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Recapitulation of points established in the preceding Chapter. Conclusions to be drawn from the oblique direction of metallic veins: various means by which their contents may have been lodged in them. Thermo-electricity that which most probably was employed. Proofs in favour of this assumption, and the manifold evidences of beneficent design in the formation, and in the location of metallic veins. Geological testimonies of the existence of amorphous rocks, capable of having occasioned the electrical currents, and other phenomena from which these metalliferous veins originate. Granitic Rocks: their genera, position, and their relation to associated and superincumbent formations. Enquiry into their supposed origin with respect to the internal structure of the Earth, and the assistance which the Dynamical Theory affords, by simplifying this difficult question.

THE mind having been prepared by the extracts and the opinions which have been given in the preceding chapter, let us now endeavour, if we can, to come to some conclusion which may assist in eventually leading to the truth. Towards the solution of this difficult problem, we are already furnished with a considerable amount of data to enable us to proceed more satisfactorily with our work; we shall take the liberty of recapitulating them. Firstly, then. We know the direction of the veins; secondly. We know their contents, and the contents of the cross courses; thirdly. We know their relative geological positions, and that they do not cause faults or dislocations amongst the formations through which they pass; Fourthly. We are convinced that a force of some kind sufficient to have caused their formation, and especially their direction must have

been employed; and, lastly. We know the nature and direction of all forces. Therefore, by the application of the differential method of reasoning we may perhaps discover that which was employed by the Creator, as the secondary cause, in forming the metallic veins.

From the perpendicular direction in which mineral veins proceed towards the surface, it has been shown, in treating of them, that they owe their origin to a combination of the centrifugal impetus occasioned by the rotation of the earth around its axis, and to the heat which was engendered thereby, especially at the axes of elevation; and if we contrast this with the oblique direction in which metallic veins proceed to the same point, we shall be at once convinced, that these latter cannot have emanated from the same cause which produced the others: unless, indeed, we should imagine, that unlike any other force, it could have simultaneously given birth to two sets of veins proceeding in different directions. We may, therefore, discard the centrifugal impetus as not being the immediate cause of the direction of the metalliferous veins; and in this manner dispose of one of the known forces.

Neither could the oblique direction of these veins result from a composition of forces, between that engendered by centrifugal impetus towards the circumference, and a tangential force at right angles thereto : because, though this might account for some of these diagonal lines, it completely fails when applied to those which cut the others at right angles; and, therefore, we may safely dismiss this also as not having been the immediate cause of the fissures in question.

With regard to infiltration from without, we may dispose of it in the same manner. For, although it is probable it may have been the means of supplying the external fissures-when once they were made-with mineral and metallic solutions, it could not have caused the fissures themselves; both on account of its inadequacy as well as the oblique direction in which these proceed. A liquid, if it could by any possibility have so penetrated as to have caused fissures in solid rock, would, by the laws governing its motion, have done so in lines perpendicular to the earth's surface. We may, therefore, eliminate this cause of origin also from the catalogue. Consequently,

the disposal of those forces, restricts us to the only remaining power at all capable of producing these metallic veins, namely, some one of the various modifications of electrical agency; a conclusion, which not only agrees with Mr. Fox's conceptions and experiments; but likewise harmonises with the results of geological research amongst the formations where these veins abound. The particular kind of electricity which seems best to accord with what has been observed, is that called Thermoelectricity; and, in consequence, after relating some particulars regarding its discovery and its manner of acting, we shall endeavour to apply it to the case in question and show its sufficiency.

"It has already been observed," says the author of the Connexion of the Sciences, "that three bodies are requisite to form a galvanic circuit, one of which must be a fluid. But in 1822, Prof. Seebeck, of Berlin, discovered that electric currents may be produced by the partial application of heat to a circuit formed of two solid conductors. For example, when a semi-circle of bismuth, joined to a semi-circle of antimony, so as to form a ring, is heated at one of the junctions by a lamp, a current of electricity flows through the circuit from the antimony to the bismuth, and such thermo-electric currents produce all the electro-magnetic effects. . . M. Nobili observed

that in all metals, except zinc, iron, and antimony, the electricity flows from the hot part towards that which is cold. That philosopher attributes terrestrial magnetism to a difference in the action of heat on the various substances of which the crust of the earth is composed; and in confirmation of his views he has produced electrical currents by the contact of two pieces of moist clay, of which one was hotter than the other.

"M. Bequerel constructed a thermo-electric battery of one kind of metal, by which he has determined the relation between the heat employed, and the intensity of the resulting electricity. He found that in most metals the intensity of the current increases with the heat to a certain limit, but that this law extends much farther in metals which are difficult to fuse, and which do not rust. The experiments of Professor Cumming show, that the mutual action of a magnet and a thermo-electric current is subject to the same laws as those of magnets and galvanic currents, consequently all the pheno

*Theorems 59 to 66.

mena of repulsions, attraction, and rotation, may be exhibited by a thermo-electric current.”

And at another place this author observes

"Dr. Faraday has proved by recent experiments on bodies, both in solution and fusion, that electrical affinity is merely a result of the electrical state of the particles of matter."*

"If the theory of internal heat," says M. de la Beche, with his usual circumspection, "be well founded, it will be evident that the two ends of a metallic vein will be differently heated, and therefore we should have a thermo-electrical apparatus on a large scale, producing effects which, though slow, might be very considerable. How far such really exists in nature remains questionable, but it may be observed that the experiments of Mr. W. Fox show the possibility of their occurrence; and should further researches in this highly interesting subject so divide it, that some of its present apparent complexity may disappear, a great advance will be made in this now obscure branch of geological enquiry."†

Professor Playfair, with his characteristic acumen, refutes the Neptunian while he vindicates the Plutonic hypothesis, as far as the formation of metals in veins is concerned, in the following conclusive passage of his Illustrations

"The state in which gold and silver are often found pervading masses of quartz, and shooting across them in every direction," he remarks," furnishes a strong argument for the igneous origin both of the metal and the stone. From such specimens it is evident, that the quartz and the metal crystallized, or passed from a fluid to a solid state, at the same time: and it is hardly less clear, that this fluidity did not proceed from solution in any menstruum: for the menstruum, whether water or the chaotic fluid, to enable it to dissolve the quartz, must have had an alkaline impregnation; and to enable it to dissolve the metal, it must have had, at the same time, an acid impregnation. But these two opposite qualities could not reside in the same subject; the acid and the alkali would unite together, and, if equally powerful, form a neutral salt, like sea salt, incapable of acting either on the metallic or the siliceous body. If the acid was

* Mrs. Somerville on the Connexion of the Sciences, pp. 345, 346, 123. + Manual, p. 524.

most powerful, the compound salt might act on the metal, but not at all upon the quartz; and if the alkali was most powerful, the compound might act on the quartz, but not at all on the metal. In no case, therefore, could it act on both at the same time. Fire or heat, if sufficiently intense, is not subject to this difficulty, as it could exercise its force with equal effect on both bodies."*

And in further confirmation of this particular point, we beg reference to the very conclusive evidence given at page 99, from Mr. Lyell's Elements, which, in consequence of having been so recently quoted, we do not here repeat.†

What has now been adduced sufficiently proves, that heat, when applied to distinct mineral substances-unequal conductors-puts those associated materials into a condition proper for eliciting currents of thermo-electricity; while, what has previously been established, leaves as little doubt on the mind, that during the first rotation of the earth around its axis, there was sufficient heat evolved to act as a primum mobile in this case, and to set those dormant currents into active operation. And if, to this, we add the corroborative consideration that the strata, at the period when these operations are supposed to have taken place, were impregnated with metallic depositions in combination with other elements, agreeing precisely with those discovered in metallic veins, we shall be convinced, that according to the wise and beneficent ordinations of the Creator, all the requisites were amply prepared for the event; so that the thermo-electrical currents, when put into exercise, had wherewithal to operate upon, and to produce, with due separation, either by sublimation, or rapid segregation, those stores of metallic riches, destined to be transmuted for the use-not for the abuse-of man.

If a view be taken of any sectional geological map, and, at the same time, it be remembered, that "the granite and Killas-the intruded masses of more recent granite-and the various kinds of porphyritic rocks, called Elvans, are considered to have occupied their present relative positions before the origin of the fissures, forming the metalliferous veins which

* Illustrations of the Huttonian Theory, vol. i. pp. 249, 250. + Elements of Geology, vol ii. p. 343.

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