76 POLAR PROBLEMS 



enced by the geological conditions of other regions, chiefly Central 

 Europe. Thus the meager and not always exact data on the geology of 

 Arctic Eurasia suffered at times from fundamentally incorrect inter- 

 pretations. 



The Role of the Positive and Negative Crustal 

 Elements in the Eurasian Arctic 



The Arctic shore of Eurasia belongs to the Atlantic type, i. e. the 

 structural lines of the earth's crust and the trend of the shore are diver- 

 gent. In general the shore line follows the parallels, and the structural 

 or tectonic lines run with the meridians. In Arctic Europe the struc- 

 tural trend northwest-southeast perhaps is more important than the 

 strictly meridional one. DifTerent geologic formations of Arctic 

 Eurasia, ranging from the Archeozoic and Proterozoic up to Recent, 

 are clearly dependent upon this structure for their geographical dis- 

 tribution. 



Arctic Eurasia is composed of seven positive crustal elements of 

 various sizes separated from each other by negative elements of equal 

 geologic importance which in their distribution follow the trend of the 

 structural lines just mentioned (Fig. i). The positive elements repre- 

 sent what might be called the steadfast regions, those that have 

 persisted throughout the greater part of geological time as more or less 

 firm units. They are in a sense parental elements, composed of 

 Archeozoic and Proterozoic rocks and marine Lower Paleozoic strata 

 not younger than the Upper Silurian. Since that time they have been 

 oldlands; that is, the sea has never again overflowed them though they 

 have been the scene of continental deposition or of basaltic intrusion 

 and overflow. Long periods of still-stand of these oldlands have afford- 

 ed erosional agencies an opportunity to dissect and degrade their sur- 

 faces, giving a certain topographical uniformity to the landscape; and 

 thus its geomorphology is to a high degree dependent upon the work of 

 erosion. All the succeeding stratigraphic history of Arctic Eurasia, 

 that is the history of ancient seas, is recorded in the negative elements 

 of the earth's crust located between the positive elements, or old- 

 lands. Such negative elements are partly geosynclinal in structure 

 and in long succession were overflowed by different ancient seas, 

 beginning -with the Devonian. It might be important also to remember 

 that the disturbances that affected the earth's crust during the greater 

 part of geological time had their most marked structural manifesta- 

 tions on the more or less rigid and unyielding borders of the oldlands. 

 These borders were repeatedly the scene of geological changes of a 

 fairly intense type — changes in which the overlapping sedimentaries, 

 originally deposited within geosynclines, were involved, and which 

 produced some of the marginal relief visible today. Thus, unlike 



