210 THORODDSEX 



Thorisvatn cover an area of only about 100 square km. each: 

 the lake-surfaces occupy therefore only a very small part of the 

 entire area of the country. The lakes are of very diverse origin, 

 the basins having been formed by tectonic movements, ice-erosion, 

 volcanic action and other natural agents. On the plateau where 

 the outlet is slight, especially in the neighbourhood of the large 

 Jokulls (ice-mountains) many lakes occur, in some places gathered 

 in large groups, as Fiskivotn on Arnarvatnshei5i NW. of Lang- 

 jokull, and VeiSivotn W. of Vatnajokull; the melting snow and ice 

 from the glacier-edges disappear in the nearest lava-streams and 

 sandy tracts and then reappear and gather into basins many kilo- 

 metres away from the glaciers from which they originated. In other 

 places the lakes occur in the immediate neighbourhood of the glacier- 

 edge, as Hvitarvatn and Hagavatn near Langjokull and Langisjor 

 near Vatnajokull; the glaciers project into these lakes and calve 

 their ice-bergs there; the water in these lakes is milky-white as in 

 the glacier rivers. In some places lakes occur in between the glaciers 

 (Graenalon near Skeidararjokull) or are dammed up in valleys by 

 glacier-tongues. The best-known lake in Iceland is Thingvallavatn 

 (105 square km.); it is situated in a new volcanic district bounded 

 on the S. and W. by steep tuff-mountains and on the N. and E. 

 by lava -streams which originate from the volcano of Skjaldbrei5; 

 these streams have afterwards flowed down between the two well- 

 known fissures Almannagja and Hrafnagja. It was here that the 

 Icelandic Althing met in the time of the Republic. It appears as if 

 the basin of the lake of Thingvalla was originally formed by sub- 

 sidence along lines of fracture from SW. to NE.; this lake has a 

 depth of 110 metres. In North Iceland Myvatn is the best-known 

 lake; it is formed in a depression in the lava-stream and has a 

 depth of only 2 7 metres; its bottom is lava and several craters 

 project above its surface like islands, while the surroundings are 

 very volcanic. Myvatn has received its name from the mosquitoes 

 (my) which are often quite a plague there. As in Thingvallavatn, 

 trout are plentiful in this lake, but it is especially known as the 

 abode of numerous birds, especially many different species of ducks. 

 The group of lakes called Vei5ivotn consists for the most part of 

 crater-lakes, of which the largest is called Storisjor. In other places 

 valley-lakes occur deeply hollowed basins in the basalt as 

 Skorradalsvatn in Borgarfjorflur and Lagarfljot in East Iceland, the 

 surface of which latter lies 2(> metres above sea-level while its bottom 



