PHILOSOPHICAL SUBJECTS

CAUSES OF EARTHQUAKES.*

FROM THE PENNSYLVANIA GAZETTE, DECEMBER 15TH, 1737

THE late earthquake felt here, and probably in all the neighbouring provinces, having made many people desirous to know what may be the natural cause of such violent concussions, we shall endeavour to gratify their curiosity, by giving them the various opinions of the learned on that head.

Here naturalists are divided. Some ascribe them to water, others to fire, and others to air; and all of them with some appearance of reason. To conceive which, it is to be observed, that the earth everywhere abounds in huge subterraneous caverns, veins, and canals, particularly about the roots of mountains; that of these cavities, veins, &c., some are full of water, whence are composed gulfs, abysses, springs, rivulets; and others. full of exhalations; and that some parts of the earth are replete with nitre, sulphur, bitumen, vitriol, &c. This premised,

1. The earth itself may sometimes be the cause of its own shaking; when, the roots or basis of some large

* This paper is contained in Duane's edition of the author's writings, but in no previous collection. It is taken from the newspaper published by Franklin; but it is dated several years earlier than any of his other pieces on philosophical subjects, and appears to be rather a compilation from various authors than an original composition. It is not without interest, however, as presenting a curious account of earthquakes, and of the theories respecting their causes.— EDITOR.

mass being dissolved, or worn away by a fluid underneath, it sinks into the same, and, with its weight, occasions a tremor of the adjacent parts, produces a noise, and frequently an inundation of water.

2. The subterraneous waters may occasion earthquakes by their overflowing, cutting out new courses, &c. Add, that the water, being heated and rarefied by the subterraneous fires, may emit fumes, blasts, &c., which by their action, either on the water or immediately on the earth itself, may occasion great succussions.

3. The air may be the cause of earthquakes; for, the air being a collection of fumes and vapors raised from the earth and water, if it be pent up in too narrow viscera of the earth, the subterraneous or its own native heat rarefying and expanding it, the force, wherewith it endeavours to escape, may shake the earth; hence there arise divers species of earthquakes, according to the different position, quantity, &c., of the imprisoned aura.

Lastly, fire is a principal cause of earthquakes; both as it produces the aforesaid subterraneous aura or vapors; and as this aura, or spirit, from the different matter and composition whereof arise sulphur, bitumen, and other inflammable matters, takes fire, either from other fire it meets withal, or from its collision against hard bodies, or its intermixture with other fluids; by which means bursting out into a greater compass, the place becomes too narrow for it; so that, pressing against it on all sides, the adjoining parts are shaken; till, having made itself a passage, it spends itself in a volcano, or burning mountain.

But to come nearer to the point. Dr. Lister is of opinion, that the material cause of thunder, lightning, and earthquakes, is one and the same, viz. the inflammable breath of the pyrites, which is a substantial sulphur, and takes fire of itself.

The difference between these three terrible phenomena, he takes only to consist in this; that this sulphur, in the former, is fired in the air, and in the latter under ground. Which is a notion that Pliny had, long before him; 66 Quid enim," says he, "aliud est in terrâ tremor, quam in nube tonitru?"

This he thinks abundantly indicated by the same sulphurous smell being found in any thing burnt with lightning, and in the waters, &c. cast up in earthquakes, and even in the air before and after them.

Add, that they agree in the manner of the noise, which is carried on, as in a train fired; the one, rolling and rattling through the air, takes fire as the vapors chance to drive; as the other fired under ground, in like manner, moves with a desultory noise.

Thunder, which is the effect of the trembling of the air, caused by the same vapors dispersed through it, has force enough to shake our houses; and why there may not be thunder and lightning under ground, in some vast repositories there, I see no reason; especially if we reflect, that the matter which composes the noisy vapor above us is in much larger quantities under ground.

That the earth abounds in cavities, everybody allows; and that these subterraneous cavities are, at certain times and in certain seasons, full of inflammable vapors, the damps in mines sufficiently witness, which fired do every thing as in an earthquake, save in a lesser degree.

Add, that the pyrites alone, of all the known minerals, yields this inflammable vapor, is highly probable; for that no mineral or ore, whatsoever, is sulphurous, but as it is wholly, or in part, a pyrites; and that there is but one species of brimstone, which the pyrites naturally and only yields. The sulphur vive, or natural

brimstone, which is found in and about the burning mountains, is certainly the effects of sublimation; and those great quantities of it, said to be found about the skirts of volcanoes, is only an argument of the long duration and vehemence of those fires. Possibly the pyrites of the volcanoes, or burning mountains, may be more sulphurous than ours; and indeed it is plain, that some of ours in England are very lean, and hold but little sulphur; others again, very much; which may be one reason why England is so little troubled with earthquakes, and Italy, and almost all round the Mediterranean Sea, so very much; though another reason is, the paucity of pyrites in England.

Comparing our earthquakes, thunder, and lightning with theirs, it is observed, that there it lightens almost daily, especially in summer-time, here seldom; there thunder and lightning is of long duration, here it is soon over; there the earthquakes are frequent, long, and terrible, with many paroxysms in a day, and that for many days; here very short, a few minutes, and scarce perceptible. To this purpose the subterraneous caverns in England are small and few compared to the vast vaults in those parts of the world; which is evident from the sudden disappearance of whole mountains and islands.

Dr. Woodward gives us another theory of earthquakes. He endeavours to show, that the subterraneous heat, or fire, (which is continually elevating water out of the abyss, to furnish the earth with rain, dew, springs, and rivers,) being stopped in any part of the earth, and so diverted from its ordinary course, by some accidental glut or obstruction in the pores or passages through which it used to ascend to the surface, becomes, by such means, preternaturally assembled in a greater quantity than usual into one place, and there

fore causeth a great rarefaction and intumescence of the water of the abyss; putting it into great commotions and disorders, and at the same time making the like effort on the earth; which being expanded upon the face of the abyss, occasions that agitation and concussion we call an earthquake.

This effort in some earthquakes, he observes, is so vehement, that it splits and tears the earth, making cracks and chasms in it some miles in length, which open at the instant of the shock, and close again in the intervals betwixt them; nay, it is sometimes so violent, that it forces the superincumbent strata, breaks them all throughout, and thereby perfectly undermines and ruins the foundation of them; so that, these failing, the whole tract, as soon as the shock is over, sinks down into the abyss, and is swallowed up by it; the water thereof immediately rising up and forming a lake in the place where the said tract before was. That, this effort being made in all directions indifferently, the fire, dilating and expanding on all hands, and endeavouring to get room and make its way through all obstacles, falls as foul on the waters of the abyss beneath, as on the earth above, forcing it forth, which way soever it can find vent or passage, as well through its ordinary exits, wells, springs, and the outlets of rivers, as through the chasms then newly opened; through the camini or spiracles of Etna, or other neighbouring volcanoes; and those hiatuses at the bottom of the sea, whereby the abyss below opens into it and communicates with it. That, as the water resident in the abyss is, in all parts of it, stored with a considerable quantity of heat, and more especially in those where those extraordinary aggregations of this fire happen, so likewise is the water which is thus forced out of it; insomuch that, when 'hrown forth and mixed with the waters of wells or