128 SEA AKD LAND 



in a recent g-eological age covered the eastern part of North 

 America as well as much of the Old World. But for our 

 immediate purpose we need onh' to note the immense extent 

 of this ice-field, its great dej)th, and the speed with which it 

 moves from the interior toward the sea. So far we have but 

 imperfect data concerning the rate at which the high northern 

 glacier passes from the land into the sea ; but it is clear that 

 the movement is much more rapid than in the case of the 

 relatively small ice-streams of the Alps. In the valley glaciers 

 of Switzerland, Norway, or the Himalayas, the speed of the 

 flow does not exceed on the average more than three feet per 

 diem. At the berg-making fronts of Greenland it probably 

 amounts on the average to more than tiiirty feet per day; 

 that is, a strip about half a mile wide would be fed into the sea 

 in tlie short summer season, and if the flow was maintained 

 during the whole year, there would be a field nearly two miles 

 wide discharged as floating ice along the whole front of the 

 streams which attain the sea. There is no satisfactory basis 

 on which to estimate the linear extent of the glacial front on 

 the Greenland sliore, but it is probably not less than two 

 hundred and fifty miles. If this be the size, we may reckon 

 that somewhere near five hundred square miles of icebergs is 

 each year set afloat along the shores of the island. Suppos- 

 ing that the original area of these masses was one-fourth of a 

 square mile, this supply would provide for a yearly fleet of two 

 thousand bergs, from which throng the ice which our Atlantic 

 ships encounter is derived. 



The history of these bergs, after they have become sepa- 

 rated froni their parent glaciers, lias not yet been carefully 

 traced. It is evident that a large part of them never attain to 

 any considerable distance from the coasts where they were 



