Page:Popular Science Monthly Volume 26.djvu/99

Rh vapors consist chiefly of carbonic acid, sulphur compounds, and water. The present solid products do not differ greatly in composition from the trachytes of the past. Audesite, or a feldspathic mineral very nearly like it, is an important constituent of the porphyritic lavas of both active and quiet volcanoes. Olivine is found in the older and in the more recent lavas of Descobezado, Antuco, and Osorno, as well as in those of Juan Fernandez, and very probably in the liquid outflows of all the other craters. Other lavas occur, among them obsidian, pearl-stone, pitch-stone, and pumice, the last being quite abundant in the Cordilleras of Talea and Chilian. Lapilli cover the eastern flank of Osorno to a depth of about sixteen feet, and through it rose as late as 1851 the great, strong-limbed trunks of dead trees, whose thickness indicated an age of about one hundred and fifty years, while it had been about fifty years since the last eruption of the mountain. But it was a laborious task to trace the lava-stream under the flourishing new growth that had taken root in the weathered surface and in the crevices of the hard deposit.

Of the still active volcanoes, we may say that Atacama emitted smoke after the earthquake of May, 1877. The group of San José was active in 1833, threw rocks into the valley of Pinquenes in 1843, and has been again active since the 2d of March, 1881. Numerous crater-openings, with ancient lava-flows, are found in the same region. Tinguiririca, to the south of this region, consists almost wholly of trachyte, and has several solfataras about five thousand feet below its summit, whence issue vapors having a temperature of 194°; its thick deposit of sulphur has caused it to be given the name of Morro de Azufre, or Sulphur Mountain. More important still is the volcano of Petesoa, at the outbreak of which, on the 3d of December, 1762, the district was desolated with lava and ashes, and the Rio Lontue was dammed up for ten days. Its last eruption, in February, 1837, was followed by destructive floods in the lower-lying regions, caused by the sudden melting and precipitation of the snows from its summit. An immense horizontal ice-cap now lies in the crater, whence rise vertically isolated columns of smoke that can be seen from a considerable distance. Beyond this is the volcanic center of Descobezado, in the southern part of which a solfatara opened in 1847 that kept the district trembling for many years.

The present region of active commotion begins at 36° 50' with the volcano of Chilian. A new crater opened northeast of the principal peak of this mountain on the 2d of August, 1861, the flow from which melted the snow and caused great floods. The streams, saturated with ashes, became rivers of mud, and covered the plains with a coating of black. The crater did not become quiet for a year, and then only to break out again in 1864 with increased violence. The dark column of smoke that rose from the crater was visible for miles around, the ash-rain was more formidable than in 1861, and the detonations were