VULCANISM, Lyre, IN ICELAND. 497 



LOCATION OF THE ACTIVE VOLCANOES. 



The interior of Icelaud forms a plateau of about (330 meters in height,, 

 "which, towards the north, northwest, and east, is cut up into a hirge 

 number of fjords and valleys; it slopes gently towards the north-, 

 northeast (with a mean inclination of 0° 23' 52" between Vatnajokull 

 and the promontory of Tjornes) ; and toward the southwest (with an 

 inclination of 0° 13' 1" between the plateau of Sprengisandr and the 

 mouth of the Thjorsd) ; while the steepest slopes are on the east and 

 northwest sides, where they form abrupt cliffs facing the sea. The 

 most elevated portions are covered with glaciers, which occupy a 

 .superficial surface of 14,000 square kilometers ; the currents of lava 

 covering 7,400, of which 3,400 result from the Odddahraun. Two 

 ■chains of volcanic mountains, the Reykjanes and the Snaefellsues, ex- 

 tend on both sides of the Gulf of Faxe easterly across the plateau. 

 The formation of the east and northwest portions of the island is 

 mostly trap, while that of the central portion is soft gravel, with banks 

 of palagonite, a formation in which the volcanic phenomena seem to 

 be prevalent. Volcanic eruptions appear to be confined to two locali- 

 ties, one in the south of the island, running southwest to northeast, 

 and the other in the north, running from south to north. Eruptions 

 of trachyte have occurred in the eastern portion of the island. Ghicial 

 and alluvial deposits cover large spaces. There are a large number 

 of extinct volcanoes; but we shall confine ourselves to those which 

 have been active within historic times. 



We may distinguish eight groups of active volcanoes in Iceland : 



(1) Group of Snaefellsnes (Eldborg). 



(2) Group of the Recla (Hecla, Randhnkambar). 



(3) Group of BeyJcjanes (Thurrarhraun, Trolladyngja, Eldeyjar). 



(4) Group of Katla (Katla, Eyjafjallajokull*). 



(5) Group of Varmdrdalr. 



(0) Group of the volcanoes south of the Vatnajokull (Oraefajokull, 

 Skeidhardijokull, Grimsvatn, Sidhujokull). 



(7) Group of the volcanoes of Odddahraim (Kverkfjall, D^-ngjufjall, 

 yveinagj4). 



(8) Group of the volcanoes of Myvatn (Krafla, Leirlmukr, Hrossar 

 dalr, Bjarnarflag, Daltjall). 



(1) Group of Snaefellsnes. — The only active volcano in this group is 

 the Eldborg (64° 47' Lat. N., 34° 54' Long. W. of Copenhagen), which 

 at about the year 950 threw out from a crater of 200 meters in diameter 

 and 53 meters depth a. current of lava 1] ,300 meters long by 3,770 meters 

 wide. 



(2) Group of tJie Hecla.— The Hecla (63° 59' N. Lat. and 32° 19' Long. 



* .Jokull is the Icelandic word for glacier. Eyjafjallajoknll, for iuttance, signifies 

 the glacier of Eyjafjall, but at the same time serves to designate the volcano or 

 mountain of that name. 



H. Mis. 15 32 



