ART. IV.-Précis de la Geographie Universelle ou Description de toutes les parties du Monde, sur un plan Nouveau D'après les grandes divisions Naturelles du Globe, &c. Par MALTE-BRUN: Bruxelles, 1829. WE place at the head of our article, which we mean to devote to Physical Geography, the title of the latest edition that we have seen of the great work of Malte-Brun. This, which has already become well known to our American public in translation, has received some additions from its Belgian editors, but has not been fully brought up to the present state of Science, nor does it contain all the new discoveries which have been made in that part, namely, physical geography, to which our attention is more immediately directed. We shall, however, endeavour to supply these deficiencies so far as lies in our power. Physical geography stands in immediate connexion with subjects which have already been presented to the readers of this journal, namely with Celestial Mechanics, and with the Phenomena of our Atmosphere. It shall be our endeavour to proceed from the facts laid down in the first of the two articles to which we have referred, to the more particular consideration of the state, the structure, and the condition of the globe we in habit. The earth is a planet of the solar system, the third in distance from the sun, revolving upon its own axis, and around that central body attended by a satellite; circumstances which affect in a most important manner the phenomena that are observed upon its surface. Composed of material substances that mutually attract each other, each particle of which has a greater or less centrifugal force in proportion to its distance from the axis of rotation, it has a figure that is consistent with a state of equilibrium under the joint action of these two forces, and which is such as. would have been assumed by a fluid body actuated by them. The figure that fulfils these conditions is an oblate spheroid, the axis of the generating ellipse coinciding with the polar diameter of the body. Had the earth a figure absolutely spherical, or less flattened than is consistent with the conditions of equilibrium, the ocean, by which so large a part of its surface is covered, would have arranged itself in a meniscoid zone around its equatorial regions; were the figure, on the other hand, one of greater oblateness, the waters would have been divided and accumulated • See American Quarterly, Vol. V. at either pole, leaving the equatorial regions dry. But did its figure fulfil the conditions of equilibrium, the fluid mass would tend to distribute itself equally over the whole surface, unless prevented by irregularities in the solid mass. The last is the actual state of things; the ocean occupies a bed formed of cavities, lying below the mean surface of the spheroid, and the land presents to us those asperities and elevations, which rise, although to a comparatively small height, above the general level. Was then the earth originally in a fluid state, and has it assumed its present form under the strict action of mechanical laws, on a body of that class? are the bed of the ocean and the continents merely crusts formed upon the surface of a liquid globe? Does the interior still remain liquid, or has the induration proceeded until the whole internal mass has become solid? Nay, may not the interior be hollow, as we have recently seen gravely maintained, and heard sage legislatures recommend to the public attention ? Mathematical investigations of incontrovertible evidence, show us that were the earth of equal density throughout, the flattening at the poles would be of the equatorial diameter; that in the hypothetical case of infinite density at the centre, and infinite rarity at the surface, the flattening would be no more than; while, were the surface more dense than the interior, or did a cavity exist within, the oblateness must be greater than Actual measurements of portions of the surface, the variation in the length of the pendulum which beats seconds in different latitudes, and the effect of the earth's figure on the lunar motions, show us that the earth cannot be flattened more than , nor less than, or may, at a mean, be considered as a spheroid, whose polar and equatorial diameters are in the relation of 299 to 300. Astronomers have ascertained the deflection of plumb lines from the vertical, by the action of mountains. The attraction of a projecting mass of known bulk and density, with one whose bulk alone is known, is thus determined, and hence the density of the latter may be calculated. Even comparatively small masses of matter may be placed. under such circumstances at the surface of the earth, that their mutual action can be observed uninfluenced by the preponderating attraction of the earth, and thus a new means of comparison obtained. The pendulum whose vibrations ought to vary according to a definite law, as we recede from the surface of the earth, has that law affected by the elevated ground on which it is placed, and here again a comparison may be instituted between the general and local attractions. All these modes of investigation concur in, and confirm the force of mutual attraction; the consideration thus caused would have produced the state of intense heat that is now kept up within by pressure; and the conducting power of the bodies would have propagated the heat nearly equal throughout the mass. The surface would then have existed in a liquid state as well as that beneath. But as the radiation from the surface of a heated body is in exact proportion to its temperature, this cause of cooling would have been intense, and a crust must soon have formed upon the outer surface; this crust would have increased in thickness so long as the heat thrown off by radiation exceeded that received from the sun. When this state of equilibrium was finally attained, all the great phenomena which a body thus heated could exhibit, would cease, and the subsequent changes would become due only to forces such as we now see acting upon the surface, or would be the completion of actions commenced during the previous state. We know, from astronomical investigations, that this state of equilibrium has existed for upwards of twenty centuries, while analogy would lead us to infer that it must have been attained at no long period after the last great catastrophe to which our planet was subjected. Let us now see whether the fact of the interior of the globe being more intensely heated than its surface, can be inferred in any other manner than from the course of reasoning whose principles are here cited. The feeble power of man, feeble at least compared to the size of the globe he inhabits, has been able to penetrate to but small depths in its outer shell, but even at these small depths, an increase of temperature has been remarked, and so frequently and carefully observed, as to leave no doubt of its being a general law. This increase, too, appears exactly consistent with that which it might be inferred ought to take place. But we, even to the present day, occasionally see the igneous fluid from beneath forced up to the surface, and spreading from volcanic craters over great regions. Observation shows us that at remote epochs such phenomena were much more frequent than at present. We want no more positive proofs that the interior of the earth is still intensely heated, and that the bed of the ocean and the solid land are mere crusts formed upon the surface of a mass in a state analogous to that of igneous fusion. Were the surface, as we have inferred it must have been, ever itself intensely heated, the volatile and gaseous matters which now constitute our atmosphere and oceans, must have united to form an atmosphere of far greater extent than it is at present. The aqueous matter rising into regions where the rarity of the air would cause cold sufficient to condense it, would have been in a state of constant motion, boiling in the lower regions, being precipitated in the higher, and acting most energetically to promote the general cooling. And so soon as the surface became cooler than 212°, the water would begin to settle upon its surface, forming at first lakes in its basins or cavities, and finally extending itself into one vast ocean, covering the whole or parts of the solid crust according to its greater or less degree of uniformity. The conversion of the igneous liquid surface into solid matter, could only have taken place in successive shells or concentric layers; hence would arise a stratified character. And as the cooling proceeded, lowering the mean temperature of the whole mass, a consequent diminution of bulk must have taken place, according to the well known law of expansion by heat and contraction on cooling. Such diminution in bulk must have broken the strata into fragments, through the fissures of which, according to the laws of hydrostatics, the fluid mass beneath would rise until the equilibrium of rotation would have been obtained, and the strata, originally concentric, would be dislocated and turned in every possible direction, pierced with veins and dikes of all possible magnitude, from slender threads to mountain masses, caused by the cooling and consolidation of the rising fluid, and occasionally spreading in overlying currents, congealed and fixed in ridges and chains. These veins and dykes would present different characters, according to the dates of their elevation. If raised at a period when the surface was still of high temperature, they must have crystallized slowly, and in a perfect manner; at diminished temperatures, the crystallization would be less complete; if raised into the mass of ocean, they would assume one character; if coming in contact with air, another. A breaking of the bed of the ocean, and bringing its waters in contact with the liquid mass beneath, might produce consequences extending in their action to districts of the globe, the most remote from those in which the convulsion occurred; for the water, rising into vapour, would tend to extend itself in one uniform atmosphere over the whole surface of the globe, and might be precipitated in unusual abundance wherever causes of condensation existed. Thus, partial, or even total deluges, may have occurred, great portions of the ocean being hurried in vapour from its bed, and precipitated upon the land whose temperature is not affected by the distant catastrophe. The waters might, in some cases, flow directly back to the ocean, in others might accumulate in basins and form lakes, fresh at first, and gradually becoming saline. These in turn might burst their bounds, carrying ruin and devastation in their course, or might by evaporation be dried up, and be again filled by a recurrence of the original cause of supply. Such violent and rapid action would finally be exhausted by the gradual cooling of the earth, but the outer crust would still press on the igneous fluid beneath, and although far less liable to rupture, its fluid action might yet enable it to force its way occasionally to the surface, but at distant intervals, and with diminished energy. Now, a new series of phenomena must occur, similar to the more familiar of those we see acting at present; at first more intense, but finally, when the state of equilibrium of temperature is reached, exactly such as we now find them both in kind and in energy. To see how far such a view of what might have occurred, under the action of well known causes, in case of a certain original order of things, is correct, let us examine the appearances our globe actually presents. To a systematized and general examination, it presents the appearance of a great ocean, covering about three-fourths of its whole surface, and surrounding two great, and a number almost infinite of smaller islands. The two great islands are the old and the new continents; the largest of those that remain is NewHolland. To exhibit this great ocean in its most general aspect, take an artificial globe, raise the south pole 50° above the horizon, and bring New-Zealand to the meridian. The hemisphere above the horizon will now be wholly of water, with the exception of the southern part of South America on the one side, and New-Holland, with the Indian archipelago, on the other. These bear, when united, but a small proportion to the entire hemisphere. The opposite hemisphere contains more land than water; and when it is in its turn placed above the horizon, the Atlantic will be seen lying almost wholly on the western side of the meridian, and forming, with the Arctic ocean, a species of channel, narrowing from the latitude of the Cape of Good Hope towards the northern pole, and communicating with the great ocean which lies principally in the opposite hemisphere by Behring's straits. On this hemisphere are also seen parts of the Pacific and Indian oceans, which are considerably more than equal in surface to the lands which project into the opposite one. If we turn our attention to the land, we find it unequal in its surface; and although compared with the whole diameter of the earth, the inequalities be very small, yet, compared with our own stature, they often present an imposing magnitude. These greater elevations are mountains; and we find them sometimes united in chains, sometimes isolated, and at other times uniting to form elevated plains or table lands. These table lands sometimes slope outwards, at others they are surrounded by eminences that prevent the efflux of the waters, or only admit them to pass through apertures made by their own action. Upon our continent, table lands of the latter description are to be found of great magnitude, entering as parts of the great system of the |