<;I:OL<M;Y 



15ft 



of the land have l>een again and again HUM! ill.-. I, 

 lull tin- -icut continental ridges, according to the 

 geological evidence, would appear to have pel-hinted 

 from tin- earliest times as dominant elevations of 

 tin- earth'.-' crust. 'The continents,' as Professor 

 I) ui. i remarks, 'have never changed places with 

 til,- , -. -.-iiis. 1 See ABYSMAL ACCUMULATIONS. 



< 'ImiKi' s <>f < 'liinute. The geological record every- 

 \\ li.'i i- l.. :irs testimony to the fact that the climate of 

 the globe has from time to time undergone changes. 

 In our day climate is differentiated into /ones; there 

 i- a marked change in the temperature as we pass 

 from the eijiiator to the poles. Latitude, and the 

 M-lativf positions of the great land and water areas, 

 ."iihtleta the chief factors in the determination 

 of the present climates of the globe, and must have 

 had a similar influence on the climate of much 

 Ider periods. Sir Charles Lyell and others have 

 Id, therefore, that such climatic vicissitudes as 

 have evidence of in the fossiliferous strata were 

 iliahly induced by changes in the distribution 

 land and sea. Others have doubted whether 

 lis will explain the facts. If it be true that the 

 reat continental ridges are of primeval antiquity, 

 icii continents and seas could not have changed 

 laces, as I, yell supposed. The climatic conditions 

 the Glacial IVriod (q.v.) cannot possibly be due 

 i such revolutions, for the distribution of land and 

 dining Pleistocene times was practically the 

 une as at present. Stated briefly, the facts of 

 eologic.al climate are these : In Paheoxoic ages 

 ic climate would appear to have been singularly 

 ' \\ and uniform over the globe. All through 

 lie times similar genial conditions seem to 

 ive extended from what are now temperate up to 

 jlar regions. But the evidence indicates appar- 

 itly that the climate of the latter was somewhat 

 i genial than that of more southern latitudes. In 

 no/oic ages, likewise, the climate continued to 

 mild even in high Arctic lands, but towards 

 ic close of the Tertiary era a general lowering of 

 temperature took place. Thereafter followed 

 the Quaternary period with its extraordinary 

 limatic changes (see GLACIAL PERIOD, PLEISTO- 

 !NE SYSTEM). It is possible, as some suppose, 

 it the uniform climates of the earlier geological 

 periods may have been due in part to the former 

 greater heat of the earth. But probably the chief 

 factor was the peculiar disposition of land and 

 \\ater. The continental areas appear for long 

 ages to have been represented oy groups of 

 larger and smaller islands a condition of things 

 which would allow of the more or less free cir- 

 culation of oceanic currents round the world. 

 I nder such conditions atmospheric temperature 

 and pressure would have a very different dis- 

 tribution from the present. It can hardly be 

 doubted, also, that cosmical causes must have 

 had some influence upon former climates. Dr 

 Croll believes that the strongly contrasted climates 

 of the Pleistocene period (glacial and inter- 

 lacial epochs) were the indirect result of in- 

 creased eccentricity of the earth's orbit combined 

 with the precession of the equinox. It has 

 been objected to this theory that we have no 

 evidence in the older geological periods of such 

 remarkable climatic changes, which, if the theory 

 be true, ought to have happened again and again 

 luring preceding periods of high eccentricity of 

 the orbit. We are not, however, without evi- 

 dence of ice-action in Palaeozoic, Meso/oic, and 

 < 'ainoxoic times. The evidence is not abundant, 

 hut, considering the conditions of sedimentation, 

 it i-- perhaps as much as could have been expected. 

 It is doubtful, however, whether the arrangement 

 of land and water in our hemisphere at any period 

 anterior to later Cainozoic times could have 

 favoured such enormous accumulations of 



and ice an those of the Pleistocene. When the 

 continents were represented by groups of inland*, 

 the condition." for the massing of such great ice- 

 fields could not have existed. And, if it be true 

 that the climate of the globe in the earliest geo- 

 logical ages was influenced by the greater inter- 

 nal heat of the earth, the effect* flowing from great 

 eccentricity of the orbit might often be modified or 

 neutralised. 



Among the many subjects connected with geology 

 which have separate articles assigned to them in 

 this work, not to speak of the sections on the geo- 

 logy of Europe, Asia, Africa, America, Australia, 

 ana the several countries, are the following : 



Abysmal Accumulations. 



Archii-an System. 



Arterial) Wells. 



Altar. 



Boulder-clay. 



Cambrian System. 



Carboniferous System. 



Caves. 



Coal. 



Coral Inlands. 



Cretaceous System. 



Denudation. 



Dislocations. 



Drift. 



Earthquakes. 



Eocene System. 



Fossils. 



Glacial Period. 



Joints. 



Jurassic System. 



Lakes. 



Landslips. 



Mineralogy. 



Miocene System. 



Mountain*. 



Old Red Sandstone. 



Oligocene System. 



Ore Deposits. 



Palaeontology. 



Peat. 



Permian System. 



PotroRrphy. 



Pleistocene System. 



Pliocene System. 



Postglacial System. 



Sand. 



Sea. 



Silurian System. 



Springs. 



Strata. 



Triassic System. 



Unconformity. 



Upheaval and Depression. 



Volcanoes. 



See, for General Geology, Lyell's Principles of Geology 

 (1876); De la Heche's Geological Observer ( 1853); Lyell's 

 Elements of Geology (1865); A. Geikie's Text-book of 

 Geoloiiy (1887); Prestwich's Otology (2 voLs. 1886-88); 

 Phillips' Gelo(iy, edited by Etliend<;e and Seeley (2 vols. 

 1885); Green's Physical Geology (1882). Thefollowing are 

 less elaborate treatises: Lyell's Student's Elements of 

 Geologn ( 1885) ; A. Geikie's Class-book of Geology ( 1886 }; 

 J. Geikie's Outlines of Geology (1888); Jukes-Brown's 

 Handbook of Geology (2 vols. 1884-86); Page and 

 Lapworth. Introductory Text-book of Geolo</y (1888). 

 Of American and continental text-books may be men- 

 tioned : Dana's Manual of Geology ( 1875 ) ; Le Conte's 

 Compend of Geology ( 1884 ) ; Credner's Elemente der 

 Geoloirie ( 1887 ) ; Naumann's Lehrbuck der Geognnsie 

 (3 vols. 1858-72); AUgemeine Erdkundf, by Hann, Von 

 Hochstetter, and Pokorny (1881) ; De Lapparent s Traiti 

 de Geologic (1884); Stoppani's Corso di Geo/txiia (1871). 

 Button's Theory of the Earth ( 1795) is interesting as con- 

 taining the groundwork of the modern system of geology. 

 See also Playfair's IllustratUms of tlie Huttonian Theory 

 ( 1822 ) Of works dealing with special branches of geology 

 the following may be cited: For Cosmical Aspects of 

 Geology, see Sir W. Thomson, 'On the Age of the Sun's 

 Heat,' in Popular Lectures and Addresses (voL L 1889) ; 

 Croll's Climate and Time ( 1875 ), Climate and Cosmology 

 ( 1885 ), and Stellar Evolution ( 1889 ). For Petrographical 

 Geology, see references under PETROGRAPHY. For 

 Dynamical Geology, see Darwin's Geological OiMPMtioM 

 on Volcanic Islands (1884), and Obsn-i-ations on South 

 America (1846; both works in 1 voL 187(5); Scrope's 

 Volcanoes of Central France ( 1858 ), and Volcanoes ( 18< 2 ) ; 

 Judd's Volcanoes ( 1881 ) ; R. and J. W. Mallet's Karthquake 

 Catalogue (1858); Milne's Earthquakes (1886); Fuchs's 

 Vulcane und Erdbeben (1875); Fouche's Let Tremble- 

 ments de Tcrre (1888) ; Twelfth Annual Report of U.S. 

 Geological and Geographical Survey of the Territories 

 (1883: for Geysers); fislier'sPhvuicnof the Earth's Crutt 

 (1882) ; T. G. Bonney, The Story of our Planet (1894) ; 

 Bischoffs Chemical ami Physical Geology (1854-59), and 

 the Supplement (in German, 1871); Roth's AUijemeine 

 und chemische Geologic (1879); Agassiz' Etudes tur let 

 Glaciers (1840); Forhes's Travel* through the Alps 

 ( 1843 ), and Papers on the Theory of Glaciers ( 1849 ) ; 

 Tyndall, Tht Glaciers of the Alps (1857); Darwin's 

 Vegetable Mould and Earthworms (1881), and Coral 

 Reefs (1874); Dana's Corals and Coral Islands (1875). 

 Further references to special works dealing with dynam- 

 ical geology will be found in the larger text-books of 

 geology. For Structural or Geotectouic Geology, consult 



