portion of the circumference of a circle to be identical with a straight line: he reasons upon this,--and founds something which is true, upon a basis which probably is false. In like. manner, it often happens in physics, that uncertain premises, when they become sufficiently numerous, afford a mean result, which corrects particular errors; and either itself constitutes the truth, or approaches it within a certain assignable distance. After discussing Kirwan's theory of a Chaotic Fluid, M. Breislak, in his 3d chapter, enters on the topic of the igneous fluidity, and succeeding consolidation, of the globe. Some general remarks on the modern doctrines of heat, pave the way to his own theory on this subject; of which, if we mistake it not, the following is the outline. He conceives caloric, or the matter of heat, to have existed in such quantity in the great original mass of materials composing our planet, as to have held them in a common state of igneous fusion. In a mass thus heterogeneously composed, he conceives that the whole might be cooled, without the total quantity of its heat being diminished; and this by the different capacities for latent caloric in different constituents of the mass. At some unknown time, and from some unknown cause, the series of changes began, producing this effect. The several substances which, in their present state, compose the atmosphere and waters of the globe, assumed the gaseous form, rose to the surface, and enveloped the central mass, consisting of earths, metallic substances, &c. These, losing the great quantity of heat absorbed by the former, while passing into the gaseous state, assumed the solid form, with a crystallization more or less perfect, according to local circumstances. Electric matter is supposed to have been present as another element in the chaotic mass. It probably developed itself, while the equilibrium was broken by the changes just described; and its agency may have been chiefly that which reduced the hydrogen, and a portion of the oxygen evolved, to the state of water; while another portion of the waters of the globe was formed by the simple union of these gases in the nascent state. The tendency of the centrifugal force to throw off the heaviest bodies towards the surface, was counteracted by the explosive power of these elastic fluids and vapours, which transported thither the lightest materials en which their action was exerted. The cooling, which took place superficially, in consequence of the rapid absorption of heat by the nascent gases, must have produced the consolidation of an exterior shell, while the interior was yet in a state of fusion. This crust, compressing the latter by its contraction, and itself reacted upon by the various forces from beneath, may. easily be conceived to have been rent open in different places

and the newly consolidated beds irregularly broken, displaced and removed from an horizontal into an inclined, or even perpendicular position. Hence, in great part, the various deviations from regularity in the present appearances of primitive rocks.

This, stripped of its details, seems to be the theory of M Breislak, as to the original state of the globe, and the consoli dation of our oldest strata. We will not object to him, that his postulates are many and of great magnitude; his supposi tions extensive and daring. We are well aware that the subject does not admit of being otherwise treated; and presume that most geological theories are liable to similar objections. The principal novelty in his views (though perhaps only in part a novelty), is that of making use of the doctrine of latent caloric, to dispose of all the heat necessary to the con dition of igneous fusion in the globe. One class of elements in the chaotic mass, absorbs it, in consequence of a tendency to the gaseous form; another class of elements give it up, and become consolidated in so doing. In vindication of this idea, our author refers to the old experiment on the burning of phosphorus, from which it is inferred that the heat contained in a pound of oxygen, is sufficient to melt 66 lib. of ice. Extending this conclusion to the total weight of the atmosphere surrounding the globe, he remarks how enormous must be the quantity of heat absorbed and rendered latent, by the passage of its constituent gases from the fluid to the aeriform state!'an inference of which we certainly cannot deny the justness, whatever may be said of the more extended assertion, that this absorption on the one side was equivalent to a total consolidation of all the other materials of the globe. We cannot equally allow M. Breislak to strengthen his proof, by speaking of the absorption of heat in the formation of water. It is true, we have no definite idea or explanation of the state in which he supposes oxygen or hydrogen to have existed in the melted chaotic mass; but it does not appear that his theory will permit him to suppose a less solid state, than that in which they occur in water; and, if so, nothing can be gained from this

source.

We may remark further of this hypothesis, that its application is chiefly to the primitive rocks of the globe; and we find M. Breislak labouring under some difficulties to keep up the appearances of an igneous theory, in explaining the origin of transition and secondary rocks. He does, indeed, suppose, that the heat of the globe was not entirely lost by the formation of gases; that the central parts, compressed by the surrounding crust, might long remain in a state of partial fusion; and

communicate something of their heat to the substance on the surface. But still his theory is that of final and total cooling, by. interchange of heat among substances having different capacities for caloric; and he does not adopt the principle of the Huttonian theory, which provides for the consolidation of rocks, and the renovation of strata.

We are surprized, indeed, that M. Breislak should have taken so little notice of a doctrine, which in some points accords with his own views, and in others might have been very useful in modifying or enlarging them. At the end of this chapter, he gives a very brief sketch of Dr Hutton's Theory, as illustrated by Professor Playfair; and accompanies it by a few critical remarks, chiefly seeking to disprove the idea of a continued central heat, sufficient to produce effects on the actually existing strata. He seems to us, however, neither very strenuous, nor very successful in these comments. The Huttonian Theory evidently affords a more enlarged, and, we think, a more philosophical view, of the changes that have occurred on the earth's surface, than that for which he contends. We say more enlarged-because its application may more successfully be made to the different classes of rocks; more philo-sophical-because its reasonings from the outset are more strictly founded on the observation of phenomena. The existence and the agency of subterraneous heat are not presumed by the Huttonian, till he has seen what he considers proof of them in actual appearances. He reasons upon the observed tendency to degradation of the earth's surface; upon the natural deposition of the materials thus separated; upon the actual consolidation of strata, which plainly appear to have been composed from the materials of more ancient rocks; upon the present position of the strata; upon the particular appearances of granitic veins, whin dykes, &c.; upon the phenomena of volcanoes, and other more casual evidences of internal heat. It is possible, that some of his conclusions may be rendered erroneous by imperfect observation, a defect which belongs to every theory; but still, all his elements are taken from nature, and combined on a just principle of reasoning. We speak the more pointedly on this subject, because the Huttonian Theory has been very unjustly censured by some of its adversaries, as a mere ingenious hypothesis, unsupported by research, or a knowledge of facts.

M. Breislak's Fourth and Fifth chapters treat of the individual rocks, classed into those which were formed during the first consolidation of the globe, and those formed subsequently to this event, a division, which nearly corresponds with the old one, of primary and secondary rocks. To his long disquisition

on Granite, we should apply the objection we have before made to the book at large, that it is too theoretical for an elementary work. On the much disputed point, as to the stratification of granite, M. Breislak adds little that is new. What surprizes us more, is, that he scarcely even alludes to the existence or origin of granitic veins, and speaks in the most cursory manner of the different formations of granite, though these facts are of such obvious importance in geology. The truth seems to be, that he is unwilling to admit the idea of any movement or projection of this substance while in a state of fusion; and he expressly declares his dissent from the opinions of Dr Hutton on this subject. The dissent is the more singular, because a great part of his proof of the crystallization of granite, as well as of sienite, porphyry, and the trap rocks, from a state of igneous fusion, is founded on the observation of analogous appearances in lavas, and other volcanic products. It might be thought, that the pursuit of this analogy should have led him not to reject totally the notion, of some of the unstratified rocks having been fused and elevated at later periods than the first consolidation of the globe.

Our author proceeds from granite to the other primitive rocks, stratified and overlying. He is more brief, and less distinct upon these; and, with respect to marble, serpentine, and some others, scarcely ventures any decided opinion as to their origin. He wishes, indeed, to avail himself of Sir James Hall's experiments, in proof of the probable igneous origin of marble; but to the benefit of these he is not fairly entitled, since his doctrine does not allow of the compression necessary to retain the carbonic acid in a fixed state. It is evident that his theory continually labours, from too speedily setting to rest some of the great agencies which it employs. He has done too much for granite; too little for all the other classes of rocks.

This remark is applicable to the account he successively gives of the transition and secondary stratas. Here, indeed, he introduces water as one of his agents; heated, during a certain period, by emanations of heat still continuing from the inner parts of the globe; and rendered, by this cause, and by the chemical principles it contained, an active solvent of the materials afterwards deposited.

Le acque del mare primitivo, bollente ed animate da molti principi chimici, potevano in qualche modo sciogliere o tenere sospese quelle terre che diedero origine alle rocce di transizione e secondarie, le quali si andarono depositando a misura che diminuiva l'intensita del calore. I gradi dunque di cristallizzazione divenivano sempre minori, come si diminuivano i gradi di calore, perchè a questi corrispondeva una maggiore o minore soluzione delle

terre.'

Here, it will be seen, that M. Breislak's theory approaches somewhat closely to the Wernerian, which elsewhere he is so much disposed to censure; and he partially recognizes, himself, this approach, in his comments on the opinions of M. Ebel, one of the advocates of this doctrine. It does not appear that he regards heat as concerned in the consolidation of the secondary rocks, or in any of the more important changes they have undergone. All the statements in this part of his work have reference to chemical or mechanical deposition from water; and we no longer discern the Plutonist, who has submitted the whole class of primitive rocks to fusion by fire. Entering thus far into the Neptunian doctrine, he subjects himself to many of its consequences; above all, to the necessity of supposing a repeated rise and depression of the waters, and of explaining their ultimate retreat from the higher parts of the earth's surface.

In speaking of the gypsum formations, M. Breislak conceives that they may have had their origin in the vapours of sulphuretted hydrogen, rising towards the surface, and passing through calcareous matter. He supports this idea by some analogous phenomena in volcanic districts. As to the origin of rock salt, he does not give any distinct opinion; speaking vaguely of intense emanations, which proceeded from the interior of the earth, still heated, producing these local deposites. He is equally unsatisfactory on the subject of coal; and appears only very partially informed as to the natural history of this interesting mineral.

In his Sixth Chapter, our author treats of different phenomena attending the consolidation of the globe. The first subject is that of veins, and other metallic depôts; and he criticizes with considerable justice the principles laid down by Werner, in his Theory of the Formation of Veins.' These principles we had occasion to notice, and to comment upon, in our review of the work of that eminent mineralogist. M. Breislak proceeds to substitute a theory of his own; applicable, he conceives, to all true metallic depôts, as distinguished from those, which af ford merely the appearance of having been open fissures, filled subsequently by transported materials. He founds this theory on the principle, that a mass, composed of different elements, may be placed under such circumstances, as to form within itself certain centres of attraction; in such manner that the homogeneous elements shall unite together, in separating themselves from the others which had been interposed. These circumstances may occur, when the mass, not yet consolidated, ia in a fluid or viscid state: they may be renewed, when the force of cohesion of the compound is so far destroyed by the action