North and east of the Fossa Magna the structure is concealed, to a very large extent, by the outpourings of the volcanoes which form so marked a feature in the northern part of Hondo.
The last phase in the history of the Caucasus was marked by the growth of the great volcanoes of Elbruz and Kasbek, which stand upon the old rocks of the central zone, and by the outflow of sheets of lava upon the sides of the chain.
In 1788 he visited Vesuvius and the volcanoes of the Lipari Islands and Sicily, and embodied the results of his researches in a large work (Viaggi alle due Sicilie ed in alcune parti dell' Apennino), published four years later.
These volcanoes are most numerous in the northern half of the country, and they stand indifferently upon the folded Mesozoic beds of the Western Cordillera (e.g.
In Tertiary times the Central Plateau was the theatre of great volcanic activity from the Miocene, to the Pleistocene periods, and many of the volcanoes remain as nearly perfect cones to the present day.
During the Tertiary period the great volcanoes of the Andes were formed, and there were smaller eruptions in the Sierras.
Mineral Springs.The presence of so many active volcanoes is partially compensated by a wealth of mineral springs.
There are often long intervals between the successive outbreaks, and many of the volcanoes (and this is especially true of the chains of craters) have only vented themselves in a solitary outburst.
The whole system is volcanic, and a considerable number of volcanoes are still intermittently active, noticeably in central and southern Chile.
Dana, Characteristics of Volcanoes with Contribution of Facts and Principles from the Hawaiian Islands (New York, 1890); W.