206 THORODDSEN 



melting of the snow their size varies from day to day and from 

 year to year; many glacier-streams which disappear entirely during 

 winter, carry in warm summers an immense volume of water. Al- 

 most all Icelandic glaciers rest on soft rocks (tulT and breccia) upon 

 which erosive action is very active; therefore, the Icelandic glacier- 

 rivers carry dow r n an immense amount of rock in the form of mud, 

 sand, gravel and blocks of stone; for this reason they are hardly 

 ever found entering fjords or deep bays, these having quickly be- 

 come filled up in cases where they formerly so entered, while the 

 Jokulls (glacier-bearing mountains) are surrounded by large sandy 

 and gravelly tracts which for the most part owe their origin to 

 the rivers. 



Taking the whole of the island into account, rivers containing 

 glacier-water are decidedly in the majority. South of Vatnajokull 

 clear water is almost unknown, as all rivers and brooks originate 

 in the glaciers. There all the rivers flow down to the coast by 

 short courses in torrential current, and during summer some of 

 them are so broad that it lakes hours to cross them but then 

 it must be remembered that it is necessary, in the middle of the 

 river, to go a long w^ay round, on account of the current and depth. 

 On the flat, sandy tracts the rivers are constantly changing their 

 course, and greater and smaller changes take place daily. All glacier- 

 rivers branch abundantly. 



In accordance with the slope of the land, the longest and 

 largest rivers flow in South Iceland towards the south-west and 

 south, and in North Iceland towards the north; the majority of 

 them rise on the plateau at a height of 600 900 metres above 

 sea-level, a fact w 7 hich should be correlated with the limits of the 

 glaciers in the interior. Although the Icelandic rivers carry a com- 

 paratively great volume of \vater yet they are not navigable, because 

 of their usually steep fall, their torrential current, and their tendency 

 to spread out and subdivide into numerous branches in the low 

 land. The largest rivers of Iceland are as follows: From the 

 south edge of Vatnajokull rise Jokulsa f Loni, Hornafjar5arfljot, 

 Jokulsa a Brei5amerkursandi, SkeiOara and Niipsvotn; the last three 

 are considered to be the most dangerous glacier-rivers of Iceland. 

 From the west edge of Vatnajokull rise Hverfisfljot, Skafta and the 

 well-supplied Ku5aflj6t; this last also receives a large supply of 

 water from M\rdalsjokull. From the latter another river flow r s down 

 the short, but torrential Jokulsa a Solheimasandi, also called 



