SECT. 1] THE CRUSTAL ROCKS 89 



Fig. 4 shows an example of a station recorded by Lamont Geological Observa- 

 tory (Officer, Ewing and Wuenschel, 1952) using Woods Hole Oceanographic 

 Institution vessels Atlantis and Caryn. It gives an example of all three layers 

 2, 3 and 4 depicted in Fig. 1. 



Fig. 5 shows a station recorded about 300 nautical miles northeast of Puerto 

 Rico. It is one of a large number of stations observed in a combined operation 

 of Woods Hole Oceanographic Institution and Lamont Geological Observatory 

 (Officer et al., 1959) in a study of the structure of the eastern Caribbean. The 

 structure here is nearly horizontal and yielded good determinations of all 

 three layers beneath the sediment. 



Fig. 6 is an example of one of the very earliest successful deep-sea refraction 



Range in miles 



Fig. 6. Composite travel-time plot of Atlantis-Caryn Stations of 15, 16 March, 1949. 

 Layer 2 velocity (estimated) = 4.31 km /sec; Layer 3 velocity = 6.64 km/sec; Layer 4 

 velocity = 7.94 km/sec. (After Hersey et al., 1952.) 



profiles to penetrate to the Mohorovicic discontinuity (Hersey et al., 1952), 

 Layer 2 was not observed directly but its presence was inferred from sub- 

 bottom echoes, and its thickness was calculated using a velocity of 4.31 km/sec 

 determined by Officer et al. (1952). Thicknesses using this assumption and the 

 intercepts of Layers 3 and 4 are: Layer 1 = 0.42 km; Layer 2 = 2.26 km; 

 Layer 3 = 2.49 km. 



Fig. 7 is an example of a Pacific station in the region between the Hawaiian 

 Islands and the coast of North America (Raitt, 1956). Three layers were 

 observed. The second layer has the characteristic high velocity of the region. 

 Because of this comparatively small velocity contrast with Layer 3 and the 



