Part ii

., p. 279; Dartigues and Fleurieu de Bellevue, in the 'Journal de Physique', t. lx., p. 456; Bischof, 'Warmelchre', s. 313 und 443.

In the latter case, the crystals are formed partly in cavities and partly inclosed in the matrix. The same materials yield the most dissimilar products, a fact that is of the greatest importance in reference to the study of the nature of erupted rocks, and of the metamorphic action which they occasion. Carbonate of lime, when fused under great pressure, does not lose its carbonic acid, but becomes, when cooled, granular limestone; when the crystallization has been effected by the dry method, saccharoidal marble; while by the humid method, calcareous spar and aragonite and produced, the former under a lesser degree of temperature than the latter.*

[footnote] *Gustav Rose, in Poggend., 'Annalen.' bd. xliii., s 364.

Differences of temperature p 259 likewise modify the direction in which the different particles arrange themselves in the act of crystallization, and also affect the form of the crystal.*

[footnote] *On the dimorphism of sulphur, see Mitscherlich, 'Lehrbuch der Chemie', 55-63.

Even when a body is not in a fluid condition, the smallest particles may undergo certain relations in their various modes of arrangement, which are manifested by the different action on light.*

[footnote] *On gypsum as a uniaxal crystal, and on the sulphate of magnesia, and the oxyds of zinc and nickel, see Mitscherlich, in Poggend., 'Annalen.' bd. xi., s. 328.

The phenomena presented by devitrification, and by the formation of steel by cementation and casting -- the transition of the fibrous in the granular tissue of the iron, from the action of heat* and probably, also, by regular and long-continued concussions -- likewise throw a considerable degree of light on the geological process of metamorphism.

[footnote] *Coste, 'Versuche am Creusot uber das bruchig werden des Stabeisens.' Elie de Beaumont, 'Mem. Geol.', t. ii., p. 411.

Heat may even simultaneously induce opposite actions in crystalline bodies; for the admirable experiments of Mitscherlich have established the fact* that calcareous spar, without altering its condition of aggregation, expands in the direction of one of its axes and contracts in the other.

[footnote] * Mitscherlich, 'Ueber die Ausdehnung der Krystallisirten Korper durch die Warmelehre', in Poggend., 'Annalen', bd. x., s. 151.

If we pass from these general considerations to individual examples, we find that schist is converted, by the vicinity of Plutonic erupted rocks, into a bluish-black, glistening roofing slate. Here the planes of stratification are intersected by another system of divisional stratification, almost at right angles with the former,* and thus indicating an action subsequent to the alteration.

[footnote] * On the double system of divisional planes, see Elie de Beaumont, 'Geologie de la France', p. 41; Credner, 'Geognosie Thuringens und des Harzes', s. 40; and Romer, 'Das Rheinische Uebergangsgebirge', 1844. s. 5 und 9.

The penetration of silica causes the argillaceous schist to be traversed by quartz, transforming it, in part, into whetstone and silicious schist; the latter sometimes containing carbon, and being then capable of producing galvanic effects on the nerves. The highest degree of silicifaction of schist is that observed in ribbon jasper, a material highly valuable in the arts,* and which is produced in the Oural Mountains p 260 by the contact and eruption of augitic porphyry (at Orsk), of dioritic porphyry (at Aufschkul), or of a mass of hypersthenic rock conglomerated into spherical masses (at Bogoslowsk). At Monte Serrato, in the island of Elba, according to Frederic Hoffman, and in Tuscany, according to Alexander Brongniart, it is formed by contact with euphotide and serpentine.

[footnote] *The silica is not merely colored by peroxyd of iron, but is accompanied by clay, lime, and potash. Rose, 'Reise', bd. ii., s. 187. On the formation of jasper by the action of dioritic porphyry, augite, and by persthene rock, see Rose, bd. ii., s. 169, 187, und 192. See, also, bd. i., s. 427, where there is a drawing of the porphyry spheres between which jasper occurs, in the calcareous graywacke of Bogoslowsk, being produced by the Plutonic influence of the augitic rock; bd. ii., s. 545; and likewise Humboldt, 'Asie Centrale', t. i., p. 486.

The contact and Plutonic action of granite have sometimes made argillaceous schist granular, as was observed by Gustav Rose and myself in the Altai Mountains (within the fortress of Buchtarminsk),* and have transformed it into a mass resembling granite, consisting of a mixture of feldspar and mica, in which larger laminae of the latter were again imbedded.**

[footnote] *Rose, 'Reise nach dem Ural', bd. i., s. 586-588.

[footnote] **In respect to the volcanic origin of mica, it is important to notice that crystals of mica are found in the basalt of the Bohemian Mittelgebirge, in the lava that in 1822 was ejected from Vesuvius (Monticelli, 'Storia del Vesuvio negli Anni 1821 e 1822', 99), and in fragments of agrillaceous alte imbedded in scoriaceous basalt at Hohenfels, not far from Gerolstein, in the Eifel (see Mitscherlich, in Leonhard, 'Basalt-Gebilde', s. 244). On the formation of feldspar in argillaceous schist, through contact with porphyry, occurring between Urval and Poïet (Forez), see Dufrenoy, in 'Geol. de la France', t. i., p. 137. It is probably to a similar contact that certain schists near Paimpol, in Brittany, with whose appearance I was much struck, while making a geological pedestrian tour through that interesting country with Professor Kunth, owe their amygdaloid and cellular character, t. i., p. 234.

Most geognosists adhere, with Leopold von Buch, to the well-known hypothesis "that all the gneiss in the silurian strata of the transition formation, between the Icy Sea and the Gulf of Finland, has been produced by the metamorphic action of granite.*

[footnote] * Leopold von Buch, in the 'Abhandlungen der Akad. der Wissenschaft zu Berlin, aus dem Jahr' 1842, s. 63, and in the 'Jahrbuchern fur Wissenschaftliche Kritik Jahrg.' 1840, s. 196.

In the Alps, at St. Gothard, calcareous marl is likewise changed from granite into mica slate, and then transformed into gneiss." Similar phenomena of the formation of gneiss and mica slate through granite present themselves in the oolitic group of the Tarantaise,* in which belemnites are p 261 found in rocks, which have some claim to be considered as mica slate, and in the schistose group in the western part of the island of Elba, near the promontory of Calamita, and the Fichtelgebirge in Baireuth, between Loomitz and Markleiten.**

[footnote] * Elie de Beaumont, in the 'Annales des Sciences Naturelles', t. xv., p. 362-372. "In approaching the primitive masses of Mont Rosa, and the mountains situated to the west of Coni, we perceive that the secondary strata gradually lose the characters inherent in their mode of deposition. Frequently assuming a character apparently arising from a perfectly distinct cause, but not losing their stratification, they somewhat resemble in their physical structure a brand of half-consumed wood, in which we can follow the traces of the ligneous fibers beyond the spots which continue to present the natural characters of wood." (See, also, the 'Annales des Sciences Naturelles', t. xiv., p. 118-122, and von Dechen, 'Geognosie', s. 553.) Among the most striking proofs of the transformation of rocks by Plutonic

## action, we must place the belemites in the schists of Nuffenen (in the

Alpine valley of Eginen and in the Gries-glaciers), and the belemnites found by M. Charpentier in the so-called primitive limestone on the western descent of the Col de la Seigne, between the Enclove de Monjovet and the 'chalet' of La Lanchette, and which he showed to me at Bex in the autumn of 1822 ('Annales de Chimie', t. xxiii., p. 262).

[footnote] ** Hoffmann, in Poggend., 'Annalen', bd. xvi., s. 552, "Strate of transition argillaceous schist in the Fichtelgebirge, which can be traced for a length of 16 miles, are transformed into gneiss only at the two extremities, where they come in contact with granite. We can there follow the gradual formation of the gneiss, and the development of the mica and of the feldspathic amygdaloids, in the interior of the argillaceous schist, which indeed contains in itself almost all the elements of these substances."

Jasper, which,* as I have already remarked, is a production formed by the volcanic action of augitic porphyry, could only be obtained in small quantities by the ancients, while another material, very generally and efficiently used by them in the arts, was granular or saccharoidal marble, which is likewise to be regarded solely as a sedimentary stratum altered by terrestrial heat and by proximity with erupted rocks.

[footnote] * Among the works of art which have come down to us from the ancient Greeks and Romans, we observe that none of any size -- as columns or large vases -- are formed from jasper; and even at the present day, this substance, in large masses, is only obtained from the Ural Mountains. The material worked as jasper from the Rhubarb Mountain (Raveniaga Sopka), in Altai, is a beautiful ribboned porphyry. The word 'jasper' is derived from the Semitic languages; and from the confused description of Theophrastus ('De Lapidibus', 23 and 27) and Pliny (xxxvii., 8 and 9), who rank jasper among the "opaque gems," the name appears to have been given to fragments of 'jaspachat', and to a substance which the ancients termed 'jasponyx', which we now know as 'opal-jasper'. Pliny considers a piece of jasper eleven inches in length so rare as to require his mentioning that he had actually seen such a specimen: "Magnitudinem jaspidis undecim unciarum vidimus, formatamque inde effigem Neronis thoracatam." According to Theophrastus, the stone which he calls emerald, and from which large obelists were cut, must have been an imperfect jasper.

This opinion is corroborated by the accurate observations on the phenomena of contact, by the remarkable experiments on fusion p 262 made by Sir James Hall more than half a century ago, and by the attentive study of granitic veins, which has contributed so largely to the establishment of modern geognosy. Sometimes the erupted rock has not transformed the compact into granular limestone to any great depth from the point of contact. Thus, for instance, we meet with a slight transformation -- a penumbra -- as at Belfast, in Ireland, where the basaltic veins traverse the chalk, and, as in the compact calcareous beds, which have been

## partially inflected by the contact of syenitic granite, at the Bridge of

Boscampo and the Cascade of Conzocoli, in the Tyrol (rendered celebrated by the mention made of it by Count Mazari Peucati).*

[footnote[ *Humboldt, 'Lettre a M. Brochant de Villiers', in the 'Annales de Chimie et de Physique', t. xxiii., p. 261; Leop. von Buch, 'Geog. Briefe uber das sudliche Tyrol', s. 101, 105, und 273.

Another mode of transformation occurs where all the strata of the compact limestone have been changed into granular limestone by the action of granite, and syenitic or dioritic porphyry.*

[footnote] *On the transformation of compact into granular limestone by the

## action of granite, in the Pyrenees at the 'Montagnes de Rancie', see

Dufrenoy, in the 'Memoires Geologiques', t. ii., p. 440; and on similar changes in the 'Montagnes de l'Oisans', see Elie de Beaumont, in the 'Mem. Geolog.', t. ii., p. 379-415; on a similar effect produced by the action of dioritic and pyroxenic porphyry (the 'ophite' described by Elie de Beaumont, in the 'Geologie de la France', t. i., p. 72), between Tolosa and St. Sebastian, see Dufrenoy, in the 'Mem. Geolog.', t. ii., p. 130; and by syenite in the Isle of Skye, where the fossils in the altered limestone may still be distinguished, see Von Dechen, in his 'Geognosie', p. 573. In the transformation of chalk by contact with basalt, the transposition of the most minute particles in the processes of crystallization and granulation is the more remarkable, because the excellent microscopic investigations of Ehrenberg have shown that the particles of chalk previously existed in the form of closed rings. See Poggend., 'Annalen der Physic', bd. xxxix., s. 105; and on the rings of aragonite deposited from solution, see Gustav Rose in vol. xlii., p. 354, of the same journal.

I would here wish to make special mention of Parian and Carrara marbles, which have acquired such celebrity from the noble works of art into which they have been converted, and which have too long been considered in our geognostic collections as the main types of primitive limestone. The action of granite has been manifested sometimes by immediate contact, as in the Pyrenees,* and sometimes, as in the main land of Greece, and in the insular groups in the gean Sea, through the intermediate layers of gneiss or mica slate.

[footnote] *Beds of granular limestone in the granite at Port d'Oo and in the Mont de Labourd. See Charpentier, 'Constitution Geologique des Pyrenes', p. 144, 146.

Both cases presuppose a simultaneous but heterogeneous process of transformation. p 263 In Attica, in the island of Euboea, and in the Peloponnesus, it has been remarked, "that the limestone, when superposed on mica slate, is beautiful and crystalline in proportion to the purity of the latter substance and to the smallness of its argillaceous contents; and, as is well known, this rock, together with beds of gneiss, appears at many points, at a considerable depth below the surface, in the islands of Paros and Antiparos."*

[footnote] *Leop. von Buch, 'Descr. des Canaries', p. 394; Fiedler, 'Reise durch das Konigreich Griechenland', th. ii., s., 181, 190, und 516.

We may here infer the existence of an imperfectly metamorphosed flotz formation, if faith can be yielded to the testimony of Origen, according to whom, the ancient Eleatic, Xenophanes of Colophon* (who supposed the whole earth's crust to have been once covered by the sea), declared that marine fossils had been found in the quarries of Syracuse, and the impression of a fish (a sardine) in the deepest rocks of Paros.

[footnote] *I have previously alluded to the remarkable passage in Origen's 'Philosophumena', cap. 14 ('Opera', ed. Delarue, t. i., p. 893). From the whole context, it seems very improbable that Xenophanes meant an impression of a laurel ([Greek words]) instead of an impression of a fish ([Greek words]). Delarue is wrong in blaming the correction of Jacob Gronovius in changing the laurel into a sardel. The petrifaction of a fish is also much more probable than the natural picture of Silenus, which, according to Pliny (lib. xxxvi., 5), the quarry-men are stated to have met with in Parian marble from Mount Marpessos. 'Servius ad Virg., AEn.', vi., 471.

The Carrara or Luna marble quarries, which constituted the principal source from which statuary marble was derived even prior to the time of Augustus, and which will probably continue to do so until the quarries of Paros shall be reopened, are beds of calcareous sandstone -- macigno -- altered by Plutonic action, and occurring in the insulated mountain of Apuana, between gneiss-like mica and talcose schist.*

[footnote] *On the geognostic relations of Carrara ('The City of the Moon', Strabo, lib. v., p. 222), see Savi 'Osservazioni sui terreni antichi Toscani', in the 'Nuova Giornale de' Letterati di Pisa', and Hoffmann, in Karsten's 'Archiv fur Mineralogie', bd. vi., s. 258-263, as well as in his 'Geogn. Reise durch Italien', s. 244-265.

Whether at some points granular limestone may not have been formed in the interior of the earth, and been raised by gneiss and syenite to the surface, where it forms vein-like fissures,* is a question on which I can not hazard an opinion, owing to my own want of personal knowledge of the subject.

[footnote] *According to the assumption of an excellent and very experienced observer, Karl von Leonhard. See his 'Jahrbuch fur Mineralogie', 1834 s. 329, and Bernhard Cotta, 'Geognosie', s. 310.

p 264 According to the admirable observations of Leopold von Buch, the masses of dolomite found in Southern Tyrol, and on the Italian side of the Alps, present the most remarkable instance of metamorphism produced by massive eruptive rocks on compact calcareous beds. The formation of the limestone seems to have proceeded from the fissures which traverse it in all directions. The cavities are every where covered with rhomboidal crystals of magnesian bitter spar, and the whole formation, without any trace of strtification, or of the fossil remains which it once contained, consists only of a granular aggregation of crystals of dolomite. Talc laminae lie scattered here and there in the newly-formed rock, traversed by masses of serpentine. In the valley of the Fassa, dolomite rises perpendicularly in smooth walls of dazzling whiteness to a height of many thousand feet. It forms sharply-pointed conical mountains, clustered together in large numbers, but yet not in contact with each other. The contour of their forms recalls to mind the beautiful landscape with which the rich imagination of Leonardi da Vinci has embellished the back-ground of the portrait of Mona Lisa.

The geognostic phenomena which we are now describing, and which excite the imagination as well as the powers of the intellect, are the result of the

## action of augite porphyry manifested in its elevating, destroying, and

transforming force.*

[footnote] *Leop. von Buch, 'Geognostische Briefe an Alex. von Humboldt', 1824, s. 86 and 82; also in the 'Annalen de Chemie', t. xxiii., p. 276, and in the 'Abhandl. der Berliner Akad. aus der Jahren 1822 'und' 1823, s. 83-136; Von Dechen, 'Geognosie.' s. 574-576.

The process by which limestone is converted into dolomite is not regarded by the illustrious investigator who first drew attention to the phenomenon as the consequence of the tale being derived from the black porphyry, but rather as a transformatiion simultaneous with the appearance of this erupted stone through wide fissures filled with vapors. It remains for future inquirers to determine how transformation can have been effected without contact with the endogenous stone, where strata of dolomite are found to be interspersed in imestone. Where, in this case, are we to seek the concealed channels by which the Plutonic action is conveyed? Even here it may not, however, be necessary, in conformity with the old Roman adage, to believe "that much that is alike in nature may have been formed in wholly different ways." When we find, over widely extended parts of the earth, that two phenomena are always associated together, as, for instance, the occurrence of melaphyre p 265 and the transformation of compact limestone into a crystaline mass differing in its chemical character, we are, to a certain degree, justified in believing, where the second phenomenon is manifested unattended by the appearance of the first, that this apparent contradiction is owing to the absence, in certain cases, of some of the conditions attendant upon the exciting causes. Who would call in question the volcanic nature and igneous fluidity of basalt merely because there are some rare instances in which basaltic veins, traversing beds of coal or strata of sandstone and chalk, have not materially deprived the coal of its carbon, nor broken and slacked the sandstone, not converted the chalk into granular marble? Wherever we have obtained even a faint light to guide us in the obscure domain of mineral formation, we ought not ungratefully to disregard it, because there may be much that is still unexplained in the history of the relations of the transitions, or in the isolated interposition of beds of unaltered strata.

After having spoken of the alteration of compact carbonate of lime into granular limestone and dolomite, it still remains for us to mention a third mode of transformation of the same mineral, which is ascribed to the emission, in the ancient periods of the world, of the vapors of sulphuric acid. This transformation of limestone into gypsum is analogous to the penetration of rock salt and sulphur, the latter being deposited from sulphureted aqueous vapor. In the lofty Cordilleras of Quindin, far from all volcanoes, I have observed deposits of sulphur in fissures in gneiss, while in Sicily (at Cattolica, near Girgenti), sulphur, gypsum, and rock salt belong to the most recent secondary strata, the chalk formations.*

[footnote] *Horrman, 'Geogn. Reise', edited by Von Dechen, s. 113-119, and 380-386; Poggend., 'Annalen der Physik', bd. xxvi., s. 41.

I have also seen on the edge of the crater of Vesuvius, fissures filled with rock salt, which occurred in such considerable masses as occasionally to lead to its being disposed of by contraband trade. On both declivities of the Pyrenees, the connection of diorite and pyroxene, and colomite, gypsum, and rock salt, can not be questioned;* and here, as in the other phenomena which we have been considering, every thing bears evidence of the action of subterranean forces on the sedimentary strata of the ancient sea.

[footnote] *Dufrenoy, in the 'Memoires Geologiques', t. ii., p. 145 and 179.

There is much difficulty in explaining the origin of the beds of pure quartz, which occur in such large quantities in South America, and impart so peculiar a character to the chain of p 266 the Andes.*

[footnote] *Humboldt, 'Essai Geogn. sur le Gisement des Roches', p. 93; 'Asie Centrale', t. iii., p. 532.

In descending toward the South Sea, from Caxamarca toward Guangamarca, I have observed vast masses of quartz, from 7000 to 8000 feet in height, superposed sometimes on porphyry devoid of quartz, and sometimes on diorite. Can these beds have been transformed from sandstone, as Elie de Beaumont conjectures in the case of the quartz strata on the Col de la Poissonniere, east of Briançon?*

[footnote] *Elie de Beaumont, in the 'Annales des Sciences Naturelles', t. xv., p. 362; Murchison, 'Silurian System', p. 286.

In the Brazils, in the diamond district of Minas Geraes and St. Paul, which has recently been so accurately investigated by Clausen, Plutonic action has developed in dioritic veins sometimes ordinary mica, and sometimes specular iron in quartzose itacolumite. The diamonds of Grammagoa are imbedded in strata of solid silica, and are occasionally enveloped in laminae of mica, like the garnets found in mica slate. The diamonds that occur furthest to the north, as those discovered in 1829 at 58 degrees lat., on the European slope of the Uralian Mountains, bear a geognostic relation to the black carboniferous dolomite of Adolffskoi* and to augitic porphyry, although more accurate observations are required in order fully to elucidate this subject.

[footnote] *Rose, 'Reise nach dem Ural', bd. i., s. 364 und 367.

Among the most remarkable phenomena of contact, we must, finally, enumerate the formation of garnets in argillaceous schist in contact with basalt and dolerite (as in Northumberland and the island of Anglesea), and the occurrence of a vast number of beautiful and most various crystals, as garnets, vesuvian, augite, and ceylanite, on the surfaces of contact between the erupted and sedimentary rock, as, for instance, on the junction of the syenite of Monzon with dolomite and compact limestone.

[footnote] *Leop. von Buch, 'Briefe', s. 109-129. See also, Elie de Beaumont 'On the Contact of Granite with the Beds of the Jura', in the 'Mem. Geol.' t. ii., p. 408.

In the island of Elba, masses of serpentine, which perhaps nowhere more clearly indicate the character of erupted rocks, have occasioned the sublimation of iron glance and red oxyd of iron in fissures of calcareous sandstone.

[footnote] *Hoffman, 'Reise', s. 30 und 37.

We still daily find the same iron glance formed by sublimation from the vapors and the walls of the fissures of open veins on the margin of the crater, and in the fresh lava currents of the volcanoes of Stromboli, Vesuvius, and AEtna.*

[footnote] *On the chemical process in the formation of specular iron, see Gay Lussac, in the 'Annales de Chimie', t. xxii., p. 415, and Mitscherlich, in Poggend., 'Annalen', bd. xv., s. 630. Moreover, crystals of olivine have been formed (probaby by sublimation) in the cavities of the obsidian of Cerro del Jacal, which I brought from Mexico (Gustav Rose, in Poggend., 'Annalen', bd. x., s. 323). Hence olivine occurs in basalt, lava, obsidian, artificial scoriae in meteoric stones, in the syenite of Elfdale, and (as hyalosiderite) in the wacke of the Kaiserstuhl.

The veins that p 267 are thus formed beneath our eyes by volcanic forces, where the contiguous rock has already attained a certain degree of solidification, show us how, in a similar manner, mineral and metallic veins may have been every where formed in the more ancient periods of the world, where the solid but thinner crust of our planet, shaken by earthquakes, and rent and fissured by the change of volume to which it was subjected in cooling, may have presented many communications with the interior, and many passages for the escape of vapors impregnated with earthy and metallic substances. The arrangement of the particles in layers parallel with the margins of the beins, the regular recurrence of analogous layers on the opposite sides of the veins (on their different walls), and, finally, the elongated cellular cavities in the middle, frequently afford direct evidence of the Plutonic process of sublimation in metalliferous veins. As the traversing rocks must be of more recent origin than the traversed, we learn from the relations of stratification existing between the porphyry and the argentiferous ores in the Saxon mines (the richest and most important in Germany), that these formations are at any rate more recent than the vegetable remains found in carboniferous strata and in the red sandstone.*

[footnote] *Constantin von Veust, 'Ueber die Porphyrgebilde', 1835, s. 89-96; also his 'Belenchtung der Werner'schen Gangtheorie', 1840, s. 6; and C. von Wissenbach, 'Abbildungen merkwurdiger Gangverhaltnisse', 1836, fig. 12. The ribbon-like structure of the veins is, however, no more to be regarded of general occurrence than the periodic order of the different members of these masses.

All the facts connected with our geological hypotheses on the formation of the earth's crust and the metamorphism of rocks have been unexpectedly elucidated by the ingenious idea which led to a comparison of the slags or scoriae of our smelting furnaces with natural minerals, and to the attempt of reproducing the latter from their elements.*

[footnote] *Mitscherlich, 'Ueber die kunstliche Darstellung der Mineralien', in the 'Abhandl. der Akademie der Wiss. zu Berlin', 1822-3, s. 25-41.

In all these operations, the same affinities manifest themselves which determine chemical combinations both in our laboratories and in the interior of the earth. The most considerable part of p 268 the simple minerals which characterize the more generally diffused Plutonic and erupted rocks, as well as those on which they have exercised a metamorphic action, have been produced in a crystalline state, and with perfect identify, in artificial mineral products. We must, however, distinguish here between the scoriae accidentally formed, and those which have been designedly produced by chemists. To the former belong feldspar, mica, augite, olivine, hornblende, crystallized oxyd of iron, magnetic iron in octahedral crystals, and metallis titanium;* to the latter, garnets, idocrase, rubies (equal in hardness to those found in the East), olivine, and augite.**

[footnote] *In scoriae crystals of feldspar have been discovered by Heine in the refuse of a furnace for copper fusing, near Sangerhausen, and analyzed by Kersten (Poggend., 'Annalen', bd. xxxiii., s. 337); crystals of augite in scoriae at Sahle (Mitscherlich, in the 'Abhandl. der Akad. zu Berlin', 1822-23, s. 40); of oliving by Seifstrom (Leonhard, 'Basalt-Gebilde', bd. ii., s. 495); of mica in old scoriae of Schloss Garpenberg (Mitscherlich, in Leonhard, op. cit., s. 506); of magnetic iron in the scoriae of Chatillon sur Seine (Leonhard, s. 441); and of micaceous iron in potter's clay (Mitscherlich, in Leohnard, op. cit., s. 234). [See Ebelmer's papers in 'Ann. de Chimie et de Physique', 1847; also 'Report on the Crystalline Slags', by John Percy, M.D., F.R.S., and William Hallows Miller, M.A., 1847. Dr. Percy, in a communication with which he has kindly favored me, says that the minerals which he has found artificially produced and proved by analysis are Humboldtilite, gehlenite, olivine, and magnetic oxyd of iron, in octahedral crystals. He suggests that the circumstance of the production of gehlenite at a high temperature in an iron furnace may possibly be made available by geologists in explaining the formation of the rocks in which the natural mineral occurs, as in Fassathal in the Tyrol.] -- Tr.

[footnote] **Of minerals purposely produced, we may mention idocrase and garnet (Mitscherlich, in Poggend., 'Annalen der Physik', bd. xxxii., s. 340); ruby (Gaudin, in the 'Comptes Rendus de l'Academie de Science', t. iv.,