At all times volcanoes have modified the physiognomy of the earth. At one time they have covered vast countries with their devastating lavas; at another they have made them disappear through the subsidence of high mountains; elsewhere they have raised the ground over an extent considerable enough to form hills and cones of great elevation. From historical times onward, there are cited principally the eruption of Vesuvius that occurred in the year 79 of the Christian era, which destroyed the cities of Pompeii and Herculaneum and ravaged all Campania; that of Larguaraco, which covered a space of twelve leagues with scoriae; that of Iceland, in 1783, which devastated a valley twenty leagues long; the sudden uplift of the country of Coutch in India in 1815, and that of the coasts of Chile in 1822, over an extent of two hundred leagues.
The volcano of Popadajan, on the island of Java, buried itself in 1772, together with forty villages built upon its flanks, and was replaced by a lake several kilometers in diameter. One will doubtless form a very incomplete idea of the upheavals produced by volcanoes when one learns that approximately two hundred and five volcanoes currently active are counted upon the globe: one hundred and seven on islands and ninety-eight on continents, without counting the extinct and submarine volcanoes, which are believed to be very numerous.
Thus, it is well demonstrated that at every historical epoch the igneous cause has never ceased to modify the structure of the globe through earthquakes and volcanoes, which have produced subsidences and uplifts, dislocations and the drying up of lakes, rivers, and streams. All these phenomena have been able to form the high calcareous, argillaceous, gypsiferous, bituminous mountains, etc.; and since there is scarcely a country that has not been ravaged by these causes, one may judge how greatly they must have influenced the configuration of the globe in its various parts.