The Physical And Final Causes Of Earthquakes.

The investigation of phenomena so powerful and mysterious as those connected with earthquakes would be interesting under any circumstance; but the enquiry becomes doubly so on the very spot where, and at the very time when, these phenomena have excited so much attention. After enjoying the unenviable privilege of witnessing such alarming concussions of the earth, we are actuated by motives page 148 higher than those of mere curiosity to ascertain by what means, and for what purposes such powerful agencies are called into operation.

The motions of earthquakes are of three kinds; undulating, succussive, and vorticose. The undulatory motion proceeds horizontally, and heaves the ground successively upwards and downwards, going onward in a uniform direction—this is the most common and the most harmless kind of earthquakes. In the succussive motion the ground is heaved up in a direction more or less approaching to the perpendicular, as in the explosion of a mine—this is more dangerous than the former; the earthquake at Lisbon in 1755 partook largely of this motion. The vorticose motion seems to be a combination of the two preceding ones, several undulations taking place contemporaneously, and thus interfering with one another, and acting like cross seas during a storm—this is the movement that has been felt in the most violent and disastrous catastrophes on record; the earthquake that ravaged the Carraccas in 1812, and destroyed 10,000 of the inhabitants, was of this kind. The motion in earthquakes sometimes proceeds from a common centre, in circular vibrations, like the concentric circles produced when a stone falls upon a smooth sheet of water; this was the case to some extent at Lisbon. More frequently the motion is linear, running parellel with some mountain range, as along the western coast of South America, where the motion runs parallel with the Andes. The motion of the ground during an earthquake is said to be due to a wave propagated along its surface from a point where it has been produced by a sudden impulse. The original impulse may either be on land or beneath the bed of the ocean; the latter is the more frequent and the more formidable, there being no vents beneath the ocean by which the forces may escape. When earthquakes originate beneath the land, an elastic wave is propagated through the solid crust of the earth, and another through the air, till both are spent or lost? in the ocean. When the force originates beneath the page 149 ocean, there are four waves produced and propagated simultaneously—one through the land; one through the air, causing a sound like cannon or thunder; a third upon the surface of the ocean, which rolls into the land long after the shock through the earth has arrived and spent itself; and a fourth wave (of sound merely) which reaches the shore, and is heard long before the great ocean wave rolls in. Whether the original impulse is produced by electric or volcanic influences is mater of dispute. From the universal diffusion of electricity, and its intimate connection with almost every process and operation in nature—from the extreme rapidity with which the motion in earthquakes is propagated—from the analogy between the noise and shock accompanying lightning, and those which are experienced during an earth quake—from the electrical state of the air both before and after the shocks—and from the sulphurous smell sometimes perceived resembling the electric shock; it has been thought that earthquakes were occasioned by subterranean discharges of electricity. Much has yet to be learned respecting this powerful and mysterious agent. But “it is not easy to persuade our selves,” says Dr. Daubeny, “that in the solid strata of the globe, consisting as it does of conductors, the same accumulation, of electricity can ever take place as that which produces the phenomena of thunder and lightning in the atmosphere. Nor indeed are the facts observed of such a nature as to baffle our attempts at referring them to their more obvious cause—volcanic processes. We have abundant instances of undulatery motions propagated through solid matter with immense velocity. A powerful blow, the fall of a large mass of stone, or the explosion of a powder magazine, has been known to cause a vibration like an earthquake to be felt to a great distance. The shoek produced by the head of a pin set to vibrate at one end of a long beam, was found by Gay-Lussac to be distinctly perceptible at the other.” In all regions of the earth we find earthquakes and volcanoes in close connection, Subterranean page 150 fire, according to its force or its locality, produces three phenomena—volcanoes, earthquakes, or thermal springs. Volcanic agency is by some ascribed to mechanical, and by others to chemical causes. It is found by experiments, that the heat in mines increases progressively with their depth; and if the ratio of increase be continued uniformly from the surface to the centre, the whole globe, with the exception of a comparatively thin external shell, must be fluid, and many times hotter than melted iron. On this theory, volcanoes, earthquakes, and hot springs are occasioned by the passage of heat from the centre to the surface. According to others, and what appears more probable, the centre is cold and quiescent, and the volcanic agency is produced by chemical causes. It is found, that when air or water comes in contact with the unoxidized metallic bases of earths and alkalies, these bases oxidize and ignite; and as air and water are continually forcing themselves into the minutest crevices on the surface of the earth, they are constantly coming in contact with these unoxidized metallic bases, and thus the conditions that produce ignition are being continually fulfilled. It is fully ascertained that all volcanoes are situated near the sea, and thus in close and constant contact with water. In South America the whole range of the Andes runs near the west coast. The islands of the West Indies abound with volcanic products. A volcanic band runs along the South of Europe, through Greece, Italy, Sicily, and the Peninsula, skirting the Continent from the Island of Santorini in the Grecian Archipelago, to the Azores in the Atlantic. A similar band of active volcanic agency skirts the continent of Asia, beginning at the Bay of Bengal, passing through Sumatra, Java, the Molnccas, the Phillippines, and terminating in the Peninsula of Kamtschatka and the Aleutian Islands. At the Molucca Islands a branch goes off, skirting, though somewhat rudely, the eastern coast of the Australian Continent, passing through New Guinea, the New Hebrides, New Caledonia, New Zealand, and is page 151 found in nearly the same parallel of longitude, 77½°S., in the lately discovered southern continent called Victoria Land, where the active crater of Mount Erebus, 12,600 feet above the level of the sea, is pouring forth its smoke and flame amid regions covered with everlasting snow and ice.

It is next asked “What are the purposes served by earthquakes? sudden, awful, and irresistible; inspiring terror, and producing destruction, are they unmixed evils—like angels commissioned by heaven, to pour nothing but vials of divine wrath upon a sinful world? or are earthquakes like the other operations in nature, attended with partial and temporary evils, but productive of general and permanent good? We have no hesitation in affirming that all the arrangements of divine providence are characterized by a principle of benificence, and are designed to promote the happiness of man.” The ground is cursed for man's sin, and “the whole creation groaneth and travaileth in pain.” All suffering must be traced up to sin, in some way or other; but the amount of suffering and death caused by the convulsions of the elements, and coming directly from the hand of God, is really small and trifling, compared with those evils that men bring upon themselves and others: the amount of suffering and death caused in a few years by war, slavery, or intemperance, is more than has been occasioned by all the eruptions of volcanoes or convulsions of earthquakes for the last forty centuries. Earthquakes serve important purposes in the economy of nature. They cause either a sudden, or gradual upheaving of the earth, and thus preserve the proper proportion between land and water, and cecure the conditions by which vegetable and animal life is produced and sustained. Astronomers have proved that there has been no change in the diameter of the earth for the last two thousand years. Fire and water, the igneous and the acqueous agencies are the two antagonistic forces by which the balance of land and water is preserved. Water is continually wearing down the higher parts of the earth, and page 152 carrying them into the sea; and unless there were some counteracting influence, the whole earth in the course of ages would be covered with water: but the internal fires—the volcanic agencies—keep up a constant process of elevation; for not a day perhaps elapses but an earthquake takes place somewhere. Mr. Darwin found that the eastern coast of South America, for a distance of 1180 miles, had been raised to the height of 100 feet in La Plata, and 400 feet in Patagonia; and in districts of the west coast even considerably higher.—“Where volcanic agencies have not operated,” says Dr. Daubeny, “as appears to be the case in the centre of Australia, the level surface of the land, receiving no fertilizing streams from the mountains, and intersected by no arms of the sea, or extensive lakes by which a communication with other parts of the globe can be maintained, seems abandoned to hopeless sterility, and becomes indeed almost unapproachable by human enterprise. Were volcanic forces ever to become rife within this vast continent—were a range of Cordilleras to stretch across its now desolate surface, a new character would be imparted to its physiognomy, and the dull uniformity of its outline be succeeded by the smiling aspect of a European landscape.”

But some may object that while earthquakes are a general benefit, they are a great local evil. We are inclined to think that earthquakes have local as well as general advantages greater than any local evils they inflict. The volcanic agencies generate and evolve carbonic acid gas, and other substances of great benefit for the fertilizing of the countries where they are in operation: volcanic countries, and those agitated by earthquakes, are in general remarkable for fertilty. “The sloping sides of Vesuvius,” says Lyell, “give nourishment to a vigorous and healthy population of about 80,000 souls, and the surrounding hills and plains, together with several of the adjoining isles, owe the fertility of their soil to matter ejected by prior eruptions. Had the fundamental page 153 limestone of the Appenines remained uncovered throughout the whole area, the country could not have sustained a twentieth part of its present population.” No country has suffered more from volcanoes and earthquakes than Campania, and yet what is its general character? “A climate,” says Forsyth, “where heaven's breath smells sweet and wooingly,—a vigorous and luxuriant nature unparalleled in its productions,—a coast which was once the fairy land of poets, and the favourite retreat of great men. Even the tyrants of creation loved this alluring region, spared it, adorned it, lived in it, and died in it.” Moral evils, those caused by men, are, beyond all comparison, more to be dreaded than those arising from physical causes, even the most terrific. Physical evils have almost invariably some greater compensating advantages, “The fertility,” says Dr. Daubeny, “of many volcanic districts is proverbial, and it may be a question whether the free extrication of carbonic acid, possibly even of ammonia, from the ground in their neighbourhood, may not exert a favourable influence upon the surrounding vegetation.

“All classical scholars recollect the luxurance attributed to the lands of Campania, which in Pliny's time bore three crops in the year, being sown once with panic and twice with wheat, and yet when allowed to rest betwixt crops, produced spontaneously roses more fragrant than those which resulted from cultivation in other places. Nor has this land like much of that which is found in the newly-settled parts of America, lost its fertility by continued cropping, but at the present day, as of old, stands distinguished even in that highly famed region for the abundant returns which it yields to the husbandman.“^* Nothing appears more certain than it is to the volcanic agency of past ages that New Zealand is indebted for its page 154 richest elements of fertility and wealth,—its lofty-mountain ranges, clothed with dense forests, that attract the clouds and secure such an amount of moisture as to feed springs, streams, and river without ever failing; so that if the resources of the country were fully developed, the description of ancient Canaan—a volcanic country, and often agitated by earthquakes—would almost literally apply to it: “A good land, a land of brooks of water, of fountains and depths, that spring out of valleys and hills; a land of wheat and barley, and vines and fig-trees, and pomegranates; a land of oil, olive, and honey; a land where thoushalt eat bread without scarceness, thou shall not lack anything in it; a land whose stones are iron, and out of whose hills thou mayst dig brass; a land which the Lord thy God careth for; the eyes of the Lord thy God are always upon it, from the beginning of the year even unto the end of the year,” (Deut, viii, 1–9. xi, 12.) If by the blessing of God we ean succeed in thoroughly leavening the community with the principles and spirit of the Bible, and thus fortify ourselves against the operation of moral evils; a very little common prudence will secure us from the effects of all the physical evils to which we are exposed—not excepting the alarming visitation of an occasional earthquake.