A History of Science, Volume 3
by
Henry Smith Williams
Part 3 out of 6
American tribe of primitive lemurs, though this is only
a conjecture.
Not all the strange beasts which have left their remains
in our "bad lands" are represented by living descendants.
The titanotheres, or brontotheridae, for example, a
gigantic tribe, offshoots of the same stock
which produced the horse and rhinoceros, represented
the culmination of a line of descent. They developed
rapidly in a geological sense, and flourished about the
middle of the tertiary period; then, to use Agassiz's
phrase," time fought against them." The story of their
evolution has been worked out by Professors Leidy,
Marsh, Cope, and H. F. Osborne.
A recent bit of paleontological evidence bearing
on the question of the introduction of species is that
presented by Dr. J. L. Wortman in connection with the
fossil lineage of the edentates. It was suggested by
Marsh, in 1877, that these creatures, whose modern
representatives are all South American, originated in
North America long before the two continents had any
land connection. The stages of degeneration by which
these animals gradually lost the enamel from their teeth,
coming finally to the unique condition of their modern
descendants of the sloth tribe, are illustrated by strikingly
graded specimens now preserved in the American
Museum of Natural History, as shown by Dr. Wortman.
All these and a multitude of other recent observations
that cannot be even outlined here tell the same story.
With one accord paleontologists of our time regard the
question of the introduction of new species as solved.
As Professor Marsh has said, "to doubt evolution today
is to doubt science; and science is only another
name for truth."
Thus the third great battle over the meaning of the
fossil records has come to a conclusion. Again there
is a truce to controversy, and it may seem to the casual
observer that the present stand of the science of fossils
is final and impregnable. But does this really mean
that a full synopsis of the story of paleontology has
been told? Or do we only await the coming of the
twentieth-century Lamarck or Darwin, who shall attack
the fortified knowledge of to-day with the batteries
of a new generalization?
IV. THE ORIGIN AND DEVELOPMENT OF MODERN GEOLOGY
JAMES HUTTON
One might naturally suppose that the science of
the earth which lies at man's feet would at least
have kept pace with the science of the distant stars.
But perhaps the very obviousness of the phenomena
delayed the study of the crust of the earth. It is the
unattainable that allures and mystifies and enchants
the developing mind. The proverbial child spurns its
toys and cries for the moon.
So in those closing days of the eighteenth century,
when astronomers had gone so far towards explaining
the mysteries of the distant portions of the universe,
we find a chaos of opinion regarding the structure and
formation of the earth. Guesses were not wanting to
explain the formation of the world, it is true, but, with
one or two exceptions, these are bizarre indeed. One
theory supposed the earth to have been at first a solid
mass of ice, which became animated only after a comet
had dashed against it. Other theories conceived the
original globe as a mass of water, over which floated
vapors containing the solid elements, which in due time
were precipitated as a crust upon the waters. In a
word, the various schemes supposed the original mass to
have been ice, or water, or a conglomerate of water and
solids, according to the random fancies of the theorists;
and the final separation into land and water was conceived
to have taken place in all the ways which fancy,
quite unchecked by any tenable data, could invent.
Whatever important changes in the general character
of the surface of the globe were conceived to have taken
place since its creation were generally associated with
the Mosaic: deluge, and the theories which attempted to
explain this catastrophe were quite on a par with those
which dealt with a remoter period of the earth's history.
Some speculators, holding that the interior
of the globe is a great abyss of waters, conceived
that the crust had dropped into this chasm and had
thus been inundated. Others held that the earth had
originally revolved on a vertical axis, and that the sudden
change to its present position bad caused the catastrophic
shifting of its oceans. But perhaps the favorite
theory was that which supposed a comet to have wandered
near the earth, and in whirling about it to have
carried the waters, through gravitation, in a vast tide
over the continents.
Thus blindly groped the majority of eighteenth-century
philosophers in their attempts to study what we
now term geology. Deluded by the old deductive
methods, they founded not a science, but the ghost of a
science, as immaterial and as unlike anything in nature
as any other phantom that could be conjured from the
depths of the speculative imagination. And all the
while the beckoning earth lay beneath the feet of these
visionaries; but their eyes were fixed in air.
At last, however, there came a man who had the
penetration to see that the phantom science of geology
needed before all else a body corporeal, and who took
to himself the task of supplying it. This was Dr. James
Hutton, of Edinburgh, physician, farmer, and manufacturing
chemist--patient, enthusiastic, level-headed
devotee of science. Inspired by his love of chemistry
to study the character of rocks and soils, Hutton had
not gone far before the earth stood revealed to him in
a new light. He saw, what generations of predecessors
had blindly refused to see, that the face of nature everywhere,
instead of being rigid and immutable, is perennially
plastic, and year by year is undergoing metamorphic
changes. The solidest rocks are day by day
disintegrated slowly, but none the less surely, by wind
and rain and frost, by mechanical attrition and chemical
decomposition, to form the pulverized earth and
clay. This soil is being swept away by perennial showers,
and carried off to the oceans. The oceans themselves
beat on their shores, and eat insidiously into the
structure of sands and rocks. Everywhere, slowly but
surely, the surface of the land is being worn away; its
substance is being carried to burial in the seas.
Should this denudation continue long enough, thinks
Hutton, the entire surface of the continents must be
worn away. Should it be continued LONG ENOUGH! And
with that thought there flashes on his mind an inspiring
conception--the idea that solar time is long,
indefinitely long. That seems a simple enough thought
--almost a truism--to the twentieth-century mind;
but it required genius to conceive it in the eighteenth.
Hutton pondered it, grasped its full import, and made
it the basis of his hypothesis, his "theory of the earth."
MODERN GEOLOGY
The hypothesis is this--that the observed changes
of the surface of the earth, continued through indefinite
lapses of time, must result in conveying all the land at
last to the sea; in wearing continents away till the
oceans overflow them. What then? Why, as the continents
wear down, the oceans are filling up. Along
their bottoms the detritus of wasted continents is deposited
in strata, together with the bodies of marine
animals and vegetables. Why might not this debris
solidify to form layers of rocks--the basis of new continents?
Why not, indeed?
But have we any proof that such formation of rocks
in an ocean-bed has, in fact, occurred? To be sure we
have. It is furnished by every bed of limestone, every
outcropping fragment of fossil-bearing rock, every
stratified cliff. How else than through such formation
in an ocean-bed came these rocks to be stratified?
How else came they to contain the shells of once living
organisms imbedded in their depths? The ancients,
finding fossil shells imbedded in the rocks, explained
them as mere freaks of "nature and the stars." Less
superstitious generations had repudiated this explanation,
but had failed to give a tenable solution of the
mystery. To Hutton it is a mystery no longer. To
him it seems clear that the basis of the present continents
was laid in ancient sea-beds, formed of the detritus
of continents yet more ancient.
But two links are still wanting to complete the chain
of Hutton's hypothesis. Through what agency has the
ooze of the ocean-bed been transformed into solid rock?
and through what agency has this rock been lifted
above the surface of the water to form new continents?
Hutton looks about him for a clew, and soon he finds
it. Everywhere about us there are outcropping rocks
that are not stratified, but which give evidence to the
observant eye of having once been in a molten state.
Different minerals are mixed together; pebbles are
scattered through masses of rock like plums in a pudding;
irregular crevices in otherwise solid masses of
rock--so-called veinings--are seen to be filled with
equally solid granite of a different variety, which can
have gotten there in no conceivable way, so Hutton
thinks, but by running in while molten, as liquid metal
is run into the moulds of the founder. Even the
stratified rocks, though they seemingly have not been
melted, give evidence in some instances of having been
subjected to the action of heat. Marble, for example,
is clearly nothing but calcined limestone.
With such evidence before him, Hutton is at no loss
to complete his hypothesis. The agency which has
solidified the ocean-beds, he says, is subterranean heat.
The same agency, acting excessively, has produced
volcanic cataclysms, upheaving ocean-beds to form
continents. The rugged and uneven surfaces of mountains,
the tilted and broken character of stratified rocks
everywhere, are the standing witnesses of these gigantic
upheavals.
And with this the imagined cycle is complete. The
continents, worn away and carried to the sea by the
action of the elements, have been made over into rocks
again in the ocean-beds, and then raised once more
into continents. And this massive cycle, In Hutton's
scheme, is supposed to have occurred not once only,
but over and over again, times without number. In
this unique view ours is indeed a world without beginning
and without end; its continents have been
making and unmaking in endless series since time
began.
Hutton formulated his hypothesis while yet a young
man, not long after the middle of the century. He
first gave it publicity in 1781, in a paper before the
Royal Society of Edinburgh:
"A solid body of land could not have answered the
purpose of a habitable world," said Hutton, "for a soil
is necessary to the growth of plants, and a soil is nothing
but the material collected from the destruction of
the solid land. Therefore the surface of this land inhabited
by man, and covered by plants and animals, is
made by nature to decay, in dissolving from that hard
and compact state in which it is found; and this soil is
necessarily washed away by the continual circulation
of the water running from the summits of the mountains
towards the general receptacle of that fluid.
"The heights of our land are thus levelled with our
shores, our fertile plains are formed from the ruins of
the mountains; and those travelling materials are still
pursued by the moving water, and propelled along the
inclined surface of the earth. These movable materials,
delivered into the sea, cannot, for a long continuance,
rest upon the shore, for by the agitation of the winds,
the tides, and the currents every movable thing is
carried farther and farther along the shelving bottom
of the sea, towards the unfathomable regions of the
ocean.
"If the vegetable soil is thus constantly removed
from the surface of the land, and if its place is then to
be supplied from the dissolution of the solid earth as
here represented, we may perceive an end to this beautiful
machine; an end arising from no error in its constitution
as a world, but from that destructibility of
its land which is so necessary in the system of the
globe, in the economy of life and vegetation.
"The immense time necessarily required for the
total destruction of the land must not be opposed to
that view of future events which is indicated by the
surest facts and most approved principles. Time,
which measures everything in our idea, and is often
deficient to our schemes, is to nature endless and as
nothing; it cannot limit that by which alone it has existence;
and as the natural course of time, which to us
seems infinite, cannot be bounded by any operation
that may have an end, the progress of things upon this
globe that in the course of nature cannot be limited by
time must proceed in a continual succession. We are,
therefore, to consider as inevitable the destruction of
our land, so far as effected by those operations which
are necessary in the purpose of the globe, considered
as a habitable world, and so far as we have not examined
any other part of the economy of nature, in
which other operations and a different intention might
appear.
"We have now considered the globe of this earth as
a machine, constructed upon chemical as well as mechanical
principles, by which its different parts are all
adapted, in form, in quality, and quantity, to a certain
end--an end attained with certainty of success, and
an end from which we may perceive wisdom in contemplating
the means employed.
"But is this world to be considered thus merely as a
machine, to last no longer than its parts retain their
present position, their proper forms and qualities?
Or may it not be also considered as an organized body
such as has a constitution, in which the necessary
decay of the machine is naturally repaired in the exertion
of those productive powers by which it has been
formed?
"This is the view in which we are now to examine
the globe; to see if there be, in the constitution of the
world, a reproductive operation by which a ruined
constitution may be again repaired and a duration of
stability thus procured to the machine considered as a
world containing plants and animals.
"If no such reproductive power, or reforming operation,
after due inquiry, is to be found in the constitution
of this world, we should have reason to conclude
that the system of this earth has either been intentionally
made imperfect or has not been the work of infinite
power and wisdom."[1]
This, then, was the important question to be
answered--the question of the constitution of the globe.
To accomplish this, it was necessary, first of all, to examine
without prejudice the material already in hand,
adding such new discoveries from time to time as
might be made, but always applying to the whole
unvarying scientific principles and inductive methods
of reasoning.
"If we are to take the written history of man for
the rule by which we should judge of the time when the
species first began," said Hutton, "that period would
be but little removed from the present state of things.
The Mosaic history places this beginning of man at no
great distance; and there has not been found, in natural
history, any document by which high antiquity might
be attributed to the human race. But this is not the
case with regard to the inferior species of animals,
particularly those which inhabit the ocean and its
shores. We find in natural history monuments which
prove that those animals had long existed; and we
thus procure a measure for the computation of a period
of time extremely remote, though far from being precisely
ascertained.
"In examining things present, we have data from
which to reason with regard to what has been; and
from what actually has been we have data for concluding
with regard to that which is to happen hereafter.
Therefore, upon the supposition that the operations of
nature are equable and steady, we find, in natural
appearances, means for concluding a certain portion of
time to have necessarily elapsed in the production of
those events of which we see the effects.
"It is thus that, in finding the relics of sea animals of
every kind in the solid body of our earth, a natural
history of those animals is formed, which includes a
certain portion of time; and for the ascertaining this
portion of time we must again have recourse to the
regular operations of this world. We shall thus arrive
at facts which indicate a period to which no other
species of chronology is able to remount.
"We find the marks of marine animals in the most
solid parts of the earth, consequently those solid parts
have been formed after the ocean was inhabited by
those animals which are proper to that fluid medium.
If, therefore, we knew the natural history of these
solid parts, and could trace the operations of the globe
by which they have been formed, we would have some
means for computing the time through which those
species of animals have continued to live. But how
shall we describe a process which nobody has seen performed
and of which no written history gives any account?
This is only to be investigated, first, in examining
the nature of those solid bodies the history of
which we want to know; and, secondly, in examining
the natural operations of the globe, in order to see if
there now exist such operations as, from the nature
of the solid bodies, appear to have been necessary for
their formation.
"There are few beds of marble or limestone in which
may not be found some of those objects which indicate
the marine object of the mass. If, for example, in a
mass of marble taken from a quarry upon the top of
the Alps or Andes there shall be found one cockle-shell
or piece of coral, it must be concluded that this bed of
stone has been originally formed at the bottom of the
sea, as much as another bed which is evidently composed
almost altogether of cockle-shells and coral. If
one bed of limestone is thus found to have been of
marine origin, every concomitant bed of the same
kind must be also concluded to have been formed in the
same manner.
"In those calcareous strata, which are evidently of
marine origin, there are many parts which are of
sparry structure--that is to say, the original texture of
those beds in such places has been dissolved, and a
new structure has been assumed which is peculiar to
a certain state of the calcareous earth. This change
is produced by crystallization, in consequence of a previous
state of fluidity, which has so disposed the concerting
parts as to allow them to assume a regular
shape and structure proper to that substance. A body
whose external form has been modified by this process
is called a CRYSTAL; one whose internal arrangement
of parts is determined by it is said to be of a SPARRY
STRUCTURE, and this is known from its fracture.
"There are, in all the regions of the earth, huge
masses of calcareous matter in that crystalline form or
sparry state in which, perhaps, no vestige can be
found of any organized body, nor any indication that
such calcareous matter has belonged to animals; but
as in other masses this sparry structure or crystalline
state is evidently assumed by the marine calcareous
substances in operations which are natural to the
globe, and which are necessary to the consolidation of
the strata, it does not appear that the sparry masses
in which no figured body is formed have been originally
different from other masses, which, being only
crystallized in part, and in part still retaining their
original form, have ample evidence of their marine
origin.
"We are led, in this manner, to conclude that all the
strata of the earth, not only those consisting of such
calcareous masses, but others superincumbent upon
these, have had their origin at the bottom of the
sea.
"The general amount of our reasoning is this, that
nine-tenths, perhaps, or ninety-nine-hundredths, of this
earth, so far as we see, have been formed by natural operations
of the globe in collecting loose materials and
depositing them at the bottom of the sea; consolidating
those collections in various degrees, and either elevating
those consolidated masses above the level on
which they were formed or lowering the level of that
sea.
"Let us now consider how far the other proposition
of strata being elevated by the power of heat above the
level of the sea may be confirmed from the examination
of natural appearances. The strata formed at the bottom
of the ocean are necessarily horizontal in their position,
or nearly so, and continuous in their horizontal
direction or extent. They may be changed and gradually
assume the nature of each other, so far as concerns
the materials of which they are formed, but there cannot
be any sudden change, fracture, or displacement
naturally in the body of a stratum. But if the strata
are cemented by the heat of fusion, and erected with
an expansive power acting below, we may 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.
"The strata of the globe are actually found in every
possible position: for from horizontal they are frequently
found vertical; from continuous they are broken
and separated in every possible direction; and from a
plane they are bent and doubled. It is impossible
that they could have originally been formed, by the
known laws of nature, in their present state and position;
and the power that has been necessarily required
for their change has not been inferior to that which
might have been required for their elevation from the
place in which they have been formed."[2]
From all this, therefore, Hutton reached the conclusion
that the elevation of the bodies of land above
the water on the earth's surface had been effected by
the same force which had acted in consolidating the
strata and giving them stability. This force he
conceived to be exerted by the expansion of heated
matter.
"We have," he said, "been now supposing that the
beginning of our present earth had been laid in the bottom
of the ocean, at the completion of the former land,
but this was only for the sake of distinctness. The
just view is this, that when the former land of the globe
had been complete, so as to begin to waste and be
impaired by the encroachment of the sea, the present
land began to appear above the surface of the ocean.
In this manner we suppose a due proportion to be always
preserved of land and water upon the surface of
the globe, for the purpose of a habitable world such as
this which we possess. We thus also allow time and
opportunity for the translation of animals and plants
to occupy the earth.
"But if the earth on which we live began to appear
in the ocean at the time when the LAST began to be resolved,
it could not be from the materials of the continent
immediately preceding this which we examine
that the present earth has been constructed; for the
bottom of the ocean must have been filled with materials
before land could be made to appear above its
surface.
"Let us suppose that the continent which is to succeed
our land is at present beginning to appear above
the water in the middle of the Pacific Ocean; it must
be evident that the materials of this great body, which
is formed and ready to be brought forth, must have
been collected from the destruction of an earth which
does not now appear. Consequently, in this true statement
of the case there is necessarily required the destruction
of an animal and vegetable earth prior to the
former land; and the materials of that earth which is
first in our account must have been collected at the
bottom of the ocean, and begun to be concocted for
the production of the present earth, when the land
immediately preceding the present had arrived at its
full extent.
"We have now got to the end of our reasoning; we
have no data further to conclude immediately from
that which actually is; but we have got enough; we
have the satisfaction to find that in nature there are
wisdom, system, and consistency. For having in the
natural history of the earth seen a succession of worlds,
we may from this conclude that there is a system in
nature; in like manner as, from seeing revolutions of
the planets, it is concluded that there is a system by
which they are intended to continue those revolutions.
But if the succession of worlds is established in
the system of nature, it is in vain to look for anything
higher in the origin of the earth. The result, therefore,
of our present inquiry is that we find no vestige of a
beginning--no prospect of an end."
Altogether remarkable as this paper seems in the
light of later knowledge, neither friend nor foe deigned
to notice it at the moment. It was not published in
book form until the last decade of the century, when
Hutton had lived with and worked over his theory for
almost fifty years. Then it caught the eye of the
world. A school of followers expounded the Huttonian
doctrines; a rival school under Werner in Germany
opposed some details of the hypothesis, and the educated
world as a whole viewed the disputants askance.
The very novelty of the new views forbade their immediate
acceptance. Bitter attacks were made upon
the "heresies," and that was meant to be a soberly
tempered judgment which in 1800 pronounced Hutton's
theories "not only hostile to sacred history, but equally
hostile to the principles of probability, to the results
of the ablest observations on the mineral kingdom,
and to the dictates of rational philosophy." And all
this because Hutton's theory presupposed the earth
to have been in existence more than six thousand
years.
Thus it appears that though the thoughts of men had
widened, in those closing days of the eighteenth century,
to include the stars, they had not as yet expanded
to receive the most patent records that are written
everywhere on the surface of the earth. Before Hutton's
views could be accepted, his pivotal conception
that time is long must be established by convincing
proofs. The evidence was being gathered by William
Smith, Cuvier, and other devotees of the budding
science of paleontology in the last days of the century,
but their labors were not brought to completion till a
subsequent epoch.
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
Society of London were making an effort to hunt
for facts and avoid compromising theories. Fact and
theory, however, were too closely linked to be thus divorced.
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 highest-
known 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
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
partially cooling it, tended to preserve the remainder
in a liquid form. The ocean will have contained, both
in solution and suspension, many of the matters carried
upward from the granitic bed in which the vapors
from whose condensation it proceeded were produced,
and which they had traversed in their rise. The dissolved
matters will have been silex, carbonates, and
sulphates of lime, and those other mineral substances
which water at an intense temperature and under such
circumstances was enabled to hold in solution. The
suspended substances will have been all the lighter and
finer particles of the upper beds where the disintegration
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
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
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.
"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
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.
"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
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
of the interior of the globe still endeavoring to put itself
in equilibrio by passing off towards the less-intensely
heated crust.
"This continually increasing expansive force must
at length have overcome the resistance opposed by the
tenacity and weight of the overlying consolidated
strata. It is reasonable to suppose that this result
took place contemporaneously, or nearly so, on many
spots, wherever accidental circumstances in the texture
or composition of the oceanic deposits led them to
yield more readily; and in this manner were produced
those original fissures in the primeval crust of the earth
through some of which (fissures of elevation) were intruded
portions of interior crystalline zones in a solid
or nearly solid state, together with more or less of the
intumescent granite, in the manner above described;
while others (fissures of eruption) gave rise to extravasations
of the heated crystalline matter, in the form
of lavas--that is, still further liquefied by the greater
comparative reduction of the pressure they endured."[3]
The Neptunists stoutly contended for the aqueous
origin of volcanic as of other mountains. But the
facts were with Scrope, and as time went on it came
to be admitted that not merely volcanoes, but many
"trap" formations not taking the form of craters, had
been made by the obtrusion of molten rock through
fissures in overlying strata. Such, for example, to cite
familiar illustrations, are Mount Holyoke, in Massachusetts,
and the well-known formation of the Palisades
along the Hudson.
But to admit the "Plutonic" origin of such widespread
formations was practically to abandon the Neptunian
hypothesis. So gradually the Huttonian explanation
of the origin of granites and other "igneous"
rocks, whether massed or in veins, came to be accepted.
Most geologists then came to think of the earth as a
molten mass, on which the crust rests as a mere film.
Some, indeed, with Lyell, preferred to believe that the
molten areas exist only as lakes in a solid crust, heated
to melting, perhaps, by electrical or chemical action, as
Davy suggested. More recently a popular theory attempts
to reconcile geological facts with the claim of
the physicists, that the earth's entire mass is at least as
rigid as steel, by supposing that a molten film rests between
the observed solid crust and the alleged solid
nucleus. But be that as it may, the theory that
subterranean heat has been instrumental in determining
the condition of "primary" rocks, and in producing
many other phenomena of the earth's crust, has never
been in dispute since the long controversy between
the Neptunists and the Plutonists led to its establishment.
LYELL AND UNIFORMITARIANISM
If molten matter exists beneath the crust of the
earth, it must contract in cooling, and in so doing it
must disturb the level of the portion of the crust already
solidified. So a plausible explanation of the
upheaval of continents and mountains was supplied by
the Plutonian theory, as Hutton had from the first
alleged. But now an important difference of opinion
arose as to the exact rationale of such upheavals.
Hutton himself, and practically every one else who
accepted his theory, had supposed that there are long
periods of relative repose, during which the level of the
crust is undisturbed, followed by short periods of active
stress, when continents are thrown up with volcanic
suddenness, as by the throes of a gigantic earthquake.
But now came Charles Lyell with his famous extension
of the "uniformitarian" doctrine, claiming that past
changes of the earth's surface have been like present
changes in degree as well as in kind. The making of
continents and mountains, he said, is going on as rapidly
to-day as at any time in the past. There have been
no gigantic cataclysmic upheavals at any time, but all
changes in level of the strata as a whole have been
gradual, by slow oscillation, or at most by repeated
earthquake shocks such as are still often experienced.
In support of this very startling contention Lyell
gathered a mass of evidence of the recent changes in
level of continental areas. He corroborated by personal
inspection the claim which had been made by Playfair
in 1802, and by Von Buch in 1807, that the coast-line of
Sweden is rising at the rate of from a few inches to
several feet in a century. He cited Darwin's observations
going to prove that Patagonia is similarly rising,
and Pingel's claim that Greenland is slowly sinking.
Proof as to sudden changes of level of several feet, over
large areas, due to earthquakes, was brought forward in
abundance. Cumulative evidence left it no longer open
to question that such oscillatory changes of level, either
upward or downward, are quite the rule, and it could
not be denied that these observed changes, if continued
long enough in one direction, would produce the highest
elevations. The possibility that the making of even
the highest ranges of mountains had been accomplished
without exaggerated catastrophic action came
to be freely admitted.
It became clear that the supposedly stable-land surfaces
are in reality much more variable than the surface
of the "shifting sea"; that continental masses, seemingly
so fixed, are really rising and falling in billows
thousands of feet in height, ages instead of moments
being consumed in the sweep between crest and hollow.
These slow oscillations of land surfaces being understood,
many geological enigmas were made clear--
such as the alternation of marine and fresh-water formations
in a vertical series, which Cuvier and Brongniart
had observed near Paris; or the sandwiching of
layers of coal, of subaerial formation, between layers
of subaqueous clay or sandstone, which may be observed
everywhere in the coal measures. In particular,
the extreme thickness of the sedimentary strata as a
whole, many times exceeding the depth of the deepest
known sea, was for the first time explicable when it
was understood that such strata had formed in slowly
sinking ocean-beds.
All doubt as to the mode of origin of stratified rocks
being thus removed, the way was opened for a more
favorable consideration of that other Huttonian doctrine of the
extremely slow denudation of land surfaces.
The enormous amount of land erosion will be patent to
any one who uses his eyes intelligently in a mountain
district. It will be evident in any region where the
strata are tilted--as, for example, the Alleghanies--
that great folds of strata which must once have risen
miles in height have in many cases been worn entirely
away, so that now a valley marks the location of the
former eminence. Where the strata are level, as in
the case of the mountains of Sicily, the Scotch Highlands,
and the familiar Catskills, the evidence of denudation
is, if possible, even more marked; for here it
is clear that elevation and valley have been carved by
the elements out of land that rose from the sea as level
plateaus.
But that this herculean labor of land-sculpturing
could have been accomplished by the slow action of
wind and frost and shower was an idea few men could
grasp within the first half-century after Hutton propounded
it; nor did it begin to gain general currency
until Lyell's crusade against catastrophism, begun
about 1830, had for a quarter of a century accustomed
geologists to the thought of slow, continuous changes
producing final results of colossal proportions. And
even long after that it was combated by such men as
Murchison, Director-General of the Geological Survey
of Great Britain, then accounted the foremost
field-geologist of his time, who continued to believe
that the existing valleys owe their main features to
subterranean forces of upheaval. Even Murchison,
however, made some recession from the belief of the
Continental authorities, Elie de Beaumont and
Leopold von Buch, who contended that the mountains had
sprung up like veritable jacks-in-the-box. Von Buch,
whom his friend and fellow-pupil Von Humboldt considered
the foremost geologist of the time, died in
1853, still firm in his early faith that the erratic bowlders
found high on the Jura had been hurled there, like
cannon-balls, across the valley of Geneva by the sudden
upheaval of a neighboring mountain-range.
AGASSIZ AND THE GLACIAL THEORY
The bowlders whose presence on the crags of the
Jura the old Gerinan accounted for in a manner so
theatrical had long been a source of contention among
geologists. They are found not merely on the Jura, but
on numberless other mountains in all north-temperate
latitudes, and often far out in the open country, as
many a farmer who has broken his plough against them
might testify. The early geologists accounted for
them, as for nearly everything else, with their supposititious
Deluge. Brongniart and Cuvier and Buckland
and their contemporaries appeared to have no
difficulty in conceiving that masses of granite weighing
hundreds of tons had been swept by this current
scores or hundreds of miles from their source. But,
of course, the uniformitarian faith permitted no such
explanation, nor could it countenance the projection
idea; so Lyell was bound to find some other means of
transportation for the puzzling erratics.
The only available medium was ice, but, fortunately,
this one seemed quite sufficient. Icebergs, said Lyell,
are observed to carry all manner of debris, and deposit
it in the sea-bottoms. Present land surfaces have often
been submerged beneath the sea. During the latest of
these submergences icebergs deposited the bowlders
now scattered here and there over the land. Nothing
could be simpler or more clearly uniformitarian. And
even the catastrophists, though they met Lyell amicably
on almost no other theoretical ground, were inclined
to admit the plausibility of his theory of erratics.
Indeed, of all Lyell's nonconformist doctrines, this
seemed the one most likely to meet with general acceptance.
Yet, even as this iceberg theory loomed large and
larger before the geological world, observations were
making in a different field that were destined to show
its fallacy. As early as 1815 a sharp-eyed chamois-
hunter of the Alps, Perraudin by name, had noted the
existence of the erratics, and, unlike most of his
companion hunters, had puzzled his head as to how the
bowlders got where he saw them. He knew nothing of
submerged continents or of icebergs, still less of
upheaving mountains; and though he doubtless had heard
of the Flood, he had no experience of heavy rocks
floating like corks in water. Moreover, he had never
observed stones rolling uphill and perching themselves
on mountain-tops, and he was a good enough uniformitarian
(though he would have been puzzled indeed
had any one told him so) to disbelieve that stones in
past times had disported themselves differently in
this regard from stones of the present. Yet there the
stones are. How did they get there?
The mountaineer thought that he could answer that
question. He saw about him those gigantic serpent-
like streams of ice called glaciers, "from their far
fountains slow rolling on," carrying with them blocks of
granite and other debris to form moraine deposits.
If these glaciers had once been much more extensive
than they now are, they might have carried the bowlders
and left them where we find them. On the other
hand, no other natural agency within the sphere of
the chamois-hunter's knowledge could have accomplished
this, ergo the glaciers must once have been
more extensive. Perraudin would probably have said
that common-sense drove him to this conclusion; but
be that as it may, he had conceived one of the few truly
original and novel ideas of which the nineteenth century
can boast.
Perraudin announced his idea to the greatest scientist
in his little world--Jean de Charpentier, director
of the mines at Bex, a skilled geologist who had been a
fellow-pupil of Von Buch and Von Humboldt under
Werner at the Freiberg School of Mines. Charpentier
laughed at the mountaineer's grotesque idea, and
thought no more about it. And ten years elapsed
before Perraudin could find any one who treated his
notion with greater respect. Then he found a listener
in M. Venetz, a civil engineer, who read a paper on the
novel glacial theory before a local society in 1823.
This brought the matter once more to the attention of
De Charpentier, who now felt that there might be
something in it worth investigation.
A survey of the field in the light of the new theory
soon convinced Charpentier that the chamois-hunter
had all along been right. He became an enthusiastic
supporter of the idea that the Alps had once been imbedded
in a mass of ice, and in 1836 he brought the
notion to the attention of Louis Agassiz, who was
spending the summer in the Alps. Agassiz was sceptical
at first, but soon became a convert.
In 1840 Agassiz published a paper in which the results
of his Alpine studies were elaborated.
"Let us consider," he says, "those more considerable
changes to which glaciers are subject, or rather, the
immense extent which they had in the prehistoric
period. This former immense extension, greater than
any that tradition has preserved, is proved, in the case
of nearly every valley in the Alps, by facts which are
both many and well established. The study of these
facts is even easy if the student is looking out for
them, and if he will seize the least indication of their
presence; and, if it were a long time before they were
observed and connected with glacial action, it is because
the evidences are often isolated and occur at
places more or less removed from the glacier which
originated them. If it be true that it is the prerogative
of the scientific observer to group in the field of his
mental vision those facts which appear to be without
connection to the vulgar herd, it is, above all, in such a
case as this that he is called upon to do so. I have
often compared these feeble effects, produced by the
glacial action of former ages, with the appearance of
the markings upon a lithographic stone, prepared for
the purpose of preservation, and upon which one
cannot see the lines of the draughtsman's work unless
it is known beforehand where and how to search for
them.
"The fact of the former existence of glaciers which
have now disappeared is proved by the survival of the
various phenomena which always accompany them,
and which continue to exist even after the ice has
melted. These phenomena are as follows:
"1. Moraines.--The disposition and composition
of moraines enable them to be always recognized, even
when they are no longer adjacent to a glacier nor
immediately surround its lower extremities. I may remark
that lateral and terminal moraines alone enable
us to recognize with certainty the limits of glacial
extension, because they can be easily distinguished from
the dikes and irregularly distributed stones carried
down by the Alpine torrents, The lateral moraines
deposited upon the sides of valleys are rarely affected
by the larger torrents, but they are, however, often
cut by the small streams which fall down the side of
a mountain, and which, by interfering with their
continuity, make them so much more difficult to recognize.
"2. The Perched Bowlders.--It often happens that
glaciers encounter projecting points of rock, the sides
of which become rounded, and around which funnel-
like cavities are formed with more or less profundity.
When glaciers diminish and retire, the blocks which
have fallen into these funnels often remain perched
upon the top of the projecting rocky point within it, in
such a state of equilibrium that any idea of a current of
water as the cause of their transportation is completely
inadmissible on account of their position. When
such points of rock project above the surface of the
glacier or appear as a more considerable islet in the
midst of its mass (such as is the case in the Jardin of
the Mer de Glace, above Montavert), such projections
become surrounded on all sides by stones which ultimately
form a sort of crown around the summit whenever
the glaciers decrease or retire completely. Water
currents never produce anything like this; but, on the
contrary, whenever a stream breaks itself against a
projecting rock, the stones which it carries down are
turned aside and form a more or less regular trail.
Never, under such circumstances, can the stones remain
either at the top or at the sides of the rock, for, if
such a thing were possible, the rapidity of the current
would be accelerated by the increased resistance, and
the moving bowlders would be carried beyond the obstruction
before they were finally deposited.
"3. The polished and striated rocks, such as have
been described in Chapter XIV., afford yet further evidence
of the presence of a glacier; for, as has been said
already, neither a current nor the action of waves upon
an extensive beach produces such effects. The general
direction of the channels and furrows indicates the
direction of the general movement of the glacier, and
the streaks which vary more or less from this direction
are produced by the local effects of oscillation and retreat,
as we shall presently see.
"4. The Lapiaz, or Lapiz, which the inhabitants of
German Switzerland call Karrenfelder, cannot always
be distinguished from erosions, because, both produced
as they are by water, they do not differ in their exterior
characteristics, but only in their positions.
Erosions due to torrents are always found in places
more or less depressed, and never occur upon large inclined
surfaces. The Lapiaz, on the contrary, are
frequently found upon the projecting parts of the sides
of valleys in places where it is not possible to suppose
that water has ever formed a current. Some geologists,
in their embarrassment to explain these phenomena,
have supposed that they were due to the infiltration
of acidulated water, but this hypothesis is purely
gratuitous.
"We will now describe the remains of these various
phenomena as they are found in the Alps outside the
actual glacial limits, in order to prove that at a certain
epoch glaciers were much larger than they are to-day.
"The ancient moraines, situated as they are at a
great distance from those of the present day, are nowhere
so distinct or so frequent as in Valais, where
MM. Venetz and J. de Charpentier noticed them for
the first time; but as their observations are as yet
unpublished, and they themselves gave me the information,
it would be an appropriation of their discovery
if I were to describe them here in detail. I will limit
myself to say that there can be found traces, more or
less distinct, of ancient terminal moraines in the form
of vaulted dikes at the foot of every glacier, at a distance
of a few minutes' walk, a quarter of an hour, a
half-hour, an hour, and even of several leagues from
their present extremities. These traces become less
distinct in proportion to their distance from the glacier,
and, since they are also often traversed by torrents,
they are not as continuous as the moraines which are
nearer to the glaciers. The farther these ancient
moraines are removed from the termination of a glacier,
the higher up they reach upon the sides of the valley,
which proves to us that the thickness of the glacier
must have been greater when its size was larger. At
the same time, their number indicates so many stopping-places
in the retreat of the glacier, or so many extreme
limits of its extension--limits which were never
reached again after it had retired. I insist upon this
point, because if it is true that all these moraines
demonstrate a larger extent of the glacier, they also prove
that their retreat into their present boundaries, far
from having been catastrophic, was marked on the
contrary by periods of repose more or less frequent,
which caused the formation of a series of concentric
moraines which even now indicate their retrogression.
"The remains of longitudinal moraines are less frequent,
less distinct, and more difficult to investigate,
because, indicating as they do the levels to which the
edges of the glacier reached at different epochs, it is
generally necessary to look for them above the line of
the paths along the escarpments of the valleys, and
hence it is not always possible to follow them along a
valley. Often, also, the sides of a valley which enclosed
a glacier are so steep that it is only here and
there that the stones have remained in place. They
are, nevertheless, very distinct in the lower part of the
valley of the Rhone, between Martigny and the Lake
of Geneva, where several parallel ridges can be observed,
one above the other, at a height of one thousand,
one thousand two hundred, and even one thousand
five hundred feet above the Rhone. It is between
St. Maurice and the cascade of Pissevache, close to
the hamlet of Chaux-Fleurie, that they are most accessible,
for at this place the sides of the valley at different
levels ascend in little terraces, upon which the
moraines have been preserved. They are also very
distinct above the Bains de Lavey, and above the
village of Monthey at the entrance of the Val d'Illiers,
where the sides of the valley are less inclined than in
many other places.
"The perched bowlders which are found in the Alpine
valleys, at considerable distances from the glaciers,
occupy at times positions so extraordinary that they
excite in a high degree the curiosity of those who see
them. For instance, when one sees an angular stone
perched upon the top of an isolated pyramid, or resting
in some way in a very steep locality, the first inquiry
of the mind is, When and how have these stones been
placed in such positions, where the least shock would
seem to turn them over? But this phenomenon is not
in the least astonishing when it is seen to occur also
within the limits of actual glaciers, and it is recalled
by what circumstances it is occasioned.
"The most curious examples of perched stones
which can be cited are those which command the
northern part of the cascade of Pissevache, close to
Chaux-Fleurie, and those above the Bains de Lavey,
close to the village of Morcles; and those, even more
curious, which I have seen in the valley of St. Nicolas
and Oberhasli. At Kirchet, near Meiringen, can be seen
some very remarkable crowns of bowlders around several
domes of rock which appear to have been projected
above the surface of the glacier which surrounded
them. Something very similar can be seen around the
top of the rock of St. Triphon.
"The extraordinary phenomenon of perched stones
could not escape the observing eye of De Saussure,
who noticed several at Saleve, of which he described
the positions in the following manner: 'One sees,'
said he, 'upon the slope of an inclined meadow, two
of these great bowlders of granite, elevated one upon
the other, above the grass at a height of two or three
feet, upon a base of limestone rock on which both rest.
This base is a continuation of the horizontal strata of
the mountain, and is even united with it visibly on its
lower face, being cut perpendicularly upon the other
sides, and is not larger than the stone which it
supports.' But seeing that the entire mountain is
composed of the same limestone, De Saussure naturally
concluded that it would be absurd to think that it was
elevated precisely and only beneath the blocks of
granite. But, on the other hand, since he did not
know the manner in which these perched stones are
deposited in our days by glacial action, he had recourse
to another explanation: He supposes that the
rock was worn away around its base by the continual
erosion of water and air, while the portion of the rock
which served as the base for the granite had been protected
by it. This explanation, although very ingenious,
could no longer be admitted after the researches
of M. Elie de Beaumont had proved that the
action of atmospheric agencies was not by a good deal
so destructive as was theretofore supposed. De Saussure
speaks also of a detached bowlder, situated upon
the opposite side of the Tete-Noire, 'which is,' he says,
'of so great a size that one is tempted to believe that it
was formed in the place it occupies; and it is called
Barme russe, because it is worn away beneath in the
form of a cave which can afford accommodation for
more than thirty persons at a time."[4]
But the implications of the theory of glaciers extend,
so Agassiz has come to believe, far beyond the
Alps. If the Alps had been covered with an ice sheet,
so had many other regions of the northern hemisphere.
Casting abroad for evidences of glacial action, Agassiz
found them everywhere in the form of transported
erratics, scratched and polished outcropping rocks,
and moraine-like deposits. Finally, he became convinced
that the ice sheet that covered the Alps had
spread over the whole of the higher latitudes of the
northern hemisphere, forming an ice cap over the globe.
Thus the common-sense induction of the chamois-
hunter blossomed in the mind of Agassiz into the
conception of a universal ice age.
In 1837 Agassiz had introduced his theory to the
world, in a paper read at Neuchatel, and three years
later he published his famous Etudes sur les Glaciers,
from which we have just quoted. Never did idea make
a more profound disturbance in the scientific world.
Von Buch treated it with alternate ridicule, contempt,
and rage; Murchison opposed it with customary vigor;
even Lyell, whose most remarkable mental endowment
was an unfailing receptiveness to new truths,
could not at once discard his iceberg theory in favor
of the new claimant. Dr. Buckland, however, after
Agassiz had shown him evidence of former glacial action
in his own Scotland, became a convert--the more
readily, perhaps, as it seemed to him to oppose the
uniformitarian idea. Gradually others fell in line, and
after the usual imbittered controversy and the inevitable
full generation of probation, the idea of an ice
age took its place among the accepted tenets of geology. All
manner of moot points still demanded attention--the
cause of the ice age, the exact extent of the
ice sheet, the precise manner in which it produced its
effects, and the exact nature of these effects; and not
all of these have even yet been determined. But, details
aside, the ice age now has full recognition from
geologists as an historical period. There may have
been many ice ages, as Dr. Croll contends; there was
surely one; and the conception of such a period is one
of the very few ideas of our century that no previous
century had even so much as faintly adumbrated.
THE GEOLOGICAL AGES
But, for that matter, the entire subject of historical
geology is one that had but the barest beginning before
our century. Until the paleontologist found out the
key to the earth's chronology, no one--not even Hutton--
could have any definite idea as to the true story
of the earth's past. The only conspicuous attempt to
classify the strata was that made by Werner, who divided
the rocks into three systems, based on their supposed
order of deposition, and called primary, transition,
and secondary.
Though Werner's observations were confined to the
small province of Saxony, he did not hesitate to affirm
that all over the world the succession of strata would be
found the same as there, the concentric layers, according
to this conception, being arranged about the earth
with the regularity of layers on an onion. But in this
Werner was as mistaken as in his theoretical explanation
of the origin of the "primary" rocks. It required
but little observation to show that the exact succession
of strata is never precisely the same in any widely separated
regions. Nevertheless, there was a germ of
truth in Werner's system. It contained the idea, however
faultily interpreted, of a chronological succession
of strata; and it furnished a working outline for the
observers who were to make out the true story of
geological development. But the correct interpretation
of the observed facts could only be made after the
Huttonian view as to the origin of strata had gained
complete acceptance.
When William Smith, having found the true key to
this story, attempted to apply it, the territory with
which he had to deal chanced to be one where the surface
rocks are of that later series which Werner termed
secondary. He made numerous subdivisions within
this system, based mainly on the fossils. Meantime it
was found that, judged by the fossils, the strata that
Brongniart and Cuvier studied near Paris were of a still
more recent period (presumed at first to be due to the
latest deluge), which came to be spoken of as tertiary.
It was in these beds, some of which seemed to have
been formed in fresh-water lakes, that many of the
strange mammals which Cuvier first described were
found.
But the "transition" rocks, underlying the "secondary"
system that Smith studied, were still practically
unexplored when, along in the thirties, they were taken
in hand by Roderick Impey Murchison, the reformed
fox-hunter and ex-captain, who had turned geologist to
such notable advantage, and Adam Sedgwick, the brilliant
Woodwardian professor at Cambridge.
Working together, these two friends classified the
transition rocks into chronological groups, since familiar
to every one in the larger outlines as the Silurian
system (age of invertebrates) and the Devonian system
(age of fishes)--names derived respectively from the
country of the ancient Silures, in Wales and Devonshire,
England. It was subsequently discovered that
these systems of strata, which crop out from beneath
newer rocks in restricted areas in Britain, are spread
out into broad, undisturbed sheets over thousands of
miles in continental Europe and in America. Later on
Murchison studied them in Russia, and described them,
conjointly with Verneuil and Von Kerserling, in a
ponderous and classical work. In America they were
studied by Hall, Newberry, Whitney, Dana, Whitfield,
and other pioneer geologists, who all but anticipated
their English contemporaries.
The rocks that are of still older formation than those
studied by Murchison and Sedgwick (corresponding in
location to the "primary" rocks of Werner's conception)
are the surface feature of vast areas in Canada,
and were first prominently studied there by William I.
Logan, of the Canadian Government Survey, as early as
1846, and later on by Sir William Dawson. These rocks
--comprising the Laurentian system--were formerly
supposed to represent parts of the original crust of the
earth, formed on first cooling from a molten state; but
they are now more generally regarded as once-stratified
deposits metamorphosed by the action of heat.
Whether "primitive" or metamorphic, however,
these Canadian rocks, and analogous ones beneath the
fossiliferous strata of other countries, are the oldest
portions of the earth's crust of which geology has any
present knowledge. Mountains of this formation, as
the Adirondacks and the Storm King range, overlooking
the Hudson near West Point, are the patriarchs of their
kind, beside which Alleghanies and Sierra Nevadas are
recent upstarts, and Rockies, Alps, and Andes are mere
parvenus of yesterday.
The Laurentian rocks were at first spoken of as representing
"Azoic" time; but in 1846 Dawson found a
formation deep in their midst which was believed to b e
the fossil relic of a very low form of life, and after that it
became customary to speak of the system as "Eozoic."
Still more recently the title of Dawson's supposed fossil
to rank as such has been questioned, and Dana's suggestion
that the early rocks be termed merely Archman
has met with general favor. Murchison and Sedgwick's
Silurian, Devonian, and Carboniferous groups
(the ages of invertebrates, of fishes, and of coal plants,
respectively) are together spoken of as representing
Paleozoic time. William Smith's system of strata,
next above these, once called "secondary," represents
Mesozoic time, or the age of reptiles. Still higher, or
more recent, are Cuvier and Brongniart's tertiary rocks,
representing the age of mammals. Lastly, the most
recent formations, dating back, however, to a period
far enough from recent in any but a geological sense,
are classed as quaternary, representing the age of
man.
It must not be supposed, however, that the successive
"ages" of the geologist are shut off from one another in
any such arbitrary way as this verbal classification
might seem to suggest. In point of fact, these "ages"
have no better warrant for existence than have the
"centuries" and the "weeks" of every-day computation.
They are convenient, and they may even stand
for local divisions in the strata, but they are bounded
by no actual gaps in the sweep of terrestrial events.
Moreover, it must be understood that the "ages" of
different continents, though described under the same
name, are not necessarily of exact contemporaneity.
There is no sure test available by which it could be
shown that the Devonian age, for instance, as outlined
in the strata of Europe, did not begin millions of years
earlier or later than the period whose records are said
to represent the Devonian age in America. In attempting
to decide such details as this, mineralogical
data fail us utterly. Even in rocks of adjoining regions
identity of structure is no proof of contemporaneous
origin; for the veritable substance of the rock of one
age is ground up to build the rocks of subsequent ages.
Furthermore, in seas where conditions change but little
the same form of rock may be made age after age. It
is believed that chalk-beds still forming in some of our
present seas may form one continuous mass dating back
to earliest geologic ages. On the other hand, rocks
different in character maybe formed at the same time in
regions not far apart--say a sandstone along shore, a
coral limestone farther seaward, and a chalk-bed beyond.
This continuous stratum, broken in the process
of upheaval, might seem the record of three different
epochs.
Paleontology, of course, supplies far better chronological
tests, but even these have their limitations.
There has been no time since rocks now in existence
were formed, if ever, when the earth had a uniform
climate and a single undiversified fauna over its entire
land surface, as the early paleontologists supposed.
Speaking broadly, the same general stages have attended
the evolution of organic forms everywhere, but there
is nothing to show that equal periods of time witnessed
corresponding changes in diverse regions, but quite the
contrary. To cite but a single illustration, the marsupial
order, which is the dominant mammalian type
of the living fauna of Australia to-day, existed in Europe
and died out there in the tertiary age. Hence a
future geologist might think the Australia of to-day
contemporaneous with a period in Europe which in
reality antedated it by perhaps millions of years.
All these puzzling features unite to render the subject
of historical geology anything but the simple matter
the fathers of the science esteemed it. No one
would now attempt to trace the exact sequence of
formation of all the mountains of the globe, as Elie de
Beaumont did a half-century ago. Even within the
limits of a single continent, the geologist must proceed
with much caution in attempting to chronicle the order
in which its various parts rose from the matrix of the
sea. The key to this story is found in the identification
of the strata that are the surface feature in each
territory. If Devonian rocks are at the surface in any
given region, for example, it would appear that this
region became a land surface in the Devonian age, or
just afterwards. But a moment's consideration shows
that there is an element of uncertainty about this, due
to the steady denudation that all land surfaces undergo.
The Devonian rocks may lie at the surface simply because
the thousands of feet of carboniferous strata that
once lay above them have been worn away. All that
the cautious geologist dare assert, therefore, is that the
region in question did not become permanent land surface
earlier than the Devonian age.
But to know even this is much--sufficient, indeed, to
establish the chronological order of elevation, if not its
exact period, for all parts of any continent that have
been geologically explored--understanding always that
there must be no scrupling about a latitude of a few
millions or perhaps tens of millions of years here and
there.
Regarding our own continent, for example, we learn
through the researches of a multitude of workers that
in the early day it was a mere archipelago. Its chief
island--the backbone of the future continent--was a
great V-shaped area surrounding what is now Hudson
Bay, an area built tip, perhaps, through denudation of a
yet more ancient polar continent, whose existence is
only conjectured. To the southeast an island that is
now the Adirondack Mountains, and another that is now
the Jersey Highlands rose above the waste of waters,
and far to the south stretched probably a line of islands
now represented by the Blue Ridge Mountains.
Far off to the westward another line of islands
foreshadowed our present Pacific border. A few minor
islands in the interior completed the archipelago.
From this bare skeleton the continent grew, partly
by the deposit of sediment from the denudation of the
original islands (which once towered miles, perhaps,
where now they rise thousands of feet), but largely also
by the deposit of organic remains, especially in the interior
sea, which teemed with life. In the Silurian
ages, invertebrates--brachiopods and crinoids and
cephalopods--were the dominant types. But very
early--no one knows just when--there came fishes of
many strange forms, some of the early ones enclosed
in turtle-like shells. Later yet, large spaces within the
interior sea having risen to the surface, great marshes
or forests of strange types of vegetation grew and
deposited their remains to form coal-beds. Many times
over such forests were formed, only to be destroyed by
the oscillations of the land surface. All told, the strata
of this Paleozoic period aggregate several miles in thickness,
and the time consumed in their formation stands
to all later time up to the present, according to Professor
Dana's estimate, as three to one.
Towards the close of this Paleozoic era the Appalachian
Mountains were slowly upheaved in great convoluted
folds, some of them probably reaching three or
four miles above the sea-level, though the tooth of time
has since gnawed them down to comparatively puny
limits. The continental areas thus enlarged were
peopled during the ensuing Mesozoic time with multitudes
of strange reptiles, many of them gigantic in size.
The waters, too, still teeming with invertebrates and
fishes, had their quota of reptilian monsters; and in the
air were flying reptiles, some of which measured twenty-
five feet from tip to tip of their batlike wings. During
this era the Sierra Nevada Mountains rose. Near the
eastern border of the forming continent the strata were
perhaps now too thick and stiff to bend into mountain
folds, for they were rent into great fissures, letting out
floods of molten lava, remnants of which are still in
evidence after ages of denudation, as the Palisades
along the Hudson, and such elevations as Mount Holyoke
in western Massachusetts.
Still there remained a vast interior sea, which later
on, in the tertiary age, was to be divided by the slow
uprising of the land, which only yesterday--that is to
say, a million, or three or five or ten million, years ago--
became the Rocky Mountains. High and erect these
young mountains stand to this day, their sharp angles
and rocky contours vouching for their youth, in strange
contrast with the shrunken forms of the old Adirondacks,
Green Mountains, and Appalachians, whose lowered
heads and rounded shoulders attest the weight of
ages. In the vast lakes which still remained on either
side of the Rocky range, tertiary strata were slowly
formed to the ultimate depth of two or three miles, enclosing
here and there those vertebrate remains which
were to be exposed again to view by denudation when
the land rose still higher, and then, in our own time, to
tell so wonderful a story to the paleontologist.
Finally, the interior seas were filled, and the shore
lines of the continent assumed nearly their present outline.
Then came the long winter of the glacial epoch--perhaps
of a succession of glacial epochs. The ice sheet
extended southward to about the fortieth parallel, driving
some animals before it, and destroying those that
were unable to migrate. At its fulness, the great ice
mass lay almost a mile in depth over New England, as
attested by the scratched and polished rock surfaces
and deposited erratics in the White Mountains. Such
a mass presses down with a weight of about one hundred
and twenty-five tons to the square foot, according
to Dr. Croll's estimate. It crushed and ground everything
beneath it more or less, and in some regions
planed off hilly surfaces into prairies. Creeping slowly
forward, it carried all manner of debris with it. When
it melted away its terminal moraine built up the nucleus
of the land masses now known as Long Island
and Staten Island; other of its deposits formed the
"drumlins" about Boston famous as Bunker and
Breed's hills; and it left a long, irregular line of ridges
of "till" or bowlder clay and scattered erratics clear
across the country at about the latitude of New York
city.
As the ice sheet slowly receded it left minor moraines
all along its course. Sometimes its deposits dammed
up river courses or inequalities in the surface, to form
the lakes which everywhere abound over Northern territories.
Some glacialists even hold the view first suggested
by Ramsey, of the British Geological Survey,
that the great glacial sheets scooped out the basins of
many lakes, including the system that feeds the St.
Lawrence. At all events, it left traces of its presence
all along the line of its retreat, and its remnants exist
to this day as mountain glaciers and the polar ice cap.
Indeed, we live on the border of the last glacial epoch,
for with the closing of this period the long geologic past
merges into the present.
PAST, PRESENT, AND FUTURE
And the present, no less than the past, is a time of
change. This is the thought which James Hutton conceived
more than a century ago, but which his contemporaries
and successors were so very slow to appreciate.
Now, however, it has become axiomatic--one can hardly
realize that it was ever doubted. Every new scientific
truth, says Agassiz, must pass through three stages
--first, men say it is not true; then they declare it hostile
to religion; finally, they assert that every one has
known it always. Hutton's truth that natural law is
changeless and eternal has reached this final stage.
Nowhere now could you find a scientist who would dispute
the truth of that text which Lyell, quoting from
Playfair's Illustrations of the Huttonian Theory, printed
on the title-page of his Principles: "Amid all the
revolutions of the globe the economy of Nature has been
uniform, and her laws are the only things that have
resisted the general movement. The rivers and the
rocks, the seas and the continents, have been changed
in all their parts; but the laws which direct those
changes, and the rules to which they are subject, have
remained invariably the same."
But, on the other hand, Hutton and Playfair, and in
particular Lyell, drew inferences from this principle
which the modern physicist can by no means admit.
To them it implied that the changes on the surface of
the earth have always been the same in degree as well
as in kind, and must so continue while present forces
hold their sway. In other words, they thought of the
world as a great perpetual-motion machine. But the
modern physicist, given truer mechanical insight by the
doctrines of the conservation and the dissipation of energy,
will have none of that. Lord Kelvin, in particular,
has urged that in the periods of our earth's in
fancy and adolescence its developmental changes must
have been, like those of any other infant organism,
vastly more rapid and pronounced than those of a later
day; and to every clear thinker this truth also must
now seem axiomatic.
Whoever thinks of the earth as a cooling globe can
hardly doubt that its crust, when thinner, may have
heaved under strain of the moon's tidal pull--whether
or not that body was nearer--into great billows, daily
rising and falling, like waves of the present seas vastly
magnified.
Under stress of that same lateral pressure from contraction
which now produces the slow depression of the
Jersey coast, the slow rise of Sweden, the occasional
belching of an insignificant volcano, the jetting of a
geyser, or the trembling of an earthquake, once large
areas were rent in twain, and vast floods of lava flowed
over thousands of square miles of the earth's surface,
perhaps, at a single jet; and, for aught we know to the
contrary, gigantic mountains may have heaped up their
contorted heads in cataclysms as spasmodic as even the
most ardent catastrophist of the elder day of geology
could have imagined.
The atmosphere of that early day, filled with vast
volumes of carbon, oxygen, and other chemicals that
have since been stored in beds of coal, limestone, and
granites, may have worn down the rocks on the one
hand and built up organic forms on the other, with a
rapidity that would now seem hardly conceivable.
And yet while all these anomalous things went on,
the same laws held sway that now are operative; and a
true doctrine of uniformitarianism would make no
unwonted concession in conceding them all--though
most of the imbittered geological controversies of the
middle of the nineteenth century were due to the failure
of both parties to realize that simple fact.
And as of the past and present, so of the future. The
same forces will continue to operate; and under operation
of these unchanging forces each day will differ
from every one that has preceded it. If it be true, as
every physicist believes, that the earth is a cooling
globe, then, whatever its present stage of refrigeration,
the time must come when its surface contour will assume
a rigidity of level not yet attained. Then, just
as surely, the slow action of the elements will continue
to wear away the land surfaces, particle by particle,
and transport them to the ocean, as it does to-day,
until, compensation no longer being afforded by the
upheaval of the continents, the last foot of dry land will
sink for the last time beneath the water, the last mountain-
peak melting away, and our globe, lapsing like
any other organism into its second childhood, will be
on the surface--as presumably it was before the first
continent rose--one vast "waste of waters." As puny
man conceives time and things, an awful cycle will
have lapsed; in the sweep of the cosmic life, a pulse-
beat will have throbbed.
V. THE NEW SCIENCE OF METEOROLOGY
METEORITES
"An astonishing miracle has just occurred in our district,"
wrote M. Marais, a worthy if undistinguished
citizen of France, from his home at L'Aigle, under date
of "the 13th Floreal, year 11"--a date which outside
of France would be interpreted as meaning May 3,
1803. This "miracle" was the appearance of a "fireball"
in broad daylight--"perhaps it was wildfire,"
says the naive chronicle--which "hung over the meadow,"
being seen by many people, and then exploded
with a loud sound, scattering thousands of stony fragments
over the surface of a territory some miles in extent.
Such a "miracle" could not have been announced at
a more opportune time. For some years the scientific
world had been agog over the question whether such a
form of lightning as that reported--appearing in a clear
sky, and hurling literal thunderbolts--had real existence.
Such cases had been reported often enough, it
is true. The "thunderbolts" themselves were exhibited
as sacred relics before many an altar, and those
who doubted their authenticity had been chided as
having "an evil heart of unbelief." But scientific
scepticism had questioned the evidence, and late in the
eighteenth century a consensus of opinion in the French
Academy had declined to admit that such stones had
been "conveyed to the earth by lightning," let alone
any more miraculous agency.
In 1802, however, Edward Howard had read a paper
before the Royal Society in which, after reviewing the
evidence recently put forward, he had reached the conclusion
that the fall of stones from the sky, sometimes
or always accompanied by lightning, must be admitted
as an actual phenomenon, however inexplicable. So
now, when the great stone-fall at L'Aigle was announced,
the French Academy made haste to send the
brilliant young physicist Jean Baptiste Biot to investigate
it, that the matter might, if possible, be set finally
at rest. The investigation was in all respects successful,
and Biot's report transferred the stony or metallic
lightning-bolt--the aerolite or meteorite--from the realm
of tradition and conjecture to that of accepted science.
But how explain this strange phenomenon? At
once speculation was rife. One theory contended
that the stony masses had not actually fallen, but had
been formed from the earth by the action of the lightning;
but this contention was early abandoned. The
chemists were disposed to believe that the aerolites had
been formed by the combination of elements floating in
the upper atmosphere. Geologists, on the other hand,
thought them of terrestrial origin, urging that they
might have been thrown up by volcanoes. The astronomers,
as represented by Olbers and Laplace, modified
this theory by suggesting that the stones might,
indeed, have been cast out by volcanoes, but by volcanoes
situated not on the earth, but on the moon.
And one speculator of the time took a step even
more daring, urging that the aerolites were neither of
telluric nor selenitic origin, nor yet children of the sun,
as the old Greeks had, many of them, contended, but
that they are visitants from the depths of cosmic space.
This bold speculator was the distinguished German
physicist Ernst F. F. Chladni, a man of no small repute
in his day. As early as 1794 he urged his cosmical
theory of meteorites, when the very existence of meteorites
was denied by most scientists. And he did
more: he declared his belief that these falling stones
were really one in origin and kind with those flashing
meteors of the upper atmosphere which are familiar
everywhere as "shooting-stars."
Each of these coruscating meteors, he affirmed, must
tell of the ignition of a bit of cosmic matter entering
the earth's atmosphere. Such wandering bits of matter
might be the fragments of shattered worlds, or, as
Chladni thought more probable, merely aggregations
of "world stuff" never hitherto connected with any
large planetary mass.
Naturally enough, so unique a view met with very
scant favor. Astronomers at that time saw little to
justify it; and the non-scientific world rejected it with
fervor as being "atheistic and heretical," because its
acceptance would seem to imply that the universe is
not a perfect mechanism.
Some light was thrown on the moot point presently
by the observations of Brandes and Benzenberg, which
tended to show that falling-stars travel at an actual
speed of from fifteen to ninety miles a second. This observation
tended to discredit the selenitic theory, since
an object, in order to acquire such speed in falling
merely from the moon, must have been projected with
an initial velocity not conceivably to be given by any
lunar volcanic impulse. Moreover, there was a growing
conviction that there are no active volcanoes on the
moon, and other considerations of the same tenor led
to the complete abandonment of the selenitic theory.
But the theory of telluric origin of aerolites was by
no means so easily disposed of. This was an epoch
when electrical phenomena were exciting unbounded
and universal interest, and there was a not unnatural
tendency to appeal to electricity in explanation of
every obscure phenomenon; and in this case the seeming
similarity between a lightning flash and the flash
of an aerolite lent color to the explanation. So we
find Thomas Forster, a meteorologist of repute, still
adhering to the atmospheric theory of formation of
aerolites in his book published in 1823; and, indeed, the
prevailing opinion of the time seemed divided between
various telluric theories, to the neglect of any cosmical
theory whatever.
But in 1833 occurred a phenomenon which set the
matter finally at rest. A great meteoric shower occurred
in November of that year, and in observing it
Professor Denison Olmstead, of Yale, noted that all the
stars of the shower appeared to come from a single
centre or vanishing-point in the heavens, and that
this centre shifted its position with the stars, and hence
was not telluric. The full significance of this observation
was at once recognized by astronomers; it demonstrated
beyond all cavil the cosmical origin of the
shooting-stars. Some conservative meteorologists kept
up the argument for the telluric origin for some decades
to come, as a matter of course--such a band trails
always in the rear of progress. But even these doubters
were silenced when the great shower of shooting-
stars appeared again in 1866, as predicted by Olbers
and Newton, radiating from the same point of the
heavens as before.
Since then the spectroscope has added its confirmatory
evidence as to the identity of meteorite and shooting-star,
and, moreover, has linked these atmospheric
meteors with such distant cosmic residents as comets
and nebulae. Thus it appears that Chladni's daring
hypothesis of 1794 has been more than verified, and
that the fragments of matter dissociated from planetary
connection--which be postulated and was declared
atheistic for postulating--have been shown to
be billions of times more numerous than any larger
cosmic bodies of which we have cognizance--so widely
does the existing universe differ from man's preconceived
notions as to what it should be.
Thus also the "miracle" of the falling stone, against
which the scientific scepticism of yesterday presented
"an evil heart of unbelief," turns out to be the most
natural phenomena, inasmuch as it is repeated in our
atmosphere some millions of times each day.
THE AURORA BOREALIS
If fire-balls were thought miraculous and portentous
in days of yore, what interpretation must needs have
been put upon that vastly more picturesque phenomenon,
the aurora? "Through all the city," says the
Book of Maccabees, "for the space of almost forty days,
there were seen horsemen running in the air, in cloth
of gold, armed with lances, like a band of soldiers: and
troops of horsemen in array encountering and running
one against another, with shaking of shields and multitude
of pikes, and drawing of swords, and casting of
darts, and glittering of golden ornaments and harness."
Dire omens these; and hardly less ominous the aurora
seemed to all succeeding generations that observed it
down well into the eighteenth century--as witness
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