194 



The Realm of Nature 



CHAP. 



descend to more than 3000 fathoms below sea-level, occur 

 symmetrically, two in each of the lateral troughs, one north 

 and one south of the equator. One of the north-western 

 groups of hollows known as International Deep, contains 

 in 20 N., just north of the Virgin Islands, the deepest 

 sounding in the Atlantic, 4561 fathoms below sea-level, or 

 nearly 18,000 feet below mean sphere level (see Fig. 36). 

 The lateral troughs unite south of the Dolphin Ridge, and 



FIG. 36. Section across Atlantic Ocean in 20 N. lat. The vertical scale is about 

 300 times greater than the horizontal ; the slopes are thus shown 300 times as 

 steep as they really are. 



appear to form one vast abyss which deepens toward the south 

 and extends far into the Southern Ocean. The deep basins 

 of the Caribbean Sea, Gulf of Mexico, and Mediterranean 

 communicate with the main Atlantic Basin over sills which 

 rise nearly to sea-level. In the north the Wyville-Thomson 

 Ridge, from an extension of which the Faroe Islands and 

 Iceland rise, shuts off the deep basin of the Norwegian and 

 Arctic Seas ( 246). 



259. Pacific Basin. The Pacific Basin is far more vast 

 than that of the Atlantic, and is still to a great extent un- 

 explored ; but the survey for a telegraph cable from Canada 

 to New Zealand is at present (1891) revealing a chain of 

 new and most important facts regarding it. The Pacific 

 Basin appears to form one grand hollow extending from 60 

 N. to 60 S., between the western edge of the Western 

 World Ridge, and the eastern edge of the Eastern. From 

 50 N. to 50 S. and right up to the steep walls to 

 east and west, the depth is .greater than 2000 fathoms, 



