Basin of the Pacific Ocean. 21 



Australia, and enclosed between the parallels of lat 30° N. and 

 lat. 30° S., is composed of a lab)'rinth of seas, separated from 

 each other by chains of islands, the projecting points of numerous 

 submarine ridges. Althoufjh extensive tracts in the Pacific 

 Ocean remain as yet untouched by the sounding-line, the obser- 

 vations made by the " Challenger," the " Gazelle," and the " Tus- 

 carora," along several sections which traverse the length and 

 breadth of this ocean, enable us to form an idea of the general 

 contours of its bottom. From the shores of North and South 

 America, the depths of the eastern half of the Pacific gradually 

 increase until, upon the line between Honolulu and Tahiti, they 

 attain 3000 fathoms. The latter depth forms extensive areas ot 

 depression in the western half of this ocean, and increases to 

 4000 fathoms in the already described hollow extending along 

 the Japanese and Kuril Islands towards the entrance of the 

 Behring Sea. Thus the idea formerly entertained of the inferior 

 depths of the Pacific in comparison with the Atlantic, founded 

 apparently upon the large number of islands scattered over its 

 surface, is proved to be erroneous. Many of these islands, 

 especially in the north-western half, rise immediately from 

 depths of 3000 fathoms and more. 



In the south-eastern portion of the Pacific there are indica- 

 tions of the existence of a submerged plateau connecting the 

 Society Islands, the Low Archipelago, the Marquesas, and the 

 intervening islands of Easter Island and Juan Fernandez with 

 the coast of Chili and Patagonia. H.M.S. " Challenger," after 

 leaving Tahiti, seems to have sounded along the southern edge 

 of this plateau down to the parallel of lat. 30° S., and as far as 

 long. 140° W. Thence, running south towards the fortieth 

 parallel, the ship entered the area of depression discovered by 

 the "Gazelle," but in her eastward course along the latter 

 parallel she once more touched the plateau in about 113° 

 long. W., with a sounding of 1600 fathoms. In long. 94° 



