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igneous

igneous

igneous Sentence Examples

  • Lava streams and other signs of volcanic action abound, but there has been no igneous activity since the Spaniards took possession.

  • The most striking feature in the geology of Russia is its remarkable freedom from disturbances, either in the form of mountain folding or of igneous intrusions.

  • The whole group is abundantly watered, and the igneous soil is marvellously fertile.

  • those derived from sedimentary and those derived from igneous rocks, or, as they have been called, the "paraschists" and the "orthoschists."

  • Those rocks which contain andalusite and staurolite are sometimes found in such associations as show that they are due to contact action by intrusive igneous masses.

  • The chlorite-schists are often of igneous derivation, such as ash-beds or fine lavas which have been metamorphosed.

  • Tremolite-schist and anthophyllite-schist are in nearly all cases the representatives of the ultra-basic igneous rocks such as peridotite in regions of high metamorphism.

  • They are soft and lustrous, with a peculiarly smooth feel, and though often confounded with mica-schists may be distinguished by their richness in magnesia; many of them contain tremolite or actinolite; others have residual grains of olivine or augite; and here also every gradation can be found between the unmodified igneous types and the perfectly metamorphic schists.

  • Crystals are found as a rarity in the amygdaloidal cavities of igneous rocks.

  • As it is, it has very fertile patches of lowland, such as the plains of Esdraelon and Jaffa; and the high levels, largely composed of disintegrated igneous rock, west of Jordan, over which the seawind carries the rains, offer excellent corn-land.

  • Much discussion had centred about fire or the "igneous principle."

  • On the one hand, it had been held that when a substance was burned or calcined, it combined with an " air "; on the other hand, the operation was supposed to be attended by the destruc tion or loss of the igneous principle.

  • Practically all the remaining area in these islands is occupied by metamorphic schists and gneisses which occur in great variety and with which are associated numerous dikes and masses of intrusive igneous rock.

  • The igneous formation of which the greater part of the Roman Campagna is, in its superior portion, composed, contains three strata known under the common name of tufa, - the " stony," " granular," and " sandy " tufa, - the last being commonly known as pozzolana.

  • Pectolite is a secondary mineral occurring as white masses with a radially fibrous structure in the veins and cavities of basic igneous rocks.

  • The foundation of the island is formed of metamorphic and igneous rocks, which appear in the Sierra Maestra and are exposed in other parts of the island wherever the comparatively thin covering of later beds has been worn away.

  • It is certain, however, that most obsidians are very acid or rhyolitic. The dark, semiopaque glassy forms of the basic igneous rocks are known as tachylytes.

  • The typical obsidians exhibit the chemical peculiarities of the acid igneous rocks (viz.

  • Amongst the most interesting features of the Bakony-wald are the volcanic and the igneous rocks.

  • Thus he carried on the narrative of orderly development from the point at which it was left by Kant and Laplace - explaining by reference to the ascertained laws of physics and chemistry the configuration of the earth, its mountains and seas, its igneous and its stratified rocks, just as the astronomers had explained by those same laws the evolution of the sun and planets from diffused gaseous matter of high temperature.

  • This consists largely of rocks of igneous origin, of which the amygdaloidal diabase of Klipriversberg forms the type.

  • A complex of igneous rocks of different ages covers immense areas in the central Transvaal.

  • Glasser, the basic igneous rocks which are associated with the mineral deposits of New Caledonia were intrusive in Cainozoic times, at the severing of the connexion between New Caledonia and New Zealand.

  • The igneous rocks occur at several geological horizons, but the great volcanic eruptions did not begin until the Tertiary period.

  • It has been variously attributed to metamorphism, consequent upon igneous intrusion, earth movements and other kinds of geothermic action, greater or less loss of volatile constituents during the period of coaly transformation, conditioned by differences of permeability in the enclosing rocks, which is greater for sandstones than for argillaceous strata, and other causes; but none of these appears to be applicable over more than limited areas.

  • The value of the product (including a small output of igneous rocks) was in 1903, $ 2, 35 1, 02 7; 1904, $ 2, 554,74 8; 1905, $ 2, 2 5 1, 3 1 9; 1906, $3,3 2 7,4 16; 1907, $ 2, 3 28, 777; 1908, $2,027,463.

  • They occur (a) in crystalline igneous and metamorphic rocks as an original constituent, (b) in veins associated with igneous rocks, and (c) in sedimentary rocks either as organic fragments or in secondary concretionary forms.

  • The first mode of occurrence is of little significance practically, for the crystalline rocks generally contain too little phosphate to be valuable, though occasionally an igneous rock may contain enough apatite to form an inferior fertilizing agent, e.g.

  • In many deposits of iron ores found in connexion with igneous or metamorphic rocks small quantities of phosphate occur.

  • Another group of phosphatic deposits connected with igneous rocks comprises the apatite veins of south Norway, Ottawa and other districts in Canada.

  • Many of the oceanic islets are composed of coral limestone, which in this way becomes phosphatized; others are igneous, consisting of trachyte or basalt, and these rocks are also phosphatized on their surfaces but are not so valuable, inasmuch as the presence of iron or alumina in any quantity renders them unsuited for the preppration of artificial manures.

  • While igneous and metamorphic crystalline rocks form the bulk of the Adirondack area, it is surrounded by a ring of ancient Palaeozoic sediments in which these peripheral lowlands have been developed.

  • On the Columbia plateau the soil is principally volcanic ash and decomposed lava; it is almost wholly volcanic ash in the more arid sections, but elsewhere more decomposed lava or other igneous rocks, and some vegetable loam is mixed with the ash.

  • Staffordshire, the diorites of Warwickshire, the phonolite of the Wolf Rock (to which he first directed attention), the pitchstones of Arran and the altered igneous rocks near the Land's End were investigated and described by him during the years1869-1879in the Quarterly Journal of the Geological Society and in the Geological Magazine.

  • ==Geology== The rocks of the Appalachian belt fall naturally into two divisions; ancient (pre-Cambrian) crystallines, including marbles, schists, gneisses, granites and other massive igneous rocks, and a great succession of Paleozoic sediments.

  • Igneous intrusions consist only of unimportant dikes of trap. The most striking and uniformly characteristic geologic feature of the mountains is their internal structure, consisting of innumerable parallel, long and narrow folds, always closely appressed in the eastern part of any crosssection (Piedmont Plateau to Great Valley), less so along a central zone (Great Valley and Valley Ridges), and increasingly open on the west (Allegheny and Cumberland Plateaus).

  • Grits, igneous rocks, ashbeds and limestones may and often do show cleavage.

  • In the neighbourhood of intrusive granites and similar plutonic igneous rocks, slates undergo "contact alteration," and great changes ensue in their appearance, structure and mineral composition.

  • It has also been observed as a product of contact-metamorphism in carbonaceous clay-slates near their contact with granite, and where igneous rocks have been intruded into beds of coal; in these cases the mineral has clearly been derived from organic matter.

  • An interesting and orderly petrological sequence of Tertiary igneous rocks has been determined.

  • Poas (8895), the scene of a violent eruption in 1834, begins a fresh series of igneous peaks, some with flooded craters, some with a constant escape of smoke and vapour.

  • Its superstructure consists of igneous rocks of all descriptions with which the original valleys between its marginal ranges have been filled by volcanic action.

  • The direction of the great volcanic cones, which rise in an irregular line above it, is not identical with the main axis of the Sierra itself, except near the Mexican frontier, but has a more southerly trend, especially towards Salvador; here the base of many of the igneous peaks rests among the southern foothills of the range.

  • "water," 12,139 ft.), so named in 1541 because it destroyed the forme(capital of Guatemala with a deluge of water from its flooded crater; and Pacaya (8390), a group of igneous peaks which were in eruption in 1870.

  • Most of them are the metamorphic products of igneous rocks, among which extrusive rocks, many of them pyroelastic, predominate.

  • On the whole, the Proterozoic rocks are predominantly sedimentary and subordinately igneous.

  • Locally both the sedimentary and igneous parts of the group have been highly metamorphosed; but as a rule the alteration of the sedimentary portions has not gone so far that stratigraphic methods are inapplicable to them, though in some places detailed study is necessary to make out their structure.

  • The commoner sorts of rock in the several Huronian systems are quartzite and slate (ranging from shale to schist); bi~t limestone is not wanting, and igneous rocks, both intrusive and extrtisive, some metamorphic and some not, abound.

  • The lower part of the Keweenawan system consists of a great succession of lava flows, of prodigious thickness.- This portion of the system is overlain by thick beds of sedimentary rock, mostly conglomerate and sandstone, derived from the igneous rocks beneath.

  • The system is without any notable amount of igneous rock.

  • _~ _______ -~ 0 + + Igneous -

  • The sedimentary rocks are affected by many dikes and sheets of igneous rock, some of the latter being extrusive and some intrusive.

  • The close of the period was marked by very profound changes which may be classed under three general headings: (1) the emergence of great areas which had been submerged until the closing stages of the period; (2) the beginning of the development of most of the great mountains of the west; (3) the inauguration of a protracted period of igneous activity, stimulated, no doubt, by the crustal and deeper-seated movements of the time.

  • The sites of deposition varied as the period progressed, for the warping and faulting of the surface, the igneous extrusions, and the deposition of sediments obliterated old basins and brought new ones into existence.

  • Igneous rocks, whether lava flows or pyroclastic ejections, are less important in the Quaternary than in the Tertiary, though volcanic activity is known to have continued into the Quaternary.

  • Igneous and metamorphic rocks.

  • He seems to have regarded the soul as composed of igneous matter, and so approximates the orthodox Pythagorean doctrine of the central fire, or Hestia, to the more detailed theories of Heraclitus.

  • The rolled crystals of sapphire occur, with garnet and other minerals, in glacial deposits, and have probably been derived from dykes of igneous rocks, like andesite and lamprophyre.

  • The folding, moreover, is less intense; but in the Dolomites of Tirol there are great outbursts of igneous rock, and faulting has occurred on an extensive scale.

  • 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 North America, the principal region of volcanic activity lay in the west; great thicknesses of igneous rocks occur in the Lower Carboniferous rocks of British Columbia, and from the middle of the period until near its close volcanoes were active from Alaska to California.

  • Woodward, The Geology of England and Wales, and ed., 1887.) The conception of an underlying " solid " geological structure covered by a superficial mantle of " drift " is still retained for certain practical purposes; thus, the Geological Survey of Great Britain issues many of the maps in two forms, the " Solid Edition," showing the " solid geology," which embraces all igneous rocks and the stratified rocks older than Pleistocene, and the " Drift Edition," which shows only such older strata as are unobscured by drift.

  • The ordinary accessory minerals of igneous rocks, apatite, in Great Britain and the continent of Europe.

  • Almost all the eminences in the Lowlands consist of hard igneous rocks, forming not only chains of hills such as those just mentioned and others in Ayrshire and Lanarkshire, but isolated crags and hills like those on which stand the castles of Edinburgh and Stirling, and others conspicuous in the scenery of Fife and the Lothians.

  • The most extensive Scottish escarpments are found among the igneous rocks.

  • The central, southern and eastern Highlands are occupied by metamorphosed sedimentary and igneous rocks, to which has been provisionally assigned the name of Dalradian, from the old Celtic kingdom of Dalriada.

  • To the east of the dislocation of the Great Glen these puzzling rocks may also be met with, though in that tract most of the surface comprises sedimentary and igneous rocks, the metamorphism of which has varied much.

  • Serpentinous and other igneous rocks of Oman.

  • We marvel at the obstinacy with which he, with inadequate mathematical knowledge, opposed the Newtonian theory of light and colour; and at his championship of "Neptunism," the theory of aqueous origin, as opposed to "Vulcanism," that of igneous origin of the earth's crust.

  • It is a large volcanic region, entirely covered with lava and other igneous rocks.

  • But the most important igneous masses are the great intrusions of syenitic granite and of basic rock which penetrate the Cretaceous beds.

  • The fossils from the Rhaetic beds belong to the Avicula contorta zone, those from the Lias to the Ammonites angulatus zone, while the blocks of limestone with chert contain Inoceramus, Cretaceous foraminifera and other organisms. The materials yielding these fossils are embedded in a course volcanic agglomerate which gives rise to crags and is pierced by acid and basic igneous ricks.

  • One of the striking features in the geology of Arran is the remarkable series of intrusive igneous rocks of Tertiary age which occupy nearly one-half of the area and form the wildest and grandest scenery in the island.

  • Of this range the central feature is the mountain of Kinabalu, which is composed of porphyritic granite and igneous rocks and attains to a height of 13,698 ft.

  • It consists for the most part of isolated igneous peaks, sometimes connected by low intervening ridges.

  • Igneous rocks are not extensively developed; in Wales they form an important feature and occur in considerable thickness; they are represented by lavas of olivine-diabase and by contemporaneous tuffs which are traversed by later granite and quartz felsite.

  • In Bohemia, North America and Canada igneous rocks have been observed.

  • The northern coast range is formed by the oldest rocks in the island, consisting chiefly of limestones and marbles with occasional masses of igneous rock.

  • The great igneous masses of Troodos, &c., consisting of diabase, basalt and serpentine, are of later date.

  • The Pliocene is of marine origin, and rests unconformably upon all the older beds, including the Post-oligocene igneous rocks, thus proving that the final folding and the last volcanic outbursts were approximately of Miocene age.

  • Lithologically they are crystalline schists, together with granite, diorite, gabbro and other igneous rocks.

  • Through the Mesozoic beds are intruded granitic and other igneous rocks of Tertiary age, and upon the folded Mesozoic foundation rise the volcanic cones of Tertiary and later date.

  • It consists chiefly of elaeolite-syenite and other rocks derived from the same igneous magma.

  • Contemporary igneous outbursts are extremely common in some of the ancient formations, and add, by their resistance to atmospheric erosion, to the extreme ruggedness of the scenery.

  • Mid Wales is built up, for the most part, of Silurian or Ordovician rocks, practically free from igneous intrusions except in the south-west.

  • There the resistance of a series of igneous dykes gives prominence to the Pembroke peninsula, in which the fine fjord-like harbour of Milford Haven lies far out towards the Atlantic. The coast north of Pembroke and Merioneth has been worked into the grand sweep of Cardigan Bay, its surface carved into gently rounded hills, green with rich grass, which sweep downward into wide rounded valleys.

  • The great variety of the rocks which meet the sea along the south of Cornwall and Devon has led to the formation of a singularly picturesque coast - the headlands being carved from the hardest igneous rocks, the bays cut back in the softer Devonian strata, The fjord-like inlets of Falmouth, Plymouth and Dartmouth are splendid natural harbours, which would have developed great commercial ports but for their remoteness from the centres of commerce and manufactures.

  • The chief minerals raised in England, as stated in the annual home office report on mines and quarries, appear in order of value, thus: coal, iron ore, clay and shale, sandstone, limestone, igneous rocks, salt, tin ore.

  • As regards igneous rocks, the Charnwood Forest quarries of Leicestershire, and those of Cornwall, are particularly noted for their granite.

  • Near the northern foot of the Caucasus, especially in the neighbourhood of the hot mineral springs of Pyatigorsk, a group of hills of igneous rocks rises above the plain.

  • Subsequent denudation has removed the sedimentary covering and exposed the igneous core.

  • Igneous.

  • Igneous Rocks.

  • Of more recent date (probably Tertiary) are some igneous rocks, rich in alkalis, occurring in certain localities in southern Abyssinia.

  • With regard to the older igneous rocks, the enormous amount they have suffered from denudation is a prominent feature.

  • Most interesting among these are the Henry Mountains, formed by the intrusion of molten igneous rock between the layers of sediments, causing the overlying layers to arch up into dome mountains.

  • Stream erosion has dissected these domes far enough to reveal the core of the igneous rock and to give a rugged topography.

  • Quartz occurs as a primary and essential constituent of igneous rocks of acidic composition such as granite, quartz-porphyry and rhyolite, being embedded in these either as irregularly shaped masses or as porphyritic crystals.

  • Vein-quartz, often of economic importance as a matrix of gold, may, however, in some cases have been of igneous origin.

  • The rocks have been greatly changed by pressure in most cases and by the intrusion of great masses of igneous material, the Namaqualand schists and Malmesbury beds being most altered.

  • They contain a great variety of sediments and igneous rocks.

  • In the New Red Sandstone, the Greensand and the upper Chalk, we find the opposite extremes; while the igneous rocks are for the most part only permeable in virtue of the open fissures they contain.

  • The land is of recent geological formation, the principal ranges being composed of igneous rock, and showing traces of much volcanic disturbance.

  • Most of the high peaks on the larger islands are basaltic, and the rocks generally are igneous, with occasional upheaved coral found sometimes over 1000 ft.

  • The foothills and lowlands throughout southern Wicklow and almost the whole of Wexford, and the corresponding country of western Wicklow and eastern Kildare, are thus formed of Silurian beds, in which numerous contemporaneous and also intrusive igneous rocks are intercalated, striking like the chain N.E.

  • The alteration of the fossiliferous Lias by dolerite at Portrush into a flinty rock that looked like basalt served at one time as a prop for the " Neptunist " theory of the origin of igneous rocks.

  • The more deep-seated type of these rocks is seen in the olivine-gabbro mass of Carlingford Mountain; but most of the igneous region became covered with sheets of basaltic lava, which filled up the hollows of the downs, baked the gravels into a layer of red flints, and built up, pile upon pile, the great plateaus of the north.

  • There are also found in both regions numerous masses of igneous rocks, both plutonic and volcanic, in some places of considerable extent, which pierce through and overflow the earlier formations.

  • (See § Palaeontology.) Igneous Rocks.

  • - The ancient or plutonic igneous rocks (including granite, syenite, diorite, gabbro, porphyry, porphyrite, norite retinite) appear at various points of the two previously described regions.

  • This folded belt gives Africa its abrupt southern Scale,n Deposits (A) 1 Ili Igneous.

  • Igneous complex of sheared igneous rocks; granites.

  • The earliest signs of igneous activity in Africa are to be found in the granites, intrusive into the older rocks of the Cape peninsula, into those of the Transvaal, and into the gneisses and schists of Central Africa.

  • The Ventersdorp boulder beds of the Transvaal may be of early palaeozoic age; but as a whole the palaeozoic period in Africa was remarkably free from volcanic and igneous disturbances.

  • The Cainozoic series includes many igneous rocks.

  • During recent times the most destructive were those of, 8 r 1, 1820, 1840 and 1893; and, although the prevailing geological formations are sedimentary, chiefly calcareous, there seems no doubt that these disturbances are of igneous origin.

  • or S.E.; in this band of weak rocks were several sheets of hard igneous rock (trap) inclined from the horizontal several degrees, and so resistant that they were not removed but remained to form the " trap ridges " such as West Rock Ridge near New Haven and the Hanging Hills of Meriden.

  • These clays are produced by the decomposition of the granite by acid vapours, which are discharged after the igneous rock has solidified ("fumarole or pneumatolytic action").

  • I'll judge if ya want Timmy (Timmy) Wed, 18 Jan 2006 lovers tiffs hehe ok igneous carl your on!

  • In igneous rocks, the potassium-argon " clock " is set the moment the rock first crystallizes from magma.

  • emplacement of magma and its solidification to igneous rock known locally as greenstones) also occurred.

  • extrusive igneous rocks.

  • See also cut-off grade Gabbro A coarse grained igneous rock consisting of calcic feldspar, pyroxene and commonly hornblende and/or olivine: appx.

  • feldspar microtextures produced by cooling of igneous rocks.

  • Mortlach Moss Aberdeenshire This small base-rich basin fen, lying upon igneous rock, is representative of Alkaline fens in northeast Scotland.

  • The study of radiogenic isotopes is the basis of many geological dating techniques and is also an important branch of igneous geochemistry.

  • graben basins infilled with carbonate and clastic sedimentary rocks unconformably overlying pre Tertiary metamorphic and igneous rocks.

  • F. Magma is intruded into older rocks and crystallizes into a pink igneous rock called granophyre.

  • The notes cover the basic principles of igneous petrology including magma crystallization, igneous petrology including magma crystallization, igneous textures, magmatic differentiation and the naming of igneous rocks.

  • igneous intrusions into the Coal Measures.

  • igneous rock formed deep within the earth.

  • igneous geology.

  • igneous provinces (LIPs )?

  • igneous complex had four phases, acid, basic, acid, basic.

  • Even hard igneous rocks get weathered away eventually over millions of years to form sand grains.

  • To the west of the Twin Towers, 14 rock groins were built using large blocks of hard, mainly igneous, rock.

  • There are also a number of igneous intrusions into the Coal Measures.

  • mafic igneous rock consisting of plagioclase feldspar and pyroxene.

  • Alkaline igneous rocks and geochemical enrichment in the lithospheric mantle.

  • Granite: An igneous rock forming much of the cairngorm mountains and other hills in Scotland.

  • Orbicular granite - this igneous rock has an unusual orbicular granite - this igneous rock has an unusual orbicular structure that is sometimes seen in granites and diorites.

  • The notes cover the basic principles of igneous petrology including magma crystallization, igneous textures, magmatic differentiation and the naming of igneous rocks.

  • Granite is a lighter colored igneous rock containing relatively large crystals of the minerals plagioclase, quartz and alkali feldspars such as orthoclase.

  • Plutonic igneous rocks.

  • The presence of water appearing thus to prevent any decomposition, I used potash in igneous fusion.

  • They relate changes of state to energy transfers in a range of contexts for example, the formation of igneous rocks.

  • When this is slow you get bigger igneous rock crystals from magma.

  • siliceous igneous rocks with crags up to very high altitude.

  • Since the specimens have become dry, it is rather more easy to distinguish the decomposed igneous rocks from the sedimentary tuffs.

  • Lava streams and other signs of volcanic action abound, but there has been no igneous activity since the Spaniards took possession.

  • The most striking feature in the geology of Russia is its remarkable freedom from disturbances, either in the form of mountain folding or of igneous intrusions.

  • The whole group is abundantly watered, and the igneous soil is marvellously fertile.

  • In production of gold in 1907 Esmeralda county ranked first with $8,533,617 (nearly 70% of the total); Nye county's output was $1,547,408, Lincoln county's $929,775, ' Apart from their commercial uses, the Sutro Tunnel and the shafts of the Comstock Lode have been employed for scientific investigations, with the object of classifying igneous rocks, determining the variations of temperature, and the character of electrical manifestations beneath the earth's surface, and the relation between the structure of rocks and their rate of cooling.

  • Transitions between schists and normal igneous or sedimentary rocks are often found.

  • Igneous rocks also may be converted readily into schists (e.g.

  • those derived from sedimentary and those derived from igneous rocks, or, as they have been called, the "paraschists" and the "orthoschists."

  • Those rocks which contain andalusite and staurolite are sometimes found in such associations as show that they are due to contact action by intrusive igneous masses.

  • The chlorite-schists are often of igneous derivation, such as ash-beds or fine lavas which have been metamorphosed.

  • Tremolite-schist and anthophyllite-schist are in nearly all cases the representatives of the ultra-basic igneous rocks such as peridotite in regions of high metamorphism.

  • They are soft and lustrous, with a peculiarly smooth feel, and though often confounded with mica-schists may be distinguished by their richness in magnesia; many of them contain tremolite or actinolite; others have residual grains of olivine or augite; and here also every gradation can be found between the unmodified igneous types and the perfectly metamorphic schists.

  • Crystals are found as a rarity in the amygdaloidal cavities of igneous rocks.

  • As it is, it has very fertile patches of lowland, such as the plains of Esdraelon and Jaffa; and the high levels, largely composed of disintegrated igneous rock, west of Jordan, over which the seawind carries the rains, offer excellent corn-land.

  • Much discussion had centred about fire or the "igneous principle."

  • On the one hand, it had been held that when a substance was burned or calcined, it combined with an " air "; on the other hand, the operation was supposed to be attended by the destruc tion or loss of the igneous principle.

  • The results of his observations were embodied in his Treatise on Primary Geology (1834), a work of considerable merit in regard to the older crystalline and igneous rocks and the subject of mineral veins.

  • Practically all the remaining area in these islands is occupied by metamorphic schists and gneisses which occur in great variety and with which are associated numerous dikes and masses of intrusive igneous rock.

  • The igneous formation of which the greater part of the Roman Campagna is, in its superior portion, composed, contains three strata known under the common name of tufa, - the " stony," " granular," and " sandy " tufa, - the last being commonly known as pozzolana.

  • Pectolite is a secondary mineral occurring as white masses with a radially fibrous structure in the veins and cavities of basic igneous rocks.

  • The foundation of the island is formed of metamorphic and igneous rocks, which appear in the Sierra Maestra and are exposed in other parts of the island wherever the comparatively thin covering of later beds has been worn away.

  • It is certain, however, that most obsidians are very acid or rhyolitic. The dark, semiopaque glassy forms of the basic igneous rocks are known as tachylytes.

  • The typical obsidians exhibit the chemical peculiarities of the acid igneous rocks (viz.

  • Mica occurs as a primary and essential constituent of igneous rocks of almost all kinds; it is also a common product of alteration of many mineral silicates, both by weathering and by contactand dynamo-metamorphic processes.

  • Amongst the most interesting features of the Bakony-wald are the volcanic and the igneous rocks.

  • Thus he carried on the narrative of orderly development from the point at which it was left by Kant and Laplace - explaining by reference to the ascertained laws of physics and chemistry the configuration of the earth, its mountains and seas, its igneous and its stratified rocks, just as the astronomers had explained by those same laws the evolution of the sun and planets from diffused gaseous matter of high temperature.

  • This consists largely of rocks of igneous origin, of which the amygdaloidal diabase of Klipriversberg forms the type.

  • The other rocks include igneous breccias, shales, coarse conglomerates and grits.

  • A complex of igneous rocks of different ages covers immense areas in the central Transvaal.

  • Glasser, the basic igneous rocks which are associated with the mineral deposits of New Caledonia were intrusive in Cainozoic times, at the severing of the connexion between New Caledonia and New Zealand.

  • The igneous rocks occur at several geological horizons, but the great volcanic eruptions did not begin until the Tertiary period.

  • It has been variously attributed to metamorphism, consequent upon igneous intrusion, earth movements and other kinds of geothermic action, greater or less loss of volatile constituents during the period of coaly transformation, conditioned by differences of permeability in the enclosing rocks, which is greater for sandstones than for argillaceous strata, and other causes; but none of these appears to be applicable over more than limited areas.

  • The value of the product (including a small output of igneous rocks) was in 1903, $ 2, 35 1, 02 7; 1904, $ 2, 554,74 8; 1905, $ 2, 2 5 1, 3 1 9; 1906, $3,3 2 7,4 16; 1907, $ 2, 3 28, 777; 1908, $2,027,463.

  • They occur (a) in crystalline igneous and metamorphic rocks as an original constituent, (b) in veins associated with igneous rocks, and (c) in sedimentary rocks either as organic fragments or in secondary concretionary forms.

  • The first mode of occurrence is of little significance practically, for the crystalline rocks generally contain too little phosphate to be valuable, though occasionally an igneous rock may contain enough apatite to form an inferior fertilizing agent, e.g.

  • In many deposits of iron ores found in connexion with igneous or metamorphic rocks small quantities of phosphate occur.

  • Another group of phosphatic deposits connected with igneous rocks comprises the apatite veins of south Norway, Ottawa and other districts in Canada.

  • Many of the oceanic islets are composed of coral limestone, which in this way becomes phosphatized; others are igneous, consisting of trachyte or basalt, and these rocks are also phosphatized on their surfaces but are not so valuable, inasmuch as the presence of iron or alumina in any quantity renders them unsuited for the preppration of artificial manures.

  • While igneous and metamorphic crystalline rocks form the bulk of the Adirondack area, it is surrounded by a ring of ancient Palaeozoic sediments in which these peripheral lowlands have been developed.

  • On the Columbia plateau the soil is principally volcanic ash and decomposed lava; it is almost wholly volcanic ash in the more arid sections, but elsewhere more decomposed lava or other igneous rocks, and some vegetable loam is mixed with the ash.

  • Staffordshire, the diorites of Warwickshire, the phonolite of the Wolf Rock (to which he first directed attention), the pitchstones of Arran and the altered igneous rocks near the Land's End were investigated and described by him during the years1869-1879in the Quarterly Journal of the Geological Society and in the Geological Magazine.

  • ==Geology== The rocks of the Appalachian belt fall naturally into two divisions; ancient (pre-Cambrian) crystallines, including marbles, schists, gneisses, granites and other massive igneous rocks, and a great succession of Paleozoic sediments.

  • Igneous intrusions consist only of unimportant dikes of trap. The most striking and uniformly characteristic geologic feature of the mountains is their internal structure, consisting of innumerable parallel, long and narrow folds, always closely appressed in the eastern part of any crosssection (Piedmont Plateau to Great Valley), less so along a central zone (Great Valley and Valley Ridges), and increasingly open on the west (Allegheny and Cumberland Plateaus).

  • Grits, igneous rocks, ashbeds and limestones may and often do show cleavage.

  • In the neighbourhood of intrusive granites and similar plutonic igneous rocks, slates undergo "contact alteration," and great changes ensue in their appearance, structure and mineral composition.

  • It has also been observed as a product of contact-metamorphism in carbonaceous clay-slates near their contact with granite, and where igneous rocks have been intruded into beds of coal; in these cases the mineral has clearly been derived from organic matter.

  • An interesting and orderly petrological sequence of Tertiary igneous rocks has been determined.

  • Poas (8895), the scene of a violent eruption in 1834, begins a fresh series of igneous peaks, some with flooded craters, some with a constant escape of smoke and vapour.

  • Its superstructure consists of igneous rocks of all descriptions with which the original valleys between its marginal ranges have been filled by volcanic action.

  • The direction of the great volcanic cones, which rise in an irregular line above it, is not identical with the main axis of the Sierra itself, except near the Mexican frontier, but has a more southerly trend, especially towards Salvador; here the base of many of the igneous peaks rests among the southern foothills of the range.

  • "water," 12,139 ft.), so named in 1541 because it destroyed the forme(capital of Guatemala with a deluge of water from its flooded crater; and Pacaya (8390), a group of igneous peaks which were in eruption in 1870.

  • Most of them are the metamorphic products of igneous rocks, among which extrusive rocks, many of them pyroelastic, predominate.

  • On the whole, the Proterozoic rocks are predominantly sedimentary and subordinately igneous.

  • Locally both the sedimentary and igneous parts of the group have been highly metamorphosed; but as a rule the alteration of the sedimentary portions has not gone so far that stratigraphic methods are inapplicable to them, though in some places detailed study is necessary to make out their structure.

  • The commoner sorts of rock in the several Huronian systems are quartzite and slate (ranging from shale to schist); bi~t limestone is not wanting, and igneous rocks, both intrusive and extrtisive, some metamorphic and some not, abound.

  • The lower part of the Keweenawan system consists of a great succession of lava flows, of prodigious thickness.- This portion of the system is overlain by thick beds of sedimentary rock, mostly conglomerate and sandstone, derived from the igneous rocks beneath.

  • The system is without any notable amount of igneous rock.

  • _~ _______ -~ 0 + + Igneous -

  • The sedimentary rocks are affected by many dikes and sheets of igneous rock, some of the latter being extrusive and some intrusive.

  • The close of the period was marked by very profound changes which may be classed under three general headings: (1) the emergence of great areas which had been submerged until the closing stages of the period; (2) the beginning of the development of most of the great mountains of the west; (3) the inauguration of a protracted period of igneous activity, stimulated, no doubt, by the crustal and deeper-seated movements of the time.

  • The sites of deposition varied as the period progressed, for the warping and faulting of the surface, the igneous extrusions, and the deposition of sediments obliterated old basins and brought new ones into existence.

  • Igneous rocks, whether lava flows or pyroclastic ejections, are less important in the Quaternary than in the Tertiary, though volcanic activity is known to have continued into the Quaternary.

  • Igneous and metamorphic rocks.

  • He seems to have regarded the soul as composed of igneous matter, and so approximates the orthodox Pythagorean doctrine of the central fire, or Hestia, to the more detailed theories of Heraclitus.

  • The rolled crystals of sapphire occur, with garnet and other minerals, in glacial deposits, and have probably been derived from dykes of igneous rocks, like andesite and lamprophyre.

  • The folding, moreover, is less intense; but in the Dolomites of Tirol there are great outbursts of igneous rock, and faulting has occurred on an extensive scale.

  • 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 North America, the principal region of volcanic activity lay in the west; great thicknesses of igneous rocks occur in the Lower Carboniferous rocks of British Columbia, and from the middle of the period until near its close volcanoes were active from Alaska to California.

  • Igneous rocks of this period are found also in Australasia.

  • Woodward, The Geology of England and Wales, and ed., 1887.) The conception of an underlying " solid " geological structure covered by a superficial mantle of " drift " is still retained for certain practical purposes; thus, the Geological Survey of Great Britain issues many of the maps in two forms, the " Solid Edition," showing the " solid geology," which embraces all igneous rocks and the stratified rocks older than Pleistocene, and the " Drift Edition," which shows only such older strata as are unobscured by drift.

  • The ordinary accessory minerals of igneous rocks, apatite, in Great Britain and the continent of Europe.

  • Almost all the eminences in the Lowlands consist of hard igneous rocks, forming not only chains of hills such as those just mentioned and others in Ayrshire and Lanarkshire, but isolated crags and hills like those on which stand the castles of Edinburgh and Stirling, and others conspicuous in the scenery of Fife and the Lothians.

  • The most extensive Scottish escarpments are found among the igneous rocks.

  • The central, southern and eastern Highlands are occupied by metamorphosed sedimentary and igneous rocks, to which has been provisionally assigned the name of Dalradian, from the old Celtic kingdom of Dalriada.

  • To the east of the dislocation of the Great Glen these puzzling rocks may also be met with, though in that tract most of the surface comprises sedimentary and igneous rocks, the metamorphism of which has varied much.

  • Serpentinous and other igneous rocks of Oman.

  • We marvel at the obstinacy with which he, with inadequate mathematical knowledge, opposed the Newtonian theory of light and colour; and at his championship of "Neptunism," the theory of aqueous origin, as opposed to "Vulcanism," that of igneous origin of the earth's crust.

  • It is a large volcanic region, entirely covered with lava and other igneous rocks.

  • But the most important igneous masses are the great intrusions of syenitic granite and of basic rock which penetrate the Cretaceous beds.

  • The fossils from the Rhaetic beds belong to the Avicula contorta zone, those from the Lias to the Ammonites angulatus zone, while the blocks of limestone with chert contain Inoceramus, Cretaceous foraminifera and other organisms. The materials yielding these fossils are embedded in a course volcanic agglomerate which gives rise to crags and is pierced by acid and basic igneous ricks.

  • One of the striking features in the geology of Arran is the remarkable series of intrusive igneous rocks of Tertiary age which occupy nearly one-half of the area and form the wildest and grandest scenery in the island.

  • Of this range the central feature is the mountain of Kinabalu, which is composed of porphyritic granite and igneous rocks and attains to a height of 13,698 ft.

  • It consists for the most part of isolated igneous peaks, sometimes connected by low intervening ridges.

  • Igneous rocks are not extensively developed; in Wales they form an important feature and occur in considerable thickness; they are represented by lavas of olivine-diabase and by contemporaneous tuffs which are traversed by later granite and quartz felsite.

  • In Bohemia, North America and Canada igneous rocks have been observed.

  • In the Ardennes the system is represented by grits and sandstones, shales, slates and quartz schists, and includes also whet slates and some igneous rocks.

  • The northern coast range is formed by the oldest rocks in the island, consisting chiefly of limestones and marbles with occasional masses of igneous rock.

  • The great igneous masses of Troodos, &c., consisting of diabase, basalt and serpentine, are of later date.

  • The Pliocene is of marine origin, and rests unconformably upon all the older beds, including the Post-oligocene igneous rocks, thus proving that the final folding and the last volcanic outbursts were approximately of Miocene age.

  • Lithologically they are crystalline schists, together with granite, diorite, gabbro and other igneous rocks.

  • Through the Mesozoic beds are intruded granitic and other igneous rocks of Tertiary age, and upon the folded Mesozoic foundation rise the volcanic cones of Tertiary and later date.

  • It consists chiefly of elaeolite-syenite and other rocks derived from the same igneous magma.

  • Contemporary igneous outbursts are extremely common in some of the ancient formations, and add, by their resistance to atmospheric erosion, to the extreme ruggedness of the scenery.

  • The mountain group of North Wales is the largest and loftiest; its scenery resembles that of the Scottish Highlands because of the juxtaposition of ancient Palaeozoic rocks - Cambrian and Ordovician, often altered into slate - and contemporaneous volcanic outbursts and igneous intrusions.

  • Mid Wales is built up, for the most part, of Silurian or Ordovician rocks, practically free from igneous intrusions except in the south-west.

  • There the resistance of a series of igneous dykes gives prominence to the Pembroke peninsula, in which the fine fjord-like harbour of Milford Haven lies far out towards the Atlantic. The coast north of Pembroke and Merioneth has been worked into the grand sweep of Cardigan Bay, its surface carved into gently rounded hills, green with rich grass, which sweep downward into wide rounded valleys.

  • The great variety of the rocks which meet the sea along the south of Cornwall and Devon has led to the formation of a singularly picturesque coast - the headlands being carved from the hardest igneous rocks, the bays cut back in the softer Devonian strata, The fjord-like inlets of Falmouth, Plymouth and Dartmouth are splendid natural harbours, which would have developed great commercial ports but for their remoteness from the centres of commerce and manufactures.

  • The chief minerals raised in England, as stated in the annual home office report on mines and quarries, appear in order of value, thus: coal, iron ore, clay and shale, sandstone, limestone, igneous rocks, salt, tin ore.

  • As regards igneous rocks, the Charnwood Forest quarries of Leicestershire, and those of Cornwall, are particularly noted for their granite.

  • Near the northern foot of the Caucasus, especially in the neighbourhood of the hot mineral springs of Pyatigorsk, a group of hills of igneous rocks rises above the plain.

  • Subsequent denudation has removed the sedimentary covering and exposed the igneous core.

  • Igneous Rocks.

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