GEOLOGY OF ARCTIC AMERICA 7 1 



many other geologists, notably Daly, support his theory with some 

 modifications. 



In a few years a redetermination of the Greenland longitudes by 

 accurate radio methods will probably settle whether that greatest 

 of islands is now moving or not. 



There are a number of facts in the distribution of polar plants and 

 animals that strongly suggest former connections between the Arctic 

 lands. The floras of Arctic America and of Arctic Europe include some 

 common species and also many species which are only slightly different 

 from one another on the two sides of the North Atlantic. The plants 

 of Spitsbergen are very like those of Arctic America and Arctic 

 Europe, and all three lands have animals which are closely related. 

 For example the American caribou differs so little from the Spits- 

 bergen and European reindeer that they must have originated in the 

 same area and from the same ancestors. 



But the separation of the Arctic lands can be accounted for in 

 other ways than by the drift of continents. De Geer has demonstrated 

 that a great block of the earth's crust has dropped between Scandi- 

 navia and Greenland, the sinking mass forcing up basaltic lavas in 

 various places ;^^ and Lauge Koch has shown that a continuation of 

 this depression, also accompanied by basic lavas, crosses south-central 

 Greenland. ^^ 



It may be, therefore, that the northern islands have been sep- 

 arated from one another and from North America by the settling down 

 of slices of the earth's crust, like rift valleys, the sinking going so 

 far as to allow the sea to enter. 



It seems improbable, however, that all of the numerous narrow 

 channels between the islands and all of the innumerable fiords have 

 been formed by the dropping of blocks, though De Geer seems to sup- 

 port this view. It is more natural to suppose that the smaller ones 

 were river valleys deeply cut at a time when the land stood higher, 

 scoured out into U shapes by glaciers, and then invaded by the rising 

 sea. 



The fact must not be overlooked that in many places the sea once 

 stood 500 or 600 feet higher than now, as shown by marine beaches 

 up to that level. Similar beaches of about the same height along the 

 St. Lawrence are generally accounted for by the rebound of the land 

 after the removal of ice during an interglacial period or at the close of 

 the Ice Age.2o 



It may prove difficult to decide in a given case whether changes 

 of level were due to epeirogenic readjustments of slices of the earth's 



18 Gerard De Geer: Kontinentale Niveauanderungen im Norden Europas, Comple Rendu Xle 

 Session Congr. Geol. Internatl. {Stockholm iqio). Vol. 2, Stockholm, 1912, pp. 849-860, with map, 

 1:8,000,000. 



^^ op. cit., pp. 59-60. 



2D A. P. Coleman: The Pleistocene of Newfoundland, Journ. of Geol., Vol. 34, 1926, pp. 193-223; 

 reference on p. 208. 



