Underground Waters in Rock Transformation.

Tuapeka Times, Volume XXIV, Issue 1890, 23 April 1892, Page 1 (Supplement)

Underground Waters in Rock Transformation.

[Translated from the French.]

Prof. G. A. Daubree upon the effect of water in rock transformation says :

We Bhall now consider how tho fountiamental faots of metamorphifim imply tb.B necessary action of subterranean waters. The mineralogioal modifications peculiar to the phenomena have incontestably taken place at a higher temperature than now prevails on the surface of tho globe. We base thia conclusion upon the anclogies of these beds with the eruptive rocks, and especially upon the presence of numerous anhydrous Eilicates, which form one of their most remarkable features. The proper heaS of the globe decreasing from the deeper parta towards the surface, tbe sediments deposited in the ocean, at the relatively low temperature that reigns there, should, when "they have been covered by other strata, acquire a higher temperature by reß?on of their greater distance from the rEdiaticg surface. The superposition of masses as heavy as ar9 thcS3 of some of the stratified beds has often been enough to deterrrine, after their disposition, a considerable heating up of the lower masses, especially at periods -when the increase of heat downward may have been at a more rapid rate than now. Thus the regular propagation of the heat of the globe has been competent to act upon entire formations.

There ia, however, another eource of hea>, at once more immediate and more energetio, for the transformations with which we are occupied, although it haa been long misunderstood. Heat is engendered by the mechanical actions that have left their marks at numerous spots on the crust of the globe. Instead of preserving the horizontal position which they assumed when they were deposited, these beds have often been thrown up, folded, and contorted in various ways ; and the resultant dislocations are observable through several thousand meters of tbiokness. At every Btep, in the Alps, for example, in tho face of escarpments where tbe rock Bhows itself to the quick, the least observable eye is attracted by the boldness of the in fi lotions, and the mind pauses, stupefied before the grandeur of the forces that have produced such effects. Not all the labor put in play in these colossal upthrows has been employed in actions purely mechanical. A part of it has been trans* formed into heat, and it is the effects of this neat that we have been Btudying.

Experience has come to confirm the last Induction also. Clay haa been foroed to flow either between cylinders like those of ironmills, or under trituration in malaxating tubs, such as aro used in some brick-yards. In either case the rock ia coneiderably heated up after a very short time, -without subjecting to any material pressure. In these operations the heating ia greater in proportion as the olayey part is harder and more resistent. We have reason then to believe that in nature, when rocks are coherent and less plastic than ordinary clay have been submitted to mechanical actions powerful enough to determine an inferior movement, even if it be of little amplitude, they will be found in conditions still more favorable to their being heated. It has, therefore, been enough for argillaceous masses to undergo a lamination under the effect of dislocations in the crust of the earth of their temperature to be notably raised.

But heat alone, however intense it may be, cannot explain the most characteristic effeosa of metamorphism, nor tha uniformity with which they have been produoed over considerables pace; for tbe conductivity of the rocks is extremely weak. Then,oontrary to what should be tbe case were the action simply a oalorflo one, the effects have not always been most energetic in the parts in contact with the eruptive rocks. The water included in ail tbe rooks, whether in their pores or in combination, has of necessity intervened as sn auxiliary to the heat. The nature of the minerals produced, of the hydrated silicates, like chloride, for example, no less than the uniformity of their disposition in vase masses, denote tbe intervention of this interior water. Thus, in thia order of geological phenomena when we might hava believed that heat, accompanied by certain chemical actions, was tbe sole agent, subterranean water has also had its part to play. Thia conclusion regarding the fundamental cause of metamorphism, although it has been justified by observation, still needed an experimental sanction. For that the investigator should put himself in circumstances as nearly as possible like thoße in which nature seems to have acted, and obtain the reproduction of characteristic minerals. I have tried to realise this. Tha principal difficulty in opciatirg under the enormous pressure acquired by the vapor of water when the temperature approaches the point of dull redness is to find walla capable of resisting it. Water having been plaoedin a glass tube, which was then sealed by a lamp, this tube introduced into a second tube of iron, with very thick walls, whioh was also closed, but not without difficulty at a forge. In order to counterbalance the tension of the vapor in the interior 0! the of the glas3 tube t which might cau-e it to burst, care was taken to pour water outside of this tube, between its walls and those of the iron tube. The apparatus v?aß set upon the dome of the furnace of a gas-factory ia contact with masonary at a dull-red heat, in a thick bed of sand, where it remained for several weeks. Under these conditions explosions of extreme violence took place. The mest strongly resistant tubes were thrown into the air, bursting with a noise oomparable to that of a cannon-Bhot. It was not possible to multiply the proofs to the extent that was de?.irable ; but those that were made were sufficient to reveal facts quite different from those whioh we had deduced in laboratories under ordinary conditions.

The water acted very energetically upon the glass, which underwent a complete transformation, in composition and appearance. It was replaced by a white mass, quite opaque, resembling porcelain, with swellings and blisters, the results of softening. There has been developed, at the expense of a part of the substance, numbers of minute oryatals, colorless and limpid like rook oryßtel with which they are identical, even to small- details in the forms. These artifioal crystals appeared, now isolated, now grouped into geodea which it was impossible to distinguish, eicept for the difference in dimeceiona, from those of nature, Another product of the same experiments deserve no leee attention, ft is pyroxene which appearr

• hula yr-tn, biiliunfc acd trsnrparpnt -}>-tajß, fxsctlv JiLelhoso of the Aipa. For 1c - c first time ir. anhydrous silicate had been -"tn to bo produced by tbe action of water. .1 )ro recently idilspar has been imitated, ■ ndereimilar processes by MM.Friedel and •rsnasin. The acquisition of a-oth fkicd of power by water under such ccndilion'? was exemplified Hy the conversion cf pine-wood into a bright via hard black eubatance resembling sithracite, and consisting chiefly of carbon •*scciated with rain&ll quantities of volatile übstances. It was ahown, by its granulaion in small globules, to have passed, in the water, through a kind of fusion. The reaetiona from which these products resulted are all the more interesting because they •vero obtained with a omall quantity of water, hardly equal to a third of the weight of the metamorphosed glaes. Furthermore, the new prodaota crystalised at a temperature coneiderably lower fthan their point of fusion. It is thus proved that water highly superheated acquires an energy that was unknown to belong to it. 16 destroys combinations thst were reputed to be stable, and in thff presence of whioh it was regarded as inert; and it composes others, among whioh are tba anhydrous eilioates. The production o! these silicates in the crust of the earth escapes our observation, because it requires a temperaturo greatly superior to that of boiling water. But i 4 must be going on in the depths of the rooks, wheie there is no lack of imprisoned water, or of temperatures and pressures incomparably higher than our most potent experiments. It is hardly necessary to say more concerning the application of these synthetic results to questions concerning tb.B metamorphio transformation of entire regions,