CAUSES OF THE COLD OF THE ICE PERIOD. 285 



north were then high, hut this cannot he said to he proved. That 

 the arctic lands have been at some time raised higher than now, is 

 shown by the fiords of the northern coasts, which, as first pointed out 

 by Dana, must have been excavated by subaerial erosion ; but a large 

 part of that erosion may have been effected in the Tertiary age, and 

 perhaps it was chiefly accomplished then. 



When a dense forest clothed the arctic lands, and spread over 

 continuous land-surfaces to Europe and Asia, these now half-sub- 

 merged fiords were valleys traversed by flowing streams; for the 

 abundant Tertiary vegetation of the far north proves the country to 

 have been well watered. That these fiords were filled with glaciers 

 during the Ice period is certain, as the bottoms and sides of many 

 of them are glaciated, but this would happen again with a depression 

 of temperature, and without a depression of sea-level. The fact that 

 the glaciated surface of the bottoms of fiords in Sweden and America 

 passes under the sea, and reaches as far as observation can be carried, 

 is not the proof of elevation it has been claimed to be, for the glaciers 

 that now reach the sea must score their beds to the depth of several 

 hundred feet, before their extremities are lifted up by the one-tenth 

 greater gravity of water, and are floated off as icebergs. 1 



Prof. J. W. Dawson holds the view that the Glacial period was 

 one of depression at the north, as he finds marine shells in the boiclder 

 clay of the St. Lawrence Valley ; and he attributes much of the gla- 

 ciation of Eastern North America to icebergs dragged over the sub- 

 merged land. 



Croll says (" Climate and Time," p. 391) : 



"The greater elevation of the land (in the Ice period) is simply assumed 33 

 an hypothesis to account for the cold. The facts of geology, however, are fast 

 establishing the opposite conclusion, viz., that when the country was covered 

 with ice, the land stood in relation to the sea at a lower level than at present, 

 and that the continental periods or times, when the land stood in relation to the 

 sea at a higher level than now, were the warm inter-glacial periods, when the 

 country was free of snow and ice, and a mild and equable condition of climate 

 prevailed. This is the conclusion toward which we are being led by the more 

 recent revelations of surface-geology, and also by certain facts connected with 

 the geographical distribution of plants and animals during the Glacial epoch." 



According to the investigations of Bohtlingk and Kjerulf, Scan- 

 dinavia was 600 feet lower during the Glacial period than now. 

 Erdmann, on the contrary, supposes that Sweden was higher during 

 the Glacial epoch than at the present day, from the fact that polished 



1 Some of the huge tabular icebergs, which have been observed off the Antarctic 

 Continent, projected more than 500 feet above the surface of the ocean ; and as for 

 every foot above water there must have been 8.T feet submerged, the whole thickness 

 of the ice-sheet, from which these bergs were detached, must have been over 5,000 feet, 

 and such a glacier must grind the sea-bottom to a depth of over 4,000 feet. (See Croll, 

 " Climate and Time," p. 385.) 



