98 W. H. Rudledon — E. Margin of N. Atlantic Basin. 



West of the meridiaa of Greenwich, with a divergence of about 12° 

 of longitude on either side. This direction it maintains for 51° of 

 latitude, or about 3,500 statute miles. From off the north-west 

 corner of Spitzbergen the suboceanic Continental slope trends 

 easterly, passing north of Franz Josef Land and the New Siberian 

 Islands. 



The persistent physical feature which I have called the suboceanic 

 Continental slope has been variously described as a ' submerged bank,' 

 and even as an 'escarpment,' though it is certainly not likely to be 

 an ' escarpment ' in the geological sense of the term. Before pro- 

 ceeding to trace this particular margin of the north-eastern Atlantic 

 basin, it may be of service to consider some of the remarks of 

 Professor Milne with reference to suboceanic continental slopes 

 generally. These are to be found in his very suggestive paper on 

 " Suboceanic Changes." ^ 



Just as we owe the beginning of oceanography to the surveys 

 which preceded the laying down of telegraph cables, so we are 

 likely to learn something about suboceanic movements owing to the 

 repairs which these cables require. Professor Milne brought this 

 subject before the Eoyal Geographical Society in 1897, and his 

 remarks regarding suboceanic continental slopes are exceedingly 

 important. After referring to submarine banks and ridges generally, 

 he points out that we have evidence of sudden changes in the details 

 of suboceanic contours in the steep slopes flanking the submarine 

 platforms which fringe continents and islands. The causes of 

 suboceanic yielding in rocks and sediments are twofold. The most 

 important is what he calls ' bradyseismical ' action, represented by 

 secular folding, thrust, or crush ; sudden acceleration in these move- 

 ments constitute earthquakes, which may be accompanied by a line 

 of fault and landslips. A second group of causes is referred to 

 sedimentation and erosion : these create unstable contours, which 

 may be destroyed by seismic action or in other ways. He calculates 

 that one-half of the earthquake shocks occurring throughout the 

 world have their origin in the suboceanic continental slopes. He 

 divides these into seismic and non-seismic districts. Slopes of con- 

 siderable horizontal extension — say 120 geographical miles — which 

 are steeper than 1 in 35 (If °), are likely to be the seat of submarine 

 earthquakes accompanied by landslips. As examples of seismic 

 districts he instances the west coast of South America, the Kurile 

 Islands, and parts of Japan ; whilst of non-seismic districts he 

 instances the coasts of Australia, Scotland, and South Norway. 



Seismic strain, due to a tendency in the earth's crust to further 

 adjustment, is greatest where earthquakes most frequently originate ; 

 and the special home of the earthquake is at the base of the steep 

 oceanic slopes, where most deformation is in progress. He further 

 observes that the results of vertical movements are those which are 

 now most apparent, but that the geotectonic structure of many 

 countries shows great horizontal displacement likewise. 



1 Geographical Journal, August and September, 1897. 



