A History of Science - v.3 (Williams)

NEPTUNISTS VERSUS PLUTONISTS

In the mean time, James Hutton's theory that continents wear away and are replaced by volcanic upheaval

gained comparatively few adherents. Even

the lucid Illustrations of the Huttonian Theory, which Playfair, the pupil and friend of the great Scotchman, published in 1802, did not at once prove convincing.

The world had become enamoured of the rival theory of Hutton's famous contemporary, Werner of Saxony

--the theory which taught that "in the beginning" all the solids of the earth's present crust were dissolved in the heated waters of a universal sea. Werner affirmed that all rocks, of whatever character, had been

formed by precipitation from this sea as the waters cooled; that even veins have originated in this way; and that mountains are gigantic crystals, not upheaved masses. In a word, he practically ignored volcanic action, and denied in toto the theory of metamorphosis of rocks through the agency of heat.

The followers of Werner came to be known as Neptunists; the Huttonians as Plutonists. The history of

geology during the first quarter of the nineteenth century is mainly a recital of the intemperate controversy

between these opposing schools; though it should not

be forgotten that, meantime, the members of the Geological

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The brunt of the controversy settled about the unstratified rocks--granites and their allies--which the

Plutonists claimed as of igneous origin. This contention had the theoretical support of the nebular hypothesis, then gaining ground, which supposed the

earth to be a cooling globe. The Plutonists laid great stress, too, on the observed fact that the temperature

of the earth increases at a pretty constant ratio as descent towards its centre is made in mines. But in particular

they appealed to the phenomena of volcanoes.

The evidence from this source was gathered and elaborated by Mr. G. Poulett Scrope, secretary of the Geological Society of England, who, in 1823, published a classical work on volcanoes in which he claimed that volcanic mountains, including some of the highestknown peaks, are merely accumulated masses of lava belched forth from a crevice in the earth's crust.

"Supposing the globe to have had any irregular

shape when detached from the sun," said Scrope, "the vaporization of its surface, and, of course, of its projecting angles, together with its rotatory motion on its

axis and the liquefaction of its outer envelope, would necessarily occasion its actual figure of an oblate

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spheroid. As the process of expansion proceeded in depth, the original granitic beds were first partially disaggregated, next disintegrated, and more or less

liquefied, the crystals being merged in the elastic vehicle produced by the vaporization of the water contained

between the laminae.

"Where this fluid was produced in abundance by great dilatation--that is, in the outer and highly

disintegrated strata, the superior specific gravity of the crystals forced it to ooze upward, and thus a great quantity of aqueous vapor was produced on the surface of

the globe. As this elastic fluid rose into outer space,

its continually increasing expansion must have proportionately lowered its temperature; and, in consequence,

a part was recondensed into water and sank back towards the more solid surface of the globe.

"And in this manner, for a certain time, a violent reciprocation of atmospheric phenomena must have continued--torrents of vapor rising outwardly, while equally tremendous torrents of condensed vapor, or rain, fell towards the earth. The accumulation of the latter on the yet unstable and unconsolidated surface of the globe constituted the primeval ocean. The

surface of this ocean was exposed to continued vaporization owing to intense heat; but this process, abstracting caloric from the stratum of the water below, by

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had been extreme; and particularly their mica,

which, owing to the tenuity of its plate-shaped crystals, would be most readily carried up by the ascending

fluid, and will have remained longest in suspension.

"But as the torrents of vapor, holding these various matters in solution and suspension, were forced upward, the greater part of the disintegrated crystals

by degrees subsided; those of felspar and quartz first, the mica being, as observed above, from the form of

its plates, of peculiar buoyancy, and therefore held longest in suspension.

"The crystals of felspar and quartz as they subsided, together with a small proportion of mica, would naturally arrange themselves so as to have their longest dimensions more or less parallel to the surface on

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which they rest; and this parallelism would be subsequently increased, as we shall see hereafter, by the

pressure of these beds sustained between the weight of the supported column of matter and the expansive force beneath them. These beds I conceive, when consolidated, to constitute the gneiss formation.

"The farther the process of expansion proceeded in depth, the more was the column of liquid matter lengthened, which, gravitating towards the centre of the globe, tended to check any further expansion.

It is, therefore, obvious that after the globe settled into its actual orbit, and thenceforward lost little of its enveloping matter, the whole of which began from

that moment to gravitate towards its centre, the progress of expansion inwardly would continually increase

in rapidity; and a moment must have at length arrived hen the forces of expansion and repression had reached an equilibrium and the process was stopped

from progressing farther inwardly by the great pressure of the gravitating column of liquid.

This column may be considered as consisting of different strata, though the passage from one extremity

of complete solidity to the other of complete expansion, in reality, must have been perfectly gradual.

The lowest stratum, immediately above the extreme limit of expansion, will have been granite barely

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DISAGGREGATED, and rendered imperfectly liquid by the partial vaporization of its contained water.

"The second stratum was granite DISINTEGRATED; aqueous vapor, having been produced in such abundance

as to be enabled to rise upward, partially disintegrating the crystals of felspar and mica, and superficially dissolving those of quartz. This mass would

reconsolidate into granite, though of a smaller grain than the preceding rock.

"The third stratum was so disintegrated that a greater part of the mica had been carried up by the escaping vapor IN SUSPENSION, and that of quartz in solution; the felspar crystals, with the remaining quartz and mica, SUBSIDING by their specific gravity and arranging themselves in horizontal planes.

"The consolidation of this stratum produced the gneiss formation.

"The fourth zone will have been composed of the

ocean of turbid and heated water, holding mica, etc., in suspension, and quartz, carbonate of lime, etc., in solution, and continually traversed by reciprocating bodies of heated water rising from below, and of cold

fluid sinking from the surface, by reason of their specific gravities.

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"The disturbance thus occasioned will have long retarded the deposition of the suspended particles. But this must by degrees have taken place, the quartz

grains and the larger and coarser plates of mica subsiding first and the finest last.

"But the fragments of quartz and mica were not deposited alone; a great proportion of the quartz held in SOLUTION must have been precipitated at the same time as the water cooled, and therefore by degrees lost its faculty of so much in solution. Thus was gradually

produced the formation of mica-schist, the mica imperfectly recrystallizing or being merely aggregated

together in horizontal plates, between which the quartz either spread itself generally in minute grains or unified into crystalline nuclei. On other spots, instead

of silex, carbonate of lime was precipitated, together with more or less of the nucaceous sediment, and gave rise to saccharoidal limestones. At a later period, when the ocean was yet further cooled down, rock-salt

and sulphate of lime were locally precipitated in a similar mode.

"The fifth stratum was aeriform, and consisted in great part of aqueous vapors; the remainder being a compound of other elastic fluids (permanent gases) which had been formed probably from the volatilization of some of the substances contained in the primitive

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granite and carried upward with the aqueous

vapor from below. These gases will have been either mixed together or otherwise disposed, according to

their different specific gravities or chemical affinities, and this stratum constituted the atmosphere or aerial envelope of the globe.

"When, in this manner, the general and positive expansion of the globe, occasioned by the sudden reduction

of outward pressure, had ceased (in consequence

of the REPRESSIVE FORCE, consisting of the weight of its fluid envelope, having reached an equilibrium with the EXPANSIVE FORCE, consisting of the caloric of the heated nucleus), the rapid superficial evaporation of the ocean continued; and, by gradually reducing its temperature, occasioned the precipitation of a proportionate quantity of the minerals it held in solution, particularly its silex. These substances falling to the bottom, accompanied by a large proportion of the matters held

in solution, particularly the mica, in consequence of the greater comparative tranquillity of the ocean, agglomerated these into more or less compact beds of rock (the mica-schist formation), producing the first crust or solid envelope of the globe. Upon this, other stratified rocks, composed sometimes of a mixture,

sometimes of an alternation of precipitations, sediments, and occasionally of conglomerates, were by

degrees deposited, giving rise to the TRANSITION formations.

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"Beneath this crust a new process now commenced.

The outer zones of crystalline matter having been suddenly refrigerated by the rapid vaporization and partial

escape of the water they contained, abstracted

caloric from the intensely heated nucleus of the globe. These crystalline zones were of unequal density, the expansion they had suffered diminishing from above downward.

"Their expansive force was, however, equal at all points, their temperature everywhere bearing an inverse ratio to their density. But when by the accession

of caloric from the inner and unliquefied nucleus

the temperature, and consequently the expansive force of the lower strata of dilated crystalline

matter, was augmented, it acted upon the upper and more liquefied strata. These being prevented from yielding OUTWARDLY by the tenacity and weight of the

solid involucrum of precipitated and sedimental deposits which overspread them, sustained a pressure out

of proportion to their expansive force, and were in consequence proportionately condensed, and by the continuance of the process, where the overlying strata were sufficiently resistant, finally consolidated.

"This process of consolidation must have progressed from above downward, with the increase of the expansive force in the lower strata, commencing from

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the upper surface, which, its temperature being lowest, offered the least resistance to the force of compression.

"By this process the upper zone of crystalline matter, which had intumesced so far as to allow of the escape of its aqueous vapor and of much of its mica and quartz, was resolidified, the component crystals arranging themselves in planes perpendicular to the direction of the pressure by which the mass was consolidated--that is, to the radius of the globe.

The gneiss formation, as already observed, was the result.

"The inferior zone of barely disintegrated granite, from which only a part of the steam and quartz and

none of the mica had escaped, reconsolidated in a confused or granitoidal manner; but exhibits marks of the

process it had undergone in its broken crystals of felspar and mica, its rounded and superficially dissolved

grains of quartz, its imbedded fragments (broken from

the more solid parts of the mass, as it rose, and enveloped by the softer parts), its concretionary nodules

and new minerals, etc.

"Beneath this, the granite which had been simply disintegrated was again solidified, and returned in all respects to its former condition. The temperature, however, and with it the expansive force of the inferior zone, was continually on the increase, the caloric

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