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GEOLOGY (from Gr. yp7, the earth, and...

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Originally appearing in Volume V11, Page 639 of the 1911 Encyclopedia Britannica.
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GEOLOGY (from Gr. yp7, the See also:earth, and Abyor, See also:science)  , the See also:science which investigates the See also:physical See also:history of the See also:earth . Its See also:object is to trace the structural progress of .our See also:planet from the earliest beginnings of its See also:separate existence, through its various stages of growth, down to the See also:present See also:condition of things . It seeks to determine the manner in which the See also:evolution of the earth's See also:great See also:surface features has been effected . It unravels the complicated processes by which each See also:continent has been built up . It follows, even into detail, the varied See also:sculpture of See also:mountain and valley, See also:crag and See also:ravine . Nor does it confine itself merely to changes in the inorganic See also:world . See also:Geology shows that the present races of See also:plants and animals are the descendants of other and very different races which once peopled the earth . It teaches that there has been a progressive development. of the inhabitants, as well as one of the globe on which they have dwelt; that each successive See also:period in the earth's history, since the introduction of living things, has been marked by characteristic types of the See also:animal and See also:vegetable kingdoms; and that, however imperfectly the remains of these organisms have been preserved or may be deciphered, materials exist for a history of See also:life upon the planet . The See also:geographical See also:distribution of existing faunas and floras is often made clear and intelligible by See also:geological See also:evidence; and in the same way See also:light is thrown upon some of the remoter phases in the history of See also:man himself . A subject so comprehensive as this must require a wide and varied basis of evidence . It is one of the characteristics of geology to gather evidence from See also:sources which at first sight seem far removed from its See also:scope, and to seek aid from almost every other leading See also:branch of science . Thus, in dealing with the earliest conditions of the planet, the geologist must fully avail himself of the labours of the astronomer .

Whatever is ascertainable by See also:

telescope, spectroscope or chemical See also:analysis, regarding the constitution of other heavenly bodies, has a geological bearing . The experiments of the physicist, undertaken to determine conditions of See also:matter and of See also:energy, may sometimes be taken as the starting-points of geological investigation . The See also:work of the chemical laboratory forms the See also:foundation of a vast and increasing See also:mass of geological inquiry . To the botanist, the zoologist, even to the unscientific, if observant, traveller by See also:land or See also:sea, the geologist turns for See also:information and assistance . But while thus culling freely from the dominions of other sciences, geology claims as its See also:peculiar territory the rocky framework of the globe . In the materials composing that framework, their See also:composition and arrangement, the processes of their formation, the changes which they have undergone, and the terrestrial revolutions to which they See also:bear See also:witness, See also:lie the See also:main data of geological history . It is the task of the geologist to See also:group these elements in such a way that they may be made to yield up their evidence as to the See also:march of events in the evolution of the planet . He finds that they have in large measure arranged themselves in See also:chronological sequence,—theoldest lying at the bottom and the newest at the See also:top . See also:Relics of an See also:ancient sea-See also:floor are overlain by traces of a vanished land-surface; these are in turn covered by the deposits ., of a former See also:lake, above which once more appear proofs of the return of the sea . Among these rocky records lie the lavas and ashes of See also:long-See also:extinct volcanoes . The ripple See also:left upon the See also:shore, the cracks formed by the See also:sun's See also:heat upon the muddy bottom of a dried-up See also:pool, the very imprint of the drops of a passing See also:rain-shower, have all been accurately preserved, and yield their evidence as to geographical conditions often widely different from those which exist where such markings are now found . But it is mainly by the remains of plants and animals imbedded in the rocks that the geologist is guided in unravelling; the chronological See also:succession of geological changes .

He has found that a certain See also:

order of See also:appearance characterizes these organic remains, that each great group of rocks is marked by its own See also:special types of life, and that these types can he recognized, and the rocks in which they occur can be correlated even in distant countries, and where no other means of comparison would be possible . At one moment he has to See also:deal with the bones of some large mammal scattered through a See also:deposit of superficial See also:gravel,at another See also:time with the See also:minute foraminifers and See also:ostra'cdds of an upraised sea-bottom . See also:Corals and crinoids crowded and crushed into a massive See also:limestone where they lived and died, ferns and terrestrial plants matted together into a See also:bed of See also:coal where they originally See also:grew, the scattered shells of a submarine See also:sand-See also:bank, the snails and lizards which lived and died within a hollow-See also:tree, the See also:insects which have been imprisoned within the exuding See also:resin of old forests, the footprints of birds and quadrupeds, the trails of. See also:worms left upon former shores—these, and innumerable other pieces of evidence, enable the geologist to realize in some measure what the faunas and floras of successive periods have been, and what geographical changes the site of every land has undergone . It is evident that to deal successfully with these varied materials, a considerable acquaintance with different branches of science is needful . Especially necessary is a tolerably wide knowledge of the processes now at work in changing the surface of the earth, and of at least those forms of plant and animal life whose remains are See also:apt to be preserved in geological deposits, or which in their structure and See also:habitat enable us to realize 'what their forerunners were . It has often been, insisted that the present is the See also:key to the past; and in a wide sense this assertion is eminently true . Only in proportion as we understand the present, where everything is open on all sides to the fullest investigation, can we expect to decipher the past, where so much is obscure, imperfectly preserved or not preserved at all . A study of the existing See also:economy of nature ought thus to be the foundation of the geologist's training . While, however, the present condition of things is thus employed, we must obviously be on our guard against the danger of unconsciously assuming that the phase of nature's operations which we now witness has been the same in all past time, that geological changes have always or generally taken See also:place in former ages in the manner and on the See also:scale which we behold to-See also:day, and that at the present time all the great geological processes, which have produced changes in the past eras of the earth's history, are still existent and active . As a working See also:hypothesis we may suppose that the nature of geological processes has remained See also:constant from the beginning; but we cannot postulate that the See also:action of these processes has never varied in energy . The few centuries wherein man has been observing nature obviously See also:form much too brief an See also:interval by which to measure the intensity of geological action in all past time.', ' For 'aught we can tell the present is an era of quietude and slow See also:change, compared with some of the eras which have preceded it . Nor perhaps can we be quite sure that, when we have explored every geological See also:process now in progress, we have exhausted all the causes of change which, even in comparatively See also:recent times, have been at work .

End of Article: GEOLOGY (from Gr. yp7, the earth, and Abyor, science)
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