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Encyclopedia Britannica - Main :: LEO-LOB |
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LIAS , in geology, the lowermost group of Jurassic strata. Originally the name seems to have been written " Lyas "; it is most probably a provincial form of ." layers," strata, employed by quarrymen in the west of England; it has been suggested, however, that the Fr. liais, Breton
ridge
The important fact is clearly demonstrated in the table, that where the Lies is seen in contact with the Trias below or the Inferior ()elite above, there is, as a rule, a gradual passage from the Liassic formation, both downwards and upwards; hence Professor de Lapparent includes in his Liassique System the zone of Ammonites opalinus at the top, and the Rhaetic beds at the bottom (see OoLITE; RHAET1C). Owing to the transgression of the Liassic sea the strata rest in places upon older Palaeozoic rocks. The thickness of the Lias varies considerably; in Dorsetshire it' is 90o ft., near Bath it has thinned to 280 ft., and beneath Oxford it is further reduced. In north Gloucester-shire it is 136o ft., Northampton 76o ft., Rutland 800 ft., Lincoln-shire 950 ft., and in Yorkshire about 500 ft. The Lias of England was laid down in conditions very similar to those which obtained at the same time in north France and north Germany, that is to say, on the floor of a shallow sea; but in the Alpine region limestones are developed upon a much greater scale. Many of the limestones are red and crystalline marbles
of March 1J73. After his death Pibrac, 'assisted by De 'Thou and Scevole de Sainte-Marthe, collected a volume of the Poemata of L'H8pital', and in 1585 his grandson published Epistolarum seu Sermonum libri sex. The complete IEuvres de l'Hopital were published for the first time by P. J.S. Dufey (5 vols., Paris, 1824-1825), They include his " Harangues " and " Remonstrances," the Epistles, the M.emoire to Charles IX., a Traiti de la reformation de la justice,'hnd'his'ivill. See also A. F. Villemain, Vie du Chancelier de l'llepital.(Parisi 1874) ; R. G. E. T. St-Rene Taillandier, Le Channcelier de l'Hospittalf (Paris, 1861); Dupre-Lasalle, Michel de l'Hospital avant son elevation
Atkinson , Michel de l'Hospital (London, 1900), containing an appendix on bibliography and sources; A. ,E. Shaw, Michllde !'Hospital and his Policy (London, 1910,5); and Eugene
Haag, La Franceprotestanle (and ed., 1877 seq.). The economic products of the Lias are of considerable importance. In the Lower Lias of Lincolnshire and the Middle Lias of Oxfordshire, Northamptonshire, Lincolnshire, Leicestershire and Yorkshire the beds of ironstone are of great value. Most of these ores are limestones that have been converted into iron carbonate with some admixture of silicates; they weather near the surface into hydrated peroxide. He removed his school to Nicomedia, where he remained five years. After another attempt to settle in Constantinople, he finally retired to Antioch (354) Though a pagan
S.W. England and Midlands. Yorkshire. Ammonite Zones.' DA. de according to A. de Lapparent.2 a Midford Sands (passage beds) Alum shale Am. jurensis tT' (Including the opalinus zone ~-a Clays with Cement-stones Jet Rock communis of the Inferior Oolite.) Limestones and Clays Grey Shale serpentinus Toarcien. annulatus 6 Marlstone and Sands Ironstone Series Am. spinatus M Charmouthien.S.a (Rock Bed and Ironstones) Sandy Series margaritatus L Micaceous Clays and Sands 1 1. Clays with occasional bands Upper Series with Am. capricornus o of Limestone Ironstone nodules Jamesoni Limestones and Clays Lower Series with and Sandy and Marly armatus Beds oxynotus Bucklandi angulatus planorbis Sinemourien. Hettangien including "White Lias." Rhetien. 1 The brackets indicate the divisions made by R. Tate and J. F. Blake. 2 Traite de geologie (5th ed., Paris, 1906). At Frodingham in Lincolnshire the oolitic iron ore reaches 30 ft. in thickness, of which 12 ft. are workable. In Gloucestershire the top beds of the Lower Lias and lower beds of the Middle division are the most ferruginous; the best ores near Woodstock and Banbury and between Market Harborough and Leicester are at the summit of the Middle Lias in the Marlstone or Rock bed. The ironstone of Fawler is sometimes known as Blenheim ore. The ores of the Cleve-land district in Yorkshire have a great reputation; the main seam is I1 ft. thick at Eston, where it rests directly upon the Pecten Seam, the two together aggregating 15 ft. 6 in. Similar iron ores of this age are worked at Meurthe-et-Moselle, Villerupt, Marbache, Longuy, Champagneulles, &c. Some of the Liassic limestones are used as building stones, the more important ones being the Lower Lias Sutton stone of Glamorganshire and Middle Lias Hornton stone, the best of the Lias building stones, from Edge Hill. The limestones are often used for paving. The limestones of the Lower Lias are much used for the production of hydraulic cement and " Blue Lias " lime at Rugby, Barrow-on-Soar, Barnstone, Lyme Regis, Abertham and many other places. Roman cement has been made from the nodules in the Upper Lias of Yorkshire; alum is obtained from the same horizon. A considerable trade was formerly done in jet, the best quality being obtained from the " Serpentinus " beds, but " bastard " or soft jet is found in many of the other strata in the Yorkshire Lias. Both Lower and Upper Lias clays have been used in making bricks and tiles. Fossils are abundant in the Lias; Lyme Regis, Shepton Mallet, Rugby, Robin Hood's Bay, Ilminster, Whitby and Golden Cap near Charmouth are well-known localities. The saurian reptiles, Ichthyosaurus and Plesiosaurus, are found in excellent preservation along with the Pterodactyl. Among the fishes are Hybodus, Dapedius, Pholidophorus, Acrodus. The crinoids, Pentacrinus and Extracrinus are locally abundant. Insect remains are very abundant in certain beds. Many ammonites occur in this formation in addition to the forms used as zonal indexes mentioned in the table. Lima gigantea, Posidonomya Bronni, Inoceramus dubius, Gryphaea cymbium and G. arcuala are common pelecypods. Amberleya capitanea, Pleurotomaria anglica are Lias gasteropods. Leptaena, Spiriferina, Terebratella and Rhynchonella tetrahedra and R. variabilis are among the brachiopods. Certain dark limestones with regular bedding which occur in the Carboniferous System are sometimes called " Black Lias " by quarrymen. See The Lias of England and Wales " (Yorkshire excepted), by H. B. Woodward, Geol. Survey Memoir (London, 1893); and, for Yorkshire, " The Jurassic Rocks of Britain, vol. i., " Yorkshire, by C. Fox-Strangways, Geol. Survey Memoir. See also JURASSIC. (J. A. H.) End of Article: LIAS If you wish, you can link directly to this article.
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