2 TRAUSTI EINARSSON 



with Europe or America in the Lower Tertiary. On the contrary, the flora 

 suggests lack of such a land connection. 



There is, in my opinion, one main evidence which suggests rather great 

 Tertiary changes in the North Atlantic area. I am referring to the sea-bottom 

 topography. This looks relatively fresh and is suggestive of considerable 

 tectonic changes which might have taken place in the Upper Tertiary. There 

 is one important tectonic event of which we know: the uphft of Iceland, 

 Greenland, Scandinavia, and Britain from low lands to the present moun- 

 tainous countries took place in the Upper Tertiary. At the same time it is 

 possible that the ocean floor changed considerably. 



The geophysicists are today inquiring into the origin and history of 

 ocean basins by way of seismic studies and through the examination of 

 bottom sediments. It is advisable to await more such investigations in the 

 North Atlantic and Arctic area before drawing further conclusions regarding 

 the geographic development in this area in the Tertiary. But palynological 

 studies also seem quite promising. 



As matters stand today, we must face the possibility that the North 

 Atlantic Ocean existed in the Lowest Tertiary and that the various remnants 

 of plateau basalts indicate as many separate and distinct volcanic regions. To 

 see, for instance, how Iceland might have originated in a deep ocean, the 

 following hypothesis may be considered (cf. Einarsson, 1960): 



Submarine volcanism produced a pile of relatively light pyroclastic material, 

 and in spite of corresponding isostatic sinking of the base of the pile, a large 

 island would eventually be formed. Assuming at the beginning a 3 km deep 

 ocean, then a 6.2 km thick pile of density 2.2 would reach the surface of the 

 sea. Adding a 6 km thick pile or plateau of subaerial basalts of mean density 

 of 2.7 would, in equilibrium, give a land surface at 1100 m above sea level, if 

 there was no compaction of the underlying pile. 



I shall now consider the Icelandic rocks more specifically. Intercalated 

 between the lava banks are very often thin seams of terrestrial sediments. 

 They consist mostly of windblown sand or dust, whereas conglomerates are 

 very rare, except in the higher parts. The sediments of the lower parts hence 

 suggest in the first place a dry lava desert, but in a few cases one also finds 

 indications of the existence of rivers. The clearest case, I think, is the well- 

 known locality Brjanslaekur. As shown in Fig. 1 we find evidence that three 

 times a lava filled up the river bed until at last more intense volcanic produc- 

 tion so completely altered the drainage that sedimentation at this place came 

 to an end. 



In the Skardsstrond area we have sediments with a total thickness of about 

 50 m. A few lavas flowed during the period of sedimentation and one of 

 these is seen to have flowed over soft mud. The lignite seams found in this 

 area are very variable from place to place. There is a seam of 80-90 cm 

 thickness at one place (Tindar), whereas at another place (Nipur) there is a 



