470 E. B. Bailey — Iceland, a Stepping -Stone. 



other direction, east from the base of the Reykjanes Peninsula, is 

 a particularly complex field of subsidence and unrest. The district 

 is broken into segments which behave independently during earth- 

 quakes, the while the great neighbouring volcanoes stand passively 

 indifferent. Far away on the northern coast are three more earth- 

 quake districts. In the interior highlands earthquakes are rare 

 unless in obvious connexion with volcanic activity. 



The boundaries of New Iceland now deserve attention. The , 

 western margin, where not concealed by superficial accumulations, 

 is seen to be largely determined by two arcuate faults, each with 

 a downthrow towards the convex eastern side. The opposite margin 

 is less definite, for here the early Tertiary lavas dip gently beneath 

 the Breccia Formation. Of the two border-faults on the west of 

 New Iceland the outer one is the older. It runs from the 

 Reykjanes Peninsula northwards to the Hruta Fiord. Its course is 

 marked by the ruins of great extinct volcanoes. The inner fault, 

 known as the Bardardal Fault, first originated after great areas had 

 been covered beneath post- Breccia dolerite lavas. The boundary of 

 New Iceland where it runs east and west between the Hruta and 

 Bardardal Faults is very obscure owing to its being hidden beneath 

 glacial and similar surface deposits. 



The topographical character of New Iceland is distinctive in the 

 extreme. Every feature in the north runs from north to south, and 

 in the south from north-east to south-west. This is all due to the 

 course taken by volcanic fissures, too numerous for individual 

 representation on a map. Many parts of the district, lowland and 

 highland, are literally striped by them. 



Often lava-flows cut \>y the fissures have undergone considerable 

 subsidence. Near the head of the northern branch of the long 

 inlet east of the Reykjanes Peninsula, an old subsidence 60-70 sq. km. 

 in extent, and 30-50 m. in depth between two fissures known as 

 Almannagja and Hrafnagja, sunk two or three additional metres 

 during a violent earthquake in 1789. Of more recent date and more 

 considerable magnitude are certain graben of the Odadahraun — the 

 district neighbouring Askja — where, in one instance a fault-scarp 

 30-40 m. high continues for a distance of several kilometres. 



In two instances fissures which have yielded lava, remain open 

 and craterless ; Eldgja, one of the two, in a single outburst yielded 



9 c.km. of lava. But almost always a crater-row has been erected 

 along the course of an active fissure. Such rows extend sometimes 

 from 10 to 35 km. The craters vary greatly in form : they may be 

 elongated, or they may have one ring within another, or one wall 

 collapsed, the other standing. Their height is commonly from 



10 to 200 m. 



A fissure sometimes continues open for as much as 15 km. at 

 a stretch. Looking down into it one generally notices water or 

 snow. It is difficult to separate the non-volcanic from the volcanic, 

 for many a fissure of non-volcanic aspect where first encountered is 

 found to have poured out lava at some other part of its course. 

 Small parallel fissures without volcanic activity often accompany the 

 more important volcanic fissures. 



