Th. Thoroddsen— Volcanic History of Iceland. 461 
situated in the centre of this desert of lava. It is a complex of 
mountain-peaks rising up to even 4500 feet high, inclosing the 
circularly formed valley called Askja (=the Basket, measuring one 
square geographical mile in extent, and situate 3900—3500 feet above 
the level of the sea), where a terrific eruption took place in 1875. 
In the 8.E. corner of this valley is found a ‘dip’ in the earth 750 
feet “down,” within which there is a round hot lake, 4000 feet 
in diameter. Around the edge of this dip many large craters are 
situated. The bottom of this valley is covered with lava, which 
represents an eastward incline of 1° 26’ towards the mouth of the 
valley, which opens into the surrounding lava-waste of Oda%ahraun. 
About the lava-plateau, called Myvatns-drefi (Mosquito-water- 
wastes), which stretches northward from the surroundings of Dyngju- 
fjoll, great eruptions occurred during the same year in which that of 
Dyngju-fj6ll was going on (in 1875) ; and in a certain hollow in this 
tract called Sveina-gja (Swains’ rift) many new craters were formed 
rising to the height of T0 to 108 feet. These craters range on a line 
in the direction from §. to N. 
All round Myvatn (Mosquito-water) there is an enormous number 
of craters, lava-formations, sulphur-mines and hot springs. This 
neighbourhood was visited by very severe eruptions during the 
period from 1724 to 1730. The chief volcanos are Kraria and Lutr- 
HNUKR (Clay-peak), which form ridges of palagonite running from 
S. to N. During the period of volcanic disturbance just mentioned 
similar activity was also going on in Hrossa-dalr (Horse-dale), 
Byarnar-flag and about the site of the so-called Reykjahli®ar-sel. 
I have now enumerated all the volcanos which are known to 
have been in a state of volcanic activity in historical times in Iceland. 
But besides these there is to be found in the country an enormous 
number of extinct volcanos; and some tracts of the island, as, for 
instance, the whole neighbourhood of Myvatn, are so thickly studded 
with these reminders of prehistoric convulsions as to give the be- 
holder an impression of having before him a map of the Moon. 
By observing the geological construction of Iceland, it will be 
found, that there are still two volcanic lines in active condition ; 
lines, which manifest themselves not only by the direction which the 
craters generally represent, or by the rifts and chasms~ of the 
volcanos, but stand in close relation to the formation of the country 
generally. The one line goes from §.W. to N.B. represented by the 
Reykjanes peaks, Hekla, and several other volcanos of Southern 
Iceland. The other line runs from §. to N., on which, in straight 
rows, are standing the craters of the voleanos round Vatnajékul and 
Myvatn. These lines, we also observe, are represented by the 
mountain-ranges, valleys, firths, and rivers of the country. Hot 
springs and mines (sulphur), we observe, occupy the same lines, 
which are also followed by the earthquakes. Ranges of peaks, of 
trachyte, which have shot up through older formations, follow this 
same law, and submarine reefs go in the same drift. 
The volcanos which are still active in Iceland seem to be mostly 
associated with palagonite-tuffa. 
