Page:The New International Encyclopædia 1st ed. v. 11.djvu/372

* JURA. 340 JUBASSIC SYSTEM. The Jura ifountains proper consist of a scries of parallel folds in the strata, forming together a plateau nearly 200 miles long and 20 to 35 miles wide. These folded ridges have in many places siilTercd transverse fractures, which in the lorm of sleep gorges, known as 'eluses,' add great- ly to the picturesque character of the landscape. The general height of the range is liOOO to 5000 feet. It is highest near the southern end, west of Lake Geneva, where the Crete tie la Neige has an altitude of aiio.i feet. Other prominent summits are the neeulet, 5043 feet ; the Dole, 5507 feet; and Jiont Tendre, 5512 feet. The east- ein slojie falls ahruptly toward the lacustrine hasin forming the ]ilain of Switzerland, and occu- pied hy the lakes of Geneva, Xeuchniel. Hienne, and Morat ; westward and northward the slope is more graihial toward the Saone Vallej-. The .lura Mountains consist entirely of sedi- mentary strata composed of fossiliferous sand- stone and limestone of Mcsozoic age. This group of rocks has given the name .Jurassic system to one of the main divisions of the geological scale. Glacial boulders are scattered over the slopes of the Jura in countless numbers. The climate of the .Tura is relatively severe, and large masse.i of snow rem,') in on the summits during a great part of the year. The slopes are largely covered with pine forests, and agriculture is chiefly confined to the valley bottoms. The principal mineral products of the mountains are litliogiapliic stones, gj'psum, and salt. JURA. An eastern frontier department of France, hounded on the south by the Department of Ain. and on the east by Switzerland (Map: France, M 5). Area. 1928 square miles. Popu- Lation, in 1S96, 260,143; in 1001. 201,288. Of its surface, two-thirds is covered liy the ,Tura Mountains, which reach their greatest altitude in the departnu-nt in Xoirmont, 50S5 feet; the re- mainder i-i a low plain about seven miles wide skirting the western border. The chief rivers are the Ain. the Dnubs, and the Lone. The soil on the mountains is tliin and stony, but yields abundant grass; on the plain the soil is rich, and agricul- ture receives considerable attention. The wines of Arbois. of Poligny, of Etoile, and of Salins have some reputation. The working of rock salt is one of the chief branches of industry: coal and iron are mined: and marble, alabaster, and lithographic stone are quarried. Gruyfre cheese is extensively made, and there is a good trade in timber from the forests of Clianx. Serre, and MoisJons. Capital, I.ons-le-Saunicr. JtTRARA, zhoo'rA-r,a', or ARRAU. . In- dian name of the great turtle of the Amazon (Podociiemis expansa), the gathering of whose flesh and eggs is important to the natives of the entire Amazon basin. See Turtle. JURAS'SIC SYSTEM. A division of the geologic colurm following the Triassic and im- mediately preceding the Cretaceous. The name is taken from the .Tura Mountains of Switzerland, where there is a great development of the rocks of this system. A fullness of detail is observable in ether parts of T^urope; but in .Vmerica the .furassie strata are of small extent, and in places it is impossible to separate them from the Trias- sic. for which reason the term .Tura-Trias is em- ploved on thi> maps of the United States Geo- logical Survey. The main subdivisions of the Jurassic svstem are as follows : ( a ) Lias, or Lower Jura; (b) Lower Oiilite, or Middle .Tura; (e) Middle Oolite; and (d) r])pcr Oiilite. or L'pper Jura. Strata of undoubted Jurassic age are not known ;ilong the Atlantic coast of the United States, although some geologists have con- sidered that the u])per beds of the Trias are referable to this system, while other authorities would class the Potomac l>eds as .Jurassic. A great area of probable .Jurassic sandstone, but lacking fossils, was deposited in an interior sea in Colorado, Wyoming, Arizona, and New Mex- ico. In California and Oregon there arc Liassic beds, while marine Upper Jurassic strata occur in northern Utah, Wyoming, and Jlontana. Upper .luras>ic slates of great thickness and interbedded with volcanic tulTs are found in the Sierra Ne- vada of California and in British CoUimbia. In Europe there is an al)undance of .Jurassic rocks, which were deposited in depressions of post-Trias- sic time. Those of the Lias or Lower Jura cover large areas of Southern and Central lCuro])e, and also extend in a band across (Jreat Britain. They are lacking, however, in Russia. In the Lower Oolite much additional land was sub- merged, and the deposits cover Central and Northern Russia, Siberia, and the Indian Penin- sula. The Jurassic rocks abound in fossils in some areas, notably Europe, where in England alone over 4000 species have been found. The plant life of the .Jurassic is similar to that of the Triii-ssic. Among the more important forms were ferns, equiseta, cycads, and conifers. It was in this era that the cycads attained their maximum development, and tree-ferns grew in great pro- fusion. Foraminifera are found in countless lumibers in some of the limestones, as were also the siliceous cases of radiolarians. and sponges. Corals were numerous, and sea-urchins and eri- noids swarmed. There were many delicate forms of life such as crustaceans, liniuloids. and insects of several orders which required special condi- tions for their perfect preservation. These are found in abundance in the homogeneous fine- grained lithographic limestones of Solenhofen, Bavaria. Brachiopods still existed in the .luras- sic, and lamcllibranchs of the oyster type were very common. The cephalopods were another class which culminated in this era. and included both nautiloids and ammonoids among the coiled forms, and belemmites in the straight shells. Among the fishes there was an advance over those of Triassic times. In the class of teleostomes. the ganoids continued to predominate, and many were covered with thick shining scales. Anipliibia are known to have existed, but the reptiles were a Iiromincnt feature of the .Turassic fauna. Among them were turtles, lizards (the first true ones known), and ichthyosaurians. or marine reptiles, the European representative being Ichthyosaurus (q.v.), and the American one Baptanodon (q.v.). .Another marine group was represented by Ple- siosaurus, which diflfered from Ichthyosaurus in having a nuich longer body and neck, and larger paddles. The dinosaurians assumed prodigious jiroportions. but were of variable sh:ipe and size. i"hey included the genera Megalosaurus, Cetio- saurus. Osinosaurus. and Compsognathus. The Pterosauria were flying reptiles, having a spread of wings of .nliout three feet. They are found in the Solenhofen slates, together with a more curi- ous fossil, the arch;eoptervx (q.v.). The latter represents the earliest bird known.