220 J. W. SPEXCER — SUBMARINE A'ALLEYS 



incision in the so named Lightning channel with a breadth of 30 miles, 

 where the col is submerged to a depth of 3,180 feet. From this trough 

 a valley descends northward to the Arctic basin, and one with more 

 rapid gradient to the deep Atlantic arm between the Rockall banks and 

 Scotland, which has been mentioned b}" Professor Hull and others, as 

 has also the Sognefjord (over 4,000 feet deep), a tributary of the Arctic 

 basin.^ 



The troughs of the Arctic basin expand and deepen west of Spitz- 

 bergen, where a depth of 15,900 feet Is reached (latitude. 78 degrees 30 

 minutes), and bej^ond this Nansen did the greatest Arctic w^ork in finding 

 the continental slope bordering the Eurasian continent, and thereby 

 establishing almost with certainty the absence of polar lands. Even the 

 occasional soundings show finely the occurrence of a great cove south- 

 west of Spitzbergen, which obtains a depth of 8,100 feet, where the plateau 

 beside it is only 2,418 feet below sealevel, and at the head of it, 10 miles 

 landward, the depth is reduced to 800 feet. An amphitheater in the 

 continental shelf off Tromsoe, Norway, attains a depth of 5,100 feet 

 where the adjacent sounding is only 1,494 feet. This northern basin is 

 most interesting and suggestive. It is modified by islands and sunken 

 plateaus, like the Caribbean and gulf of Mexico basins, and its features 

 as far as known are in harmon}^ with the tropical ones between the two 

 Americas. 



VALLEYS BETWEEN AMERICA AND BRITISH ISLES 



Between America and the British isles the North Atlantic plateau rises 

 to the summit described. There are a few troughs which show arms of 

 the Atlantic basin deepl}^ indenting it, enough to suggest that when 

 fuller soundings are made south of the Icelandic ridge valleys trending 

 from that ridge may be traceable to the indentations of valley form at 

 depths of 12,000 feet in about latitude 52 degrees, made known by cable 

 soundings. Similar suggestions of deep valleys or embayments appear 

 northwestward of the ridge of the Azores. 



On the Origin of the Submarine Valleys 



The origin of submarine valleys attaining a depth of even 1,000 or 

 2,000 feet in the continental shelf, and whose outer edge is submerged 

 300 or 400 feet, although implying a recent elevation of 2.000 or 3,000 

 feet, need scarcel}^ be called into question. While these channels pass 

 through canyons and descend abruj^tly into the deeper valleys which 

 open out into emba3anents in the great continental slope to depths of 



*See Professor Hull's papers cited before. 



