82 POLAR PROBLEMS 



During the Tertiary (Eocene) period the sea overflowed large 

 areas of Western Siberia along the eastern side of the Ural Mountains, 

 where it probably communicated with the Arctic sea. Another 

 Tertiary (Miocene) sea has left its sediments with marine fauna of 

 Pacific type in the eastern part of Arctic Eurasia, in the Anadvr 

 region. 



Geological History of the Continental Deposits 



The continental geological history of Arctic Eurasia, where recorded 

 by continental deposits, is not less varied than the marine history. 

 The presence of land during the Lower Paleozoic is suggested by the 

 lithological character of the sedimentary rocks, though the greatest 

 part of old Eurasia was permanently covered with sea. The old 

 horsts, dry land since the Silurian, usually offer very scanty records 

 of their long continental duration. In many cases their surface is 

 composed of the oldest primary bed rock, not always covered even 

 with a thin layer of soil. 



Abundant continental deposits are known in Arctic Eurasia, 

 starting from the Upper Paleozoic only. Coal-bearing deposits of 

 that period, discovered in the northern part of the Central Siberian 

 Plateau (on the Yenisei, Khatanga, Anabar, Olenek Rivers), bear 

 witness to a comparatively warm, humid climate favorable to the 

 development of an exuberant flora of Gondwana character, considered 

 by geologists as Upper Carboniferous or Permian. Glossopteris is an 

 especially typical plant of this flora, which is therefore often known as 

 Glossopteris flora. 



The Upper Permian continental deposits of northern Europe record 

 a rather dry and often hot climate corresponding perhaps to that of 

 recent steppes like those of Turkestan today. The Permian strata 

 .of northern Europe are widely known on account of a rich and dis- 

 tinctive amphibian and reptilian fauna found within old river deposits. 

 Among reptilians a herbivorous Pareiasaurus and carnivorous Inos- 

 tranzewia are the most conspicuous members. Some of these old rep- 

 tilians had a few characters of organization common with amphibians. 

 Others were related to Triassic reptilians and had even some of the 

 ancestral trends of mammals. 



Triassic land must have had a very great extension in Eurasia, 

 but Triassic deposits with a land flora are known only in a few isolated 

 localities on the islands of the Arctic Sea. 



Jurassic continental strata with a rich flora, often also containing 

 workable seams of good coal, have been found in many places in 

 Arctic Eurasia. Especially interesting are the localities on the islands 

 of the Arctic Sea — Spitsbergen, Franz Josef Land, the New Siberian 

 Islands, and others. All of them are remnants of a continuous land 



