TRANSACTIONS OF SECTION C. 881 



4. The Eastern Margin of the North Atlantic Basin. 

 By W. H. HuDLESTON, F.B.S. 



Definition of the Subject. — Importance of oceanography in a geological 

 sense. The submerged continental shelf, the ' edge,' the suboceanic continental 

 slope, and the abyssal flat. The suboceanic conthiental slopes are the true 

 margins of the several oceans. Limit of region dealt with in the paper from 

 the Polar Ocean to about the 30th parallel of N. latitude. The suboceanic slope 

 has sometimes been described as a ' submerged bank,' a ' terrace,' or an ' escarp- 

 ment ; ' these terms, it is believed, are in many cases misleading. Remarks of 

 Professor Milne on the tectonic importance of the suboceanic continental slope ; 

 he calculates that one-half of the earthquake shocks occurring throughout the 

 world have their origin in these slopes, especially towards the base ; his division 

 into seismic and non-seismic districts. 



Authorities for the Line Selected. — Allowing for sinuosities and for the 

 easterly extension beyond Spitzbergen, this marginal line is not less than 5,000 

 miles. The principal authorities are Nansen's paper ' On Some Results of the 

 Norwegian Arctic Expedition,' Mohn's work ' On the Norwegian North Atlantic 

 Expedition,' Bartholomew's ' Physical Chart of the North Polar Regions,' and, 

 lastly, several of the British Admiralty charts from Shetland to Gibraltar. 



Descriptive and Hypothetical. — Section 1. Antic and Sub-Arctic. Hydro- 

 graphical details of the marginal line of the North Polar Ocean (outside Franz 

 Josef Land and Spitzbergen) and of the Norwegian Atlantic are given. As a 

 whole, so far as is known, the marginal slopes appear to be less steep than in the 

 British-Biscayan region. 



Discussion on the geological bearing of these details. It is contended that 

 the North Atlantic, the Norwegian Atlantic, and such portions of the North 

 Polar Ocean as have yet been sounded belong to one and the same great geo- 

 synchnal depression, which has locally been interrupted by volcanic extravasation. 

 These facts serve to remind us of the two principal schools of geographical evolu- 

 tion, and of the theories relating to the permanence or non-permanence of the 

 major features of the earth's crust. The arguments for and against permanence, 

 both generally, and in reference to this particular region. It is suggested that a 

 considerable amount of change throughout geological time may have taken place 

 on the margins, of the great oceans without materially affecting the great ocean 

 basins themselves. In this way the crust of the earth still retains traces of its 

 congenital features in the great ocean depths, and also in the position of the chief 

 continental areas. Lord Kelvin's view that continents and ocean depths were 

 due to heterogeneousness of composition in different parts of the liquid which con- 

 stituted the earth's surface before solidification ; from thLs heterogeneousness, he 

 considers that the irregularities of the present surface followed as a dynamical 

 necessity. 



Section 2. The Icelandic Shallows. — Here the volcanic masses of Iceland and 

 Faeroe with their submarine attachments have produced a marked eifect on the 

 depths of the ocean. The Norwegian Atlantic connects with the main Atlantic by 

 three channels ; minimum depth in the Faeroe-Shetland or Lightning Channel 319 

 fathoms ; so that a little over 1,900 feet uprise is required to effect a land con- 

 nection with Iceland and South-east Greenland. (N.B. — There is some difference in 

 the maps on this point.) The suboceanic continental slope may be traced along 

 the south-east side of this channel, though the steepest declivity is only 2^° ; 

 thence along the Vidal Bank to the Porcupine Ridge, oif the coast of Counaught. 



Former land connection with Iceland and Greenland required by the 

 biologists. The views of Professor Spencer as to epeirogenic uplift on this side of 

 the Atlantic. 



Section 3. The British-Biscayan Begion. — Hydrographical details between 

 the South of Ireland and Ushant. Great width of the submerged continental 



k shelf or 100-fathom platform in this quarter. Increased steepness of the sub- 

 oceanic continental slope as the depths of the Bay of Biscay are approached. 

 Irregularity of the contours in places ; an incline of 6° to be taken as representing 

 1898. 3 L 



