386 T. C. CHAMBERLIN 



and the deeps, shallows, and islands connected with them, though 

 the region to the east as far as the New Siberian Islands and beyond 

 is involved. It is not necessary, however, to dwell on the intricate 

 details of circulation in this connecting tract, except so far as it 

 affected the interchange between the generating basins on either 

 end, for the gist of our present problem centers in the Polar Basin, 

 where cold waters are generated, and in the Atlantic Basin, where 

 warm waters are generated. Let us, therefore, look upon the con- 

 necting tract merely as an oceanic thoroughfare with ridge-dams 

 and weirs at either end. There is so Uttle exchange through the 

 channels of the American Archipelago and through Behring Strait 

 that these may be neglected here. 



THE INTERCONTINENTAL RIDGES 



The Southern Intercontinental Ridge. — ^The more southerly of 

 the partially submerged ridges that connect Eurasia and North 

 America has for its best-known section the Wyville-Thompson 

 Ridge, but this is merely the most exploited sag in a much greater 

 feature. The ridge is continuous from the Wyville-Thompson sag 

 southeastward through the British Isles to the European continent, 

 and northwestward through the Faroes, Iceland, Greenland, Davis 

 Strait, and Baffin Land to the American continent. This Southern 

 Intercontinental Ridge has, at present, more critical climatic bear- 

 ings on the Atlantic-Polar exchange than the Northern Ridge, 

 because its lowest notches have less depth and give a shallower weir 

 or a higher dam as one chooses to look at it. It is, of course, to be 

 kept in mind that the exchanging waters pour over this weir in both 

 directions as they do at the Straits of Gibraltar, the Dardanelles, 

 and many other such weirs. The greatest depth of water over this 

 Southern Ridge thus far disclosed by soundings is 314 fathoms, or 

 about 600 meters, but the exploration is as yet incomplete. 



The Northern Intercontinental Ridge. — Separated from the South- 

 ern Intercontinental Ridge by about 20° latitude is the Northern 

 Intercontinental Ridge, connecting the northerly border of the Eura- 

 sian continent, by way of Franz Joseph Land, Spitzbergen, North 

 Greenland, and Grinnell Land, with the northern islands of the 

 American Arcliipelago and the northern border of the American 



