GEOLOGY OF ARCTIC EURASIA 



77 



the oldlands, the intermediate regions exhibit landforms dependent 

 not only upon erosion, but also upon geological structure. The mu- 

 tual relations of the positive and negative elements, the resistance pro- 

 duced by the oldlands, are better expressed where the latter are of large 

 dimensions. Smaller oldlands were overlapped and overthrust by the 

 younger elements originating in the geosynclines, even to the extent of 

 being buried beneath or among the newer folds. Their true geological 



Fig. I — Sketch profile and map showing the relation of the positive and negative crustal elements 

 in Arctic Eurasia. Horizontal scale of profile and map, 1:54,000,000; vertical exaggeration of profile 

 about 1000 times. In order to make graphic the conceptions here presented, the positive elements 

 are emphasized at the expense of the negative. 



nature could be easily overlooked in such a case, especially when 

 the process was repeated. Besides that, owing to their small dimen- 

 sions such oldlands did not offer sufficient rigidity and resistance to 

 maintain their integrity but gave way under lateral pressure. 



The oldlands of continental dimensions cannot be considered ab- 

 solutely immobile — as uplifted in some geological time and remaining 

 in the same position ever since. They were repeatedly uplifted or 

 depressed, but with the uplifts finally exceeding the depressions as 

 compared with the intermediate (i. e. negative) sections of the earth's 

 crust; hence the appellation, "positive" and "negative" elements. 

 But such uplifts are of a broad regional character and of a totally 

 different class from the detailed and intimate plications, crumplings, 

 overthrusts, and the like, traces of which may be found in old strata 

 within the different parts of the positive elements. Only on the bor- 

 ders of the positive elements were the overlapping and overthrusting of 

 younger folds carried so far as to exceed the oldlands in height, and 

 even this was a rare occurrence. 



