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See also:EOCENE (Gr. *In, See also:dawn, icauvos, See also:recent) , in See also:geology, the name suggested by See also:Sir C . See also:Lyell in 1833 for the See also:lower subdivision of the rocks of the See also:Tertiary Era . The See also:term was intended to convey the See also:idea that this was the See also:period which saw the See also:dawn of the See also:recent or existing forms of See also:life, because it was estimated that among the fossils of this period only 32 % of the See also:species are still living . Since Lyell's See also:time much has been learned about the See also:fauna and See also:flora of the period; and many palaeontologists doubt if any of the See also:Eocene species are still extant, unless it be some of the lowest forms of life . Nevertheless the name is a convenient one and is in See also:general use . The Eocene as originally defined was not See also:long See also:left intact, for E . See also:Beyrich in 1854 proposed the term " Oligocene " for the upper portion, and later, in 1874, K . Schirnper suggested " Paleocene " as a See also:separate appellation for the lower portion . The Oligocene See also:division has been generally accepted as a distinct period, but " Paleocene " is not so widely used . In See also:north-western See also:Europe the See also:close of the Cretaceous period was marked by an extensive emergence of the See also:land, accompanied, in many places, by considerable erosion of the Mesozoic rocks; a prolonged See also:interval elapsed before a relative depression of the land set in and the first Eocene deposits were formed . The See also:early Eocene formations of the See also:London-See also:Paris-Belgian See also:basin were of fresh-See also:water and brackish origin; towards the See also:middle of the period they had become marine, while later they reverted to the See also:original type . In See also:southern and eastern Europe changes of See also:sea-level were less pronounced in See also:character; here the See also:late Cretaceous seas were followed without much modification by those of the Eocene period, so See also:rich in foraminiferal life . In many other regions, the See also:great See also:gap which separates the Tertiary from the Mesozoic rocks in the neighbourhood of London and Paris does not exist, and the boundary See also:line is difficult to draw . Eocene strata succeed Cretaceous rocks without serious unconformity in the Libyan See also:area, parts of See also:Denmark, S.E . See also:Alps, See also:India, New See also:Zealand and central N . See also:America . The unconformity is marked in See also:England, parts of See also:Egypt, on the See also:Atlantic coastal See also:plain and in the eastern gulf region of N . America, as well as in the marine Eocene of western See also:Oregon . The clastic See also:Flysch formation of the Carpathians and See also:northern Alps appears to be of Eocene See also:age in the upper and Cretaceous in the lower See also:part . The Eocene sea covered at various times a See also:strip of the Atlantic See also:coast from New See also:Jersey southward and sent a great See also:tongue or See also:bay up the See also:Mississippi valley; similar epicontinental seas spread over parts of the Pacific border, but the plains of the interior with the mountains on the See also:west were meanwhile being filled with terrestrial and lacustrine deposits which attained an enormous development . This great See also:extension of non-marine formations in the Eocene of different countries has introduced difficulties in the way of exact correlation; it is safer, therefore, in the See also:present See also:state of know-ledge, to make no See also:attempt to find in the Eocene strata of America and India, &c., the precise See also:equivalent of subdivisions that have been determined with more or less exactitude in the London-Paris-Belgian area . It is possible that in Eocene times there existed a greater continuity of the northern land masses than obtains to-See also:day . Europe at that time was probably See also:united with N . America through See also:Iceland and See also:Greenland; while on the other See also:side, America may have joined See also:Asia by the way of See also:Alaska . On the other See also:hand, the great central, mediterranean sea which stretched across the See also:Eurasian continents sent an See also:arm northward somewhere just See also:east of the Ural mountains, and thus divided the northern land See also:mass in that region . S . America, See also:Australia and perhaps See also:Africa may have been connected more or less directly with the See also:Antarctic See also:continent . Associated, no doubt, with the crustal movements which closed the Cretaceous and inaugurated the Eocene period, there were See also:local and intermittent manifestations of volcanic activity throughout the period . Diabases, gabbros, serpentines, soda-potash granites, &c., are found in the Eocene of the central and northern See also:Apennines . Tuffs occur in the Veronese and Vicentin Alps—Ronca and Spelecco See also:schists . Tuffs, basalts and other igneous rocks appear also in See also:Montana, See also:Wyoming, See also:California, Oregon, See also:Washington, See also:Idaho, See also:Colorado; also') in Central America, the Antillean region and S . America . It has been very generally assumed by geologists, mainly upon the See also:evidence of plant remains, that the Eocene period opened with a temperate See also:climate in northern latitudes; later, as indicated by the London See also:Clay, See also:Alum Bay and See also:Bournemouth beds, &c., the temperature appears to have been at least subtropical . But it should be observed that the frequent admixture of temperate forms with what are now tropical species makes it difficult to speak with certainty as to the degree of warmth experienced . The occurrence of lignites in the Eocene of the Paris basin, See also:Tirol and N . America is worthy of See also:consideration in this connexion .
On the other hand, the coarse See also:boulder beds in the lower Flysch have been regarded as evidence of local glaciation; this would not be inconsistent with a period of widespread geniality of climate, as is indicated by the large See also:size of the nummulites and the See also:dispersion of the marine MolIusca, but the evidence for glaciation is not yet conclusive
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Eocene Stratigraphy.—InBritain, with the exception of the Bovey beds (q.v.) and the See also:leaf-bearing beds of See also:Antrim and See also:Mull, Eocene rocks are confined to the See also:south-eastern portion of England
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They See also:lie in the two well-marked synclinal basins of London and See also:Hampshire which are conterminous in the western area (Hampshire, See also:Berkshire), but are separated towards the east by the denuded anticline of the See also:Weald
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The strata in these two basins have been grouped in the following manner:
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London Basin
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Hampshire Basin
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Upper Upper Bagshot Sands
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Headon See also:
The Thanet sands have not been recognized in the Hampshire basin; they are usually See also:pale yellow and greenish sands 'with streaks of clay and at the See also:base; resting on an evenly denuded See also:surface of See also:chalk is a very See also:constant layer of See also:green-coated, well-rounded chalk See also:flint pebbles
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It is a marine formation, but fossils are scarce except in E
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See also:Kent, where it attains its most See also:complete development
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The Woolwich and See also:Reading beds (see READING BEDS) contain both marine and estuarine fossils
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In western Kent, between the Woolwich beds and the London Clay are the Oldhaven beds or Blackheath pebbles, 20 to 40 ft., made up almost entirely of well-rounded flint pebbles set in See also:sand; the fossils are marine and estuarine
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The London Clay, 500 ft. thick, is a marine See also:deposit consisting of See also:blue or See also:
The numerous quarries and mines for See also:building See also: Eocene, Lutetian) See also:star de Lapq,ent Lower London Clay and the equivalent Bognor Beds, Woolwich and Reading Beds . non-local rocks of enormous dimensions included in the argillaceous or sandy See also:matrix . The occurrence of these large boulders together with the scarceness of fossils has suggested a glacial origin for the formation; but the evidence hitherto collected is not conclusive . C . W. von See also:Gumbel has classified the Eocene of the northern Alps (See also:Bavaria, &c.) as follows: Upper Eocene Flysch and Vienna sandstone, with younger num- mulitic beds and Haring See also:group . Middle „ Kressenberg Beds, with older nummulitic beds . Lower Burberg Beds, Greensands with small nummulites . The Haring group of northern Tirol contains See also:lignite beds of some importance: In the southern and S.E . Alps the following divisions are recognized . Upper Eocene Macigno or Tassello—Vienna Sandstone, conglomerates, marls and shales . Middle „ Nummulitic limestones, three subdivisions . Liburnian See also:stage (or Proteocene), foraminiferal limestones with fresh-water intercalations at the See also:top and bottom, the Cosina beds, fresh-water in the middle of the series . In the central and northern Apennines the Eocene strata have been subdivided by Prof . F . Sacco into an upper Bartonian, a middle Parisian and a lower Suessonian series . In the middle member are the representatives of the Flysch and the Macigno . These Eocene strata are upwards of 5500 ft. thick . In northern Africa the nummulitic limestones and sandstones are widely spread; the lower portions comprise the Libyan group and the shales of Esneh on the See also:Nile (Flandrien), the Alveolina beds of See also:Sokotra and others; the Mokattam stage of Egypt is a representative of the later Eocene . Much of the N . See also:African Eocene contains phosphatic beds . In India strata of Eocene age are extensively developed ; in See also:Sind the marine Ranikot beds, 1500 to 2000 ft., consisting of See also:clays with See also:gypsum and lignite, shales and sandstones; these beds have, side by side with Eocene nummulites, a few fossils of Cretaceous See also:affinities . Above the Ranikot beds are the massive nummulitic limestones and sand-stones of the Kirthar group; these are succeeded by the nummulitic limestones and shales at the base of the Nari group . In the southern Himalayan region the nummulitic phase of Eocene deposit is well developed, but there are difficulties in fixing the line of demarcation between this and the younger formations . The lower part of the See also:Sirmur series of the See also:Simla See also:district may belong to this period ; it is subdivided into the Kasauli group and the Dagshai group with the Subathu group at the base .
Beneath the thick nummulitic Eocene limestone of the See also:Salt Range are shales and marls with a few See also:coal seams
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The marine Eocene rocks of N
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America are most extensively developed round the coast of the Gulf of See also:Mexico, whence they spread into the valley of the Mississippi and, as a comparatively narrow strip, along the Atlantic coastal plain to New Jersey
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The series in See also:Alabama, which may be taken as typical of the Gulf coast Eocene, is as follows:
Upper Jacksonian, See also: The See also:total thickness of this formation has been estimated at 20,000 ft . (it may prove to be less than this), but it is probable that only the lower portion is of Eocene age . The most interesting of the N . See also:American Eocene deposits are those of the Rocky Mountains and the adjacent western plains, in Wyoming, See also:Nevada, See also:Nebraska, Colorado, &c.; they are of terrestrial, lacustrine or aeolian origin, and on this See also:account and because they were not strictly synchronous, there is considerable difficulty in placing them in their true position in the time-See also:scale . The See also:main divisions or See also:groups are generally recognized as follows: Mammalian Zonal Forms . Diplacodon . l Telmatotherium . Middle 2 Bridger Group, 2000 ft . ( ? = Clai- bornian) . . . . Uintatherium . a See also:Wind See also:River Group, 800 ft . Bathyopsis . Lower " Wasatch Group, 2000 ft . ( ? = Chicka- sawan) Coryphodon . Basal i 5 Torrejon Group, 300 ft . Pantolambda . Puerco Group, 500 to 1000 ft . . Polymastodon . ' South of the Uinta Mts. in See also:Utah . 2 Fort Bridger Basin . 2 Wind river in Wyoming .
" Wasatch Mts. in Utah
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Torrejon in New Mexico
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6 Puerco river New Mexico.663
The Fort See also:Union beds of See also:Canada and parts of Montana and N
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Dakota are probably the See also:oldest Eocene strata of the Western Interior; they are some 2000 ft. thick and possibly are equivalent to the Midwayan group
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But in these beds, as in those known as Arapahoe, See also:Livingston, See also:Denver, See also:Ohio and See also:Ruby, which are now often classed as belonging to the upper See also:Laramie formation, it is safer to regard them as a transitional series between the Mesozoic and Tertiary systems
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There is, however, a marked unconformity between the Eocene Telluride or See also:San See also:Miguel and See also:Poison See also:Canyon formations of Colorado and the underlying Laramie rocks
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Many local aspects of Eocene rocks have received See also:special names, but too little is known about them to enable them to be correctly placed in the Eocene series
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Such are the Clarno formation (late Eocene) of the See also: Australia (and in the Great Australian See also:Bight), New Zealand, in See also:Seymour See also:Island near See also:Graham Land in the Antarctic Regions, Japan, See also:Java, Borneo, New See also:Guinea, See also:Moluccas, Philippines, New See also:Caledonia, also in Greenland, See also:Bear Island, Spitzbergen and See also:Siberia . Organic Life of the Eocene Period.—As it has been observed above, the name Eocene was given to this period on the ground that in its fauna only a small percentage of living species were present; this estimation was founded upon the assemblage of invertebrate remains in which, from the commencement of this period until the present day, there has been comparatively little See also:change . The real biological See also:interest of the period centres around the higher vertebrate types . In the marine See also:mollusca the most noteworthy change is the entire See also:absence of ammonoids, the group which throughout the Mesozoic era had taken so prominent a See also:place, but disappeared completely with the close of the Cretaceous . Nautiloids were more abundant than they are at present, but as a whole the Cephalopods took a more subordinate part than they had done in previous periods . On the other hand, Gasteropods and Pelecypods found in the numerous shallow seas a very suitable environment and flourished exceedingly, and their shells are often preserved in a state of great perfection and in enormous See also:numbers . Of the Gasteropod genera Cerithium with its estuarine and lagoonal forms Potamides, Potamidopsis, &c., is very characteristic; Rostellaria, Voluta, Fusus, Pleurotoma, Conus, Typhis, may also be cited . Cardium, Venericardia, Crassatella, Corbulomya, Cytherea, See also:Lucina, Anomia, Ostrea are a few of the many Pelecypod genera . Echinoderms were represented by abundant sea-urchins, Echinolampas, Linthia, Conoclypeus, &c . See also:Corals flourished on the numerous reefs and approximated to See also:modern forms (Trochosmilia, Dendrophyllia) . But by far the most abundant marine organisms were the See also:foraminifera which flourished in the warm seas in countless myriads . Foremost among these are the Nummulites, which by their extraordinary numerical development and great size, as well as by their wide distribution, demand special recognition . Many other genera of almost equal importance as See also:rock builders, lived at the same time: Orthophragma, Operculina, Assilina, Orbitolites, Miliola, Alveolina . Crus' acea were fairly abundant (Xanthopsis, See also:Portunus), and most of the Orders and many families of modern See also:insects were represented . When we turn to the higher forms of life, the See also:reptiles and mammals, we find a remarkable contrast between the fauna of the Eocene and those periods which preceded and succeeded it . The great group of Saurian reptiles, whose members had held dominion on land and sea during most of the Mesozoic time, had completely disappeared by the beginning of the Eocene; in their place placental mammals made their See also:appearance and rapidly became the dominant group . Among the early Eocene mammals no trace can be found of the numerous and clearly-marked orders with which we are See also:familiar to-day; instead we find obscurely differentiated forms, which cannot be fitted without violence into any of the modern orders . The early placental mammals were generalized types (with certain non'-placental characters) with potentialities for rapid divergence and development in the direction of the more specialized modern orders . Thus, the See also:Creodonta foreshadowed the See also:Carnivora, the Lower Upper 1 Uinta Group, 800 ft . ( ? = Jacksonian) . Stages . Paris Basin . England . Belgian Basin . Mediterranean Flysch North America . regions and Phase . Great Central sea . Bartonien.' Limestone of Saint-Ouen . Barton beds . Uinta Group and Sands of Mortefontaine . Sands of Lede . Jacksonian . Sands of Beauchamp . Upper Bagshot sands . Sands of Auvers . a a o - , Bracklesham and See also:Bourne- Laekenien . Lutetien . Calcaire grossier. mouth beds . Bruxellien . a Bridger Group and Lower Bagshot sands . Paniselien . Claibornian . Ypresien . Nummulitic sands of Alum Bay leaf beds . Sands of See also:Mons en d a Wind River Group . Wasatch Group Soissons and Sands of Pevele. o c and Cuise and Aizy . See also:Flanders Clay. a a: a a a c E N a' London Clay . m m Oldhaven beds . Upper Landenien a El' a [ Plastic Clay and lignite sands . El ~ Chickasawan . V a beds . Woolwich and Reading beds . o .b.c u7 Sands of Ostri- a a° , Limestones of Rilly and Thanet sands. See also:court . E a. o Torrejon Group Sezanne . a ~- a and Z d Sands of Rill y and Bra- Landenien See also:tuff- a . Midwayan . cheux . eau . a F Marls of Gelinden . Puerco Group . Condylarthra presaged the herbivorous groups; but before the close of this period, so favourable were the conditions of life to a rapid See also:evolution of types, that most of the great orders had been clearly defined, though none of the Eocene genera are still extant . Among the early carnivores were Arctocyon,Palaeonictis, Amblyclonus, Hyaenodon, Cynodon, Provivera, Patriofelis . The See also:primitive See also:dog-like forms did not appear until late in the period, in Europe; and true See also:cats did not arrive until later, though they were represented by Eusmilus in the Upper Eocene of France . The primitive ungulates (Condylarths) were generalized forms with five effective toes, exemplified in See also:Phenacodus . The See also:gross See also:Amblypoda, with five-toed stumpy feet (Coryphodon), were prominent in the early Eocene; particularly striking forms were the Dinoceratidae, Dinoceras, with three pairs of horns or protuberances on its massive See also:skull and a pair of huge canine See also:teeth projecting downwards; Tinoceras, Ulntatherium, Loxophodon, &c.; these elephantine creatures, whose remains are so abundant in the Eocene deposits of western America, died out before the close of the period . The divergence of the hcofed mammals into the two prominent divisions, the See also:odd-toed and even-toed, began in this period, but the former did not get beyond the three-toed stage . The least differentiated of the odd-toed group were the Lophiodonts: tapirs were foreshadowed by Systemodon and similar forms (See also:Palaeotherium, Paloplotherium); the See also:peccary-like Hyracotherium was a forerunner of the See also:horse, Hyrochinus was a primitive See also:rhinoceros . The evolution of the horse through such forms as Hyracotherium, Pachynolophus, Eohippus, &c., appears to have proceeded along parallel lines in Eurasia and America, but the true horse did not arrive until later . Ancestral See also:deer were represented by Dichobune, Amphitragulus and others, while many small hog-like forms existed (Diplopus, Eohyus, Hyopotamus, Homacodon) . The primitive stock of the See also:camel group developed in N . America in late Eocene time and sent branches into S . America and Eurasia . The edentates were very generalized forms at this period (Gan- ' Bartonien from Barton, England . Lutetien „ Lutetia = Paris . Ypresien „ See also:Ypres, Flanders . Landenien „ See also:Landen, Belgium . Thanetien „ The Isle of Thanet . Sparnacien „ Sparnacum = See also:Epernay . Laekenien „ Laeken, Belgium . Bruxellien ., See also:Brussels . Panisehen Mont Panieel, near Mons . Other names that have been applied to subdivisions of the Eocene not included in the table are Parisien and Suessonien (Soissons) ; Ludien (Ludes in the Paris basin) and Priabonien (Priabona in the Vicentine Alps) ; Heersien (Heer near See also:Maastricht) and Wemmelien :Wemmel, Belgium); very many more might be mentioned,odonta); the rodents (See also:Tillodontia) attained a large size for members of this group, e.g . Tillotherium . The Insectivores had Eocene forerunners, and the Lemuroids—probable ancestors of the apes—were forms of great interest, Anaptomorphus; Microsyops, Heterohyus, Microchaerus, Coenopithecus; even the Cetaceans were well represented by Zeuglodon and others . The non-placental mammals although abundant were taking a secondary place; Didelphys, the primitive See also:opossum, is See also:note-worthy on account of its wide See also:geographical range . Among the birds, the large flightless forms, Eupterornis, Gastornis, were prominent, and many others were present, such as the ancestral forms of our modern gulls, albatrosses, herons, buzzards, eagles, owls, quails, plovers . Reptiles were poorly represented, with the exception of crocodilians, tortoises, turtles and some large See also:snakes . The flora of the Eocene period, although full of interest, does not convey the impression of newness that is afforded by the fauna of the period . The See also:reason for this difference is this: the newer flora had been introduced and had developed to a considerable extent in the Cretaceous period, and there is no See also:sharp break between the flora of the earlier and that of the later period; in both we find a mixed assemblage—what we should now regard as tropical palms, growing side by side with mild-temperate trees . Early Eocene See also:plants in N . Europe, oaks, willows, chestnuts (Castanea), laurels, indicate a more temperate climate than existed in Middle Eocene when in the Isle of See also:Wight, Hampshire and the adjacent portions of the continent, palms, See also:figs, See also:cinnamon flourished along with the See also:cactus, See also:magnolia, See also:sequoia, See also:cypress and ferns . The late Eocene flora of Europe was very similar to its descendant in modern See also:Australasia . See A. de See also:Lapparent, Traite de geologie, vol. iii . (5th ed., 1906), which contains a good general account of the period, with numerous references to original papers . Also R . B . See also:Newton, Systematic, See also:List of the See also: |