400 



IIEEZEN AND EWING 



[CHAP. 16 



ill great miin1)ors in tlio contra! grabeii, each aligned parallel to the main faults 

 of the graben. From a stutly of the gja he estimates the post-glacial extension 

 in Icelandic graben at 3.50 m/km/1000 years. This geology and structure have 

 striking similarities with the East African rift valleys. 



Dietrich (1959) and Ulrich (1960) report that in their survey of the Rekyjanes 



Boyd (1948) 



Scole In noutlcal miles 

 Vtrtlcol exoggvrotion 4011 



Fig. 1(>. Profiles across the Arctic Ocean and the Norwegian Sea. The two Arctic Ocean 

 profiles are speculative interpretations of scattered soundings. The individual sound- 

 ings are indicated as short vertical lines along the upper margin of eacli profile. 

 Profiles IV and V an^ ])l()tted from the early (1937-38) continuous echo-soundings 

 published by lioyd (1948). The eastern half of profile IT! is based on continuous 

 echo-soundings while tlie western half is plotted from discrete soundings (after Boyd, 

 1948). Note the strong similarity Ijetween profiles of this figure and profiles (»f 

 Fig. 6. 



Ridge south of Iceland tlie rift valley was typically absent north of 57 3()'N 

 but was present on 5 crossings between G2"N and 62° 30'N. 



In the Norwegian Sea the epicenter belt is continuous and is a reliable guide 

 for following the structure in this complicated, narrow, and ])oorly-sounded 

 region. The Mid-Atlantic Ridge, which in the south hugs the coast of Greenland, 

 is found again in the north close to the continental margin off Spitsbergen. 

 It is possible that this offset is due to a right-slip fault near Jan Mayen, 



