GEOLOGY OF ARCTIC EURASIA 79 



Paleozoic strata, also found on the surface of the plateau, are often 

 traversed by basalt dikes. 



The Chukchi Peninsula is built up of a variety of slates, limestones, 

 and igneous rocks. Among the latter, the most important are granite, 

 porphyry, basalt, etc. Because no fossils have yet been discovered on 

 the peninsula, the age of the sedimentary rocks is not positively known, 

 but in the western section of the peninsula they have been considered 

 to be Pre-Devonian, thus corresponding to the Lower Paleozoic 

 deposits of the Central Siberian Plateau. Later investigation may show 

 that the geological structure of the Chukchi Peninsula is more com- 

 plicated than this description would suggest and that a part of the 

 slates as well as the limestones, especially in the eastern part of the 

 peninsula, may be of younger age and involved in the relatively 

 youthful folds of the Pacific border, piled up or pushed over upon the 

 oldland. 



The Four Minor Oldlands 



Between these principal oldlands are located others of the same 

 geological structure and origin but of smaller dimensions (Fig. i). 



On the border of Europe and Asia is located the linear belt of the 

 Ural Mountains, the Arctic part of which is known as Pai-Khoi 

 Ridge. It includes a number of oldland masses composed of granites, 

 syenites, and other igneous rocks, as well as gneisses of different origin, 

 together with slates and limestones. As some of the latter probably 

 belong to the .Silurian and Cambrian, the geological structure of the 

 Ural Mountains closely corresponds to that of the oldlands, considered 

 above, with this difference, that, owing to the small dimensions of 

 the old masses, as compared with the overlapping and over thrust 

 folds of Devonian, Carboniferous, and Permian strata, it appears more 

 complicated. 



Timan Ridge, located in the northern part of European Russia 

 west of the Ural Mountains, has the same geological structure as the 

 oldland just discussed and is usually considered a small northwestern 

 branch of the Ural structural region. It runs in a northwest-southeast 

 direction, or parallel to the Pai-Khoi, and, like the Urals, is reflected 

 in the structure of Novaya Zemlya. The northeastern, or Arctic, shore 

 of the Scandinavian Peninsula trends in the same direction. The 

 triangular area between both ridges is very little known, but a few 

 outcrops of old formations have been found here as well. 



A few oldland masses are known near the Arctic shore between the 

 Yana and the Indigirka. Southwards they continue as a large, very 

 little known ridge, Tas-Khaya-Khtakh, with granites and gneisses 

 within its central part. 



Still less known is the Verkhoyansk Ridge, situated between the 

 Lena and Yana Rivers. It is composed partly of folded Cretaceous 



