Cosmos: A Sketch of the Physical Description of the Universe Part 26

The Sicilian coast, the island of Ascension, and King George's Sound in Australia, are instances of this mode of formation. On the coasts of the Antilles, these formations of the present ocean contain articles of pottery, and other objects of human industry, and in Guadaloupe even human skeletons of the Carib tribes.*

[footnote] *[In most instances the bones are dispersed; but a large slab of rock, in which considerable portion of the skeleton of a female is embedded, is preserved in the British Museum. The presence of these bones has been explained by the circ.u.mstance of a battle, and the ma.s.sacre of a tribe of Gallibis by the Caribs, which took place near the spot in which they are found, about 120 years ago; for, as the bodies of the slain were interred on the sea-sh.o.r.e, their skeletons may have been subsequently covered by sand-drift, which has since consolidated into limestone. Dr. Moultrie, of the Medical College, Charleston, South Carolina, U.S., is, however, of opinion that these bones did not belong to individuals of the Carib tribe, but of the Peruvian race, or of a tribe possessing a similar craniological development.] --Tr.

The negroes of the French colonies designate these formations by the name of 'Maconne-bon-Dieu'.*

Moreau de Jonnes, 'Hist. Phys. des Antilles', t. i., p. 136, 138, and 543; Humboldt, 'Relation Historique', t. iii., p. 367.

A small colitic bed, formed in Lancerote, one of the Canary Islands, and which, notwithstanding p 251 its recent formation, bears a resemblance to Jura Limestone, has been recognized as a product of the sea and of tempests.*

[footnote] *Near Teguiza. Leop. von Buch, 'Canarische Inseln', s. 301.

Composite rocks are definite a.s.sociations of certain crytonostic, simple minerals, as feldspar, mica, solid silex, augite, and nepheline. Rocks very similar to these consisting of the same elements, but grouped differently, are still formed by volcanic processes, as in the earlier periods of the world. The character of rocks, as we have already remarked is so independent of geographical relations of s.p.a.ce,* that the geologist recognizes with surprise, alike to the north or the south of the equator, in the remotest and most dissimilar zones, the familiar aspect, and the repet.i.tion of even the most minute characteristics in the periodic stratification of the silurian strata, and in the effects of contact with augitic ma.s.ses of eruption.

[footnote] *Leop. von Buch, op. cit., p. 9.

We will now enter more fully into the consideration of the four modes in which rocks are formed -- the four phases of their formative processes manifested in the stratified and unstratified portions of the earth's surface; thus, in the 'endogenous' or 'erupted rocks', designated by modern geognosists as compact and abnormal rocks, we may enumerate the following princ.i.p.al groups as immediate products of terrestrial activity:

1. 'Granite and syenite' of very different respective ages; the granite is frequently the more recent,* traversing the syenite in veins, and being, in that case, the active upheaving agent. "Where the granite occurs in large, insulated ma.s.ses of a faintly-arched, ellipsoidal form, it is covered by a crust of sh.e.l.l cleft into blocks, instances of which are met with alike in the Hartz district, in Mysore, and in Lower Peru.

[footnote] *Bernhard Cotta, 'Geognosie', 1839, s. 273.

This surface of the granite, owing to the great expansion that accompanied its first upheaval."*

[footnote] *Leop. von Buch, 'Ueber Granit and Gneiss', in the 'Abhandl. der Berl. Akad.' for the year 1842, s. 60.

Both in Northern Asia,* on the charming and romantic sh.o.r.es of the Lake of Kolivan, on the northwest declivity of p. 252 the Altai Mountains, and at Las Trincheras, on the slop of the littoral chain of Caraccas,** I have seen granite divided into ledges, owing probably to a similar contraction, although the divisions appeared to penetrate far into the interior.

[footnote] * In the projecting mural ma.s.ses of granite of Lake Kolivan, divided into narrow parallel beds, there are numerous crystals of feldspar and albite, and a few of t.i.tanium (Humboldt, 'Asie Centrale', t. i., p. 295, Gustav Rose, 'Reise mach dem Ural', bd. i., s. 524).

[footnote] *Humboldt, 'Relation Historique', t. ii., p. 99

Further to the south of Lake Kolivan, toward the boundaries of the Chinese province Ili (between Buchtarminsk and the River Narym), the formation of the erupted rock, in which there is no gneiss, is more remarkable than I ever observed in any other part of the earth. The granite, which is always covered with scales and characterized by tabular divisions, rises in the steppes, either in small hemispherical eminences, scarcely six or eight feet in height, or like basalt, in mounds, terminating on either side of their bases in narrow streams.*

[footnote] ** See the sketch of Biri-tau, which I took from the south side, where the Kirghis tents stood, and which is given in Rose's 'Reise', bd. i., s. 584. On spheres of granite scaling off concentrically, see my 'Relat.

Hist.', t. ii., p. 497, and 'Essai Geogn. sur les Gis.e.m.e.nt des Roches', p.

78.

At the cataracts of the Orinoco, as well as in the district of the Fichtelgebirge (Seissen), in Galicia, and between the Pacific and the highlands of Mexico (on the Papagallo), I have seen granite in large, flattened spherical ma.s.ses, which could be divided, like basalt, into concentric layers. In the valley of Irtysch, between Buchtarminsk and Ustkamenogorsk, granite covers transition slate for a s.p.a.ce of four miles,*

penetrating into it from above in narrow, variously ramified, wedge-like veins.

[footnote] *Humboldt, 'Asie Centrale', t. i., p. 299-311, and the drawings in Rose's 'Reise', bd. i., s. 611, in which we see the curvature in the layers of granite which Leop. von Buch has pointed out as chracteristic.

I have only instanced these peculiarities in order to designate the individual character of one of the most generally diffused erupted-rocks.

As granite is superposed on slate in Siberia and in the Departement de Finisterre (Isle de Mihau), so it covers the Jura limestone in the mountains of Oisons (Fermonts), and syenite, and indirectly also chalk, in Saxony, near Weinbohla.*

[footnote] *This remarkable superposition was first described by Weiss in Krsten's 'Archiv fur Bergbau und Httenwesen', bd. xvi., 1827, s. 5.

Near Mursinsk, in the Uralian district, granite is of a drusous character, and here the pores, like the fissures and cavities of recent volcanic products, inclose many kinds of magnificent crystals, especially beryls and topazes.

2. 'Quartzose porphyry' is often found in the relation of veins to other rocks. The base is generally a finely granular mixture of the same elements which occur in the larger imbedded p 253 crystals. In granitic porphyry that is very poor in quartz, the feldspathic base is almost granular and laminated.*

[footnote] *Dufrenoy et Elie de Beaumont, 'Geologie de la France', t. i., p. 130.

3. 'Greenstones, Diorite', are granular mixtures of white albite and blackish-green hornblende, forming dioritic porphyry when the crystals are deposited in a base of denser tissue. The greenstones, either pure, or inclosing laminae of diallage (as in the Fichtelgebirge), and pa.s.sing into serpentine, have sometimes penetrated, in the form of strata, into the old stratified fissures of green argillaceous slate, but they more frequently traverse the rocks in veins, or appear as globular ma.s.ses of greenstone, similar to domes of basalt and porphyry.*

[footnote] *These intercalated beds of diorite play an important part in the mountain district of Nailau, near Steben, where I was engaged in mining operations in the last century, and with which the happiest a.s.sociations of my early life are connected. Compare Hoffmann, in Poggendorf's 'Annalen', bd. xvi., s. 558.

'Hypersthene rock' is a granular mixture of labradorite and hypersthene.

'Euphotide' and serpentine, containing sometimes crystald of augite and uralite instead of diallage, are thus nearly allied to another more frequent, and I might almost say, more 'energetic' eruptive rock -- augitic porphyry.*

[footnote] *In the southern and Bashkirian portion of the Ural. Rose, 'Reise', bd. ii., s. 171.

'Melaphyre', augitic, uralitic, and oligoklastic porphyries. To the last-named species belongs the genuine 'verd-antique', so celebrated in the arts.

'Basalt', containing olivine and const.i.tuents which gelatinize in acids; phonolithe (porphyritic slate), trachyte, and colerite; the first of these rocks is only paartially, and the second always, divided into thin laminae, which give them an appearance of stratification when extended over a large s.p.a.ce. Mesotype and nepheline const.i.tute, according to Girard, an important part in the composition and internal texture of basalt. The nepheline contained in basalt reminds the geognosist both of the miascite of the Ilmen Mountains in the Ural,* which has been confounded with granite, and sometimes contains zirconium, and of the pyroxenic nepheline discovered by Gumprecht near Lobau and Chemnitz.

[footnote] *G. Rose, 'Reise nach dem Ural', bd. ii., s. 47-52. Respecting the ident.i.ty of eleolite and uepheline (the latter containing rather the more lime), see Scheerer, in Poggend., 'Annalen', bd. xlix., s. 359-381.