E. B. Bailey — Iceland, a Stepping -Stone. 469 



The differentiation of the New Iceland from the Old seems to 

 have been effected at the close of the Miocene Period, when the 

 basaltic plateau developed fractures and began to sink. In Pliocene 

 times numberless outbursts gave rise to a great bow of palagonite 

 tuff and breccia, which, with its later associated lavas, is the 

 country rock of New Iceland from coast to coast. Since then 

 volcanic activity has been more or less continuous, always within 

 the same restricted area: in late Pliocene times and probably also 

 during the Glacial Period, extensive lava fields of dolerite were 

 produced, followed throughout post-Glacial time, by widespread 

 outpourings*, of basalt with very subordinate liparite ; the post- 

 Glacial basalts, considered by themselves, cover an area of little less 

 than 11,200 sq. km. 



Erosion has stripped Old Iceland of much of the spectacular 

 accoutrements of vulcanieity. What meets the eye for the most 

 part, is an immense pile of basalt flows dipping very gently inwards 

 from either side towards the arcuate belt of tuff, breccia, and later 

 lavas. Often, indeed, the early lavas are practically horizontal, 

 more especially in the much-faulted coastal region lying between 

 the Bardardal and Hruta Fiord Faults. 



In some ways the most interesting feature of Old Iceland is the 

 ring-fracture system (Kreishuche) of the north-west peninsula. 

 There, lignites, clays, and leaf-beds, interbedded with the lavas, 

 serve as valuable indices to the displacements the country has 

 undergone. The lines of ring-fracture are sometimes marked 

 by warm springs and parallel open cracks. And according to Suess, 

 who evidently relies on the paper in which Thoroddsen elaborates 

 his discovery, each ring-fault steps both the geology and the 

 topography down towards the centre, while the intervening annular 

 strips slope gently outwards towards the periphery. 



In harmony with the ring-faults of the north-west peninsula are 

 the cauldron -subsidences of Breidi Fiord and Faxa Flow. 



The Snaefellsness Peninsula, separating these two great bays, is 

 a horst, and consists mostly of. old basalt, in part covered by the 

 Breccia Formation and later basaltic lavas. It is cut by cross- 

 faults locally depressing the old basalt platform below sea-level. 



The sunken area of Breidi Fiord on the north, includes on its 

 bottom a grabe called Kollual, 75km. long and 9 km. broad. That 

 of Faxa Flow, on the south, is bounded by faults, with a downthrow 

 of 200-300 m., lined with hot springs and crater-rows. Faxa Flow 

 is very liable to earthquakes, and altogether, both in its rocks and in 

 its behaviour is perhaps in as close alliance with the New Iceland as 

 it is with the Old. In Old Iceland, close fractures, faults, and lines 

 of hot alkali springs occur, but not solfataras; while, except about 

 Faxa Flow, earthquakes and glacial and recent volcanoes, including 

 crater-rows, are rare. In New Iceland, gaping fissures, graben, and 

 solfataras (with subordinate alkali springs) are all common ; so too 

 are earthquakes, crater-rows, and big volcanoes. 



There are five earthquake districts in Iceland. All border the 

 coast, and all, save Faxa Flow, belong to New Iceland. 



About as extensive as the Faxa Flow district, but reaching in the 



