James Hutton, the notable Scotch geologist, was born at Edinburgh
on June 3, 1726. In 1743 he was apprenticed to a Writer to the
Signet; but his apprenticeship was of short duration and in the
following year he began to study medicine at Edinburgh University,
and in 1749 graduated as an M.D. Later he determined to study
agriculture, and went, in 1752, to live with a Norfolk farmer to
learn practical farming. He did not devote himself entirely to
agriculture, but gave a considerable amount of his time to chemical
and geological researches. His geological researches culminated in
his great work, "The Theory of the Earth," published at Edinburgh
in 1795. In this work he propounds the theory that the present
continents have been formed at the bottom of the sea by the
precipitation of the detritus of former continents, and that the
precipitate had been hardened by heat and elevated above the sea by
the expansive power of heat. He died on March 26, 1797. Other works
are his "Theory of Rain," "Elements of Agriculture," "Natural
Philosophy," and "Nature of Coal."
_I.--Origin and Consolidation of the Land_
The solid surface of the earth is mainly composed of gravel, of
calcareous, and argillaceous strata. Sand is separated by streams and
currents, gravel is formed by the attrition of stones agitated in water,
and argillaceous strata are deposited by water containing argillaceous
material. Accordingly, the solid earth would seem to have been mainly
produced by water, wind, and tides, and this theory is confirmed by the
discovery that all the masses of marble and limestone are composed of
the calcareous matter of marine bodies. All these materials were, in the
first place, deposited at the bottom of the sea, and we have to
consider, firstly, how they were consolidated; and secondly, how they
came to be dry land, elevated above the sea.
It is plain that consolidation may have been effected either through
the concretion of substances dissolved in water or through fusion by
fire. Consolidation through the concretion of substances dissolved in
the sea is unlikely, for, in the first place, there are strata, such as
siliceous matter, which are insoluble, and which could not therefore
have been in solution; and, in the second place, the appearance of the
strata is contrary to this supposition. Consolidation was probably
effected by heat and fusion. All the substances in the earth may be
rendered fluid by heat, and all the appearances in the earth's crust are
consistent with the consolidation and crystallisation of fused
substances. Not only so, but we find rents and separations and veins in
the strata, such as would naturally occur in strata consolidated by the
cooling of fused masses, and other phenomena pointing to fusion by heat.
We may conclude, then, that all the solid strata of the globe have been
hardened from a state of fusion.
But how were these strata raised up from the bottom of the sea and
transformed into dry land? Even as heat was the consolidating power, so
heat was also probably the elevating power. The power of heat for the
expansion of bodies is, as we know, unlimited, and the expansive power
of heat was certainly competent to raise the strata above the sea. Heat
was certainly competent, and if we examine the crust of the earth we
find evidence that heat was used.
If the strata cemented by the heat of fusion were created by the
expansive power of heat acting from below, we should expect to find
every species of fracture, dislocation, and contortion in those bodies,
and every degree of departure from a horizontal towards a vertical
position. And this is just what we do find. From horizontal, the strata
are frequently found vertical; from continuous, broken, and separated in
every possible direction; and from a plane, bent and doubled. The theory
is confirmed by an examination of the veins and fissures of the earth
which contain matter foreign to the strata they traverse, and evidently
forced into them as a fluid under great pressure. Active volcanoes, and
extinct volcanoes, and the marks everywhere of volcanic action likewise
support the theory of expansion and elevation by heat. A volcano is not
made on purpose to frighten superstitious people into fits of piety and
devotion; it is to be considered as a spiracle of a subterranean
furnace.
Such being the manner of the formation of the crust of the world, can we
form any judgment of its duration and durability? If we could measure
the rate of the attrition of the present continents, we might estimate
the duration of the older continents whose attrition supplied the
material for the present dry land. But as we cannot measure the
wearing-away of the land, we can merely state generally, first, that the
present dry land required an indefinitely long period for its formation;
second, that the previous dry land which supplied material for its
formation required equal time to make; third, that there is at present
land forming at the bottom of the sea which in time will appear above
the surface; fourth, that we find no vestige of a beginning, or of an
end.
Granite has in its own nature no claim to originality, for it is found
to vary greatly in its composition. But, further, it is certain that
granite, or a species of the same kind of stone, is found stratified. It
is the _granit feuilletée_ of M. de Sauffure, and, if I mistake not, is
called _gneiss_ by the Germans. Granite being thus found stratified, the
masses of this stone cannot be allowed to any right of priority over the
schistus, its companion in Alpine countries.
Lack of stratification, then, cannot be considered a proof of primitive
rock. Nor can lack of organized bodies, such as shells, in these rocks,
be considered a proof; for the traces of organized bodies may be
obliterated by the many subsequent operations of the mineral region. In
any case, signs of organized bodies are sometimes found in "primitive"
mountains.
Nor can metallic veins, found plentifully in "primitive" mountains,
prove anything, for mineral veins are found in various strata.
We maintain that _all_ the land was produced from fused substances
elevated from the bottom of the sea. But we do not hold that all parts
of the earth have undergone exactly similar and simultaneous
vicissitudes; and in respect to the changes which various parts of the
land have undergone we may distinguish between primary and secondary
strata. Nothing is more certain than that there have been several
repeated operations of the mineralising power exerted upon the strata in
particular places, and all those mineral operations tend to
consolidation. It is quite possible that "primitive" masses which differ
from the ordinary strata of the globe have been twice subjected to
mineral operations, having been first consolidated and raised as land,
and then submerged in order to be again fused and elevated.
_II.--The Nature of Mineral Coal_
Mineral, or fossil, coal is a species of stratum distinguished by its
inflammable and combustible nature. We find that it differs in respect
to its purity, and also in respect to its inflammability. As is well
known, some coals have almost no earthy ash, some a great deal; and,
again, some coals burn with much smoke and fire, while others burn like
coke. Where, then, did coal come from, and how can we account for its
different species?
A substance proper for the formation of coaly matter is found in
vegetable bodies. But how did it become mixed with earthy matter?
Vegetable bodies may be resolved into bituminous or coaly matter either
by means of fire or by means of water. Both may be used by nature in
the formation of coal.
By the force of subterranean heat vegetable matter may have been charred
at the bottom of the sea, and the oleaginous, bituminous, and fuliginous
substances diffused through the sea as a result of the burning may have
been deposited at the bottom of the sea as coal. Further, the bituminous
matter from the smoke of vegetable substances burned on land would
ultimately be deposited from the atmosphere and settle at the bottom of
the sea.
Many of the rivers contain in solution an immense quantity of
inflammable vegetable substance, and this is carried into the sea, and
precipitated there.
From these two sources, then, the sea gets bituminous material, and this
material, condensed and consolidated by compression and by heat, at the
bottom of the sea, would form a black body of a most uniform structure,
breaking with a polished surface, and burning with more or less smoke or
flame in proportion as it be distilled less or more by subterranean
heat. And such a body exactly represents our purest fossil coal, which
gives the most heat and leaves the least ash.
In some cases the bituminous material in suspension in the sea would be
mixed more or less with argillaceous, calcareous, and other earthy
substances; and these being precipitated along with the bituminous
matter would form layers of impure coal with a considerable amount of
ash.
But there is still a third source of coal. Vegetable bodies macerated in
water, and consolidated by compression, form a body almost
indistinguishable from some species of coal, as is seen in peat
compressed under a great load of earth; and there can be no doubt that
coal sometimes originates in this way, for much fossil coal shows
abundance of vegetable bodies in its composition.
There remains only to consider the change in the disposition of coal
strata. Coal strata, which had been originally in a horizontal position,
are now found sometimes standing erect, even perpendicular. This, also,
is consistent with our theory of the earth. Indeed, there is not a
substance in the mineral kingdom in which the action of subterranean
heat is better shown. These strata are evidently a deposit of
inflammable substances which all come originally from vegetable bodies.
In this stage of their formation they must all contain volatile
oleaginous constituents. But some coal strata contain no volatile
constituents, and the disappearance of the volatile oleaginous
substances must have been produced by distillation, proceeding perhaps
under the restraining force of immense compression.
We cannot doubt that such distillation does take place in the mineral
regions, when we consider that in most places of the earth we find the
evident effects of such distillation in the naphtha and petroleum that
are constantly emitted along with water in certain springs. We have,
therefore, sufficient proof of this operation of distillation.
_III.--The Disintegration and Dissolution of Land_
Whether we examine the mountain or the plain, whether we consider the
disintegration of the rocks or the softer strata of the earth, whether
we regard the shores of seas or the central plains of continents,
whether we contemplate fertile lands or deserts, we find evidence of a
general dissolution and decay of the solid surface of the globe. Every
great river and deep valley gives evidence of the attrition of the land.
The purpose of the dry land is to sustain a system of plants and
animals; and for this purpose a soil is required, and to make a soil the
solid strata must be crumbled down. The earth is nothing more than an
indefinite number of soils and situations suitable for various animals
and plants, and it must consist of both solid rock and tender earth, of
both moist and dry districts; for all these are requisite for the world
we inhabit.
But not only is the solid rock crumbling into soil by the action of air
and water, but the soil gradually progresses towards the sea, and sooner
or later the sea must swallow up the land. Vegetation and masses of
solid rock retard the seaward flow of the soil; but they merely retard,
they cannot wholly prevent. In proportion as the mountains are
diminished, the haugh, or plain, between them grows more wide, and also
on a lower level; but while there is a river running on a plain, and
floods produced in the seasons of rain, there is nothing stable in the
constitution of the surface of the land.
The theory of the earth which I propound is founded upon the great
catastrophes that can happen to the earth. It supposes strata raised
from the bottom of the sea and elevated into mountainous continents.
But, between the catastrophes, it requires nothing further than the
ordinary everyday effects of air and water. Every shower of rain, every
stream, participates in the dissolution of the land, and helps to
transport to the sea the material for future continents.
The prodigious waste of the land we see in places has seemed to some to
require some other explanation; but I maintain that the natural
operations of air and water would suffice in time to produce the effects
observed. It is true that the wastage would be slow; but slow
destruction of rock with gradual formation of soil is just what is
required in the economy of nature. A world sustaining plants and animals
requires continents which endure for more than a day.
If this continent of land, first collected in the sea, is to remain a
habitable earth, and to resist the moving waters of the globe, certain
degrees of solidity or consolidation must be given to that collection of
loose materials; and certain degrees of hardness must be given to
bodies which are soft and incoherent, and consequently so extremely
perishable in the situation in which they are now placed.
But, at the same time that this earth must have solidity and hardness to
resist the sudden changes which its moving fluids would occasion, it
must be made subject to decay and waste upon the surface exposed to the
atmosphere; for such an earth as were made incapable of change, or not
subject to decay, would not afford that fertile soil which is required
in the system of this world--a soil on which depends the growth of
plants and life of animals--the end of its intention.
Now, we find this earth endued precisely with such degree of hardness
and consolidation as qualifies it at the same time to be a fruitful
earth, and to maintain its station with all the permanency compatible
with the nature of things, which are not formed to remain unchangeable.
Thus we have a view of the most perfect wisdom in the contrivance of
that constitution by which the earth is made to answer, in the best
manner possible, the purpose of its intention, that is, to maintain and
perpetuate a system of vegetation, or the various races of useful
plants, or a system of living animals, which are in their turn
subservient to a system still infinitely more important--I mean a system
of intellect. Without fertility in the earth, many races of plants and
animals would soon perish, or be extinct; and with permanency in our
land it were impossible for the various tribes of plants and animals to
be dispersed over the surface of a changing earth. The fact is that
fertility, adequate to the various ends in view, is found in all the
quarters of the world, or in every country of the earth; and the
permanency of our land is such as to make it appear unalterable to
mankind in general and even to impose upon men of science, who have
endeavoured to persuade us that this earth is not to change.
Nothing but supreme power and wisdom could have reconciled those two
opposite ends of intention, so as both to be equally pursued in the
system of nature, and so equally attained as to be imperceptible to
common observation, and at the same time a proper object of the human
understanding.