8'0 POLAR PROBLEMS 



Strata and is therefore a mountain of comparatively recent origin, in 

 contrast to the pre-Cambrian and Paleozoic rocks of the oldlands. 

 But since granites and gneisses have been found in the central part of 

 the ridge, and Cambrian and Silurian sedimentaries in its northern 

 part (Khara-Ulakh Mountains), the Verkhoyansk Ridge must be to 

 some extent of ancient origin. 



The Formation of These Oldlands 



Thus Arctic Eurasia is characterized by the presence of seven old- 

 land masses ranging in size from continental dimensions to compar- 

 atively small islands or groups of islands. While they vary in size 

 their geological differences are moderate and secondary. In the larger 

 continental land masses the old geological structure is perfectly clear. 

 Confusion is possible only near the borders, upon which may be 

 piled newer formations, but these borders represent only small outer 

 parts bordering a central oldland. In smaller insular masses sometimes 

 only an insignificant part of the surface remains unaffected by the 

 later border structures. The mountains of this group of smaller 

 oldlands are composed chiefly of younger strata rather than those of 

 the oldland, and their primary origin is often obscure. Such is the 

 case with the Verkhoyansk Ridge and to a smaller extent with the 

 Ural and Timan Ridges. In many cases topographical and geological 

 contrasts among the oldlands have been produced by differential 

 erosion, which, for example, was more extensive in Fennoscandia than 

 on the Central Siberian Plateau. All the oldlands are well reflected in 

 the relief of Arctic Eurasia, as they determine the location and features 

 of the ridges and high plateaus. A remarkable symmetry in their 

 distribution has also to be noticed. They form the projecting penin- 

 sulas and related offshore islands, all of which have close geological 

 connection with the mainland and originally were parts of it. The 

 best examples of this connection are: Vaigach and Novaya Zemlya 

 north of the Ural Mountains, Northern Land (Nicholas II Land) 

 north of Taimyr Peninsula, and the New Siberian Islands north of 

 the Tas-Khaya-Khtakh Mountains. Even in the case of the islands 

 that are built up of glacial drift, the drift has probably been deposited 

 around a nucleus of bed rock. 



All these masses are parts of the same geological body, of the old 

 Eurasian continent, separated through the sinking of intermediate 

 sections along zones of faulting. The projecting land masses are horsts, 

 or positive elements; the sunken tracts are graben, or negative ele- 

 ments. This is inferred from the distribution of younger strata within 

 graben on the same level or lower than that of the older strata in 

 the oldlands, from the occurrence of old eruptions on the borders of 

 the horsts, and from other evidence. 



