In my geological studies I have had a good deal of trouble with the
sedimentary rocks, trying to trace their genealogy and getting them
properly fathered and mothered. I do not think the geologists fully
appreciate what a difficult problem the origin of these rocks
presents to the lay mind. They bulk so large, while the mass of
original crystalline rocks from which they are supposed to have been
derived is so small in comparison. In the case of our own continent
we have, to begin with, about two million of square miles of
Archaean rocks in detached lines and masses, rising here and there
above the primordial ocean; a large triangular mass in Canada, and
two broken lines of smaller masses running south from it on each
side of the continent, inclosing a vast interior sea between them.
To end with, we have the finished continent of eight million or more
square miles, of an average height of two thousand feet above the
sea, built up or developed from and around these granite centres
very much as the body is built up and around the bones, and of such
prodigious weight that some of our later geologists seek to account
for the continental submarine shelf that surrounds the continent on
the theory that the land has slowly crept out into the sea under the
pressure of its own weight. And all this,--to say nothing of the
vast amount of rock, in some places a mile or two in thickness, that
has been eroded from the land surfaces of the globe in later
geological time, and now lies buried in the seas and lakes,--we are
told, is the contribution of those detached portions of Archaean
rock that first rose above the primordial seas. It is a greater
miracle than that of the loaves and the fishes. We have vastly more
to end with than we had to begin with. The more the rocks have been
destroyed, the more they have increased; the more the waters have
devoured them, the more they have multiplied and waxed strong.
Either the geologists have greatly underestimated the amount of
Archaean rock above the waters at the start, or else there are
factors in the problem that have not been taken into the account.
Lyell seems to have appreciated the difficulties of the problem,
and, to account for the forty thousand feet of sediment deposited in
Palaeozoic times in the region of the Appalachians, he presupposes a
neighboring continent to the east, probably formed of Laurentian
rocks, where now rolls the Atlantic. But if such a continent once
existed, would not some vestige of it still remain? The fact that no
trace of it as been found, it seems to me, invalidates Lyell's
theory.
Archaean time in geologic history answers to pre-historic time in
human history; all is dark and uncertain, though we are probably
safe in assuming that there was more strife and turmoil among the
earth-building forces than there has ever been since. The body of
unstratified rock within the limits of North America may have been
much greater than is supposed, but it seems to me impossible that it
could have been anything like as massive as the continent now is. If
this had been the case there would have been no great interior sea,
and no wide sea-margins in which the sediments of the stratified
rocks could have been deposited. More than four fifths of the
continent is of secondary origin and shows that vast geologic eras
went to the making of it.
It is equally hard to believe that the primary or igneous rocks,
where they did appear, were sufficiently elevated to have furnished
through erosion the all but incalculable amount of material that
went to the making of our vast land areas. But the geologists give
me the impression that this is what we are to believe.
Chamberlin and Salisbury, in their recent college geology, teach
that each new formation implies the destruction of an equivalent
amount of older rock--every system being entirely built up out of
the older one beneath it. Lyell and Dana teach the same thing. If
this were true, could there have been any continental growth at all?
Could a city grow by the process of pulling down the old buildings
for material to build the new? If the geology is correct, I fail to
see how there would be any more land surface to-day then there was
in Archaean times. Each new formation would only have replaced the
old from which it came. The Silurian would only have made good the
waste of the Cambrian, and the Devonian made good the waste of the
Silurian, and so on to the top of the series, and in the end we
should still have been at the foot of the stairs. That vast interior
sea that in Archaean times stretched from the rudimentary
Appalachian Mountains to the rudimentary Rocky Mountains, and which
is now the heart of the continent, would still have been a part of
the primordial ocean. But instead of that, this sea is filled and
piled up with sedimentary rocks thousands of feet thick, that have
given birth on their surfaces to thousands of square miles of as
fertile soil as the earth holds.
That the original crystalline rocks played the major part in the
genealogy of the subsequent stratified rocks, it would be folly to
deny. But it seems to me that chemical and cosmic processes, working
through the air and the water, have contributed more than they have
been credited with.
It looks as if in all cases when the soil is carried to the
seabottom as sediment, and again, during the course of ages,
consolidated into rocks, the rocks thus formed have exceeded in bulk
the rocks that gave them birth. Something analogous to vital growth
takes place. It seems as if the original granite centres set the
world-building forces at work. They served as nuclei around which
the materials gathered. These rocks bred other rocks, and these
still others, and yet others, till the framework of the land was
fairly established. They were like the pioneer settlers who plant
homes here and there in the wilderness, and then in due time all the
land is peopled.
The granite is the Adam rock, and through a long line of descent the
major part of all the other rocks directly or indirectly may be
traced. Thus the granite begot the Algonquin, the Algonquin begot
the Cambrian, the Cambrian begot the Silurian, the Silurian begot
the Devonian, and so on up through the Carboniferous, the Permian,
the Mesozoic rocks, the Tertiary rocks, to the latest Quaternary
deposit.
But the curious thing about it all is the enormous progeny from so
small a beginning; the rocks seem really to have grown and
multiplied like organic beings; the seed of the granite seems to
have fertilized the whole world of waters, and in due time they
brought forth this huge family of stratified rocks. There stands the
Archaean Adam, his head and chest in Canada, his two unequal legs
running, one down the Pacific coast, and one down the Atlantic
Coast, and from his loins, we are told, all the progeny of rocks and
soils that make up the continent have sprung, one generation
succeeding another in regular order. His latest offspring is in the
South and Southwest, and in the interior. These are the new
countries, geologically speaking, as well as humanly speaking.
The great interior sea, epicontinental, the geologists call it,
seems to have been fermenting and laboring for untold aeons in
building up these parts of the continent. In the older Eastern
States we find the sons and grandsons of the old Adam granite; but
in the South and West we find his offspring of the twentieth or
twenty-fifth generation, and so unlike their forebears; the Permian
rocks, for instance, and the Cretaceous rocks, are soft and
unenduring, for the most part. The later slates, too, are
degenerates, and much of the sandstones have the hearts of
prodigals. In the Bad Lands of Arizona I could have cut my way into
some of the Eocene formations with my pocket-knife. Apparently the
farther away we get from the parent granite, the more easily is the
rock eroded. Nearly all the wonderful and beautiful sculpturing of
the rocks in the West and Southwest is in rocks of comparatively
recent date.
Can we say that all the organic matter of our time is from
preexisting organic matter? one organism torn down to build up
another? that the beginning of the series was as great as the end?
There may have been as much matter in a state of vital organization
in Carboniferous or in Cretaceous times as in our own, but there is
certainly more now than in early Palaeozoic times. Yet every grain
of this matter has existed somewhere in some form for all time. Or
we might ask if all the wealth of our day is from preexisting
wealth--one fortune pulled down to build up another,--too often the
case, it is true,--thus passing the accumulated wealth along from
one generation to another. On the contrary, has there not been a
steady gain of that we call wealth through the ingenuity and the
industry of man directed towards the latent wealth of the earth? In
a parallel manner has there been a gain in the bulk of the secondary
rocks through the action of the world-building forces directed to
the sea, the air, and the preexisting rocks. Had there been no gain,
the fact would suggest the ill luck of a man investing his capital
in business and turning it over and over, and having no more money
at the end than he had in the beginning.
Nothing is in the sedimentary rock that was not at one time in the
original granite, or in the primordial seas, or in the primordial
atmosphere, or in the heavens above, or in the interior of the earth
beneath. We must sweep the heavens, strain the seas, and leach the
air, to obtain all this material. Evidently the growth of these
rocks has been mainly a chemical process--a chemical organization of
preexisting material, as much so as the growth of a plant or a tree
or an animal. The color and texture and volume of each formation
differ so radically from those of the one immediately before it as
to suggest something more than a mere mechanical derivation of one
from the other. New factors, new sources, are implied. "The farther
we recede from the present time," says Lyell, "and the higher the
antiquity of the formations which we examine, the greater are the
changes which the sedimentary deposits have undergone." Above all
have chemical processes produced changes. This constant passage of
the mineral elements of the rocks through the cycle of erosion,
sedimentation, and reinduration has exposed them to the action of
the air, the light, the sea, and has thus undoubtedly brought about
a steady growth in their volume and a constant change in their color
and texture. Marl and clay and green sand and salt and gypsum and
shale, all have their genesis, all came down to us in some way or in
some degree, from the aboriginal crystalline rocks; but what
transformations and transmutations they have undergone! They have
passed through Nature's laboratory and taken on new forms and
characteristics.
"All sediments deposited in the sea," says my geology, "undergo more
or less chemical change," and many chemical changes involve notable
changes in volume of the mineral matter concerned. It has been
estimated that the conversion of granite rock into soil increases
its volume eighty-eight per cent, largely as the result of
hydration, or the taking up of water in the chemical union. The
processes of oxidation and carbonation are also expansive processes.
Whether any of this gain in volume is lost in the process of
sedimentation and reconsolidation, I do not know. Probably all the
elements that water takes from the rocks by solution, it returns to
them when the disintegrated parts, in the form of sediment in the
sea, is again converted into strata. It is in this cycle of rock
disintegration and rock re-formation that the processes of life go
on. Without the decay of the rock there could be no life on the
land. Water and air are always the go-betweens of the organic and
inorganic. After the rains have depleted the rocks of their soluble
parts and carried them to the sea, they come back and aid vegetable
life to unlock and appropriate other soluble parts, and thus build
up the vegetable and, indirectly, the animal world.
That the growth of the continents owes much to the denudation of the
sea-bottom, brought about by the tides and the ocean-currents, which
were probably much more powerful in early than in late geologic
times, and to submarine mineral springs and volcanic eruptions of
ashes and mud, admits of little doubt. That it owes much to
extra-terrestrial sources--to meteorites and meteoric dust--also
admits of little doubt.
It seems reasonable that earlier in the history of the evolution of
our solar system there should have been much more meteoric matter
drifting through the interplanetary spaces than during the later
ages, and that a large amount of this matter should have found its
way to the earth, in the form either of solids or of gases. Probably
much more material has been contributed by volcanic eruptions than
there is any evidence of apparent. The amount of mineral matter held
in solution by the primordial seas must have been enormous. The
amount of rock laid down in Palaeozoic times is estimated at fifty
thousand feet, and of this thirteen thousand feet were limestone;
while the amount laid down in Mesozoic times, for aught we know a
period quite as long, amounts to eight thousand feet, indicating, it
seems to me, that the deposition of sediment went on much more
rapidly in early geologic times. We are nearer the beginning of
things. All chemical processes in the earth's crust were probably
more rapid. Doubtless the rainfall was more, but the land areas must
have been less. The greater amount of carbon dioxide in the air
during Palaeozoic times would have favored more rapid carbonation.
When granite is dissolved by weathering, carbon unites with the
potash, the soda, the lime, the magnesia, and the iron, and turns
them into carbonates and swells their bulk. The one thing that is
passed along from formation to formation unchanged is the quartz
sand. Quartz is tough, and the sand we find to-day is practically
the same that was dissolved out of the first crystalline rocks.
Take out of the soil and out of the rocks all that they owe to the
air,--the oxygen and the carbon,--and how would they dwindle! The
limestone rocks would practically disappear.
Probably not less that one fourth of all the sedimentary rocks are
limestone, which is of animal origin. How much of the lime of which
these rocks were built was leached out of the land-areas, and how
much was held in solution by the original sea-water, is of course a
question. But all the carbon they hold came out of the air. The
waters of the primordial ocean were probably highly charged with
mineral matter, with various chlorides and sulphates and carbonates,
such as the sulphate of soda, the sulphate of lime, the sulphate of
magnesia, the chloride of sodium, and the like. The chloride of
sodium, or salt, remains, while most of the other compounds have
been precipitated through the agency of minute forms of life, and
now form parts of the soil and of the stratified rocks beneath it.
If the original granite is the father of the rocks, the sea is the
mother. In her womb they were gestated and formed. Had not this
seesaw of land and ocean taken place, there could have been no
continental growth. Every time the land took a bath in the sea, it
came up enriched and augmented. Each new layer of rocky strata taken
on showed a marked change in color and texture. It was a kind of
evolution from that which preceded it. Whether the land always went
down, or whether the sea at times came up, by reason of some
disturbance of the ocean floors in its abysmal depths, we have no
means of knowing. In any case, most of the land has taken a sea bath
many times, not all taking the plunge at the same time, but
different parts going down in successive geologic ages. The original
granite upheavals in British America, and in New York and New
England, seem never to have taken this plunge, except an area about
Lake Superior which geologists say has gone down four or five times.
The Laurentian and Adirondack ranges have never been in pickle in
the sea since they first saw the light. In most other parts of the
continent, the seesaw between the sea and the land has gone on
steadily from the first, and has been the chief means of the
upbuilding of the land.
To the slow and oft-repeated labor-throes of the sea we owe the
continents. But the sea devours her children. Large areas, probably
continental in extent, have gone down and have not yet come up, if
they ever will. The great Mississippi Valley was under water and
above water time after time during the Palaeozoic period. The last
great invasion of the land by the sea, and probably the greatest of
all, seems to have been in Cretaceous times, at the end of the
Mesozoic period. There were many minor invasions during Tertiary
times, but none on so large a scale as this Cretaceous invasion. At
this time a large part of North and South America, and of Europe,
and parts of Asia and Australia went under the ocean. It was as if
the earth had exhaled her breath and let her abdomen fall. The sea
united the Gulf of Mexico with the Arctic Ocean, and covered the
Prairie and the Gulf States and came up over New Jersey to the foot
of the Archaean Highlands. This great marine inundation probably
took place several million years ago. It was this visitation of the
sea that added the vast chalk beds to England and France. In parts
of this country limestone beds five or six thousand feet thick were
laid down, as well as extensive chalk beds. The earth seems to have
taken another hitch in her girdle during this era. As the land went
down, the mountains came up. Most of the great Western
mountain-chains were formed during this movement, and the mountains
of Mexico were pushed up. The Alps were still under the sea, but the
Sierra and the Alleghanies were again lifted.
It is very interesting to me to know that in Colorado charred wood,
and even charcoal, have been found in Cretaceous deposits. The fact
seems to give a human touch to that long-gone time. It was, of
course, long ages before the evolution of man, as man, had taken
place, yet such is the power of association, that those charred
sticks instantly call him to mind, as if we had come upon the place
of his last campfire. At any rate, it is something to know that man,
when he did come, did not have to discover or invent fire, but that
this element, which has played such a large part in his development
and civilization, was here before him, waiting, like so many other
things in nature, to be his servant and friend. As Vulcan was
everywhere rampant during this age, throwing out enough lava in
India alone to put a lava blanket four or five feet thick over the
whole surface of the globe, it was probably this fire that charred
the wood. It would be interesting to know if these enormous
lava-flows always followed the subsidence of some part of the
earth's crust. In Cretaceous times both the subsidence and the lava-
flows seem to have been worldwide.