xi The Bed of the Oceans 195 



and close under the edge of the Western World Ridge, off 

 the west coast of South America, hollows more than 4000 

 fathoms below sea -level have recently been discovered. 

 The map shows the nature of the slopes of the Pacific Basin 

 to east and west, and brings out the fact that the Pacific 

 and Indian Oceans are connected by shallow water across 

 the top of a steep ridge pitted with small sea-basins of great 

 depth. The floor of the basin slopes up very gradually in 

 the south to form the gently swelling Antarctic Elevation. 

 Numerous groups of long narrow ridges and isolated peaks, 

 rising close to or above the surface of the water, with 

 depressions of various forms between them, stretch roughly 

 parallel to each other from south-east to north-west across 

 the basin, becoming more numerous toward the west. 



260. The Tuscarora Deep. In the extreme north-west 

 the steepest part of the bounding wall of the Pacific Basin 

 rises abruptly, barring off the seas of Japan and Okhotsk, 

 and bearing the chain of Japanese and Kurile Islands. In 

 front of it lies the deepest abyss in the Earth's crust, the 

 Tuscarora Deep. It extends from 20 N. to 50 N. in a 

 crescent-shaped curve, deepening toward the steep slope of 

 the World Ridge to the north-west, where a mighty gully 

 1000 miles long and 20 wide lies at a depth greater than 

 4000 fathoms (see Fig. 37). Here the United States survey- 

 ing ship Tuscarora, obtained at least one sounding of 

 almost 4700 fathoms below the surface, or 20,000 feet below 



FIG. 37. Steep slopes. The diagram is divided into squares representing 10 miles 

 in the side. The upper black figure shows the true average slope from the 

 summit of Mount Everest to sea-level ; the lower shows the true average 

 slope from sea-level to the bottom of the Tuscarora Deep. 



mean sphere level. H.M.S. Egeria obtained an equally 

 deep sounding in a very small depression south-east of the 

 Friendly Islands ; but there is no satisfactory proof of greater 

 depths existing in any ocean. 



