EARTHQUAKES.

Gisborne Standard and Cook County Gazette, Volume III, Issue 317, 27 June 1889, Page 2

EARTHQUAKES.

WHAT IS THE CAUSE OF THEM J Sinox the recent earthquake there has been much disouulon ae to the cause of earthquakes, and as the Interest in the subject has not been abated, tbe following article on “ Tbe stability of the earth," from Scribner’s Magazine, will be very instructive Although aoosss to the deeper earth is da nied us, we are probably safe in our belief that tbe steadfast upward growth ot the lands is due to a simple, cause, which is as follows, viz.:—The diameter of the earth depends, io part, upon ths amount of heat it contains. This heat is constantly flying out into space. Each moment, from every part of its surface, some portion of the original store escapes into the cold realms of space. With every volcanic eruption a great outrush ot heat occurs. Thus, the earth is steadfastly shrinking ; each age it is girdled by a shorter line. If, by this escape of heat, every part of the earth were equally cooled, there would be no continents, for the whole mass would fail equally toward the centre ; but the deeper parts of the earth loss by fir the most heat, for the simple reason that they have tho moot to part with. The superficial portions long einoe parted with tha larger part of their original caloric. Thus, the upper portion, or crust, as it is commonly called, does not oontraot as much as the interior mass, and therefore the inner part tends to leave the outer crust behind. But for the weight of this outer seotion, it would be left more or less separated from the interior mass ; but as its weight is much greater than it can sustain, it is compelled to wrinkle, or, in other words, to form the great ridges and furrows which constitute the continents and the ocean basins. Geologists are still in debate as to tho precise manner in which this wrinkling comes about, and as to the way in which it has effected the construction of continents and mountains ; but they very generally believe that it is due to the oau-e above mentioned—i,e ,to the loss of heat, which is greater from the interior than from ths superficial parts ut the earth. In a rough way, this folding of the outer part of the earth may be compared to the wrinkling of the skin of a dried apple ; only in the fruit the shrinkage of the interior is doe to the escape of water, while in tbe case of the earth it is due to the loss of energy in tha form of hast. It is easy for the reader to see that this wrinkling sets a vast amount ot machinery in operation, and compels tho movemeht of masses which cannot be expected to stir without shock. We have seen that ths power which urgai the continents into their great folds, or the mountains into the lesser corrugations, afford a simple and, indeed, neoa.sjry cause of certain violent strains, which in tend to compress tho rocks into a than they originally occupied. influence of these strains, any one or more the following accidents may occur : The rocks may wrinkle into folds like those we find Iq mountains ; they may be broken along their natural joints or fracture-planes, and the sundered parts may slip over each other, or the rocks may be squeezed oat like doogh under the cook’s rotter, and an escape to a region of loss pressure. In taking any ot these methods ot relief, the rooks are naoHsarily liable to many sudden starte, each accompanied by readings and other violent movements. When, in winter, the frocan ground rives asynder, though tho crevice is but a small fraction nt an inch wide, end a foot nr two deep, the ground is often so violently jarred that a sensible earthquake is produced, which may be felt hundreds ot feet away from the souros of tbe disturbance. It is, indeed, likely that many of the slight local w hioh are obroniclod may be due to this cause. We eon, therefore, readily see that when the fracture has a length of miles, and the depth of thousands of feet, as is tbe ease in many faults, tha jar occasioned may produce a disastrous shook, which may involve a great area of country. But it is only the rending ot the fissures which produces the jar; after the rift is formed, the several masses of rook slip over each other—the rocks on one aide rising, while those on the other side slip down. These two great walls on either aide of the fault are not smooth, but each la jagged with projections, which are often ruptured ae they grind against each other in their opposed movement. By each of these minor tendings, as well as by the formation of tho principal fracture, the rocka are set a-quivering. These faults are, indeed, earthquake factories. The greatest shock is produced at the time of their formation; but from time to time they art freshly ruptured, perhaps after a vein deposit has bound their adjacent walls together, and the disturbance io again and again renewed. It Is evident that many great faults—those in which the slipping of the tides on each other haa amounted to a thousand feet or more—have moved only a few inches at any one time, so that a singlb such fracture may have given rise to hundreds, if not thousands, of ealthquake shocks.