkable, and particularly worthy of notice as strengthening the argument that all the members of the solar system, and perhaps of other systems, have a similar constitution, no new elements are found in these bodies; they contain the ordinary materials of the earth, but associated in a manner altogether new, and unlike anything known in terrestrial mineralogy.-Note by a Correspondent.

theory, when all the relative phenomena are in harmony with it. This is eminently the case with the Laplacian cosmogony, for here the associated facts cannot be explained on any other supposition.' It remains that a few words should be said of the well-known hypothesis of a central heat. The immediate surface of the earth exhibits only the temperature which might be expected to be imparted to such materials by the heat of the sun. There is a point a very short way down, but varying in different climes, where all effect from the sun's rays ceases. Then com

mences a temperature from an entirely different cause, one which evidently has its source in the interior of the earth, and which regularly increases as we descend to greater and greater depths, the rate of increment being, in general, about one degree Fahrenheit for every fifty feet; and of this high temperature there are other evidences, in the phenomena of volcanoes and thermal springs, as well as in what is ascertained with regard to the density of the entire mass of the earth. This approximates five and a half times the weight of water; but the actual weight of the principal solid substances composing the outer crust is as two and a half times the weight of water; and this, we know, if the globe were solid and cold, should increase greatly towards the centre, water acquiring the density of quicksilver at 362 miles below the surface, and other things in proportion, and these densities becoming much greater at greater depths; so that the entire mass of a cool globe should be of a gravity infinitely exceeding five and a half times the weight of water. From these considerations arose the hypothesis of a central heat, causing an expansion of the materials. This is now, however, losing favour, in consequence of experiments which show that substances. cannot be maintained at a high, while in contact with similar substances at a lower temperature. It is now thought that

2

See Proofs, Illustrations, &c., No. 2.

The researches on this subject were chiefly conducted by the late Baron Fourier, Perpetual Secretary of the Academy of Sciences of Paris. See his Theorie Analytique de la Chaleur, 1822.

electric currents will yet account for the high temperature of the interior. While the matter remains undetermined, it may be pointed to as one tending to support the Laplacian cosmogony; the statical fact alone, which is not questioned, appears in remarkable harmony therewith, in as far as it proves a rarity of materials in the interior.

28

THE EARTH FORMED GEOLOGICAL
CHANGES.

IN our version of the romance of nature, we now descend from the consideration of orb-filled space and the character of the universal elements, to trace the history of our own globe. We shall see that it falls into connexion in an interesting manner with the primary order of things indicated by Laplace's Theory.

The nature of the materials of the externe or crust of our globe, is known to a greater depth than might be supposed, in consequence of the relation of position of its various masses. Confused as these at first appear, an order of arrangement, connected with time, has been detected in them by the labours of modern geologists. It is found that a certain kind of rock, below which there is never, in ordinary circumstances, any other kind, is of crystalline character. Sometimes elevated in naked mountain masses, sometimes found only at great depths below other rocks of a different kind, Granite (for such is its name) appears as the basis rock of the earth's crust; the form into which the once fluid matter of our planet was primarily resolved, although, in many instances, subjected, under heat, to new movements at times long subsequent. The crystals of granite are of distinct substances-quartz, felspar, mica, and hornblende (each of which is, again, a combination of a certain number of the simple or elementary substances); two of these, sometimes three, associated in various proportions, compose the rock, which thus appears in many varieties, passing under different names.

Where granite does not appear upon the surface, or else some