« ПредыдущаяПродолжить »
Ar. VIII. The Transactions of the Royal Irish Academy,
Vol. VIII. 4to. pp. 600. Dublin. 1802. London, Payne
and Mackinlay ; Price il. 43. Boards. The contents of this volume are arranged in those depart
ments in which the Society usually distribute their papers; and we shall continue to analyse them in the same order, commencing with the class of
SCIENCE Observations on the Proofs of the Huttonian Theory of the Earth, adduced by Sir James Hall, Bart. By Richard Kirwan, Esq. LL.D. F.R.S. & P.R.I.A.-In the third and fifth volumes of the Edinburgh Transactions, Sir James Hall attempted, by arguments and experiments, to invalidate some of the positions laid down by Mr. Kirwan, in his explanation of Dr. Hutton's Theory of the Earth. The present paper is therefore written with the view of examining the force of the reasoning employed by Sir James, as well as of determining the consequences fairly deducible from his experiments. Some difficulties had been started against the opinion that granite was ever in a state of fusion, from the feltspar contained in it being, though the most fusible of the two substances, found in this stone with its crystals regularly defined, while the quartz formed a confused and irregular mass, moulded on the crystals of feltspar; and Sir James replied to them by arguments which Mr. K. here endeavours to refute. As the principal circumstances, however, on which Sir James rests his opinions respecting the subject of granite, depend on some experiments on whin, we shall immediately pass on to them. Whin, it may be ob. served, comprehends in Scotland, grunstein, basalt, trap, wacken, and porphyry; stones in which (except the last) none of the component ingredients are found regularly crystallized. Grunstein, a compound of feltspar and hornblende, intimately mixed with each other, but imperfectly and confusedly crystallized in minute grains, was the subject of the experiments here related.
• This substance,' says the author : Sir James vitrified by a strong heat and subsequent rapid cooling. A fragment of the glass thug produced being introduced under a narrow muffle and heated to 21° in one minute became so soft as to yield readily to the pressure of an iron rod, but after a second minute it became quite hard though the temperaturę had been stationary; the substance thus hardened under: went a thorough change, it lost its vitreous character, its fracture was like that of porcelain (that is even) and it was fusible only in a heat of 31°. In another experiment he found this change to take place even before the glass was in perfect fusion ; for while both ends of a
fragment of this glass were supported on rests of clay, it was found not to sink down between them until the heat was raised to 30°.-10 another experiment he found the consolidation which he (improperly as I think) calls crystallization, to take place even while the heat was gradually increased, and the substance still so viscid as to retain the original shape of the fragments.-In another experiment where the glass was slowly cooled; its texture was found completely to resemble that of whinstone, the fracture was rough, stony, and crystalline, with a number of shining facettes interspersed through the mass, and a few crystals in the cavities produced by air bubbles.'
In order to shew that these experiments are deceitful in the conclusions to which they lead, the author compares the discriminating characters of natural whin with those of the artifi. cial:
imo, The natural whins,' says he, particularly amygdaloids (vulgarly called toadstones) frequently contain calcareous spar and zeolyte ; now as the former contains fixed air, and the latter a nutable proportion of water, I hardly think Sir James, who professes not to agree with Dr. Hutton in all points, will allow these to havç been vitrified or fused.
• 2do, The natural whins, according to Dr. Kennedy's statement, lose five per cent. of water and other volatile matter when heated to redness. It is not said whether the artificial lose any part of their weight by such treatment, but it is plain they would not, since even the lavas of Catania and Piedemont, though of antient date, lost none, as Dr. Kennedy expressly notices, and have thus afforded an excellent criterion for distinguishing the long contested origination of these substances.
! 3tio, As Sir James has neglected giving a complete account of the external characters of the natural whins, which were the subject of his experiments, as also of regenerated or artificial whins derived from them, and as I have not myself seen them, it is difficult for me to compare them with each other, and would indeed be impossible if some account of them had not been given by Mr. Pictet in his valu. able Journal Britannique, copied into the 5th Vol. of the new Rozier's Journal, p. 313. It is the result of the examination both of the natural and artificial whins by the Society of Natural History at Geneva.
i As to the natural grunstein, No. 1. they remark that it betrays not the least mark of an igneous origin; but that the whins which Sir James produced from it had every distinctive character of a lava, and even of a porous lava.
« The basalt (or rather trapp) on which the castle of Edinburgh stands is of a compact structure ; the artificial produced from it, Sir Jamės tells us, so greatly resembles it both in colour and texture that it would be difficult or perhaps impossible to distinguish them, but for a few minute air bubbles, distinguishable in the artificial. Neptunists will
, however, consider this as a leading character of distinction. The mineralogists of Geneva add, that the colour of the artificial is deeper, and its hardness greater than that of the natural. If the specific
gravity and other characters of both were given, it is probable that other differences might be perceived. It is only in these characters that any difference can be expected, as the internal composition must be the same in both.
• Of the remaining artificial whins I can give no account, their external characters having been omitted ; I cannot, however, pass over the general inferences that Sir James deduces from his experiments, namely, “ that the arguments against the subterraneous fusion of whinstone, derived from its stony character, seem now to be fully refuted ;" for, not to repeat what has been already said, that many of them contain substances whose existence is incompatible with that hypothesis, I must farther add that the upright state in which many of them exist, for instance, the basaltic pillars of Stiffa, and of the Giants Causeway, and of many other countries, the basis they rest on, sometimes granite, sometimes gneis, sometimes coal or limestone, and the total absence of all signs of the operation of fire, forbid us to entertain any doubt of their production in the moist way. Nay, the college of Dublin now possesses fragments of basaltic pillars in which marine shells are imbedded ; if such evidence can be resisted it is in vain to seek for greater.'
An Illustration and Confirmation of some Facts mentioned in an Essay on the Primitive State of the Globe (in Vol. VI. of these Transactions). By the Same.- In the essay which the present paper is intended to illustrate, the author considered it as an established fact, that the emersion of some portion of land from the primæval ocean occurred previously to the creation of fishes. The circumstance on which he rested for the proof of this fact, and which accorded with the Mosaic account of the subject, was that
• No petrifactions were found imbedded and incorporated in masses of stone in such countries as were elevated 8500 or gooo feet above the actual level of the sea ; for instance, in the great Tartarian plat. form and the elevated regions of Siberia, though in all inferior regions of the same extent such petrifactions were abundantly found, at least in limestones; but even in these none were found in those elevated tracts, as was proved by the testimonies of all the philosophic tra. yellers who have traversed and examined them.
• To repel this proof of the Mosaic account, it has been replied by the laborious, learned, and eloquent writer of the Histoire du Monde primitif and others, that the keen air existing in these elevated regions had long ago decomposed and consumed the shells that might have been there deposited ; but as the stones still remain, it is evident that the shells incorporated in their interior must also have remained, if any such were ever contained in them.'
It is, however, asserted by Don Ulloa, in his Mémoires Philosophiques, and by Gentil, in the Mem. Par. 1771, that shells have been found in the Cordelieres at the height of 13,869 English feet above the level of the sea. That the height was
so great as is here stated, the author attempts to disprove, by the evidence of other writers; as well as from the probable inaccuracy of the barometers by which the former gentlemen made their calculation :--but, let the height be what it may, Mr. Kirwan adds,
• It is certain that these shells were deposited there after the emer. sion of land from the primitive ocean, and consequently by a subsequent deluge ; for Don Ulioa expressly tells us, that in the same rocks in which these stells are found, petrified wood is also found, Mem. Philosophiques, p. 372. This wood must have grown on dry land, and must have been floated when the shells were deposited, since both are found in the same rocks. It must have been brought thither by a deluge, as no wood can at present grow there, as Don Ulloa also attests. The shells are for the most part bivalves, which geologists allow to form petrifactions of the most modern date.'
An Essay on the Declivities of Mountains. By the Same.-It is a fact in geology, established by numerous observations, that, in mountains which extend from north to south, the Western flank is the steepest, and the eastern the gentlest; and that, where they run east and west, the southern declivity is the steepest, and the northern the most gentle. In this paper, the author brings forwards the principal facts in support of that deduction; and he considers it as clearly proved that mountains are not mere fortuitous eruptions, unconnected with transactions on the surface of the earth :' since it has been uniformly found by Foster that the north and north-west sides are gently covered, and connected with secondary strata, in which organic remains abound,' while the south and southwest sides are almost invariably steep.
In order to account for this nearly universal allotment of unequal declivities to opposite points, and for the greatest being directed to the west and south, and the gentlest to the east and north, Mr. K. supposes,
ist, That all mountains were formed while covered with water. ' 2d, That the earth was universally covered with water at two different ras, that of the creation, and that of the Noachian deluge.
3d, That in the first æra we must distinguish two different periods, that which preceded the appearance of dry land, and that which succeeded the creation of fish, but before the sea had been reduced nearly to its present level; during the former, the primæval mountains were formed, and during the last, most of the secondary mountains and strata were formed.
**• 4th, That all mountains extend either from E. to W. or from Ñ. to S., or in some intermediate direction between these 'cardinal points"(!!) which need not be particularly mentioned here, as the same species of reasoning niust be applied to them, as to those to. whose aspect they approack most.
· These preliminary circumstances being noticed, we are next to observe that during the first æra, this vast mass of water moved in
two general directions, at right angles with each other, the one from E, to W. which needs not to be proved, being the course of tides which still continue, but were in that ocean necessarily stronger and higher than at present: the other from N. to S. the water tending to those vast abysses then formed in the vicinity of the south pole, as shewn in my former essays. Before either motion could be propagated, a considerable time must have elapsed.
• Now the primæval mountains formed' at the commencement of the first æra, and before this doubic direction of the waters took place, must have opposed a considerable obstacle to the motion of that fluid in the sense that crossed that of the direction of these mountains. Thus the mountains that stretch from N. to S. must, have opposed the motion of the waters ftom E. to W.: this opposition, diminishing the motion of that fluid, disposed it to suffer the carthy particles with which in those early periods it must have been impregnated to crystallize, or be deposiied on these eastern flanks, and particularly on those of the highest mountains, for over the lower it could easily pass ; these depositions, being incessantly repeated at heights gradually diminishing as the level of the waters gradually lowered, must have rendered the eastern declivities or descents, gentle, gradual, and moderate, while the western sides receiving no such accessions from depositions must have remained steep and craggy
• Again, the primæval mountains that run from E. to W. by opposing a similar resistance to the course of the waters from N. to S. must have occasioned similar depositions on the northern sides of these mountains against which these waters impinged, and thus smoothed them.
· Where mountains intersect each other in an oblique direction, the N. E. side of one range being contiguous to the S. W, flanks of another range, there the afflux of adventitious particles on the north-east side of the one, must have frequently extended to the S. W. side of the other, particularly if that afflux were strong and copious.'
Chemical and Mineralogical Nomenclature. By the Same. This article is written with the intention of vindicating its au. thor from the censure which has been thrown on him by some philosophers, for retaining a few of the old denominations, where the new names appeared to him exceptionable. He enters into a minute examination of the principles adopted by the French chemists in the formation of their nomenclature, and is of opinion that they are in many instances defective.
Description of an Apparatus for impregnating Water and other Substances strongly with Carbonic Acid Gas. By the Rev. Gilbert Austin, M.R.I.A.; with an Engraving.- In this apparatus, a condensing syringe is fixed to the tube, by which the vessel inclosing the gas is connected to that which contains the water to be impregnated. By means of this syringe, and of 8