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prevalent rocks, to be 2.5. By direct experiment, and comparison of the local attraction of mountains and insulated masses of matter with the general attraction of the globe, the mean density of our planet has been inferred to be about five times that of water. This result is found sufficiently in accordance with astronomical considerations, to allow us to adopt it for geological reasoning.

"The interior parts of the globe must therefore be denser than the exterior rocks.

"From the influence of the earth on the moon's motions, it is inferred, that the internal mass of our planet augments in density towards the centre; the surfaces of equal density being symmetrical with the external spheroidal surface. The materials of the earth have therefore collected round the centre in obedience to the laws of gravitation and rotatory movement, and the internal substances, as having fallen to the lower place when freedom of motion was allowed, would probably be heavier under the same circumstances than the superficial substances, and so forth. . . . . . Now though we cannot presume that the laws of compression would hold in these bodies to such an extent, enough is known to justify a confident belief, that the mean density of our planet would be very much greater than it is, were not the tendency to enormous condensation in the central masses, counteracted by some powerful agent of expansion, such as heat, or neutralized by some peculiar or unknown constitution of the substances themselves."*

Dr. M'Culloch, when treating incidentally on this, says

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Notwithstanding its inferiority in position, we must not grant, as asserted, that granite constitutes the mass of the globe, or is the lowest rock in existence. Of the interior of the globe we know nothing; but its weight is sufficient to prove, that it is not formed of granite... Some unstratified matter, solid or fluid, does doubtless lie beneath the stratified surface of the earth; but while conjectures are fruitless, it might, if solid, be basalt as well as granite."+

We find others expressing bolder and more startling views of this perplexing subject, derived, no doubt, from the gradual

Treatise on Geology, pp. 9-11.

+ Vol. ii. p. 87.

increase of heat which is experienced when perforations are made into the solid parts of the earth's crust.

"That the whole interior portion of the earth, or at least a great part of it, is an ocean of melted rock, agitated by violent winds, though I dare not affirm it, is still rendered highly probable by the phenomena of volcanoes. The facts connected with their eruption have been ascertained and placed beyond a doubt. How then are they to be accounted for? The theory prevalent some years since, that they are caused by the combustion of immense coal beds, is puerile and now entirely abandoned. All the coal in the world could not afford fuel enough for one of these tremendous eruptions of Vesuvius."*

How infinitely would the first of these conceptions-that of Mrs. Somerville-if eventually found to be correct, tend to exalt our ideas of the wisdom, and the power of God, who disposed and prepared the rocky shell in such a way, that while, by his command, it was transformed from a level sphere, "without form and void," into a spheroid, adorned with continents and ocean beds, hills and dales, yet was so cemented and welded together, in the very act of its transformation, that neither the elastic fluids were permitted to escape from within, nor the water to penetrate the superficial crust!

But, as we have before remarked, while this recondite point in cosmogony is shut up from experimental investigation, and thereby exposed, less or more, to conjecture, its importance seems to be inversely as the difficulty of its determination. The earth's formation can be satisfactorily accounted for even should this be assumed, merely in conformity with the requirements of interplanetary laws.

Nevertheless, we take occasion to observe, that this abstruse question has been so far benefitted by the Dynamical Theory, that it has removed the seeming necessity which there appeared to be, for not only taking fierce internal heat into the resolution of the problem, but for subordinating all the other conditions to this datum, supposed to be so well established.

* Professor Silliman. Am. Journal of Science.

Henceforward, we trust, that the heat, discoverable in mines and other perforations, will be attributed to that which was caused by the friction of the moving mineral masses, during the earth's protorotation, and whose foci resided in mountain nucleii; as this of itself is quite sufficient to have produced the phenomena in question; while the Dynamical Theory would have been incomplete without the existing demonstrations of fierce heat in these localities.

K

SECTION VI.

GEOLOGICAL PHENOMENA RESULTING FROM THE EARTH'S

PROTOROTATION.

CHAPTER XXV.

The immediate consequences of the two established positions: the non-rotation of the earth until all the strata, up to the coal measures, had been formed; and its subsequent protorotation, considered with reference, firstly, to the rush of water which took place from the poles towards the equator; and, secondly, to the disintegration which accompanied the upbursting of the amorphous rocks, during these violent movements of the primitive water. This conflux of water attempted to be explained analogically by currents of wind; and applied to the peculiar case under consideration. The attention then directed to another simultaneous series of events. The upbursting of the amorphous masses, and the disintegration which must have ensued, together with the disseminating effects of the violent aqueous currents towards the equator. Geological evidences. Some brief concluding observations.

HAVING thus established the fundamental positions, That the earth existed in a state of non-rotation during a period sufficiently long to admit of the deposition of all the stratified formations up to the completion of the coal measures; and, that its protorotation took place on the first day of the Mosaic week; we have, in continuation, to consider two of the more important of the manifold consequences which resulted from the commencement of the earth's diurnal motion at the period to which we have alluded. These are so intimately allied to each other in the effects which they, in turn, produced on the geological developments of the earth, that it would be most desirable could they, by any means, be described simultaneously, but this not being possible, we must submit to their being

considered in immediate sequence. We allude, firstly, to the rush of water which took place from the polar seas towards the equatorial regions to complete the figure of equilibrium; and, secondly, to the comminuting and disintegrating influence conjointly of this sudden movement of the water, and of the upheaving of the unstratified masses, when they burst through the strata in obedience to the centrifugal impetus occasioned by the first rotation of the earth around its axis.

A rush of water, similar to that which is here alluded to, never having been thought of by philosophers, no provision has been made for it; and, therefore, in place of being able to produce direct testimony to show what would be the consequences of a world of water thus thrown into sudden and violent movement, and sweeping over rocky masses in the act of disintegration and comminution, and also in agitation, we are necessitated to reason by analogy, and to adopt the case which nearest approaches to it. For this purpose, we find the clear and convincing exposition which has been given of the trade winds, to be very analogous, the appropriate points of which compose the thirty-fifth Theorem, which states, "That a satisfactory explanation of the trade winds has been given upon certain well-known and established principles, amongst which the following are relevant to the present subject: 1st. That all portions of the earth's surface have a velocity of rotation in direct proportion to the radii of the circle of latitude to which they correspond; 2nd. That the air, when relatively and apparently at rest, is only so because it participates in the motion of rotation proper to that part of the earth; 3rd. That, consequently, when currents of air set towards the equator from the north or south, they must lag, hang back, or drag upon the surface, in a direction opposite to that of the earth's rotation, or from east to west; and, lastly. That the polar currents, from a deficiency of rotatory velocity, tend by their friction, near the equator, to diminish the velocity."

The following evidences corroborate the truth of this interesting Theorem, although they are necessarily restricted to the points which alone affect this theory:

"Another great geographical phenomenon, which owes its existence to the earth's rotation, is the trade winds. These arise from,

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