78 POLAR PROBLEMS 



The deformations of both terrestrial and marine deposits laid 

 down in the depressions between the positive elements reveal much of 

 that long history which was lost through the excessive erosion upon 

 the surfaces of the oldlands, or positive elements. Again and again 

 the sea invaded certain of the negative elements and submerged them. 

 The retreat of the sea at last brought into view the surfaces of the 

 negative elements. This makes it possible now to see both positive 

 and negative elements in their full geographical distribution and 

 structural relationship. It enables us to trace the history of the land- 

 scape from one geological age to another and to understand topo- 

 graphic and other relations that are as important geographically as 

 they are geologically, because they give the history of the terrain upon 

 which, in turn, the history of life forms was worked out. They show 

 also the relations of the Arctic islands to the continent, as well as the 

 relations of mountains or plateaus to plains or of coast line to river 

 systems and old geological lines of disturbance. 



The Three Major Oldlands, or Positive Elements 



The most typical and largest old regions are (i) Fennoscandia 

 (Finland and Scandinavia, in general) at the western end of Arctic 

 Eurasia, (2) the Chukchi Peninsula at the extreme eastern end (be- 

 tween the Kolyma River and Bering Strait), and (3) the Central 

 Siberian Plateau (including the Taimyr Peninsula) located in the 

 middle part of northern Eurasia (Fig. i). 



Fennoscandia is composed of a variety of gneisses, slates, and 

 granites. Since remnants of fossil-bearing Cambrian and Ordovician 

 sediments have been found in some localities partly preserved as 

 structural inliers in the granites, the Lower Paleozoic sediments of 

 which they form a part must be considered as once more extensive. 

 They formed in fact a cover to the older granites, slates, and gneisses 

 which were the old foundation rock, and are now removed from the 

 surface of the Scandinavian Peninsula because of subsequent strong 

 erosion. 



The Central Siberian Plateau is composed chiefly of Cambrian, 

 Ordovician, and Silurian strata. Pre-Cambrian rocks, represented 

 by gneisses, granites, and a variety of slates (the slates are widely 

 known on the Taimyr Peninsula), are here more extensively coveied 

 by Paleozoic sedimentary slates, and these are usually but little dis- 

 turbed. Some well-marked but local folds have been produced by 

 intrusions of basalt and are of laccolithic origin. The same basalts, 

 in effusive form, cover many thousands of square miles of the surface 

 of the plateau and form one of the largest known lava fields in the 

 world. Their eruption was going on, probably, during the whole Upper 

 Paleozoic and was continued into the Mesozoic, as coal-bearing Upper 



