They are found chiefly in the neighbourhood of the eruptive masses.
The number of main craters may be about twenty-five, but there are very many small eruptive cones on the flanks of the old volcanoes.
Ausbruchsgebirge - Eruptive mountains.
They include gypsum, dolomite, conglomerates, phyllites, and a basic series of eruptive rocks (gabbros, peridotites, serpentines).
With the J urassic beds is associated an extensive series of eruptive rocks (gabbro, peridotite, serpentine, diorite, granite, &c.); they are chiefly of Jurassic age, but the eruptions may have continued into the Lower Cretaceous.
His studies of the eruptive rocks of Corsica, Santorin and elsewhere; his researches on the artificial reproduction of eruptive rocks, and his treatise on the optical characters of felspars deserve special mention; but he was perhaps best known for the joint work which he carried on with his friend Michel Levy.
The mounds were probably formed by some gentle eruptive action like that exhibited in the " mud hills " along the Mississippi below New Orleans; but no explanation is generally accepted.
Next, proceeding from this region in an easterly direction, are the Neogene freshwater formations, filling up the greatest part of the north-east of Bosnia, as also a zone of flysch intermingled with several strips of eruptive rock.
The crystalline floor is exposed in the valleys of the Madeira, Xingu, &c. Some of the rocks thus exposed are, however, eruptive (e.g.
Eruptive rocks occur in the Devonian and Carboniferous beds, but there is no evidence of volcanic activity since the Palaeozoic epoch.
Throughout the world, primary deposits of tinstone are in or closely connected with granite or acid eruptive rocks of the same type, its mineral associates being tourmaline, fluorspar, topaz, wolfram and arsenical pyrites, and the invariable gangue being quartz: the only exception to this mode of occurrence is to be found in Bolivia, where the tin ore occurs intimately associated with silver ores, bismuth ores and various sulphides, whilst the gangue includes barytes and certain carbonates.
The most common eruptive rock is andesite.
Farther northwards they give way again, as in the south, to schists and eruptive rocks.
North of Tanganyika the valley is suddenly interrupted by a line of ancient eruptive ridges, which dam back the waters of Lake Kivu, but have been recently cut through by the outlet of that lake, the Rusizi, which enters Tanganyika by several mouths at its northern end.
The geological formations thus exposed show that the plateaus are composed of a base of eruptive material, overlaid by enormous deposits of reddish sandstones, conglomerates and quartzites, exposed in parts to a depth of 2000 feet.
Gneiss, granite and quartz - the decomposed granite giving the red " African " clay - are the leading features in the formations of the Northern province, of Buganda, and of the Western province, with some sandstone in the littoral districts of Buganda and in Ankole, and eruptive rocks.
In the Rocky Mountains proper no eruptive rocks have broken through, so that no ore deposits of importance are known from them, but in the Cretaceous synclines which they enclose valuable coal basins exist.
The Selkirks and Gold Ranges west of the Rockies, with their great areas of eruptive rocks, both ancient and modern, include most of the important mines of gold, silver, copper and lead which give British Columbia its leadership among the Canadian provinces as a producer of metals.
The heat, however, is greatly modified on the coast by the south-east trade winds, and the climate is generally considered healthy, though beri-beri and eruptive diseases are common on the coast.
All the islands are of volcanic origin, and have been built up by the eruptive process from a base about 15,000 ft.
Eruptive rocks of supposed Cretaceous age are met with in these outer islands, but Tertiary and recent volcanic lavas are confined to the innermost arc. Halmahera lies outside these arcs.
It appears to consist chiefly of gabbro, peridotite, serpentine and other very basic eruptive rocks, which are believed to be of Cretaceous age.
They also show less extensive bright flocculi, usually in the immediate neighbourhood of sunspots, and frequently eruptive in character.
From a low level, and sometimes reach considerable elevations in the form of eruptive prominences.
They are generally of lenticular form, and usually occur in or near the contact of eruptive rocks with schists or slates; the presence of the igneous rock being probably connected genetically with their origin.
In the river-beds, however, and at some distance from the sea, older strata and eruptive rocks underlie the alluvium.
Carvill Lewis believed the blue ground to be true eruptive rock, and the carbon to have been derived from the bituminous shales of which it contains fragments.
Curacao consists of eruptive rocks, chiefly diorite and diabase, and is surrounded by coral reefs.
They consist chiefly of gneiss and schist, with granite and other eruptive rocks.
Immense -sheets of dolerite, gabbro, or allied basic rocks indicate eruptive materials intruded as sills or poured out as lavas contemporaneously with the sedimentary formations among which they lie.
The Eastern Cordillera is composed of gneiss, mica and chlorite schist and other crystalline rocks of ancient date; the Western Cordillera, on the other hand, is formed of porphyritic eruptive rocks of Mesozoic age, together with sedimentary deposits containing Cretaceous fossils.
The Jurassic and Cretaceous formations, which in the Southern Cordillera are situated outside of the range to the east, form to a considerable extent the mass of the great range, together with quartz porphyry, the Tertiary, granite and other eruptive rocks, which have been observed along all the chain in South America up to Alaska in the north.
These three peaks are formed of eruptive rocks, surrounded by Jurassic beds which have undergone a thorough metamorphosis.
Von Hochstetter of the Austrian expedition classified the most important formations thus: eruptive, serpentine and gabbro; marine deposits, probably late Tertiary, consisting of sandstones, slates, clay, marls, and plastic clay; recent corals.
Among the minor, areas occupied by them may be especially mentioned those which occur in the Trinssic districts, Of rocks included in the eruptive series the most abundant is granite.
The massif is composed of Archean, Palaeozoic and eruptive rocks, partly concealed by a covering of Tertiary strata~ but characterized by the absence, excepting on its margins, of an~ marine deposits of Mesozoic age.
- Recent volcanic eruptive rocks (including rhyolite, trachyte, phonolite, andesite and basalt) have been examined at a number of points throughout both the geological regions of the island.
But as the mean density exceeds that of water, and probably falls but little from the centre to the surface, these gases are gases only in the sense that if the pressure of neighbouring and outward parts gravitating towards the centre were relaxed, they would expand explosively, as we see happening in the eruptive prominences.
Adams make its direction downwards; but round the rim and on bridges the characteristic distortions due to eruptive prominences are often observed.
Mitchell records an eruptive prominence followed next day in the same place by the appearance of a small spot.
The eruptive prominences, called also metallic, because it is they which show at their bases a complete bright line spectrum of the metallic elements, rush upwards at speeds which it is difficult to associate with transfers of matter; the velocity often exceeds loo m.
And whereas the main range is built up of hard eruptive or crystalline rocks, the subsidiary chains are composed of softer (Cretaceous and Tertiary) laminated formations, which easily become disintegrated and dislocated.