of all those masses regarded as eruptive, it refers to the great central reservoir, it is undoubtedly extremely attractive on account of its simplicity and intelligibility. When, however, it is required, that not only the rocks composed of silicates, but also limestones, therefore, in short, the most heterogeneous masses, are to be regarded as having burst forth from the interior of the earth, this theory, as has been remarked by others, no longer possesses the qualities just mentioned; for, instead of producing light, it only leads us into still greater darkness. If, however, it should be the case that the geognostical phenomenon in question is less correctly represented for the purpose of rendering the eruption-hypothesis available, it must be confessed that that doubtful relief is dearly purchased. I do not, indeed, venture to assert that the description quoted of the phenomenon at Auerbach is incorrect, for it scarcely contains any absolute impossibility. It can very well be supposed that the gneiss received from above the upfilling of limestone into an existing fissure, nay, if necessary, we may even imagine a filling proceeding from beneath, and standing in no connection whatever with volcanic action; for, it might be assumed, perhaps, that an internal mass of limestone had been brought to the state of a sort of moya, in some way or other, for example, by the movement of the overlying rock and the entrance of water, and that in this way it could be pressed upwards into the fissure. But the real question is, if we have here actually before us a filling up of a fissure, and if the phenomenon has not assumed that character in the description on account of the theory. Leonhard terms the mass a vein, and, from his sketch, the conclusion must be drawn that it really cuts through the gneiss strata; but, in the description which I have seen (Leonhard's Populäre Vorlesungen über Geologie, vol. ii. p. 215), this latter and most important circumstance is passed over in silence, which seems not a little suspicious. Is it not the case here, as has undoubtedly happened in other similar instances, that an error has been committed in making a vein of a mass which ought, perhaps, more correctly to be included among the beds?

But it is now time to close these remarks on contact-phenomena, and to pass to another important subject, in the consi

deration of which erroneous paths have also been followed, in consequence of the prevailing, and, as it is pretended, highly philosophical, but, in fact, altogether incorrect maxims. It is to the crystalline silicide slates that we are now to direct our attention.

CRYSTALLINE SILICIDE SLATES.

Regarding these formations, we see one party directly denying palpable facts, and proposing the most unnatural hypotheses, in order to keep on good terms with chemistry, whose claim to the office of judge in the matter no one has yet examined with attention; while the other party, overpowered by the evidence of the phenomena as displayed in nature, certainly are near seeing the truth, but still, in consequence of traditional scruples, stop short of its full perception, and, at the same time, affect a language which sounds like homage paid to the principle,—that geological results must always be chemically comprehensible.

The hypothesis of the Wernerian school of the direct hydrogenic formation of gneiss, mica-slate, &c., meets with no support either from chemistry or geology, and is now scarcely adopted by any one. Some have brought forward the opinion that these formations must be masses derived from the interior of the earth,* which became what they now are from a melted condition; while others suppose that they are sedimentary products, which have been transmuted by volcanic agents.

The idea of the crystallization of such rocks after a previous condition of liquidity, is shewn to be quite absurd even by the consideration of their petrographical constitution; for they are slates. If such are to be regarded as produced by the solidification of masses which have been in a burning liquid state, then that which receives no support from any one observation is assumed to be possible, and thus the very rule to which

* Leonhard includes these formations among those which are of direct plutonic derivation; and by this he means that they ascended from the depths of the earth in the form in which they now are (?" als solche," that is to say as gneiss, &c.), and that they were the first solidified crust of the red-hot globe. It is not easy to perceive how both these suppositions can be admitted together.

VOL. XXXVII. NO. LXXIII.-JULY 1844.

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these geologists so strongly profess to adhere is directly violated by themselves. The notion that a solidification under strong pressure, or great tension, and so forth, might. possibly have produced the peculiar texture in these rocks, should least of all have been heard from those theorists at whom we are now aiming, who, according to their own account, follow such strict principles. But it is still worse that this party must deny the very clearest geognostical facts, in order to maintain their opinion. It has now been observed in many places, that strata of rock, which can be recognised by any one, by means of the usual characters, as masses that have been produced in the mechanical way, and deposited in water, present themselves for a longer or shorter portion of their extent as gneiss, mica-slate, or some one of the rocks now under discussion, and thus plainly exhibit a transmutation in these portions, inasmuch as a direct “Neptunian" crystallization can just as little be supposed here as in other cases. As here the geognostical fact itself decides the question in dispute in the most complete manner, inasmuch as the confirmation of these geognostical observations gives it to us as a pure result of observation, as a fact, that sedimentary, originally uncrystalline masses, have, at certain points, been converted into gneiss, mica-slate, &c., it must be flatly denied by the just mentioned party that such strata exist, which are partly crystalline silicide masses, but in their other portions have retained that condition which betrays the original formation of the whole by means of deposition in water; and, accordingly, this mode of proceeding has not been omitted.

The opponents of the principle of transmutation have a much better field in regard to conversions that have taken place on the great scale. Where we see no unaltered remains of the transmuted masses, the conviction of the change that has occurred does not follow directly from the geognostical phenomena themselves, but can only be founded on the conclusions derived from other evident cases. As in this way the knowledge was obtained that entire large countries, which are almost entirely composed of gneiss and similar rocks, are enormous altered formations of sandstone, clay-slate, &c., this result did not fail to be termed an hypothesis; and under this

designation it was brought before the judgment-seat of chemistry. As those who adopted the doctrine of transmutation had committed the fault of not distinctly separating what was the incontrovertible result of geognostical observations from those immature explanations with which they deemed it necessary to accompany this result, it thus undeniably acquired an aspect of uncertainty. Thus proclaimed by its adversaries to be a mere idea, and obscured in this manner by its champions, it was rejected by the chemists, who estimated the whole according to the subjoined chemical suppositions. "The most distinguished chemists of our time," says Leonhard, “have, as was to be expected, expressed themselves strongly against the transmutation theory; they characterized it as founded on an insecure basis. Although there are many of the higher problems of geology which chemistry may not be in a position to solve, yet it certainly does not become the former science to hasten beyond the latter; and especially in such bold hypotheses as those in this theory, geologists require recognition on the part of chemistry as a guarantee. Can we blame chemists for keenly finding fault with the adoption of obscure processes without taking into consideration the how and wherefore, without naming the agent which produced these very strange phenomena, without pointing out whence this or that element in the newly produced formations was derived, and without indicating the manner in which the others disappeared?" Now, it is well to notice that, in this reasoning of the influential author, those chemical speculations brought forward by certain geologists, and which have produced misbelief regarding the result as to transmutations, are alone to be understood as included in the expression insecure basis of the "conversion theory;" for the true basis of our knowledge of the conversions in question lies beyond the proper limits of chemistry. When two equally good geological hypotheses, which regard a subject of a chemical nature, stand side by side, it is then quite proper that the decision should be referred to chemistry. But we repeat it again and again, that this is by no means the case here; for, whoever wishes, can see, that transmutations of uncrystalline strata into crystalline silicide rocks have taken place. The question no longer turns by any

means on the possibility or probability of the transmutations, inasmuch as it is now absolutely certain that they have really occurred. Although, in the mean time, they may be chemically inexplicable, yet this can have no influence on the incontrovertibility of the result. How many other facts are there not which still remain chemical mysteries. When, for example, certain after-crystals of augite are found, containing a considerable quantity of alkali, whose origin is incomprehensible to chemists, the conviction is not therefore suppressed, that in this case augite has been transmuted. It is only the explanations added to the matter of fact which can here be blamed by the chemist; and, certainly, in some of these occasion has been given for their propounders being cut short by the "how" and "wherefore," or it has been found necessary to advance beyond the limits within which the experimental investigator must remain, and which are often regarded by him as the boundaries of the science itself.*

It will thus be perceived that, in two respects, we consider that party to be in error, who prefer considering the crystalline silicide rocks as erupted masses which have been solidified from an originally burning liquid condition, instead of the regarding them as transmuted, originally uncrystalline, slates, sandstones, &c. 1. Because that party have turned away from nature, which tells them that such transmutations are actually met with, and have addressed themselves to an incompetent authority with the unnecessary question, whether such processes are possible; and, 2. Because, after receiving a negative answer, they believe themselves obliged to reject palpable facts. If we are not wrong in these accusations, nothing else is required to shew the disposition and the judgment with which these theorists proceed. It is not at present necessary to consider other weak points of their geological result.

The lamentable part performed by geologists as to the question of the formation of dolomite also naturally occurs to us in speaking of this subject. Instead of, at all events, at first, adhering simply to what personal observation taught them, namely, that dolomite is incontrovertibly a transmuted carbonate of lime, and instead of enriching their science with this result of observation, as with an incontestable fact, they went with their discovery to the chemists, presenting it in the form of a theory. Now, as this theory could receive no approbation from the chemists, the good people remained standing with empty hands, notwithstanding the great discovery which they had really made.