For supposing that the chain of the highest mountains which cross South America from the Magellanic lands to New Grenada, and the Gulph of Darien, had been produced by an earthquake, and then let us see by calculations the effect of this explosion. This chain of mountains is near 1700 leagues in length, and commonly 40 in breadth, comprehending the Sieras, which are not so lofty as the Andes. The surface therefore is 68,000 square leagues; I suppose the thickness of the matter displaced by the earthquake to be about one league, that is, the height of these mountains taken from the top to the caverns, which according to this hypothesis must support them, is one league, then I say, the power of an explosion must have raised a quantity of earth equal to 68,000 cubical leagues to a league in height. Now the action being equal to the re-action, this explosion must have communicated the same motion to the rest of the globe. The whole globe consists of 12,310,523,801 cubical leagues, from which subtracting 68,000, there remains 12,310,455,801 cubical leagues, the quantity of which motion will be equal to that of 68,000 cubical leagues raised one league; from whence we perceive that the force which will have been great enough to elevate 68,000 cubical leagues would not have displaced the whole globe a single inch. There would therefore be no absolute impossibility in the supposition that mountains have been raised by earthquakes, if their internal composition as well as their external form were not evident proofs of their being the work of the sea. Their internal parts are composed of regular and parallel strata, intermingled with shells, and their external consists of a figure whose angles are every where correspondent: is it credible then that this uniform composition and regular form should have been produced by irregular shocks and sudden explosions? But as this opinion has prevailed among some philosophers, and as the nature and effects of earthquakes are not well understood, it may possibly be pertinent to hazard a few ideas with a view of explaining those intricate subjects.