Equally indecisive is the further exploration as to evidence for the opinion held by other naturalists that the endemic species of the different islands have resulted from subsidences, through volcanic action, which have reduced one large island mass into a number of islets, wherein the separated species became differentiated during their isolation.
The islands are, indeed, plainly volcanic in their nature.
Its fires are not volcanic, but result from the combustion of coal some distance underground, giving off much smoke and steam; geologists estimate that the burning has been going on for at least 800 years.
Of these Ischia and Procida, close to the northern headland of the Bay of Naples, are of volcanic origin, as is the case also with the more distant group of the Ponza Islands.
In connection with the volcanic districts we may mention Le Mofete, the pools of Ampsanctus, in a wooded valley S.E.
The Hauraki Gulf, a great square inlet opening northward, is studded with islands of considerable elevation; Rangitoto, which protects the harbour, is a volcanic cone reaching nearly l000 ft.
Professor Suess, to whom the above description is due, finds that the Mediterranean forms no exception to the rule in affording no evidence of elevation or depression within historic times; but it is noteworthy that its present basin is remarkable in Europe for its volcanic and seismic activity.
The Tertiary deposits cover the whole of the central depression, where they are associated with extensive flows of lava and beds of volcanic ash.
Contemporaneous volcanic rocks are associated with the Ordovician beds and with the Rhaetic sandstones in several places.
Jurassic Oeuonian Volcanic Rock, country was free from outbursts, except in the regions of the Alps and Pyrenees.
The extraordinary number of craters, a few of which are reported still to be active, gives evidence that the archipelago is the result of volcanic action.
But it is notable that all recent volcanic action was confined to a wide belt parallel to the coast.
The Lower Devonian beds are in the main terrestrial, or coarse littoral deposits, and volcanic rocks.
The Kainozoic period opened with fresh earth movements, the most striking evidence of which are the volcanic outbreaks all round the Australian coasts.
Similar deposits, of approximately the same age, occur in Tasmania and New Zealand; and at about the same time there began the Kainozoic volcanic period of Australasia.
It belongs to the same volcanic system as the mainland near it, and the Monte Epomeo (anc. 'Eirwircbs, viewpoint), the highest point of the island (2588 ft.), lies on the N.
The hot spring which still survive from the period of volcanic activity, rise at a temperature of 147° Fahr.
Numerous warm springs are scattered about this volcanic region.
North of the fiftieth parallel the depths diminish towards the north-east, two long submarine ridges of volcanic origin extend north-eastwards to the southwest of Iceland and to the Faeroe Islands, and these, with their intervening valleys, end in a transverse ridge connecting Greenland, through Iceland and the Faeroe Islands, with Northwestern Scotland and the continental mass of Europe.
The terrigenous deposits consist of blue muds, red muds (abundant along the coast of Brazil, where the amount of organic matter present is insufficient to reduce the iron in the matter brought down by the great rivers to produce blue muds), green muds and sands, and volcanic and coral detritus.
It contains many mountains volcanic in origin (Plomb du Cantal, Puy de Dome, Mont Dore), fertile valleys such as that of Limagne, vast pasturelands, and numerous medicinal springs.
The rest of this tract is for the most part a hilly, broken country, of moderate elevation, but Monte Amiata, near Radicofani, an isolated mass of volcanic origin, attains a height of 5650 ft.
This volcanic tract extends across the Campagna of Rome, till it rises again in the lofty group of the Alban hills, the highest summit of which, the Monte Cavo, is 3160 ft.
By the undulating volcanic plain of the Roman Campagna, from which the mountains rise in a wall-like barrier, of which the highest point, the Monte Gennaro, attains 4165 ft.
The Monte Volture, which rises in the neighborhood of Melfi and Venosa to 4357 ft., is of volcanic origin, and in great measure detached from the adjoining mass of the Apennines.
All the other lakes of Central Italy, which are scattered through the volcanic districts west of the Apennines, are of an entirely difierent formation, and occupy deep cup-shaped hollows, which have undoubtedly at one time formed the craters of extinct volcanoes.
The Aeolian or Lipari Islands, a remarkable volcanic group, belong rather to Sicily than to Italy, though Stromboli, the most easterly of them, is about equidistant from Sicily and from the mainland.
Besides these, and leaving out of account the islands, the Italian peninsula presents four distinct volcanic districts.
By 28, and appears to be partly of volcanic origin and to consist partly of older rocks corresponding with those of Sumatra.
Sulphur dioxide and sulphuretted hydrogen are present in volcanic exhalations and in many mineral waters.
The geological formation includes (like that of Java) three regions - the central volcanic, the southern peninsula of Tertiary limestone, and alluvial plains between the older formations.
Many of the block mountains of the Great Basin are of complicated internal structure, showing rocks of all ages - slate, limestone, quartzites, granite, multi-coloured volcanic rocks, and large areas of lava overflow.
There have been repeated stories of diamonds obtained from the Finley Mountains (which are volcanic) in the central province, but all specimens sent home, except one, have hitherto proved to be quartz crystals.
The dioxide has been known since the earliest times and is found as a naturally occurring product in the gaseous exhalations of volcanoes and in solution in some volcanic springs.