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GEOLOGICAL MEMOIRS. 



On the Jura-formation of Russia. By Herr Eichwald. 



[Leonhard u. Bronn's Jahrbuch f. Min. u.s.w. 1850, pp. 225-227 ; and Erman's 

 Archiv, vi. 378, et seq.} 



The "Jura" is found in several districts, but with the exception of 

 the Crimea and Caucasus, it forms no mountain-chain. In 1830, the 

 author examined the first Jurassic beds near the Popilani on the 

 Windau, in the government of Wilna, and since that time they have 

 been also traced in the interior of Russia. In the Indet-system they 

 contain much argillaceous iron-stone, and in the system of the Sando- 

 mir-formation they are characterized by white sandstone. The or- 

 ganic remains contained in the latter differ very much from those in 

 the "Jura" at Popilani. There are Serpula lineata, S. articulata, 

 Asterias Jurensis, Pentacrinus basaltiformis, Terebrat. varians, T. 

 Rogerana, Gryphcea dilatata, Gervillia aviculoides, Panopcea Mur- 

 chisonce, Isocardia corculum, Astarte Voltzi, Lyriodon navis, many 

 Pleurotomarice, Belemnites, and Ammonites. These beds are covered 

 with a black and brown, micaceous and very soft loam, which at some 

 places passes into potter's clay. Distant from this small Jurassic basin, 

 we find eastward another large one, in the middle of Russia, in the 

 centre of which Moscow is situated ; and from hence the Jurassic strata 

 extend into the governments of Rjasan, Vladimir, Nijni Novgorod, 

 Tambf, and Simbirsk. This basin is separated from another, which 

 covers the northern declivity of the Obschey Sirt, and is chiefly de- 

 veloped in Orenburg, near Ilezkaja, here forming the banks of the 

 Ilek and the Ural. Besides this there is another large northern 

 Jurassic basin which extends through the governments of Kostroma 

 and Wologda, towards that of Archangel, where the Jurassic beds 

 occupy the Timan hills, and end at the shore of the Frozen Ocean. 

 Parallel with this runs another chain to the east of the Ural moun- 

 tains, along the rivers Soswa and Tolga. 



Thus, almost everywhere in Russia we find "Jura" -basins, and these 

 contain more or less different forms of marine animals. The rocks 

 mostly consist of dark pyritous schists, of sand [?] and sandstone, of 

 marl, and less frequently, however, of limestone, in which, as in 

 England, large nodules of marly limestone are often found. These 

 Jurassic beds everywhere represent the Middle or Oxfordian formations 

 of England ; only here and there appear beds that are similar to the 

 Lias, as for instance those in the government of Moscow and Simbirsk, 

 which contain bones of Ichthyosaurus and Plesiosaurus of very large 

 size. Only at Petrowsk, near the boundary of the government of 

 Charkow, are the upper developed together with the middle Jurassic 

 beds ; and here they form a small isolated basin. 



The " Jura" -formation around Moscow has been most minutely 

 examined. Here it takes its place immediately upon the mountain 

 limestone. The strata are of calcareous marl, which at some places 

 passes into ferruginous marly loam with small grains of Linsenerz [?] 

 [Pea-ore — octahedral arseniate of copper], as near the villages of 

 Miatschkovo and Grigorjew. At other places the compact limestone 

 itself contains the Linsenerz, and at the same time crystals of iron- 



