. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] TOPOGRAPHY OF THE DEEP-SEA FLOOR 275 tica; but at about 55° south latitude, the crest bends sharply to the east. Apparent fault scarps suggest that the bend is an offset caused by faulting or else a discontinuity along the margin of a large crustal block. It is only in the Central and North Pacific that an obvious correlation between the geometric median line 140° 160° 180° 160° 140° 120° 100° 80° 60° 40° 20' 20° 40° 60° 80° 100°. 140° 160° 180° 160° 140° 120° 100° 80° 60 40 20 20° 40° 60 80° 100° Fig. 37. Positio
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] TOPOGRAPHY OF THE DEEP-SEA FLOOR 275 tica; but at about 55° south latitude, the crest bends sharply to the east. Apparent fault scarps suggest that the bend is an offset caused by faulting or else a discontinuity along the margin of a large crustal block. It is only in the Central and North Pacific that an obvious correlation between the geometric median line 140° 160° 180° 160° 140° 120° 100° 80° 60° 40° 20' 20° 40° 60° 80° 100°. 140° 160° 180° 160° 140° 120° 100° 80° 60 40 20 20° 40° 60 80° 100° Fig. 37. Position of the crest of the mid-oceanic ridge in ocean basins compared with the center hne of the ocean basins as defined by an arbitrary method discussed in the text. (After Menard, 1959.) and a broad median elevation is not found. However, there is a correlation with another type of submarine topography—long, narrow, steep-sided ridges capped with atolls and seamounts. The median line of the whole basin trends north- west from Easter Island to the Tuamotu Islands and the Line Islands to Johnston Island. Tuamotu Ridge has an area of 200,000 km^ shoaler than 3 km, and about 100 atolls and seamounts rise above the ridge. Some of the sea- mounts are guyots or former islands, now submerged. The Line Islands rise from the Christmas Island Ridge, which also has an extensive area, perhaps 100,000 mi^ above 3 km in depth, and many seamounts and guyots between the islands. From Johnston Island, the median line has three spurs. The north- eastern spur is not related to any conspicuous topography. The northern spur lies somewhat east but parallel to the Emperor Seamounts, which are a line of large guyots rising from a ridge with about 1 km relief. The western spur corresponds to the Marquis-Necker Rise, which, in its eastern half, the Mid- Pacific Mountains, has an area of 60,000 km^ shoaler than 3 km. The Mid-Pacific Mountains include about 50 seamounts, mostly g
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