Cosmos: A Sketch of the Physical Description of the Universe Part 29

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

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

In descending toward the South Sea, from Caxamarca toward Guangamarca, I have observed vast ma.s.ses 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 Brianon?*

[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, ma.s.ses 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 pa.s.sages 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 a.n.a.logous 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 ma.s.ses.

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 t.i.tanium;* 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 a.n.a.lyzed by Kersten (Poggend., 'Annalen', bd. x.x.xiii., 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 a.n.a.lysis are Humboldtilite, gehlenite, olivine, and magnetic oxyd of iron, in octahedral crystals. He suggests that the circ.u.mstance 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 Fa.s.sathal in the Tyrol.] -- Tr.

[footnote] **Of minerals purposely produced, we may mention idocrase and garnet (Mitscherlich, in Poggend., 'Annalen der Physik', bd. x.x.xii., s.

340); ruby (Gaudin, in the 'Comptes Rendus de l'Academie de Science', t.

iv., Part i., p. 999); olivine and augite (Mitscherlich and Berthier, in the 'Annales de Chimie et de Physique', t. xxiv., p. 376). Notwithstanding the greatest possible similarity in crystalline form, and perfect ident.i.ty in chemical composition, existing, according to Gustav Rose, between augite and hornblende, hornblende has never been found accompanying augite in scoriae, nor have chemists ever succeeded in artificially producing either hornblende or feldspar (Mitscherlich in Poggend., 'Annalen', bd. x.x.xiii., s. 340, and Rose, 'Reise nach dem Ural', bd. ii., s. 358 und 363). See also, Beaudant, in the 'Mem. de l'Acad. des Sciences', t. viii., p. 221, and Becquerel's ingenious experiments in his 'Trait de l'Electricite,' t. i., p. 334; t.

iii., p. 218; and t. v., p. 148 and 185.

These minerals const.i.tute the main const.i.tuents of granite, gneiss, and mica schist, of basalt, dolerite, and many porphyries. The artificial production of feldspar and mica is of most especial geognostic importance with reference to the theory of the formation of gneiss by the metamorphic agency of argillaceous schist, which contains all the const.i.tuents of granite, p 269 potash not excepted.*

[footnote] *D'Aubuisson, in the 'Journal de Physique', t. lxviii., p. 128.

It would not be very surprising, therefore, as is well observed by the distinguished geognosist, Von Dechen, if we were to meet with a fragment of gneiss formed on the walls of a smelting furnace which was built of argillaceous slate and graywacke.

After having taken this general view of the three cla.s.ses of erupted, sedimentary, and metamorphic rocks of the earth's crust, it still remains for us to consider the fourth cla.s.s, comprising 'conglomerates', or 'rocks of detrius'. The very term recalls the destruction which the earth's crust has suffered, and likewise, perhaps reminds us of the process of cementation, which has connected together, by means of oxyd of iron, or of some argillaceous and calcareous substances, the sometimes rounded and sometimes angular portions of fragments. Conglomerates and rocks of detritus, when considered in the widest sense of the term, manifest characters of a double origin. The substances which enter into their mechanical composition have not been alone acc.u.mulated by the action of the waves of the sea or currents of fresh water, for there are some of these rocks the formation of which can not be attributed to the action of water.

"When basaltic islands and trachytic rocks rise on fissures, friction of the elevated rock against the walls of the fissures causes the elevated rock to be inclosed by conglomerates composed of its own matter. The granules composing the sandstones of many formations have been separated rather by friction against the erupted volcanic or Plutonic rock than destroyed by the erosive force of a neighboring sea. The existence of these friction 'conglomerates', which are met with in enormous ma.s.ses in both hemispheres, testifies the intensity of the force with which the erupted rocks have been propelled from the interior through the earth's crust. This detritus has subsequently been taken up by the waters, which have then deposited it in the strata which it still covers."*

[footnote] *Leop. von Buck, 'Geognost. Briefe', s. 75-82, where it is also shown why the new red sandstone (the 'Todtliegende' of the Thuringian flotz formation) and the coal measures must be regarded as produced by erupted porphyry.

Sandstone formations are found imbedded in all strata, from the lower silurian transition stone to the beds of the tertiary formations, superposed on the chalk. They are found on the margin of the boundless plains of the New Continent, both within and without the tropics, extending like breast-works along the ancient sh.o.r.e, against which the sea once broke its foaming waves.

p 270 If we cast a glance on the geographical distribution of rocks, and their relations in s.p.a.ce, in that portion of the earth's crust which is accessible to us, we shall find that the most universally distributed chemical substance is 'silicic acid', generally in a variously-colored and opaque form. Next to solid silicic acid we must reckon carbonate of lime, and then the combinations of silicic acid with alumina, potash, and soda, with lime, magnesia, and oxyd of iron.

The substances which we designate as 'rocks' are determinate a.s.sociations of a small number of minerals, in which some combine parasitically, as it were, with others, but only under definite relations; thus, for instance, although quartz (silica), feldspar, and mica are the princ.i.p.al const.i.tuents of granite, these minerals also occur, either individually or collectively, in many other formations. By way of ill.u.s.trating how the quant.i.tative relations of one feldspathic rock differ from another, richer in mica than the former, I would mention that, according to Mitscherlich, three times more alumina and one third more silica than that ossessed by feldspar, give the const.i.tuents that enter into the composition of mica. Potash is contained in both -- a substance whose existence in many kinds of rocks is probably antecedent to the dawn of vegetation on the earth's surface.

The order of succession, and the relative age of the different formations, may be recognized by the superposition of the sedimentary, metamorphic, and conglomerate strata; by the nature of the formations traversed by the erupted ma.s.ses, and -- with the greatest certainty -- by the presence of organic remains and the differences of their structure. The application of botanical and zoological evidence to determine the relative age of rocks -- this chronometry of the earth's surface, which was already present to the lofty mind of Hooke -- indicates one of the most glorious epochs of modern geognosy, which has finally, on the Continent at least, been emanc.i.p.ated from the sway of Semitic doctrines. Palaeontological investigations have imparted a vivifying breath of grace and diversity to the science of the solid structure of the earth.

The fossiliferous strata contain, entombed within them, the floras and faunas of by-gone ages. We ascend the stream of time, as in our study of the relations of superposition we descend deeper and deeper through the different strata, in which lies revealed before us a past world of animal and vegetable life. Far-extending disturbances, the elevation of great mountain chains, whose relative ages we are able to define, attest the p 271 destruction of ancient and the manifestation of recent organisms. A few of these older structures have remained in the midst of more recent species.

Owing to the limited nature of our knowledge of existence, and from the figurative terms by which we seek to hide our ignorance, we apply the appellation 'recent structure' to the historical henomena of transition manifested in the organisms as well as in the forms of primitive seas and of elevated lands. In some cases these organized structures have been preserved perfect in the minutest details of tissues, integument, and articulated parts, while in others, the animal, pa.s.sing over soft argillaceous mud, has left nothing but the traces of its course,* or the remains of its undigested food, as in the coprolites.**

[footnote] *[In certain localities of the new red sandstone, in the Valley of the Connecticut, numerous tridactyl markings have been occasionally observed on the surface of the slabs of stone when split asunder, in like manner as the ripple-marks appear on the successive layers of sandstone in Tilgate Forest. Some remarkably distinct impressions of this kind, at Turner's Falls (Ma.s.sachusetts), happening to attract the attention of Dr.

James Deane, of Greenfield, that sagacious observer was struck with their resemblance to the foot-marks left on the mud-banks of the adjacent river by the aquatic birds which had recenty frequented the spot. The specimens collected were submitted to Professor G. Hitchc.o.c.k, who followed up the inquiry with a zeal and success that have led to the most interesting results. No reasonable doubt now exists that the imprints in question have been produced by the tracks of bipeds impressed on the stone when in a soft state. The announcement of this extraordinary phenomenon was first made by Professor Hitchc.o.c.k, in the 'American Journal of Science' (January, 1836), and that eminent geologist has since published full descriptions of the different species of imprints which he has detected, in his splendid work on the geology of Ma.s.sachusetts. -- Mantell's 'Medals of Creation', vol. ii., p. 310. In the work of Dr. Mantell above referred to, there is, in vol.

ii., p. 815, an admirable diagram of a slab from Turner's Falls, covered with numerous foot-marks of birds, indicating the track of ten or twelve individuals of different sizes.] -- Tr.

[footnote] **[From the examination of the fossils spoken of by geologists under the name of 'Coprolites', it is easy to determine the nature of the food of the animals, and some other points; and when, as happened occasionally, the animal was killed while the process of digestion was going on, the stomach and intestines being partly filled with half-digested food, and exhibiting the coprolites actually 'in situ', we can make out with certainty not only the true nature of the food, but the proportionate size of the stomach, and the length and nature of the intestinal ca.n.a.l. Within the cavity of the rib of an extinct animal, the palaeontologist thus finds recorded, in indelible characters, some of those hieroglyphics upon which he founds his history. -- 'The Ancient World', by D. T. Ansted, 1847, p. 173.] -- Tr.