OLTFANT RIVER 



OLIGOCENE SYSTEM 



597 



occurs in commerce in semi-transparent yellowish 

 tears and masses ; has a bitter nauseous taste ; is 

 hard, brittle, and capable of being pulverised ; anil 

 diffuses a strong aromatic odour when burned. It 

 was formerly used in medicine, chiefly to restrain 

 excessive mucous discharges ; but its use for such 

 purposes is now rare. It sometimes enters as an 

 ingredient into stimulating plasters. It is chiefly 

 employed for fumigation, and is used as incense 

 in Roman Catholic churches and Indian temples. 

 Its odour is obnoxious to mosquitoes and other 

 insects. The inner layers of the bast of B. frereana 

 are transparent, resembling oiled paper, and are 

 used by the natives for writing on. Aden is the 

 great port where it is chiefly received. The imports 

 there in 1888 were 16,248 cwt. of ordinary olibanum 

 and 3600 cwt. of that termed Mayeti, the name 

 of the port from which it is received in Somali 

 Land. This is the produce of B. frereana, and 

 much resembles Tacamahac. The exports of oli- 

 hanum from Aden in 1888 were 23,000 cwt. In 

 India, where it is much used, the imports increase 

 year by year, and reached 26,680 cwt. in 1888. 

 Some is sent to China, and about 17,000 cwt. 

 comes to England, valued at about 41,000. 



Olifant River, a forked stream of Cape 

 Colony, rises in the mountains north-east of Cape- 

 town, and, after a north-westerly course of 130 

 miles, enters the Atlantic. Area of drainage 

 basin, 13,000 sq. m. Another stream bearing the 

 same name rises in the Transvaal, and goes east to 

 join the Limpopo. 



Oligarchy ( oligos, 'few.'andnrcAo, 'I govern'), 

 a term applied by Greek political writers to that 

 perversion of an aristocracy in which the efforts <>f 

 the dominant and ruling party are chiefly devoted 

 to their own aggrandisement and the extension of 

 tli'.'ir [>ower and privileges. Thus it bears the same 

 relation to aristocracy that despotism does to 

 monarchy and ochlocracy to democracy. 



Olisi'oeeiie System. The British strata 

 belonging to this system occur only in Hampshire, 

 the Isle of Wight, and Devonshire. The series is 

 as follows : 



4. HEMFSTEAD BEDS : froth-water marl anil clays overlaid by 

 marine sepUrian clays. About 280 feet 



5. BEMBRIDGE DEDH: mar-In and limestone; fresh- water below, 

 estuarine above. A I mut 110 feet. 



J. OABORNE BED : freh-wat*r clays, marls, sands, and llme- 

 tone. About 10) feet. 



1. HEADOX BEDS : variable series of clys. marls, sands, and 

 limestones. Tlie lower division is of fn-xh- and brackish- 

 water origin; the middle partly marine, partly fresh- water ; 

 the upper fresh-water. About 160 feet. 



I'sually included as Oligorene are the lacustrine 

 beds of IJovey Tracey in Devonshire, consisting of 

 sands and clays with lignites. lletween the basalt- 

 beds that coin|iose the denuded plateaus of Antrim 

 and the Inner Hebrides (Mull, &c.) occur thin 

 layers of clay and lignite the so called leaf-beds 

 which are probably of the same age. 



Forciijn Kijini-nlmtx. olig ne strata, chiefly 



of fresh- and brackish water origin, but containing 

 intercalations of marine lieds, overlie the Eocene 

 of the Paris basin and that of Belgium. They like- 

 wise appear in Germany, where they form the 

 oldest Tertiary deposits no E<icene "having yet 

 l-en detected in that region. The German Oligo- 

 cene is mainly of fresh-water origin in its lower and 

 upper portions, while marine dejxjsits predominate 

 in the middle of the series. It is noted for it* 

 Iwds of lignite or brown coal. In Switzerland the 

 Oligorenc attains a thickness of several thousand 

 feet, chiefly conglomerates and sandstones, known 

 as Molaiwe, ami mostly of fresh-water origin ; the 

 basal portions, however, are marine and brackish- 

 water. Other areas of fresh- water Oligocene more 

 or less notable are met with in Alsace, Breisgait, 



and Wurtemherg. In Auvergne, central France, 

 lacustrine deposits of the same age are well 

 developed, and, like most of the Oligocene strata, 

 have yielded great numljers of organic remains. 



Life oftlie Period. The flora of Oligocene times 

 was abundant and varied. Palm-trees (Sabal, 

 Flabellaria), both large and small, seem to have 

 grown over all Europe. Amongst conifers were 

 various American types ( Libocedrus, Chanifecy- 

 paris, Sequoia, Taxodium ) and other forms, such 

 as Glvptostrohns, like G. heterophyllus of Japan 

 and China, Widdringtonia, a genus now found 

 only in South Africa and Madagascar. There were 

 also proteaceous plants (Dryandra) of Australian 

 affinities, and species of custard-apple, gum-tree, 

 spindle-tree, maple, acacia, mimosa, lotus, aralia, 

 camphor-tree, cinnamon-tree, evergreen oak, laurel, 

 &c. , besides such familiar forms as birch, horn- 

 beam, elder, elm, poplar, walnut, &c. Evergreens 

 were the prevalent forms. The invertebrate fauna 

 needs but little notice. Amongst notable molluscs 

 were volutes, cowries, olives, cones, spindle shells, 

 &c. Cerithium was particularly plentiful in the 

 estuaries of the |>eriod ; while lamellibranchs were 

 well represented by modern types of marine and 

 fresh-water habitats. Amongst the birds common 

 in Europe were |iroi|iiets, trogons, marabouts, 

 enines, flamingoes, ibises, pelicans, eagles, secretary- 

 birds, sand-grouse, &c. At the beginning of the 

 period many mammals of extinct ty[>e8 lived in 

 Europe, such as Pala>otlierinm and Anchitherium, 

 survivals from the Eocene ; certain transitional 

 forms of ungulates, such as C'ainotherium (a small 

 animal somewhat resembling the living chevrotains 

 in outward appearance ), Xiphodon (a slenderly 

 built deer-like animal ), and Anoplotherium ( a long- 

 tailed animal about the size of an ass, with two 

 toes on each foot > ; various tupiroid animals, small 

 rhinoceroses, Hyii-nodon (a carnivore), also forms 

 of souirrel, civet, martin, mole, musk-rat, &c. 



Physical Conditions. During Oligocene times a 

 wide Innd surface appears to nave extended over 

 all the British area. In the region lying between 

 what is now Antrim and the west coast of 

 Scotland great fissure-eruptions took place, and 

 sheet after sheet of basalt was poured out, so as 

 eventually to form broad plateaux that extended 

 northwards lieyond Skye. In the intervals between 

 successive eruptions these plateaus became clothed 

 with vegetation, the debris of which has l>een here 

 and there preserved in the de-posits of shallow lakes 

 that dotted the surface of the volcanic country. It 

 is probable that at this time there was land- 

 connection between Europe and North America 

 by way of the Faroe Islands and Iceland, in both 

 of which tracts similar basaltic plateaus occur, 

 containing intercalated layers of lignite, &c. like 

 those of Antrim and the Western Islands of Scotland. 

 The Oligocene strata of the south of England and 

 the Franco- Belgian area are evidence that the sea 

 or estnarine waters which occupied that region in 

 Eocene times (see EOCENE SYSTEM) were gradu- 

 ally silted up. In Germany there existed great 

 fresh water lakes, fringed by wide marsh-lands and 

 by dense forests of a subtropical character. As the 

 lakes became partially silted or dried up vegetation 

 encroached upon their deserted beds, only to be 

 buried under fresh accumulations of sand and 

 mud when the water had again risen. That these 

 lakes were now and again in direct communication 

 with the sea is shown by the occurrence of thick 

 layers of marine origin intercalated amongst tho 

 fresh-water beds. For some time, indeed, the 

 lacustrine areas were entirely nmrped by the sea, 

 which may have entered them from submerged 

 regions in the east of Europe. In Switzerland, in 

 like manner, we have evidence of changing con- 

 ditions. At first the sea covered a considerable 



