Cosmos: A Sketch of the Physical Description of the Universe Part 25

In order to explain the necessity of the vicinity of the sea, recourse has been had, even in modern times, to the hypothesis of the penetration of sea water into the foci of volcanic agency, that is to say, into deep-seated terrestrial strata. When I collect together all the facts that may be derived from my own observation and the laborious researches of others, it appears to me that every thing in this great quant.i.ty of aqueous vapors, which are unquestionably exhaled from volcanoes even when in a state of rest, be derived from sea water impregnated with salt, or rather, perhaps with fresh meteoric water; or whether the expansive force of the vapors (which, at a depth of nearly 94,000 feet, is equal to 2800 atmospheres) would be able at different depths to counterbalance the hydrostatic pressure of the sea, and thus afford them, under certain conditions, a free access to the focus;* or whether the formation of metallic chlorids, the presence of chlorid of sodium in the fissures of the crater, and the frequent mixture of hydrochloric acid with the aqueous vapors, necessarily imply access of sea water; or, finally, whether the repose of volcanoes (either when temporary, or permanent and complete) depends upon the closure of the channels by which the sea or meteoric water was conveyed, or whether the absence of flames and of exhalations of hydrogen (and sulphureted hydrogen gas seems more characteristic of solfataras than of active volcanoes) is not directly at variance p 245 with the hypothesis of the decomposition of great ma.s.ses of water?**

[footnote] * Compare Gay-Lussac, 'Sur les Volcans', in the 'Annales de Chimie', t. xxii., p. 427, and Bischof, 'Warmelehre', s. 272. The eruptions of smoke and steam which have at different periods been seen in Lancerote, Iceland, and the Kurile Islands, during the eruption of the neighboring volcanoes, afford indications of the reaction of volcanic foci through tense columns of water; that is to say, these phenomena occur when the expansive force of the vapor exceeds the hydrostatic pressure.

[footnote] ** [See Daubeney 'On Volcanoes', Part iii., ch. x.x.xvi., x.x.xviii., x.x.xix.] -- Tr.

The discussion of these important physical questions does not come within the scope of a work of this nature; but, while we are considering these phenomena, we would enter somewhat more into the question of the geographical distribution of still active volcanoes. We find, for instance, that in the New World, three, viz., Jorullo, Popocatepetl, and the volcano of De la Fragua, are situated at the respective distances of 80, 132, and 196 miles from the sea-coast, while in Central Asia, as Abel Remusat* first made known to geognosists, the Thianschan (Celestial Mountains), in which are situated the lava-emitting mountain of Pe-schan, the solfatara of Urumtsi, and the still active igneous mountain (Ho-tscheu) of Turfan, lie at an almost equal distance (1480 to 1528 miles) from the sh.o.r.es of the Polar Sea and those of the Indian Ocean.

[footnote] *Abel Remusat, 'Lettre a M. Cordier', in the 'Annales de Chimie', t. v., p. 137.

Pe-schan is also fully 1360 miles distant from the Caspian Sea,* and 172 and 218 miles from the seas of Issikul and Balkasch.

[footnote] *Humboldt, 'Asie Centrale', t. ii., p. 30-33, 38-52, 70-80, and 426-428. The existence of active volcanoes in Kordofan, 540 miles from the Red Sea, has been recently contradicted by Ruppell, 'Reisen in Nubien', 1829, s. 151.

It is a fact worthy of notice, that among the four great parallel mountain chains which traverse the Asiatic continent from east to west, the Altai, the Thianschan, the Kuen-lun, and the Himalaya, it is not the latter chain, which is nearest to Kuen-lun, at the distance of 1600 and 720 miles from the sea, which have fire-emitting mountains like Aetna and Vesuvius, and generate ammonia like the volcano of Guatimala. Chinese writers undoubtedly speak of lava streams when they describe the emissions of smoke and flame, which, issuing from Pe-schan, devastated a s.p.a.ce measuring ten li* in the first and seventh centuries of our era.

[footnote] *[A 'li' is a Chinese measurement, equal to about one thirtieth of a mile.] -- Tr.

Burning ma.s.ses of stone flowed, according to their description "like thin melted fat." The facts that have been enumerated, and to which sufficient attention has not been bestowed, render it probable that the vicinity of the sea, and the penetration of sea water to the foci of volcanoes, are not absolutely necessary to the eruption of p 246 subterranean fire, and that littoral situations only favor the eruption by forming the margin of a deep sea basin, which, covered by strata of water, and lying many thousand feet lower than the interior continent, can offer but an inconsiderable degree of resistance.

The present active volcanoes, which communicate by permanent craters simultaneously with the interior of the earth and with the atmosphere, must have been formed at a subsequent period, when the upper chalk strta and all the tertiary formations were already present: this is shown to be the fact by the trachytic and basaltic eruptions which frequently form the walls of the crater of elevation. Melaphyres extend to the middle tertiary formations, but are found already in the Jura limestone, where they break through the variegated sandstone.*

[footnote] *Dufrenoy et Elie de Beaumont, 'Explication de la Carte Geologique de la France', t. i., p. 89.

We must not confound the earlier outpourings of granite, quartzose porphyry, and euphotide from temporary fissures in the old transition rocks with the present active volcanic craters.

The extinction of volcanic activity is either only partial -- in which case the subterranean fire seeks another pa.s.sage of escape in the same mountain chain -- or it is total, as in Auvergne. More recent examples are recorded in historical times, of the total extinction of the volcano of Mosychlos,*

on the island sacred to Hephaestos (Vulcan), whose "high whirling flames"

were known to Sophocles; and of the volcano of Medina, which according to Burckhardt, still continued to pour out a stream of lava on the 2d of November, 1276.

[footnote] *Sophocl., 'Philoct.', v. 971 and 972. On the supposed epoch of the extinction of the Lemnian fire in the time of Alexander, compare b.u.t.tmann, in the 'Museum der Alterhumswissenschaft', bd. i., 1807, s. 295; Dureau de la Malle, in Malte-Brun, 'Annales des Voyages', t. ix., 1809, p.

5; Ukert in Bertuch, 'Geogr. Ephemeriden', bd. x.x.xix., 1812, s. 361; Rhode, 'Res Lemnicae', 1829, p. 8; and Walter, 'Ueber Abnahame der Vulken.

Thatigkeit in Historischen Zeiten', 1844, s. 24. The chart of Lemmos, constructed by Choiseul, makes it extremely probable that the extinct crater of Mosychlos, and the island of Chryse, the desert habitation of Philoctetes (Otfried Muller, 'Minyer', s. 300), have been long swallowed up by the sea.

Reefs and shoals, to the northeast of Lemnos, still indicate the spot where the Aegean Sea once possessed an active volcano like Aetna, Vesuvius, Stromboli, and Volcano (in the Lipari Isles).

Every stage of volcanic activity, from its first origin to its extinction, is characterized by peculiar products; first by ignited scoriae, streams of lava consisting of trachyte, pyroxene, and obsidian, and by rapilli and tufaceous ashes, accompanied by the development p 247 of large quant.i.ties of pure aqueous vapor; subsequently, when the volcano becomes a solfatara, by aqueous vapors mixed with sulphureted hydrogen and carbonic acid gases; and, finally, when it is completely cooled, by exhalations of carbonic acid alone. There is a remarkable cla.s.s of igneous mountains which do not eject lava, but merely devastating streams of hot water,* impregnated with burning sulphur and rocks reduced to a state of dust (as, for instance, the Galungung in Java); but whether these mountains present a normal condition, or only a certain transitory modification of the volcanic process, must remain undecided until they are visited by geologists possessed of a knowledge of chemistry in its present condition.

[footnote] *Compare Reinwardt and Hoffmann, in Poggendorf's 'Annalen', bd.

xii., s. 607; Leop. von Buch, 'Descr. des Iles Canaries', p. 424-426. The eruptions of argillaceous mud at Carguairazo, when that volcano was destroyed in 1698, the Lodazales of Igualata, and the Moya of Pelileo -- all on the table-land of Quito -- are volcanic phenomena of a similar nature.

I have endeavored in the above remarks to furnish a general description of volcanoes -- comprising one of the most important sections of the history of terrestrial activity -- and I have based my statements partly on my own observations, but more in their general bearing on the results yielded by the labors of my old friend, Leopold von Buch, the greatest geognosist of our own age, and the first who recognized the intimate connection of volcanic phenomena, and their mutual dependence upon one another, considered with reference to their relations in s.p.a.ce.

Volcanic action, or the reaction of the interior of a planet on its external crust and surface, was long regarded only as an isolated phenomenon, and was considered solely with respect to the disturbing action of the subterranean force; and it is only in recent times that -- greatly to the advantage of geognostical views based on physical a.n.a.logies -- volcanic forces have been regarded as 'forming new rocks, and transforming those that already existed'. We here arrive at the point to which I have already alluded, at which a well-grounded study of the activity of volcanoes, whether igneous or merely such as emit gaseous exhalations, leads us, on the one hand, to the mineralogical branch of geognosy (the science of the texture and the succession of terrestrial strata), and, on the other, to the science of geographical forms and outlines -- the configuration of continents and insular groups elevated above the level p 248 of the sea. This extended insight into the connection of natural phenomena is the result of the philosophical direction which has been so generally a.s.sumed by the more earnest study of geognosy. Increased cultivation of science and enlargement of political views alike tend to unite elements that had long been divided.

This material taken from pages 248-

COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 by Alexander von Humboldt

Translated by E C Otte

from the 1858 Harper & Brothers edition of Cosmos, volume 1 --------------------------------------------------

p 248

If, instead of cla.s.sifying rocks according to their varieties of form and superposition into stratified and unstratified, schistose and compact, normal and abnormal, we investigate those phenomena of formation and transformation which are still going on before our eyes, we shall find that rocks admit of being arranged according to four modes of origin.

'Rocks of eruption', which have issued from the interior of the earth either in a state of fusion from volcanic action, or in a more or less soft, viscous condition, from Plutonic action.

'Sedimentary rocks', which have been precipitated and deposited on the earth's surface from a fluid, in which the most minute particles were either dissolved or held in suspension const.i.tuting the greater part of the secondary (or flotz) and tertiary groups.

'Transformed or metamorphic rocks',* in which the internal texture and the mode of stratification have been changed, either p 249 by contact or proximity with a Plutonic or volcanic endogenous rock of eruption,** or, what is more frequently the case, by a gaseous sublimation of substances*** which accompany certain ma.s.ses erupted in a hot, fluid condition.

[footnote] *[As the doctrine of mineral metamorphism is now exciting very general attention, we subjoin a few explanatory observations by the 'New Philos. Journ.', Jan., 1848: "In its widest sense, mineral metamorphism means every change of aggregation, structure, or chemical condition which rocks have undergone subsequently to their deposition and stratification, or the effects which have been produced by other forces than gravity and cohesion. There fall under this definition, the discoloration of the surface of black limestone by the loss of carbon; the formation of brownish-red crusts on rocks of limestone, sandstone, many slate structures, serpentine, granite, etc., by the decomposition of iton pyrites, or magnetic iron, finely disseminated in the ma.s.s of the rock; the conversion of anhydrite into gypsum, in consequence of the absorption of water; the crumbling of many granites and porphyries into gravel, occasioned by the decomposition of the mica and feldspar. In its more limited sense, the term metamorphic is confined to those changes of the rock which are produced, not by the effect of the atmosphere or of water on the exposed surfaces, but which are produced, directly or indirectly, by agencies seated in the interior of the earth. In many cases the mode of change may be explained by our physical or chemical theories, and may be viewed as the effect of temperature or of electro-chemical actions. Adjoining rocks, or connecting communications with the interior of the earth, also distinctly point out the seat from which the change proceeds. In many other cases the metamorphic process itself remains a mystery, and from the nature of the products alone do we conclude that such a metamorphic action has taken place.] -- Tr.

[footnote] ** In a plan of the neighborhood of Tezcuco, Totonilco, and Moran ('Atlas Geographique et Physique', pl. vii.), which I originally (1803) intended for a work which I never published, ent.i.tled 'Pasigrafia Geognostica destinada al uso de los Jovenes del Colegio de Mineria de Mexico', I names (in 1832) the Plutonic and volcanic eruptive rocks 'endogenous' (generated in the interior), and the sedimentary and flotz rocks 'exogenous' (or generated externally on the surface of the earth).

Pasiward, [upward arrow] and the latter by the same symbol directed downward [downward arrow]. These signs have at least some advantage over the ascending lines, which in the older systems represent arbitrarily and ungracefully the horizontally ranged sedimentary strata, and their penetration through ma.s.ses of basalt, porphyry, and syenite. The names proposed in the pasigraphico-geognostic plan were borrowed from De Candolle's nomenclature, in which 'endogenous' is synonymous with monocotyledonous, and 'exogenous' with dicotyledonous plants. Mohl's more accurate examination of vegetable tissues has, however, shown that the growth of monocotyledons from within, and dicotyledons from without, is not strictly and generally true for vegetable organisms (Link, 'Elementa Philosophiae Botanicae', t. i., 1837, p. 287; Endlicher and Unger, 'Grundzugeder Botanik', 1843, s. 89; and Jussieu, 'Traite de Botanique', t.

i., p. 85). The rocks which I have termed endogenous are characteristically distinguished by Lyell, in his 'Principles of Geology', 1833, vol. iii., p.

374, as "nether-formed" or "hypogene rocks."

[footnote] *** Compare Leop. von Buch, 'Ueber Dolomit als Gebirgsart', 1823, s. 36; and his remarks on the degree of fluidity to be ascribed to Plutonic rocks at the period of their eruption, as well as on the formation of gneiss from schist, through the action of granite and of the substances upheaved with it, to be found in the 'Abhandl. der Akad. der Wissensch. zu Berlin'

for the year 1842, s. 58 und 63, and in the 'Jahrbuch fur Wissenschaftliche Kritik', 1840, s. 195.

'Conglomerates'; coa.r.s.e or finely granular sandstones, or breccias composed of mechanically-divided ma.s.ses of the three previous species.

These four modes of formation -- by the emission of volcanic ma.s.ses, as narrow lava streams; by the action of these ma.s.ses on rocks previously hardened; by mechanical separation or chemical precipitation from liquids impregnated with carbonic acid; and, finally, by the cementation of disintegrated rocks of heterogeneous nature -- are phenomena and formative processes which must merely be regarded as a faint reflection of that more energetic activity which must have characterized the chaotic condition of the earlier world under wholly different conditions of pressure and at a higher temperature, not only in the whole crust of the earth, but likewise in the more p 250 extended atmosphere, overloaded with vapors. The vast fissures which were formerly open in the solid crust of the earth have since been filled up or closed by the protrusion of elevated mountain chains, or by the penetration of veins of rocks of eruption (granite, porphyry, basalt, and melaphyre); and while, scarcely more than four volcanoes remaining through which fire and stones are erupted, the thinner, more fissured, and unstable crust of the earth was anciently almost every where covered by channels of communication between the fused interior and the external atmosphere.

Gaseous emanations rising from very unequal depths, and therefore conveying substances differing in their chemical nature, imparted greater activity to the Plutonic processes of formation and transformation. The sedimentary formations, the deposits of liquid fluids from cold and hot springs, which we daily see producing the travertine strata near Rome, and near Hobart Town in Van Diemen's Land, afford but a faint idea of the flotz formation. In our seas, small banks of limestone, almost equal in hardness at some parts to Carrara marble,* are in the course of formation, by gradual precipitation, acc.u.mulation, and cementation -- processes whose mode of action has not been sufficiently well investigated.

[footnote] Darwin, 'Volcanic Islands', 1844, p. 49 and 154.