90 



RAITT 



[chap. 6 



scatter of points caused by the rough bottom, Layer 2 is not prominent. How- 

 ever, the systematic decrease in velocity for the innermost shots on all profiles 

 is unmistakable evidence for its presence. Calculated thicknesses are : Layer 1 = 

 0.2() km; Layer 2 = 0.93 km; Layer 3 = 6.24 km. 



Fig. 8 is an unusual case of a very thick Layer 2 recorded near the equator 

 in the Central Pacific on the "Capricorn" expedition (Raitt, 1956). The second 

 layer arrivals are observed out to 20 km on either profile. Calculated thicknesses 

 are : Layer 1 = 0.20 km ; Layer 2 = 5.40 km ; Layer 3 = 7.41 km. 



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Fig. 7. Travel-time plot of Mid-Pacific Station Ml. Layer 2 velocity = 5.88 km/sec; 

 Layer 3 velocity = 6.91 km/sec; Layer 4 velocity = 8.41 km/sec. (After Raitt, 19.56.) 



The measured velocities and thicknesses of Layers 2 and 3 as observed at 

 134 deep-sea stations are tabulated in Tables I to VI, broadl}'^ grouped into six 

 different oceanic areas : I. Western North Atlantic Ocean ; II. Eastern North 

 Atlantic Ocean ; III. Eastern North Pacific Ocean ; IV. Western North Pacific 

 Ocean ; V. South Pacific Ocean ; VI. Indian Ocean. These results were taken 

 from articles sometimes containing stations obviously atypical of a deep-ocean 

 basin. Such stations have been excluded from this tabulation. The stations 

 excluded have been those in ocean depths less than 3 km, in deep trenches such 

 as the Tonga Trench, on the continental slope, on the flanks of islands, and on 



