The Wonder Book of Volcanoes and Earthquakes

by Edwin J. Houston

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: