GEOLOGY OF ARCTIC EURASIA 83 



of immense area which was once connected with corresponding land 

 masses of continental Arctic Eurasia and North America. It was dis- 

 membered by a great diastrophic movement, which greatly contributed 

 to the origin of the Arctic Sea in its present outline and form, and 

 isolated masses were mostly destroyed by waves, small islands perhaps 

 being preserved only under special conditions, as, for example, where 

 they enjoyed the protection of a basalt cover. Fossil floras in all these 

 distant localities are very similar to each other and to the corresponding 

 floras of southern latitudes — a usual condition for Middle Jurassic 

 floras, which were surprisingly cosmopolitan. This flora consisted of 

 rushes, herbaceous plants, tree ferns, cycads, gingkoes, and conifers, 

 the descendants of which are now found mainly in southern lands. 

 The cycads were especially abundant and diversified in the Jurassic, 

 the latter being often called the Age of Cycads. 



Cretaceous continental deposits are also known on the Arctic 

 islands and on the Arctic shore of Asia. They have a smaller distribu- 

 tional range than the Jurassic, with which they are often immediately 

 connected and from which they are perhaps not always well differen- 

 tiated. The Cretaceous flora here was similar to the Jurassic flora 

 as well, though more specialized. 



Remnants of Tertiary land with fossil floras are known on the 

 New Siberian Islands, on the neighboring coasts of the mainland, and 

 in the Anadyr region. Although they are of early Tertiary (Eocene) 

 age they have been so well preserved at the first locality that the fossil 

 tree trunks for a long time were considered recent driftwood and 

 cliffs were christened "Wood Hills." All these localities, like those 

 of the Jurassic, are disconnected parts of a large land of circumpolar 

 extension, as the same rich fossil flora is known in North America and 

 in Greenland. The dismembering of this Tertiary land concluded, 

 probably, the shaping of the present Arctic Sea, at least in its most 

 essential form. 



Post-Tertiary History 



In post-Tertiary time Arctic Eurasia suffered great oscillations. 

 The present Arctic shore, from the Scandinavian Peninsula on the 

 west to the Lena River on the east, including offshore islands, is 

 covered with sediments of Boreal transgression with a marine fauna 

 similar to the Recent one of the Arctic Sea. It bears witness to a 

 broad regional subsidence and a succeeding emergence. The latter 

 was more marked in Europe than in Asia, as the elevation at which 

 Boreal shells, Yoldia, Cyprina, Tellina, Mytilus, etc., are now found 

 gradually decreases towards the east. On the continent they are not 

 known east of the Lena River but have been found farther east in the 

 New Siberian Islands. In fact near the eastern end of their distri- 



