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 space 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 masses 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 passage 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
Buttmann, 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. xxxix., 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 quantities 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 class 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 space.
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 analogies -- 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
assumed 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 classifying 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 constituting 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 masses 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 mass 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, entitled '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 masses 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'; coarse or finely granular sandstones, or breccias composed
of mechanically-divided masses of the three previous species.
These four modes of formation -- by the emission of volcanic masses, as
narrow lava streams; by the action of these masses 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, accumulation, and cementation -- processes whose mode of
action has not been sufficiently well investigated.
[footnote] Darwin, 'Volcanic Islands', 1844, p. 49 and 154.
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 circumstance of a battle, and the massacre 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-shore, 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 associations 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 space,* 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
repetition of even the most minute characteristics in the periodic
stratification of the silurian strata, and in the effects of contact with
augitic masses 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
principal 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 masses of a faintly-arched, ellipsoidal form, it is covered by a
crust of shell 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 shores 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 masses of granite of Lake Kolivan,
divided into narrow parallel beds, there are numerous crystals of feldspar
and albite, and a few of titanium (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 Gisement 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 masses, which could be divided, like basalt, into
concentric layers. In the valley of Irtysch, between Buchtarminsk and
Ustkamenogorsk, granite covers transition slate for a space 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 H¨ttenwesen', 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 passing 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 masses 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 associations 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 constituents 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
space. Mesotype and nepheline constitute, 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 identity of eleolite and uepheline (the latter containing rather the
more lime), see Scheerer, in Poggend., 'Annalen', bd. xlix., s. 359-381.