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THORODDSEN 



jokull, and extends down to the south coast near Eyrarbakki, covers 

 an area of 1550 square km. In the low land this lava-field is 

 covered by a thick layer of soil upon which dense settlements have 

 arisen. In addition, extensive lava-fields (1530 square km.), which 

 originated from 28 volcanoes, occur on Reykjanes; and upon the 

 plateau on either side of Langjokull, there are also other large lava- 

 fields (1030 square km.) of which Hallmundarhraun is the best 

 known; in it is the lava-cavern, Surtshellir, which is P/z km. in 



Fig. 7. Lava-stream (apalhraun) ; upon the outer south-west slope of Dyngjufjoll. 



(Phot. Heinrich Erkes.) 



length. Large tracts of lava occur also around Hekla, near Myvatn, 

 Kelduhverfi and in several other places. 



The surface of the lava-streams varies greatly ; often it is very 

 rugged and jagged and is then, in Iceland, called apalhraun, and 

 in the Sandwich Islands, aa. Such streams consist exclusively of 

 porous and brittle lava and slaggy fragments heaped together pell- 

 mell. Such lava-streams are comparatively narrow, with high edges 

 which, seen from a distance, look like fences or ridges upon the 

 level land. A lava-stream of this description is very difficult to cross, 

 owing to the fragments being put together so loosely that they are 

 disturbed by the slightest touch. Other lava-fields, especially the 



