EARTHQUAKES OF THE GEOLOGICAL PAST--CATACLYSMS
There were numerous volcanoes in the geological past; therefore, since
volcanic eruptions are generally attended by earthquake shocks, it
follows that during that remote past the earth has been violently
shaken by earthquakes. Indeed, if we assume, as we believe to be the
case, that the cause of earthquakes is correctly to be traced to an
originally heated globe which is gradually cooling, it follows that
the earth was necessarily subject to great earthquakes almost from the
time when it began to cool.
But to establish as a fact the occurrence of an earthquake at so
remote a time in the earth's history is far more difficult than to
detect the occurrence of a volcano at that time. While the earthquake
shocks may produce fissures in the earth's crust, and may be
accompanied by great changes of level, yet the great time that has
elapsed between such occurrences and the present would permit the
various geological agencies that are at work either to cover these
fissures completely, or completely to remove by erosion, or in other
similar ways, the rocks in which they occurred. It is different in
the case of a volcano; for the volcanic craters are in many cases
still left standing, and then there are the voluminous sheets of lava
that have spread over great areas of the earth, as well as numerous
volcanic cones. Besides, there are thousands of square miles of
surface that have been covered, often to great depths, by deposits of
volcanic dust thrown out at one time or another from the craters of
the then active volcanoes.
I am sure you will acknowledge that any force capable of causing great
cracks or fissures in the earth's crust, must, while doing this, have
produced violent shakings of the earth. Great cracks or fissures are
to be found in the rocks of all the geological formations. These are a
record of the earthquakes that must have attended these convulsions.
And there is plenty of evidence to show that the earth's crust has
been torn into these fissures in places deep down below the present
surface; for, by the action of water, many of these portions have
been uncovered so that these great cracks or fissures which have been
afterwards filled with a molten rock that has hardened can be seen in
the great dikes that still remain.
But there are still other evidences of the existence of earthquakes
during the geological past. There are found in the different strata
of the earth's crust fossil remains of the plants and animals that
lived on the earth long before the creation of man. By a careful study
of these fossils we know positively the kinds of animals and plants
that lived on the earth, in its waters, or in its atmosphere, when
these strata were being deposited. It is in this way possible for a
geologist to trace the life of the earth and its development as it
is written on the great book of which the earth's different strata
form the separate pages. Now, a careful study of the earth's fauna
and flora during the geological past, shows, beyond any question,
that occasionally great changes have occurred in the earth; for, here
and there, during different times, we find that certain species of
animals and plants have completely disappeared, to be followed, after
certain intervals, by entirely different species. It is evident,
therefore, that changes have occurred that have made it impossible for
the animals and plants that formerly lived on the earth to exist under
the changed conditions. These occurrences are known to geologists
as _exterminations_, _catastrophes_, or _cataclysms_. They are also
sometimes called _revolutions_, for they mark a more or less complete
wiping-out of the animals living at the time they occurred.
If you will try to think you will readily understand how great a
catastrophe must be, that would be able to wipe out or completely
destroy an entire race of animals.
You have doubtless read with astonishment the terrible catastrophe
that accompanied the eruption of Krakatoa, especially at the loss of
life and property caused by the great waves that were set up in the
ocean, but far reaching as these losses were they have nevertheless
affected but a limited portion of the earth. The plain truth is even
more stupendous, for catastrophes of the geological past appear to
have been so far-reaching and powerful as to affect the whole surface
of the earth, and to have annihilated entire races of animals and
plants as if they had never existed.
Geologists are all practically agreed that there are only two ways in
which such exterminations of the earth's life could have been caused,
and these are changes in the earth's climate, or the starting of waves
in the sea by great earthquakes. In the sea; for it must be borne
in mind that in the geological past the greater part of the earth's
surface was covered by water, and the land areas were comparatively
small and low, so that waves created by earthquakes might easily have
overwhelmed the entire land surface.
Of course, it is fair to suppose that in many cases these
exterminations may have been caused by sudden changes of climate, such
as would naturally have resulted from any change in the direction
of hot ocean currents which formerly flowed from the equator to the
poles. The appearance of a fairly large mass of land in the central
parts of the ocean might readily have turned aside the hot ocean
currents that formerly swept over the polar regions, thus greatly
lowering the earth's average temperature in these regions.
But it seems probable that the principal cause of the destruction of
life in the geological past was produced by earthquake waves in the
sea, sweeping over the continents. Let us, therefore, examine two of
the earth's principal geological revolutions or cataclysms; namely,
that which occurred at the close of an early geological time known as
the Palaeozoic, and that which occurred at the end of a geological
time intermediate between the Palaeozoic time or the time of ancient
life, called the Mesozoic time, and the Cenozoic time, or the time
immediately preceding the present time. These two revolutions are
called by Dana, _the Post-Palaeozoic_, or _Appalachian Revolution_,
and the _Post-Mesozoic Revolution_. Both were characterized by the
making of great mountain systems, and were, therefore, especially
liable to repetitions of tremendous earthquakes that must have
produced enormous waves in the ocean.
"Palaeozoic time," says Dana, "closed with the making of one of the
great mountain ranges of North America--the Appalachian, besides
ranges in other lands, and in producing one of the most universal and
abrupt disappearances of life in geological history. So great an event
is properly styled a revolution."
Towards the close of the Palaeozoic time immense disturbances of
the earth's crust occurred during the uplifting of the Appalachian
Mountain System. One may, perhaps, form some faint idea of the
immensity of the forces at work, from the fact that there were
great faults produced by the uplifting of the lands attended with
displacement amounting to 10,000 or 20,000 feet or more; that in parts
of southwestern Virginia there were flexure faults 100 miles in length.
As to the probability of the extensive exterminations that have
occurred during these times being produced by earthquake waves, Dana
speaks thus:
"The causes of the extermination are two.... (1) a colder
climate.... (2) earthquake waves produced by orogenic
movements (movements producing mountain ranges). If North
America from the west of the Carolinas to the Mississippi
Valley can be shaken in consequence of a little slip along
a fracture in times of perfect quiet (the allusion here
to the Charleston earthquake, in 1886), and ruin mark its
movements, incalculable violence and great surgings of
the ocean should have occurred and been often repeated
during the progress of flexures, miles in height and
space, and slips along newly opened fractures that kept up
their interrupted progress through thousands of feet of
displacements....
"Under such circumstances the devastation of the sea-border
and the low-lying land of the period, the destruction of
their animals and plants, would have been a sure result.
The survivors within a long distance of the coastline
would have been few. The same waves would have swept over
European land and seas, and there found coadjutors for new
strife in earthquake waves of European origin. These times
of catastrophe may have continued in America through half
of the following Triassic period; for fully two thirds of
the Triassic period are unrepresented by rocks and fossils
on the Atlantic border."
Coming now to the Post-Mesozoic revolution this period was marked by
the making of the greatest of the North American mountain systems.
Dana points out that this revolution affected the summit region of the
Rocky Mountains over a broad belt probably as long as the western side
of the continent.
This great belt of mountain-making extended from the Arctic regions
through North America, probably paralleled by like work, of equal
extent, in South America, but on a more eastern line.
"The disappearance of species," says Dana, "at the close of Mesozoic
time was one of the two most noted in all geological history. Probably
not a tenth part of the animal species of the world disappeared
at the time, and far less of the vegetable life and terrestrial
Invertebrates; yet the change was so comprehensive that no Cretaceous
species of Vertebrate is yet known to occur in the rocks of the
American Tertiary, and not even a marine Invertebrate."
In tracing the causes of these disappearances, Dana points out that,
perhaps, the principal cause was a decrease in the temperature of the
ocean, since the destructions were limited in large measure to marine
life. He regards, however, the other most probable cause as traceable
to earthquake waves; for the making of a great mountain range along
the entire length of the continent resulted in displacements of
the rock formations along lines hundreds of miles in length. Such
displacements must have been attended by a succession of earthquakes
of unusual violence, causing the destruction by sudden shocks beneath,
and resulting, directly and indirectly, in waves sweeping over the
continent. Since at this time the land was still low for the greater
part, the huge waves must have repeatedly swept over the greater part
of the land, leaving only the smaller species of animals and the
vegetation.
It is evident, therefore, that during the geological past earthquakes
occurred that were probably vastly greater than any that have occurred
on the earth during more recent times.