The rocks are volcanic. Cumberland Bay on the north side is the only fair anchorage, and even there, from the great depth of water, there is some risk.
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.
Lava streams and other signs of volcanic action abound, but there has been no igneous activity since the Spaniards took possession.
The Tertiary deposits cover the whole of the central depression, where they are associated with extensive flows of lava and beds of volcanic ash.
370) or in other volcanic regions, where he is the cause of eruptions.
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.
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.
But it is notable that all recent volcanic action was confined to a wide belt parallel to the coast.
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.
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.
Deep, is almost circular, and was the central point of a large volcanic district, though it is probably not itself an extinct crater.
Numerous warm springs are scattered about this volcanic region.
The islands are, indeed, plainly volcanic in their nature.
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.
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.
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.
The volcanic region of the Terra di Lavoro is separated by the Volscian mountains from the Roman district.
The Apulian volcanic formation consists of the great mass of Monte Volture, which rises at the west end of the plains of Apulia, on the frontier of Basilicata, and is surrounded by the Apennines on its south-west and north-west sides.
In connection with the volcanic districts we may mention Le Mofete, the pools of Ampsanctus, in a wooded valley S.E.
Lava is much used for paving-stones in the neighborhood of volcanic districts, where pozzolana (for cement) and pumice stone are also important.
With the exception just named, the islands, which agree very closely in geological structure, are mountainous, and present, perhaps, the most wonderful example of volcanic rocks to be found on the globe.
There are raised coral beds high up the mountains, and lava occurs in a variety of forms, even in solid flows; but all active volcanic agency has so long ceased that the craters have.
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.
This place may either be a point, as in a volcanic cone, or a line, as in a mountain range or ridge of hills.
A region where volcanic activity has led to the embedding of dykes or bosses of hard rock amongst softer strata produces a plain broken by abrupt and isolated eminences.'
From the morphological point of view it is more important to distinguish the associations of forms, such as the mountain mass or group of mountains radiating from a centre, with the valleys furrowing their flanks spreading towards every direction; the mountain chain or line of heights, forming a long narrow ridge or series of ridges separated by parallel valleys; the dissected plateau or highland, divided into mountains of circumdenudation by a system of deeply-cut valleys; and the isolated peak, usually a volcanic cone or a hard rock mass left projecting after the softer strata which embedded it have been worn away (Monadnock of Professor Davis).
By 28, and appears to be partly of volcanic origin and to consist partly of older rocks corresponding with those of Sumatra.
Volcanic sulphur usually occurs as a sublimate around or on the walls of the vents, and has probably been formed in many cases by the interaction of sulphur dioxide and hydrogen sulphide.
It was formerly believed that the sulphur had a volcanic origin, but it is now generally held that it has either been reduced from gypsum by organic agencies, or more probably deposited from sulphur-bearing waters.
A complete list of localities for sulphur would include all the volcanic regions of the world.
Sulphur dioxide and sulphuretted hydrogen, are present in volcanic exhalations (see Volcano) and in many mineral waters.
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.
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.
The picturesque Bureya Mountains above the Amur, the forest-clad Sikhota-alin on the Pacific, and the volcanic chains of Kamchatka belong, however, to quite another orographical construction, being the border-ridges of the terraces by which the great plateau formation descends to the depths of the Pacific Ocean.
Although there are no active cones, Upolu has in comparatively recent times been subject to volcanic disturbances, and according to a local tradition, outbreaks must have occurred in the 17th or 18th century.
Of these Nisyros alone is of volcanic origin; the others belong to the same limestone formation with the rocky headlands of the coast.