Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/376

Rh 36?. animal with long tail, and two-toed feet, forming a kind of intermediate type between a hog and a deer or antelope ; ])icIwbune, allied to the last named ; also 1)icho¢lon, II_;/opo- tamus, C’/ueropotamus, II_z/cenodon-, &c. The top of the Eocene series in the Isle of Wight has been removed by denudation, so that we have no evidence in Britain of what took place after the close of the Eocene period. CONTI.’E‘.'TAL Evaorl-:.——Geologists on the continent of Europe, ﬁnding it impossible to carry out the principle of percentage of recent species, as originally formulated by Lyell in his terminology of the Tertiary series, have made various modiﬁcations of this nomenclature. By some the three terms Eocene, Miocene, and Pliocene are retained, but, following Beyrich, they subdivide the Miocene into two, keeping that term for the upper half and calling the lower Oligocene, which corresponds with Lyell’s Lower Miocene. Others would consider the whole Tertiary and post-Tertiary series as divisible into three groups, the Eocene or Older Tertiary, corresponding pretty closely to the Lyellian use of the term, the Neogene or Younger Tertiary, embracing both Miocene and Pliocene, and the Diluvial and Alluvial. In the Paris basin the Eocene formations assume a somewhat different type from that which they present in England, though the occurrence of a number of the same species of fossils in both allows of their being paralleled in a general way. The lower Eocene consists there of sand and clay answering in lithological character to the Thanet Sand and Plastic Clay of the London basin. The common species in that basin (0strca Bclloracina) occurs there in great numbers, while the brackish water-beds contain some of the common species at Voolwich, such as Cyrcna cmmforinis and Jlclania inquinata. Beds of lignite occur in this division, likewise bones of Coryphorlon Eocwnus, I'2'vcrra giga-ntca, and the bird Gastonlis. The Middle Eocene is made up of the character- istic “ Calcaire grossicr"’—a mass of limestone, sometimes tender and crumbling, in other places so compact as to be largely quarried as a building stone. Some portions are entirely composed of minute fora- minifera (miliolitic limestone). Among the characteristic fossils of this division are Nmnnzulitcs, Ocritlzizmt giganteum, with bones of Dichobunc, Lophiozlon, Paloploth/:rz'um, &c. The Upper Eocene con- sists of sand (Sables moycns) overlaid by the great gypsum and gypscons marl group of lIontmartre. This is the deposit from which so many of the mammals of the Eocene period have been recovered. It is divided into three zones, and among its fossils are upwards of 50 species of quadrupeds, including many Palzeotheres, Anoplo- theres, Paloplothcrcs, with X iphodon, Dzchobmw, Adapts, C’ha':ro- potamus, .lIyo.1:us, Ca-nis Pa:-isicnsis, V ircr-ra I’arz'sz'ens2's, Vesper- tilio, Didclphys Cuvieri, and about 17 species of birds. The Eocene formations of the north-west of Europe occupy but a few detached basins, and consist for the most part of soft clays, sands, marls, and thin limestones. They were laid down partly in estuaries, rivers, or lakes, partly in shallow seas near land. 'I‘hey contain abundantly the vegetation, with some remains of the quadrupeds and birds, of that land, and show that still in older Ter- tiary times, as during the long Palaeozoie and Secondary ages, the chief area of land lay to the north-west. But when we turn to the corresponding formations in central and southern Europe, they pre- sent a totally different aspect. In the first place, they at once im- press us with the idea of their antiquity, for they consist chiefly of massive, hard, crystalline, and sometimes even marble-like lime- stones, which suggest some of the Palzeozoic rocks rather than those of so modern a date as the London Clay and Calcaire Grossier. Again, instead of being confined to a few local basins, they cover an enormous geographical area and play a notable part in the structure of some of the great mountain chains of the globe. Crowded as they are with nummulites, they must have been deposited not in estuaries and shallow bays but in a wide and clear sea, which, traced by the area of these limestones, must have ranged across the whole of the south of Europe and north of Africa, through Greece, Turkey, Asia Minor, and the heart of Asia, to the far shores of China and Japan. Since the time when this wide channel connected the Atlantic and the Paciﬁc across the heart of the Old Vorld, the great mountain ranges of the Pyrenees, Alps, Apennines, Carpathians, and of Cen- tral Asia, have been upheaved to their present altitude. Some of the prominent peaks along their ﬂanks consist of the hardened and crumpled calcareous mud of the Eocene sea. In the northern and southern Alps the Eocene formations consist of nurnmulitic limestone—a grey, yellow, sometimes reddish com- pact rock, usually containing and often made up of nummulites; nummnlite sandstone ; Vienna sandstonc—an enormous mass of arenaceous rock almost destitute of organic remains. and referred GEOLOGY [vr. STRATIGRAPEIICAL. partly to the Cretaceous and partly to the Eocene series ; and F lysch ——a massive development of dark shales or schists, sandstones, and argillaceous limestone, sometimes charged with the remains of fucoids and (at Matt, Glarus) of fish. The nummulitic series of southern Europe is divided into zones characterized by fossils, and brought into a kind of broad parallelism with the sulnlivisions of the English and French Eocene basins. In the eastern Alps, near Vienna and elsewhere, some of the nmnmulitic sandstones contain enormous blocks of granite, gneiss, and other crystalline rocks, which are believed to have been ice-borne, and therefore to prove the existence of Alpine glaciers even in Eocene times. These moun- tains already existed, as it were, in embryo, even far back in the Secondary and Palzcozoic ages. During the later part of the Eocene period they seem to have been clothed with an abundant flora. among which the fan-palm, Bazzksin, I)r_:/amlrirt, and other plants remind one of the living vegetation of tropical Alncrica, the East Indies, and Australia. Out of these plants the important coal- seams of Haring in Tyrol were formed. lIIOCE1‘E. According to the original nomenclature proposed by Lyell, this subdivision of the Tertiary series was meant to include those strata in which 17 per cent. or thereabouts of the shells belong to still living species. As the system of nomenclature was adopted at a time when our knowledge both of living and fossil species was still very defective, it could not but require modiﬁcation with the progress of science. Some strata, classed at one time as Miocene from their proportion of recent forms, might, on more ex- tended research, prove to contain a much larger percentage, and therefore to be referable to a later part of the Tertiary series. The term, however, is used as a convenient and long- established designation for a series of strata younger than the Eocene, which they seem to have succeeded, though in some parts of the European area after enormous geographi- cal changes. GREAT BRI'rA1‘.*.—-——Miocene formations, in the ordinary sense of the term, are almost entirely absent from the British Islands. In Dcvonshire, at Bovey Tracey, a small but interesting group of sand, clay, and lignite beds, from 200 to 300 feet thick, lies between the granite of Dartmoor and the Greensand hills, in what was evidently the hollow of a Miocene lake. From these beds Heer of Zurich, who has thrown so much light on the Miocene flora of both the Old Vorld and the New, has described about 50 species of plants, which, he says, place this Dcvonshire group of strata on the same geological horizon with some part of the Lower Miocene formations of Switzerland. Among the species are a number of ferns (Lastrcea sliriaca, [’eco/dc)-is Ugnitzmz, &c.) ; some conifers, particularly a ll'ellz'72_r/tom'a called the Sequoia Couttsite, the debris of which forms one of the lignite beds ; a few grasses, water-lilies, and a palm. Leaves of oaks, ﬁgs, laurels, willows, and seeds of grapes have also been detected—the whole vegetation implying a subtropical climate. In the north of Ireland lies a great plateau of basalt, presenting along the coast of Antrim a magni- ﬁcent range of mural escarpments. The basalt-beds mark successive outpourings of lava, which took place on a prodigious scale from the Antrim region northwards through the Vestern Islands and the F aroe Islands into Iceland, and even far up into Arctic Greenland. In Ireland the basalts attain a maximum thickness of 900 feet; in Mull about 3000 feet. They are associated with tuffs, pitchstones, trachytes, and granitoid rocks, which mark the position of the main vents of eruption. It is evident that long-continued and vigorous volcanic action took place in these north-western regions. The geological date of this activity can be approximately ﬁxed by the fossil plants here and there to be found in leaf—beds between the sheets of basalt. They agree generally with species found in the Older Miocene beds of Switzerland; and hence the date of this marked volcanic era in the north-west of Europe and in Greenland is placed in the older part of the