The Virginia Gazette

He having in our last given an Account of the Earthquake felt in several Places to the Northward, and many People being desirous to know what may be the natural Cause of such violent Convulsions, we shall endeavour to gratify their Curiosity, by giving them the various Opinions of the Learned on this Head.

Causes of Earthquakes.

Naturalists are divided. Some ascribe them to Water, others to Fire, and others to Air; and all of 'em with some Appearance of Reason. To conceive which, it's to be observed, that the Earth every where abounds in huge subterraneous Caverns, Veins, and Canals, particularly about the Roots of Mountains: That of these Caverns, Veins, &c. some are full of Water, whence are composed Gulphs, Abyes, Springs, Rivers, 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 Mass being dissolved, or wore 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. And, that the Water, being heated and rarified 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 Vapours rais'd from the Earth and Water: if it be pent up in too narrow Viscera of the Earth, the subterraneous, or its own native Heat, rarifying 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 imprison'd Aura.

Lastly, Fire is a principal Cause of Earthquakes: both as it produces the aforesaid subterraneous Aura or Vapours; and as this Aura, or Spirit, from the different Matter and Composition whereof arise Sulphur, Bitumen, and other inflammable Matters, takes Fire, either from some 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; 'til 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 Phaenomena 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: Guid enim. says he, aliud est in Terra Tremor. quam in Nube Tonitru?

This he thinks abundantly indicated by the same sulphureous Smell being found in any Thing burnt with Lightning; and in the Waters, &c. cast up in Earthquake; 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 Vapours 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 Vapours dispersed through it, is Force enough to shake our Houses; and why may not there be Thunder and Lightning under Ground, in some vast Repositories there. In Reason. For certainly, if we reflect, that the Matter which composes the noisy Vapour above us, is in much larger Quantities under Ground.

That the Earth abounds in Cavities, every Body knows: and that these subterraneous Cavities are, at certain Times, and in certain Seasons, full of inflammable Vapours, the Damps in Mines sufficiently witness, which fired, do every Thing as in an Earthquake, have in a lesser Degree.

Add, that the Pyrites alone, of all the known Minerals, yields this inflammable Vapour, is highly probable: For that no Mineral, or ore whatever, 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, if natural Brimstone, which is found in and about the Burning Mountains, is certainly the Effect of Sublimation; and those great Quantities of it laid 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 Volcano, or burning Mountains, may be more fully 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: Tho' 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 frequently 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 shew, that the subterraneous Heat or Fire (which is continually elevating Water out of the Abys, to furnish the Earth with Rain, Dews, Springs, and Rivers) being stopped in any Part of the Earth, and so diverted from its ordinary Course, by some accident) Glut or Obstruction in the Pores or Passages thro' which it used to ascend to the Surface, becomes, by such Means, preternaturally assembled in a greater Quantity than usual, into one Place, and therefore causeth great Rarifaction and Intumescence of the Water of the Abyss
By an Effort of the Fire in 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 between them: Nay, it is sometimes so violent that it forces the super incumbent Strata, breaks them all through, and thereby perfectly undermines sundry Towns the Foundation of them; so that they falling, as the Shock goes off, sinks down into the Abyss, and is swallowed 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, tumbles the Waters of the Abyss beneath, as on the Earth above, forcing it forth, which Way 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 open'd; through the Crater or Spiracles of Etna, or other neighbouring Volcanoes, and those Fissures at the Bottom of the Sea, whereby the Abyss breaks up into it and communicates with it. That as the Water incident in the Abyss is, in all Parts of it, tinged with a considerable Quantity of Heat, and more intensely in those where those extraordinary Aggregators of this Fire happen, to likewise is the Water, which is thus forced out of it; insomuch, that when thrown up and mixed with the Waters of Wells, Springs, and the Sea, it renders them very terribly hot.

He adds, that tho' the Abyss be liable to Commotions in all Parts: yet the Effects are no where very remarkable, except in those Countries which are mountainous, and consequently full of Caverns underneath; and especially, where the Stratum of the Sea, lies such, that those Caverns open into the Abyss, and so freely admit and entertain the Fire, which fermenteth therein is the Cause of the Shock; it naturally tending that Way where it finds the readiest Reception, which is towards those Caverns. Besides, those Parts of the Earth which abound with Strata of Stone or Marble, making the strongest Opposition to this Effort, receive the most furiously shatter'd; and suffer much more by it, than those which consist of Gravel, Sand, and the like laxer Matter, which more easily give Way, and make not so great Resistance; but above all, those Countries which yield great Store of Sulphur and Nitre, are, by far, the most injured by Earthquakes; those Minerals constituting in the Earth a kind of natural Quick-fire, which taking Fire upon this Assemblage and Approach of it, occasions that murmuring Noise, like Thunder, which is heard rumbling in the Bowels of the Earth, during Earthquakes; and by the Assistance of its explosive Power, renders the Shock much greater, so as sometimes to make miserable Havock and utter Confusion.

And it is for this Reason, that Italy, Sicily, Apulia, and some Parts of Greece, have been so long, and often alarm'd and harass'd by Earthquakes: these Countries being all mountainous and cavernous, abounding with Stone and Marble, and affording Sulphur and Nitre in great Plenty.

Further, that Etna, Vesuvius, Hecla, and the other Volcanoes, are only so many Spiracles, serving for the Discharge of this subterraneous Fire, when it is thus preternaturally assembled. That where there happens to be such a Structure and Conformation of the interior Parts of the Earth; as that the Fire may pass freely, and without Impediment from the Caverns wherein it assembles unto those Spiracles, it then readily and easily gets out from Time to Time, without shaking or disturbing the Earth: But where such Communication is wanting, or Passage not sufficiently large and open, so that it cannot come at the Spiracles, it heaves up and strokes the Earth with greater or lesser Impetuosity, according to the Quantity Fire thus assembled, 'til it has made its Way to the Mouth of the Volcano. That there are scarce any Countries much annoy'd with Earthquakes, but have one or those fiery Vents, which are constantly in Flames, when any Earthquake happens; as discovering that Fire, which without them was the Cause of the Disaster. Lastly, that were it not for these Liverticula, it would rage much more furiously, and make greater Havock than it doth.

[The Remainder in our next.]